Increasing WOT RPM

[146C]

Other than to reprop is there another way to increase WOT RPM.

I get a maximum of 20MPH at 4000RPM

The prop fitted is a Solas 13.5 X 15P

The motor is a 91’ DT85 Suzuki fitted to a Nova 5m Cuddy Cab.

The motor is a little difficult to start when cold but generally runs good thereafter.

Don’t know the total weight of outfit and don’t have any pics yet.

Not sure if it is a motor problem or just needs a smaller prop pitch(I think there is only one available @ 13.5 X 13P).

Any help would be greatly appreciated.

Dave.

[Blackened]

G'day

If 4000 is WOT, you need to come way down in prop size, FNQ will be best to advise on this

Dave

[BM]

Something is wrong here. A 17pitch prop should be reasonable on that hull, a 15 inch prop should be great. You are around 1500rpm shy of where you should be and as such you are damaging the engine due to overloading.

I would be checking compression, spark and fuel delivery before going any further.

Cheers

[146C]

I had the same thoughts BM, will check fuel and spark tomorrow. Had a compression test about a month ago and was told all 3 cylinders were the same 125 each.

Dave.

[FNQCairns]

Agree with BM there could be something mechanical wrong with it, but also certain other factors could gang up like to give you low numbers (although 4000 is very low) like leg way low, a lot of weight overall and forward also poor use of trim but best to sort out the mechanical options first as it has the potential to junk the engine fast depending on the cause.

Think Roughasguts has your engine on a like sized boat, not sure...

cheers fnq

[146C]

Spark is blue and fuel delivery to the carbies seem fine.

I also put in a new set of plugs today.

What else mechanically could I look at to help rule out a mechanical problem.

I did notice that a small amount of air seems trapped in the pimer bulb this is particularly noticable when squeezing it. Is this normal?
The primer bulb is brand new and just been installed a couple of weeks ago.

Cheers,

Dave

[FNQCairns]

There are a number of things that can point to an engine not producing full HP but first have you selected full throttle at the controls then viewed if there is any extra further movement available at the throttle linkage?

cheers fnq

[FNQCairns]

It may be worth double checking all fuel line connections by pulling then remaking them with an eye toward air leaks.
9/10 the simple things are the culprit, although it can something more complex.

Do you know your leg ratio?

cheers fnq

cheers fnq

[146C]

Hi FNQ,

Yes, throttle travel was one of the first things I checked.

I replaced the fuel hose from the seperator to the motor when I replaced the primer bulb, the hose was showing signs of cracking.

Have yet to thoroughly inspect the hose from the underfloor fuel tank to water seperator but at a glance seemed fine, cheap enough to replace it however.

Gear ratio is 2.08 (27/13)

Dave

[FNQCairns]

Hey Dave, how close are the numbers you gave? Very precise or just general? Was the speed GPS etc

Because I just ran them with your leg ratio and the outcome points to a prop/setup/trim/weight problem in any order/combination, not a mechanical problem.

cheers fnq

[gone_fishing]

sounds like a prop prob to wieght issue
depends if the prob has always been there or just devloped
of what youve been saying in tests see if you can get your hands on anther prop to test run
there is a way to increase wot rpm bigger hp motor
all the best

[146C]

FNQ the numbers came from tacho and speedo gauges fitted to boat.
I'm assuming they are accurate.

When using the motor trim I can get another 2 miles faster but no noticable difference in RPM.

Weight could be the problem, the boat is quite heavy. There is a fair bit of marine ply in its construction and it does not have much of a vee shape in the bottom of the hull, the bow also seems much more broader than a lot of other glass boats I have seen much like a tinnies bow.

gone_fishing I have not had the boat all that long.
It wasn't until I got the tacho working that I realised I was only getting 4000rpm.

Unfortunately no one I know has a prop I can try.

I will have to buy one hence the reason for the questions.

Suzuki lists only one prop available for my motor with a smaller pitch 13.5x13p.

Do you think dropping down to a 13 pitch would bring the rpm up near the 5500?

Does anyone else know of any other options I have regarding prop sizes.

Thanks for all the advice it is greatly appreciated.

Dave

[FNQCairns]

Dave speedos are usually very inaccurate, suspect yours is reading high at that speed, shame because it pointed well away from an engine problem.
Back to the start, the 13.5x13 will increase revs but it will be a slow boat, a right pain really, any prop with 15p and you will be happy to have on the water, the deal is to find a prop with less diameter (Like 13.25 to increase rpm) but stay with 15p as a minimum if at all possible, will put lots of money in your pocket over time with fuel prices the way they are.

Send roughasguts a pm about his engine I think it is a dt85 we could use his prop and numbers as a benchmark to estimate where you should be.

In view of the speedo as the speed reading it does sounds like a mechanical problem somewhere unless the speed is correct but that would be a bigger assumption than assuming it is wrong.

Things like engine height can make a couple of hundred rpm difference at this speed so can trim and so can extra weight or a lot of weight forward.

My engine is a 90yam 3cyl and has a 13.5x15 (5100rpm)cut down to 13.3x15p + cup taken out(5650rpm) on it, both engines have the same leg ratio and mine pushes a 6m tinny CC, so if it were my engine and using your prop getting 4000rpm I would be heading head straight toward the engine to rule that out first.

Unless of coarse there is something else that stands out like weight/legheight etc.

cheers fnq

[Splash]

There are a number of things that can point to an engine not producing full HP but first have you selected full throttle at the controls then viewed if there is any extra further movement available at the throttle linkage?

cheers fnq


FNQ -Best way to check for potential extra movement at throttle linkage without removing throttle cable to link?

D-A-V-E - do you have an additional fin on your motor (just above prop)?


SPlash

[FNQCairns]

FNQ -Best way to check for potential extra movement at throttle linkage without removing throttle cable to link?

D-A-V-E - do you have an additional fin on your motor (just above prop)?


SPlash

Splash probably no better way, can get pretty close just by visual inspection.

cheers fnq

[Roughasguts]

Hi Dave, I run a 13.5'-15 pitch prop and get max Rpm of 5300 at full throttle and that is the max HP Rpm as well. So i'm thinking you need to get those rev's to go anywhere.

Mind you I have hardly any weight' hull 450 Kg plus motor, and fuel and a few other bits and pieces.

I cruise at 4200 Rpm and probably getting 37 mph, Gps indicated 42 mph so theres some error in speedos, compared to gps.

Have you had the timing checked on your motor, ? 4000 rpm and 20 mph would still have my hull in the hole, but full throttle. If so I would need to move weight forward to get anywhere.

Example get any one down the back to move forward to get the arse end out of the water and the hull flatter in other words the nose has to come down to get some speed and fuel economy. Then hopfully the rev's will pick up, Mine does and accelerates nicely sometimes up to 50 Mph depending on conditions.

[Noelm]

I think the one very important fact we are over looking here is, "was it ever capable of more than 4,000RPM"? if not then before any fiddling about with the Motor is done we need to at the very minimum get another prop (borrow maybe) to test it out, as well as checking Motor height, fooling about with setttings and stuff MAY introduce a problem that was not there before, if you get what I mean!

[FNQCairns]

Well thats it then, if Gut's has the same prop and we assume all of those motors have the same leg ratio then Dave should be pushing nearer to 5K than 4k anyway.

If you find no standout in your search for a problem book it in for a link and sinc, should include timing I dunno the history with you and your motor but it's a nice place to be after this has been done on any new to owner engine.

cheers fnq

[SunnyCoastMark]

Hey Guys,
There are a couple of more things we may be overlooking here:-

1) Old Boat - is there any water trapped in the hull? Such as foam filled & full of water?

2)How does the motor run on Muffs? What RPM do you get then?

3) What condition is the prop in? has it had a rough life and been knocked around and repaired a few times?


I hit a rock upstream in the Maroochy River on the weekend - bent the blades a little and chewed up one of the leading edges a bit. This resulted in a loss of about 12km/hr off the top speed. (No vibration)

Mark

[146C]

Hi Guys,

Took the boat out today with gps which showed 38kph which is very close to the 20mph that the speedo had displayed.

I know it probably isn't too good for the motor but was curious to see if it would idle past the 4000 it reached 5000 before I stopped and am sure it would have reached its limit at 5500 no problem.

I have included some photos I took of my boat and motor today to see if this helps.

Thanks,

Dave

[FNQCairns]

Bugger me the leg height is completly crook and throw the foil away, you have now found the problem, if the speedo is correct when I ran the numbers you got 25% slip at the prop, your setup is entirely to blame.

cheers fnq

[BM]

Hard to see in those pics but your engine looks too low.

With a straight edge along the bottom of your keel extrusion it should be more or less level with the cavitation plate with the engine at right angles to the keel line.

Some will say it should be level with the bottom of the hull. This is true for a fibreglass boat that has no keel extrusion. They may also say that regardless of the extrusion it should still be level with the bottom of the hull.

In my experience I have found that level with the bottom of the hull on an alloy boat usually causes cavitation/ventilation in turns and can in some cases cause cavitation/ventilation in straight line running.

An engine too low will cause excessive drag and will have a 3 fold effect:

1) Rob you of rpm's

2) Rob you of top speed

3) Empty your wallet faster in terms of fuel usage

Cheers

[FNQCairns]

Like BM said, I think you actually have a 25inch engine on a 20inch transom, it cannot get any worse from a setup pint of view and then someone stuck a fin on it...as if the leg height was not enough already!!!!

PS. when you get it sorted you will not know this boat by comparison, the things people do.

cheers fnq

[Angla]

I will go with the others on this one. Motor is too low, but I still like fins once the motor is at the right height.

Chris

Here is a pic of my motor leg height. Note also that when I am planing with the motor trimmed up, the fin is not in the water.

[SunnyCoastMark]

Yeah Dave - nearly fell off me chair when I saw the photo's
,
Other guys beat me to it - that leg is way to long. It's also a lot of Boat for an 85 suzi.

Are you able to repower up to around 115/120hp?

Geeze, a picture paints a thousand words doesn't it?:)

Mark

Actually having a second look - it appears as though there is a spacer in the leg.

I'm not 100% sure - but you should be abe to remove that.

Anyone else?

[146C]

Thanks guys,

Sounds like I have an answer to the problem.

After having a look at the motor height adjustments there is only about an inch or so height adjustment available and needs to be five or so inches, is there something that can be done to remedy this and fix the problem such as building up the transom a little higher?

Has anyone seen this done before?

Thanks,

Dave

[FNQCairns]

You can pull the spacer, buy a 20inch leg (driveshaft on yours is 25inch) also replace the shift shaft with the shorter one and refit (may need to pull powerhead) or you can bracket (few designs around) the outboard up the 5 inches needed -I know the option I would choose and did choose -the bracket or you can get the transom raised which is probably the best allround choice

cheers fnq

[SunnyCoastMark]

You can pull the spacer, buy a 20inch leg (driveshaft on yours is 25inch) also replace the shift shaft with the shorter one and refit (may need to pull powerhead) or you can bracket (few designs around) the outboard up the 5 inches needed -I know the option I would choose and did choose -the bracket or you can get the transom raised which is probably the best allround choice

cheers fnq


Ummmm.....yeah/No:-/ Raising the transom is probably the easiest solution for this motor as long as you intend to keep it. Same goes for the bracket (if you can get for the Suzi?

However, you also restrict yourself to buying longer shaft outboards down the track and if you ever want to upgrade to something a bit bigger in secondhand - there are fewer options.

Just food for thought?

Nice looking Boat though.

Mark

[BM]

Dave,

Probably the cheapest alternative is to fit a plate to the transom.

I have fitted plenty on glass boats and a good mate has fitted lots more over the years.

To do it on an alloy boat will require a bit of planning for the bolt holes to catch the support ribs.

Usually the plate is about 350x460x25mm thick. Cost about $140. Your two bottom bolts go through the engine, the plate and will need to go through the support ribs on the transom.

2 bolts go up high external to the engine mount bracket and only through the plate and the top support rail for the transom.

The 2 top engine mounts then go through only the plate.

I'll see if I can find a pic of one finished.

Cheers

[Noelm]

could be worth a try to lift the Motor to the very top holes and see how it goes, with the foil off and the Motor up the extra holes MAY just get him out of trouble, with no cost and bugger all work, the Motor will still be a bit low, but still way better than it is now.

[Splash]

D-A-V-E.

Astounding!

The guys here have the best advice!

From my own expereience, you will notice a huge diff in performance after recs have been implemented.

Good luck mate!

SPlash

[Fed]

After a lot of squinting at the pics I'm not convinced the motor height is out by more than the available adjustment at all.
You need to trim in until the prop shaft/cavitation plate is parallel to the bottom of the hull then take some measurements and some clearer pictures.
Also compare your measurements to the available adjustments on the existing holes.

[Noelm]

I think the one very important fact we are over looking here is, "was it ever capable of more than 4,000RPM"? if not then before any fiddling about with the Motor is done we need to at the very minimum get another prop (borrow maybe) to test it out, as well as checking Motor height, fooling about with setttings and stuff MAY introduce a problem that was not there before, if you get what I mean!
Remember when I said this way way back? well this is the reason why, ALWAYS check the very obvious first!

[146C]

Have decided to remove spacer and replace gearbox with one that suits a 20in transom. It is also cheaper than building up the transom and less restricting when the time comes to repower.

I have removed all but one stud used for holding the spacer to the shaft housing.
The problem seems to be the stud is sticking inside the spacer.
The stud moves easily within the shaft housing when spacer is turned along with it, problem is that the water tube prevents the spacer from turning completely. I have managed to unbolt the stud about three millimeters with a huge amount of effort but now wont budge. Have tried heating it a few times but still no success.

Can anybody offer any other suggestions to remove the stud without stripping back the motor to remove the water tube?

I hope to pick up the replacement gearbox Friday.

Thanks to those who have previously offered their advice it has been greatly appreciated.

Cheers,

Dave.

[SunnyCoastMark]

WE might need to see photo's of the offending stud

Mark

[FNQCairns]

Hey Dave have you checked out what is the deal is with the shift shaft? Some engines need to have the powerhead removed to replace this, dunno about yours.

Possibly lots of white corrosion inside the stud tube through spacer.

cheers fnq

[BM]

FNQ, in a 20 to 25 conversion the shift shaft usually has an extension piece that fits onto the existing spline with a new spline at the bottom since its a no load linkage.

I fail to see however, that an alloy plate to raise the engine could be dearer than converting his current box back to long shaft or replacing it with another box to suit a long shaft application. Unless the replacement box came for $100??

Dave, heat, penetrating lubricant, scratching device and a mallet will get it apart. I had similar recently with a pair of XL Yammies on a cat and both extension housings were jammed on by salt.

Gotta love Jap engines mate, fantastic when they are new but don't try pulling them apart when they have a few years on them coz they are the worst of the bunch.... :(

Cheers

[Roughasguts]

Dave you tried tightening then loosening the stud, keep going back and forward, use plenty of lube mainly to wash the thread out and she should come out.

[FNQCairns]

FNQ, in a 20 to 25 conversion the shift shaft usually has an extension piece that fits onto the existing spline with a new spline at the bottom since its a no load linkage.

I fail to see however, that an alloy plate to raise the engine could be dearer than converting his current box back to long shaft or replacing it with another box to suit a long shaft application. Unless the replacement box came for $100??

Dave, heat, penetrating lubricant, scratching device and a mallet will get it apart. I had similar recently with a pair of XL Yammies on a cat and both extension housings were jammed on by salt.

Gotta love Jap engines mate, fantastic when they are new but don't try pulling them apart when they have a few years on them coz they are the worst of the bunch.... :(

Cheers

Yeah BM but if it is a factory 25 then the shaft may be one piece like my bloody Yam, last thing Dave needs to do is pull a powerhead when a plate like you say or even a simple bracket will do the job. Hope Suzuki did do the extension thing in the factory.

I ended up grinding the yam spacer into tiny little bits to get it off, brain surgery style :).

cheers fnq

[BM]

But there is a spacer plate in there so it has to have been converted. I don't know any engines that came from the factory as a converted 20 inch with a spacer plate and 25 inch shift shaft as a solid unit.

Not saying it hasn't happened but the very presence of the spacer plate suggests not.

But you never know. It is a Suzuki we are talking about..........

[146C]

Hey Dave have you checked out what is the deal is with the shift shaft? Some engines need to have the powerhead removed to replace this, dunno about yours.

Possibly lots of white corrosion inside the stud tube through spacer.

cheers fnq



The manuals say installation is the reverse of removal making the clutch shaft one of the very last things to be reconnected.

Dave

[FNQCairns]

Yeah dunno on the Zuk, although they are almost a design copy of the Yam 3cyl or vice versa but the Yam came with spacers from the factory for the 25 inch models dunno about all of the HP sizes though.

cheers fnq

[BM]

I believe Zuk definitely copied Yam. Yam was around from the early 70's but marketed under the name of Mariner and distributed by Mercury.

Come to think of it, the Suzuki engines were not too far behind the Mariner (Yams) maybe only by about 3 yrs.

Cheers

[146C]

But there is a spacer plate in there so it has to have been converted. I don't know any engines that came from the factory as a converted 20 inch with a spacer plate and 25 inch shift shaft as a solid unit.

Not saying it hasn't happened but the very presence of the spacer plate suggests not.

But you never know. It is a Suzuki we are talking about..........


Hi BM the service manual I have lists both 20in(L) and 25(UL) with a 5kg difference in weight. However I have so far found no reference of the spacer in the manual.

The clutch shaft is also one piece. This took me a while to work out because the manual said remove the cover in front of he clutch rod connector pin my motor does not have this so had to disconect it from near the powerhead.

Cheers,

Dave

[BM]

Spacer plates dont usually show up under normal parts listings. I just checked a site that is good for Suzi parts and could not find it. They normally come under accesory items or something similarly obscure.

There is definitely a spacer fitted to your engine.

The figures quoted would be right also. Most spacer kits add approx 5kg to the weight of the engine.

You probably need to speak to a Suzuki dealer of old as many "new breed" Suxi dealers will simply not want to know about what they perceive to be "old stuff".

Try Leisure Sports Marine here in Vic (Dromana/Safety Beach area). They are a Suzi dealer of old and have many parts in stock. They will be able to answer your questions.

Cheer
Cheers

[146C]

Dave you tried tightening then loosening the stud, keep going back and forward, use plenty of lube mainly to wash the thread out and she should come out.


Yes, also left it saturated with wd40 will try again tomorrow.

Dave

[146C]

FNQ, in a 20 to 25 conversion the shift shaft usually has an extension piece that fits onto the existing spline with a new spline at the bottom since its a no load linkage.

I fail to see however, that an alloy plate to raise the engine could be dearer than converting his current box back to long shaft or replacing it with another box to suit a long shaft application. Unless the replacement box came for $100??

Dave, heat, penetrating lubricant, scratching device and a mallet will get it apart. I had similar recently with a pair of XL Yammies on a cat and both extension housings were jammed on by salt.

Gotta love Jap engines mate, fantastic when they are new but don't try pulling them apart when they have a few years on them coz they are the worst of the bunch.... :(

Cheers

I didn't end up getting a quote for a bracket/brace the few marine companies I spoke to suggested I not do this but recommended that the transom be built up with fibreglass. The quotes I was given were upwards of $1000. Second hand gearbox $400-$700 a couple of the service guys I had spoken with were very helpfull with regard to replacing the gearbox.

Thanks for tips.

Dave

[Splash]

Splash probably no better way, can get pretty close just by visual inspection.

cheers fnq

FNQ - At WOT, the throttle lever bush was not at full end of groove in throttle lever - but rather about 1.5" away from end of groove.

Does this imply adjustment is needed so that this lever bush is at end of travel at WOT position?

Splash

[BM]

Dave, I had typed a lovely long response but it vanished..

Anyway, long story short. Why were you told not to add a 25mm thick alloy plate to the boat to mount the engine?

I and an old hand in the trade have been doing this for 25yrs without a problem.

Did they suggest building up the transom with an extension piece and dowls??? If so, I have seen these fail and I saw one sink a boat (about 2 yrs ago in Melb). Saw the boat sitting in my mates workshop post recovery with the so called "you beaut extension with dowls" setup ripped off....

I'm sorry to sound arrogant mate but what I have suggested, we have been collectively doing for a very long time without incident or issue and whatever you have been told is absolute bullshit, no doubt to extract more money from you.

The choice is yours, but I'm giving you experience from a professional who isn't after your money.

Cheers

[Noelm]

yep, agree there BM, I have seen heaps of Boats with "jack plates" to raise the Motor height, and I have also fabricated a couple as well, as long as the existing Transom is good, then it will pose no problem, after making a few I have come to the conclusion that to buy a non adjustable one is probably the way to go, they are not too hard to make, but the standard "store bought" ones are not that dear, the adjustable ones start to get a bit pricey though.

[FNQCairns]

FNQ - At WOT, the throttle lever bush was not at full end of groove in throttle lever - but rather about 1.5" away from end of groove.

Does this imply adjustment is needed so that this lever bush is at end of travel at WOT position?

Splash

Having trouble visualizing the groove in relation to where the bush is but no matter, pull the induction baffle of the front of the carbs, select full throttle and peek in and spy the butterflies - if they are fully open or even a little past then you have as much full throttle as is possible.

cheers fnq

[Splash]

FNQ - See attached pics..

I have also checked the butterflies - fully open at WOT.

In the pic., you will see the bush at WOT near top of groove on lever - with about 20 mm left before top.

Do i need to adjust anything so that the bush meets top of groove at WOT?

Also, in another pic, you will see top of flywheel - with 3 threaded holes - what is supposed to fit inside these holes?

SPLash

[FNQCairns]

Hi splash the linkages are a concert between throttle and spark timing/advance, there is stricly no idle adjustment outside of mixture which is a poor way to do achieve it.
Because of this concert of linkages througout throttle range all designed to give you the correct idle at idle spark advance right through to full power and full spark advance as the linkages allow under throttle movement gaps like this are normal and esp so if you have viewed the butterflies at full throttle and they are fully open.

Those holes are for the flywheel puller.

cheers fnq

[Splash]

Thanks FNQ - My manual says I shoudl be idling at 600-700RPM.

I currently idle around 1000 - 1100RPM.

Best way to adjust this idle down on this donk?

SPlash

[FNQCairns]

It's hard to do it properly without a full link and sync, the spark advance at idle adjustment controls the idle speed. If it is idling too high then this points toward too much spark advance at idle which due to the way advance is linier on theses engine then the max spark advance will be too high also.

If what you say is how the mechanic that last touched the linkages and timing gave it back to you then he didn't do a very competent job, although sometimes owners think these are designed like a lawnmower carb in idle adjustment and go at it themselves.

If you choose you can adjust the carb stop to obtain a lower idle but it shouldn't be strictly necessary but it obviously is.

cheers fnq

[Splash]

Thansk FNQ.

Good memory mate. Yes a Linc/sinc was performed by a professional mechanical in Melbourne early 2007 - before rig came up here..

Where can i find the carb stop?

Splash

[FNQCairns]

Actually splash I think this is a place you had better not play with it's too much of a concert and because of the inherent risk of altering the timing not a nice place to adjust.

IMO pay someone it may be a simple cam adjustment needed or even a throttle cable but without seeing it work and how it rests in real time not worth the risk.

cheers fnq

[Splash]

ok thanks mate

[BM]

FNQ,

Just on the timing. If the pickup timing is advanced beyond where it should be this wont affect the max advance. This is because the max advance is a mechanical stop, so the pickup timing point has no relevance to the max advance.

Splash,

Make sure that at idle the butterflies are fully closed in the carbs. Also check that the throttle cam is just touching the throttle cam follower in the idle position. Most OMC engines from approx 1972 onwards had fixed jets so there is no adjustment possible on the carbs. However, certain models from time to time did come out with adjustable carbs.

If the above is how you are set up then your pickup timing needs to be checked. Easy to do if you have a timing light. Just run it at idle and check the timing.

Is it 1000-1100rpm IN the water? or on the muffs? Whats the in water idle speed?

Also is the tacho correctly set. Needs to be on 6 pulse.

And lastly, your model is likely to have quickstart (what year 110 is it again?). If one of the overheat sensors has a white wire with a black trace then you have quickstart. This wire goes back to the powerpack and it controls the shutdown of the quickstart condition and returns your idle from say 1200rpm back to normal idle speed of say 750rpm.

Quickstart advances your pickup timing to facilitate easier starting. With a warm engine when you start it the quickstart condition will last for about 10 seconds and you will hear the engine idle down.

Cheers

[Splash]

Thanks BM - Will check it out!

How do I check for if throttle cam is just touching the throttle cam follower in the idle position?

1989 is my OMC model.

No white quickstart wire sensor.

tacho on 6 pulse.

Cannot remember if idle in ocean , muffs?

Splash

[FNQCairns]

Splash reading above got me thinking, it's been a long time since I got messy with these engines, I think there is an idle screw per say, located near the arm that drives the timer base and below where the timing mark is located (I think) this will achieve what you are looking for but could depending on how much you need to turn it induce a stumble just off idle etc, anyway it's a concert but give it a go when the engine is fully warm - if I am not actually thinking of another engine it should be there, you can always go back to where it was before you started.

Hi BM I sort of agree but because advancing the spark on these even 1 deg must also advance the idle timing an identical degree as a solid block because the timing plate is a solid 1 piece unit, bit like a slot size, not one that can be stretched independently at any end, if I explained it well enough.

Bit like the trap for people new to outboards who think that if the specs call for 28btdc max spark advance they think that if the set it to this figure like say a person can do with the spec for a car it will work and not go pop! always a shame.
No manual I have ever seen actually states the max advance spec must have the idle advance subtracted from it and this figure is the TRUE max advance specification because advance in these is as a solid block of degrees there is no vacume or centrifical advance like in a car. Reliable but in the age of the dinosaurs.

cheers fnq

[Splash]

thanks FNQ - will check it out.

[BM]

FNQ,

It won't matter if pickup timing was 0 degrees or 4atdc or 4btdc because the max advance is set by the max advance stop screw, so lets say you retarded the pickup timing by 5 degrees that won't alter the actual degrees of max advance.

It simply means the timer base is moving through a larger arc thats all. I understand your thinking, it just not correct.

The idle for splash's engines as with most outboards is achieved via the adjusting of the pckup timing. The Yams differ from this by an actual carb adjustment for idle speed.

[FNQCairns]

Hi BM yeah you could be right about Splashs engine and it's what I thought earlier but an idle screw rings a bell, wish I had a manual still, it should be in there if it exists, might be the 90deg V6 crossflows I am thinking of.

Still cannot agree, unless we are actually near saying the same thing but I have not twigged.

No worries, think we will need to agree to disagree this time around....again??

cheers fnq

[Splash]

I have an electronic manual that I am currently having issues opeining on my PC.

When I am able to open it, I will delve into this section and provide scanned images of the above related text.

Splash

[BM]

I'm not quite sure where your confused FNQ but run with me here mate.

Lets say we disconnected the timer base and with the engine running rotated the timer base to the TDC position (using a timing light obviously).

Now, you have two stops for the timer base, one in a retarded direction and one in an advanced direction agreed??

Lets say the max spark stop is set to 24 degrees for example. The distance between TDC and max spark is a set distance. TDC is TDC and we have mechanically stopped the timer base from going beyond 24 degrees of advance.

Likewise with the pickup or idle timing stop. We set that to whatever the case may be.

TDC on the timer base remains a known constant and the arc of the timer base swings between the pickup/idle timing stop and the max spark stop. Therefore, retarding the pickup/idle timing by whatever amount doesn't alter the position of TDC or max spark it simply allows the arc to become larger and therefore retard the engine further.

Does this clarify any better for you?

Cheers

[146C]

Took the boat for a test drive after replacing gearbox and left hydrofoil off.

I am now getting 45kph @ 4700rpm.

The motor will reach 4800-4900rpm if I trim the motor up more but then starts porpoising, I had an adult and child passenger and did not make any real difference them sitting at the stern or standing at the helm, boat still porpoises.

The cav plate now sits somewhere between 15-20mm higher than the bottom of the boat.

Is this okay?

Sometimes the prop did ventilate a little on turns.

What prop pitch would allow the motor to obtain the extra rpms needed?

Will it also help stop the porpoising.

Cheers,

Dave

[Angla]

Dave,

It looks like you are getting an extra 11 km per hour using an extra 700 rpm which you could not get before and then you still have around 200 rpm left.

A question on the porpoising is, What were the water conditions like. Were you on the bay with a little chop or on a waterway with no waves to speak of, near glass.

When you trimmed the boat up, can you trim it to a point where it starts to lose speed and you hear ir start to aerate, or are you not being able to trim it far from the transom because of the porpoising.

Did anyone check to see where the cav plate was when you were travelling at speed.



It sounds like you are on the right track with lifting the propeller (removing the spacer). It may still need to have the prop changed to get more WOT. I cannot offer any more advice there.

In relation to the cavitating during turns, that is why I have the foil on my motor. It stops the air being sucked down easily during highspeed directional changes.


I will attatch some more pics showing
A/ the distance the motor is away from the transom - trimmed in all the way
B/ the distance the motor is away from the transom - trimmed to maximum planing speed at WOT ( any more and it draws air)
C/ the line of the keel when the motor is fully trimmed in
D/ the line of the keel when the motor is trimmed parallel to the keel line ( the cav plate is about 25 mm above the keel line which is a little hard to tell from the picture)

Hope my 2 cents helps

Chris

[146C]

Thanks for the informative post Angla.

The water was flat with small ripples.

The motor will not trim out far enough to make it aerate.

Not really too sure what depth the cav plate sat in the water.

Cheers,

Dave

[FNQCairns]

Dave sounds like you are winning, I forget your leg ratio so cannot chase up where you really are with your figures but much better regardless, you have a 13.5 diameter prop which is your problem now it seems, your choices to go down in P really suck, you will get your rpm up easily but at the expense of efficiency. If it were me I would look long and hard to find a 13.25x15p any brand, this will allow more revs + keep the boat traveling forward at an acceptable rate. You are not traveling faster enough ATM to get the hull working so if you can fit a prop with less dia once it gets to over 50kph somewhere the hull will lift prop slip will reduce and the effect will gather up and you should be away toward 60kph - in theory. if you go down in P and keep the same diameter you may not ever travel fast enough to find the sweet spot where it all comes together.

Exactly where my boat is, nothing on the shelf that suits in any way but badly, so I make my own.

You sound handy you could always work the prop diameter yourself and get there, I know how I would fix the prob but each is to their own.

If you decide ot get jiggy with it can let you know basicly how to go about it -back yard style or you can give it to someone, hope it is alum.

cheers fnq

[Angla]

Dave,

One other thing that someone has already stated is that this could be a small motor to be pushing this boat.
With that in mind - it could get to a point where it is doing the best that it can, and will never achieve better results.

It's "Your call" on this given the advice from quite a few minds and the changes you have made

I must say that I had a 5.2 metre fibreglas half cabin with a 115 hp on it and it ran very well. Then again if it had a 85 on it I think it may have struggled. It could be worthwile to look around at other boats that are the same and see what they are powered by.

Chris