Bad Idle, and can't find airleak

[dreemon]

Hello all, this engine will start good, but setting the air/fuel needles at 1 1/2 turns out will rev, drop, rev, drop, pop, stall, re-start. it surges so bad that when put into gear will stall,

I did spray wd40 and found that there was play within the pin in the carb butterfly, so changed carbs, and still does it, But, with the needles backed out to 3 full turns it idles well, the manual says these carbs are meant to be 1 1/2 out, should I still look for an airleak? or am I overlooking something, I've sprayed wd40 all around suspect areas with no change in rpm.

the motor belongs to a mate, it's 92 mariner 2st 2cyl 2 carb 40 hp any:helpa: will really be appreaciated :D

[FNQCairns]

Your running on the idle circuit here so if only concentrating on the fuel system, each carb must be known to hold the correct float level AND the correct 'link and sync' adjustment when at idle rpm taking into account wear and tear of the linkages etc, only then can the idle mixture be adjusted as per the specs, often with a little age or straight from the box the manufacturers spec are only a base line.

Does it cough or does it backfire at idle?, when cold and/or when warm, which one, way or dozen?

Has the good carbs bowl been flushed? and known fresh fuel to discount water contamination.

chers fnq

[Kleyny]

for a minute there i thought it was your motor. Which was a bit concerning as its newish.

Try using water in a mister insted of wd40. When i used to chase air leaks wd was no where near as good as water mist.

neil

ps i just thought the read valve check the read vavle for holes or poor contacts.
you sgould be able to see them with the carbs off

[dreemon]

Yes FNQ it backfires/pops then will stall and will do it all the time hot or cold, it has new floats (non adjustable) and are level to float body when turned upside down, and the carbs " both sets " are very clean, I used my fuel and tank and same thing, but maybee this engine happens to like more fuel for its age like you said,

one thing is a lil weird, it can idle for a long time b4 it quits while the choke is on?, my engine choke has to off as fast as it starts,

Honky dory I'll try the water spray mist, and see if it changes rpms , and the reeds are all good, had a good look at em.

thanks guys

[Roughasguts]

Hows the compressions on the motor, it could be one pot is down and not sucking very well. But while your there clean the plugs, they should be all wet and dirty by now.

[FNQCairns]

Yes FNQ it backfires/pops then will stall and will do it all the time hot or cold, it has new floats (non adjustable) and are level to float body when turned upside down, and the carbs " both sets " are very clean, I used my fuel and tank and same thing, but maybee this engine happens to like more fuel for its age like you said,

one thing is a lil weird, it can idle for a long time b4 it quits while the choke is on?, my engine choke has to off as fast as it starts,

Honky dory I'll try the water spray mist, and see if it changes rpms , and the reeds are all good, had a good look at em.

thanks guys

If it does it hot and cold then I would be likely on the surface to discount an air leak from the induction side of the engine anyway but anythings possible as well as probable until the cause is found.

Are both carbs hold the same mixture screw adjustment out when it runs ok?

I would take particular care and notice of how the link and sync is applying it's self, are both carbs opening at exactly the right time, does the timer base move in concert with the sync of the carbs on initial crack of the throttle, is before alll else the butterfly's in both carbs adjusted to the same amount of closure at idle rpm. The mis synchronisation of this above will cause your problem to a T but so can other things.

If you do run it with any suspicion of an air leak the sparkplug colour will tell all, do a plug chop a few times all the while gaining confidence in the amount of load you place it under.

History is always important, if the timing has been fiddled with then best to get that looked at, short of this take particular notice and nail the synchronisation of the carb linkages first.

Oh yeah I didn't ask very well, does it 'sneeze' at any time out the carb/s? Hot or cold when just idling.

cheers fnq

[dreemon]

Did a comp test before and aft a de-carb and showed the same 129 and 130,

the mixture screws are both backed out the 3 full turns, and it will idle good as it should for 2 cyl, but at say 2 turns out will sneeze at idle only and hot or cold, but it does have a rythym about it.... revs 3-4 times pop , again and again then stalls,

the butterflys are really good, shuts tight with no pressure of the idle screw , and opens even, as for timing I dont play with that side of the engine but the plate does move free to advance as the throttle goes to run fast, it may need to have sync and link checked,

we'll keep an eye on what the plugs are saying , next time we take it out i'll run it WOT for a bit then stop motor and pull plugs out and see if its seems happy,

mostly all I want to know it's not trying to melt due to an air leak,

Thanks all heaps for your time n advise , will let you know how she goes or if it blows :D

[FNQCairns]

Yeah a melt would be bad, to do a plug chop don't cut fuel only ignition on the spot and keep it cut, forget the gears also, just let the prop clack to a stop with the boat. Then pull the plugs.

It does sound lean if that's what it is doing, trouble is as you know all of your testing has been on the idle/slow speed circuit, if by chance it is a vacuum leak it may compound under load .

An interesting test is to pull the choke on when the boat is on the plane if it accelerates slightly before choking out, the engine is a little lean at that rpm, if it chokes straight out it's probably rich or more or less OK.

Gotta say if the engine is behaving at 3 turns out exactly as it should and all of the link n sync is ok then I would also run it and let the plugs do the talking but be careful and ease up to long runs gradually with chops along the way.

good luck, Interested to hear how you go.

cheers fnq

[Kleyny]

I cant see it melting anything just because its got an air leak (if it has one) unless the leak is huge which you would/should have found with the WD40.

I also just remembered another little trick that i used to do to think down the road of air leak is put your hands halfway over the carb/s and if its got an air leak the revs should change (pick up from memory).

By the way I'm only a ex motor mech not a marine one. but most of the principles are similar.

neil

[FNQCairns]

I used to do that too Neil and had forgot all about it! but with a piece of cardboard across the throat of 4 strokes.

In the 2 strokes they run very rich, this is for cooling purposes only it actually robs performance - enter the e-tec engines etc to see just how rich they run as the difference in economy is virtually this alone.
If it is leaking some air it will melt, doesn't take very much at all in a 2 stroke bit like a high boost race car.

Not many people get to wear a 2 stroke out :) :(

cheers fnq

[Kleyny]

like i said only and ex car mech. Was unaware a little leak would do damage on a two stoke.

neil

[FNQCairns]

yeah thats cool, our outboards are a constant throttle 2 stroke so they are even more at risk than say a 2 stroke bike, still lots of fun to be had when they are working:)

cheers fnq

[Roughasguts]

So are you certain theres fuel in your carbs ? EG: you cleaned out and checked that the needle and seat, to see if there working?.

Pretty easy to do prime the fuel bowl until you can't pump petrol no more, that means the carb float bowls should be full.

Then drain them with out running the motor if theres around 40ml of fuel in each there about right.

Then do the same with the engine running, that's to check the fuel pump, is getting fuel up there, the fuel pump might not be able to suck, due to a bad hose or conection.

If your only getting a dribble from your float bowls then it's a fuel delivery problem.

I'm sure you done all that, just covering the basics first.

Then again could be a dud coil not delivering a good spark when it should.

[dreemon]

What I have is two of the same engines , mine is a 91 and my mates is a 92, ( Honky dory, my motor isn't new either, but the paint is ;) ) so with this I get to compare the diff between the 2,

I've been taking notes for checking next time we take his out, spray the water mist, choke test, plugs etc..... his engine seems to have this problem thats been ongoing and this is why I got anouther set of carbs for it, and same thing, only the next tests will tell us more, the new carbs are better and the throttle response is more "snappy"

we'll let you know the results, now I have to find a way to force those old twin carbs onto my 150cc 4 st quad bike ::) ,

have a happy fathers day !

[Kleyny]

What I have is two of the same engines , mine is a 91 and my mates is a 92, ( Honky dory, my motor isn't new either, but the paint is ;) ) so with this I get to compare the diff between the 2,

I've been taking notes for checking next time we take his out, spray the water mist, choke test, plugs etc..... his engine seems to have this problem thats been ongoing and this is why I got anouther set of carbs for it, and same thing, only the next tests will tell us more, the new carbs are better and the throttle response is more "snappy"

we'll let you know the results, now I have to find a way to force those old twin carbs onto my 150cc 4 st quad bike ::) ,

have a happy fathers day !

sneeky

thanks

neil

[dreemon]

Here's some reports,
I did spray mist of water around everyware I thought air could get in, no change,
then did the chop test , wot for about a min and cut the motor, I could hold my hand on the head for close to 10 seconds, and pulled plugs, they were a light /med tan colour and dry , only at times it will begin to sneeze, spit, pop, backfire, ( I cant tell the diff anymore) but if we hit the choke switch for 1/2 sec it comes good, so it seems ok? I did talk to a mechanic and he mentioned that it could be the lower crank seal leaking and that spraying wouldn't effect it cause of it's area, or maybe worn reeds, otherwise it runs good,

Cheers :D

[tunaticer]

Check one of the petals on the reed valve isnt gummed up causing inconsistent flows. Often causes sneezing.

I just bypassed the fuel connector on the motor and now run a hose directly from the fuel filter to the fuel pump and got rid of the worst offender for a air leak. Motor runs sweet as now even if it is 13 years old and done a zillion miles.

Jack.

[FNQCairns]

Well assuming I trust your example of a plug chop and both showed light to medium tan there is no problem with the sum of all circuits.

The only other place i would do a chop at is around the 3000rpm mark just to be sure (the spot where the motor is working hardest (and held there) to get the boat on the plane).

On the surface all seems good to go, although I cannot see it here from my desk.

cheers fnq

[Kleyny]

Here's some reports,
I did spray mist of water around everyware I thought air could get in, no change,
then did the chop test , wot for about a min and cut the motor, I could hold my hand on the head for close to 10 seconds, and pulled plugs, they were a light /med tan colour and dry , only at times it will begin to sneeze, spit, pop, backfire, ( I cant tell the diff anymore) but if we hit the choke switch for 1/2 sec it comes good, so it seems ok? I did talk to a mechanic and he mentioned that it could be the lower crank seal leaking and that spraying wouldn't effect it cause of it's area, or maybe worn reeds, otherwise it runs good,

Cheers :D


for a minute there i thought it was your motor. Which was a bit concerning as its newish.

Try using water in a mister insted of wd40. When i used to chase air leaks wd was no where near as good as water mist.

neil

ps i just thought the read valve check the read vavle for holes or poor contacts.
you sgould be able to see them with the carbs off

I was sure i said that:P ;D

if you do decide to take the reeds out a few tricks that i used to do with my 2st motor bike was to lightly sand the valve seats and turn the reeds around if its possible (som reeds you can some you cant). it seemed to make them seal harder as over time the can lose the spring or tend to keep a slight bend. turning them around can sometimes fix it.

neil

[dreemon]

T.T. looks like this engine has near the same hrs as yours, I recon they have alot more yrs left em, ,
FNQ , allways appeciate your top advice and help,
H. Dory , If it were my motor I'd prob turn the reeds around or if it didn't sneeze so much I'd stick boyesen reeds in it, but I'm not getting paid for the work, but I don't want him out with his wife and kids and have probs, he's the kinda guy that doesn't know what an impeller is,

I'll keep an eye on it anyways, Thanks Guys ;D