Help me troubleshoot this motor!!

[ThePinkPanther]

I have a Whittley Cruisemaster with an inboard OMC Cobra V8 that is in top condition with a low 500 hours runing time albeit over many years.

It has just come back from a service a few months ago and in addition I have performed the following:

1. New Starter motor
2. New coil
3. New spark plugs and leads
4. Had the distributor serviced
5. Likewise the Holley twin-barreled carbi
6. New batteries
7. New exhaust risers
8. New manifolds

......... and everything is as shiny and clean as a new pin so to the problem.....

The V8 howls and bellows its way across and around the Bay for well over an hour and a half with no problems whatsoever. This involves drifting with motor off and the numerous stops/starts with a days fishing - it never misses a beat!

Invariably after this time (usually on the way home) it starts to miss badly at about 3500 RPM. I drop the revs back a bit and it runs fine, then a few minutes it starts missing again. this goes on and on til I eventually craw home at about 2,000 RPM.

During this troublesome period, if I rev the motor up out of gear, it peaks at 5500 RPM and all stops in between without a miss or a drop in revs - absolutely perfect. But the instant I slip it back into gear and power up again, back comes the missing - pretty badly. Pushing the throttle up causes the motor to stop instantly.

OK, I reckon it is fuel starvation and as the fuel level drops it causes a vacuum in the tank produced as the result of a possible (?) fuel vent blockage somewhere and causes this missing. But if this is the case, why does it run out of gear at top RPM without a miss?

I guess next time it happens, I will simply pull off the fuel filler cap and see if that fixes the problem ..........

It doesn't sound like an electrical problem to me but I also wonder if the ignition module is starting to break down, but again the perfect performance at high RPM out of gear seems to discount this idea!

There is not a sign of water in the fuel and a new filter was fitted during the service. Maybe the fuel pump? Perhaps I should install an electric fuel pump as well? I always keep the fuel tank well (260L) well topped up.

It may be a red herring but the flawless running of the motor when out of gear at any RPM kind of shoots down the above thoughts. Why does engaging the gearshift introduce the problem and why does it appear only after about an hour and a half?

There is not a sign of water in the oil so that discounts a cracked head/manifold!

And suggestions appreciated!

[Noelm]

OK a couple of things here, first off, post in the right section for more help! but almost any Motor will rev OK in neutral, it does not test anything, before you do too much pulling to bits, can you use a portable tank and hose to test the fuel tank/filter/vent system? do the easy stuff first, do not assume anything and do not buy a bag of parts and start replacing everything, it needs to be done methodicaly, easy fuel test first, check plugs to see if they all look the same, do a compression check, then get back to us.

[TimiBoy]

Happened to me in a car once, same issue. It was a condenser in the distributor. But I haven't a clue on what else it might be, probably a list as long as my arm.

I love ignorance!

Cheers and good luck with it,

Tim

[FNQCairns]

If mine I would head straight towards the electrical side of things, I would look for light shows in the dark. I would also wait until it played up, stop spray the daylights out of everything with a water dispersant, fish for 20min with the cover up then head home and see what happens.

It's amazing what the salt air and humidity can cause and it can take a while to cause the problem. sounds just like a moisture related short somewhere.

Once I had an outboard engine playing up in a near identical way, so frustrating I could have burnt it all...anyway on the off chance because every thing else checked out I baked the cdi in the oven for an hour then dipped it in polyester resin, once refitted the problem was gone, moisture can play havoc and the crack sometimes cannot be easily seen without an xray or microscope IMO.

cheers fnq

[Noelm]

we also need to remember that there has been a dozen new bits in this Motor, anyone of which could be faulty, incorrectly fitted or adjusted!

[Roughasguts]

Is she running Hot! hows the temperature in the motor?

Im thinking fuel vapour lock because it slowly gets worse and rev's out in nuetral but has no power in gear. But if it cools down all is good right, like the next morning it runs well until she finally heats up.

I had a motor do this constantly.

[oldboot]

Now when you say missing......there is a different sound fo an ignition miss to other misses.......

It's sounding like fuel problem to me.... is there an automatic choke... thermal or electric......

often if a motor is choked it will not run at high rpm, because there isnt enough air flow to draw fuel thru the main jets.
I had exactly the same problem with one of my cars when I was young.....( stupid).... i pulled out the choke leaving work ( in winter) and 20 minutes int the trip home it was doing simliar.....I wont teel the whole embarasing story.

the fuel starvation theory sounds plausable.

there may be a blockage in one of the jets or such...... how is the float level and float valve?

is there an observation glass in the fuel pump or a filter after the fuel pump you can observe fuel flow in?

the more I re read your fisrt post the more it sounds like fuel supply.

But these things can be baffelin'....absolutely baaffelin'.

cheers

[Roughasguts]

Holleys are pretty simple carbys if you wan't to check that fuel is up there.
They have a fuel level screw on the side and the float bowl level can be adjusted from the top by loosening the hex lock nut and screwing the adjuster until fuel comes out the level plug. There be two of those if she's a 4 barrel.

Motor needs to be running for that!

Could be sucking water as well, as the fuel gets lower in the tank.

Did the motor do this before all the new bits and full service?

It doesn't sound like a big problem unless it is heat build up! then she needs all the scale and rust removed from the block so the motor can cool down properly.

[Scott nthQld]

................

[thelump]

What you explain is exactly what my motor has been doing over the last 2 weekends. Albeit an outboard and a 2 stroke at that. Mine is in getting fixed as we speak(or type) It was a powerpack in the ignition(apparently).May have absolutely nothing in common with your motor I know but maybe will direct you toward electrical rather than fuel. I put a new filter on mine and cleaned the tank out before i put it in to be looked at. Hope this random babble helps:-/

[Roughasguts]

What you explain is exactly what my motor has been doing over the last 2 weekends. Albeit an outboard and a 2 stroke at that. Mine is in getting fixed as we speak(or type) It was a powerpack in the ignition(apparently).May have absolutely nothing in common with your motor I know but maybe will direct you toward electrical rather than fuel. I put a new filter on mine and cleaned the tank out before i put it in to be looked at. Hope this random babble helps:-/

Yup an outboard is more inclined to do a power pack specially a Johno.
And the fuel delivery system is not prone to that much heat.

Many years ago when dads boat vapour locked I could get it going again by syphoning some fuel out of the tank in to a Beer bottle! plenty of those around and pouring it down the throat of the carby with the cleaner removed.8-)

If you get the right pour going you could go a long way on a stubby of fuel! Oh yeah but that was in a Ford Anglia 8Hp 4 cyl.;D

But don't blow yourself up I was an imortal 15 year old, and just to prove it I bear all the scars and aches and pains many years later.:-/

Soon as she cooled down or over nighted she would purr like a kitten until temp built up again.

[ThePinkPanther]

Thanks for all the advice and suggestions folks, much appreciated!

The main problem with this donk is the fact that the problem only occurs after a good hour and a half's running so trying to troubleshoot a perfectly good motor is nigh on impossible i.e. everything checks out and works fine at the time! No water in tank, petrol spews out of the main and power jets at power whilst in gear but I'll have to lift the air cleaner off and have a squiz at them when it is playing up. Bit hard with only me on the boat!

As this motor reaches it's operating temp - about 180 C within minutes of cruising - then it follows that most of the accessories would similarly become temperature-stable fairly quickly on the trip. So if a high temp is going to cause some componant to fail it would surely fail quite early and not wait out the above time?

So I figure that the only thing that significently changes after the 90 minutes is the fuel level, about 50-60 litres (gulp!) and that points towards a slow but steady fuel starvation problem with possibly a vacuum forming in the tank.

I would imagine units like the fuel pump, plugs, distributor, coil etc. would break down as soon as the "problem" temperature is reached - or shortly thereafter.

With this stinking weather around I have not had the chance to run it with the suggested remote petrol tank supplying the fuel. On this matter, if I were to remove the fuel filler cap during the "troubles" this would (?) immediately relieve any vacuum in the 260 litre tank to my way of thinking as it is a 25 cm supply hose directly into the underfloor tank. I haven't had the opportunity to do that yet ..........

I still suspect the ignition module as I have seen these brutes display all sorts of starting and running problems, particularly intermittantly like mine. Trouble is they cost about $650 each and as suggested, no point replacing parts til they are proven defective.

I'll just sit out these stinking winds and then go for another (expensive) test run and get back to this forum, again many thanks to all.

I'll be back!!

[james1]

Maybe she just does'nt like going home :)

[Roughasguts]

Wheres your boat PP I love this sort of thing if it's close by! I would make a trip to try and sort it for you! Just for the chalenge of course and maybe the beer, in fact only for the beer, nah not really I do like a chalenge, still think it's heat.

So has the motor been doing this long ? How long you had the boat ? has it always done this?.

Have you changed things like zinc anodes in the motor, or cleaned the heat exchanger to stop the rust? and keep it cool.

[Noelm]

when a Motor reaches operating temp, there is lots of other stuff that gets hotter later on, the only thing that is 180 degrees is the coolant at the sensor, coils and all sorts of other stuff can take ages to get "hot" a simple test for vacuum/vent lock is just to remove the fuel filler cap when it gives trouble, don't think it is that though, remember what I said way way back, do the easy non invasive stuff first, do not assume anything, we don't know what it is, so we must eliminate what it isn't, bit by bit without introducing a whole new set of problems by replacing or fooling around with stuff willy nilly!

[oldboot]

remember what I said way way back, do the easy non invasive stuff first, do not assume anything, we don't know what it is, so we must eliminate what it isn't, bit by bit without introducing a whole new set of problems by replacing or fooling around with stuff willy nilly!

Here here it is so easy to just start replacing things and altering things and end up doing nothing more than confusing the issue.:hammer:

I don't see any way round dragging it down to the water prepared to do nothing else but work thru the issues.

cheers

[cormorant]

My turn to guess

1st one

The fuel line or system under vacume is letting in air as it is cracked, or where a fitting clamp has cut the line . Happening when motor is hot as in engine bay temp has risen and fuel line has sagged or kinking if unsupported. Replacing fuel lines with poorer quality can cause this and it leads to a fuel restriction.


Years ago a mate had an intermittant fault. We narrowed it down to fuel restriction at high revs. We busted our brains trying to work out what was going on. Ended up being a new stored rod in a gunnel rod holder putting enough pressure on the fuel line to kink it. Rods were in different places at random. So simple but we had every component of that fuel system on and off for months. The simpler it is the harder it is to find.

2nd one
Ethanol fuel is being used? . A rubber oring or seal is swelling after imersion and allowing air into system.Possibly at fuel filter if a screw on as service guy may not have tightened enough?

3rd one

Possible outdrive seizing- check oil for water etc etc?

Is it running lean or rich when you come in at 2000rpm? Splutter or missfire? Check for a loose choke butterfly or linkage or broken return spring.

there willbe a fuel tank breather or 2 so blow into them and confirm they are clear.

Does the motor have any sort of computer that places it in "get home mode"when it has a fault?

Sediment in fuel filter being stirred up? Ethanol fuel or water swelling paper in filter restricting fuel flow?


Put a temperature crayon set of marks on the motor to see that a part of it is not overheating. Check routing of electrics a shot wires don't carry current and my cause a breakdown to computer?

Too tired- must sleep - let us know what you try and what has any affect.

[ThePinkPanther]

Solved it!!!!

Had a good look around and found that the pipe from the back of the fuel vent had fallen off (loose hoseclip).

The pipe had dropped down into the bottem of the boat, was filling with some fuel overflow causing a blockage but also this vent requires airflow over it to create a type of "suction" effect to help pull out the fumes and as it wasn't connected, the motor kept starving of fuel!

Thanks again for all the replies!

[ozscott]

Well done matey. Big relief. Just on the HEI amp module, I would be looking around now (before it inevitably plays up) and checking compatibility. Chances are there is an Australian Bosch HEI module that will work fine with that motor $50-$60 a throw. If you find the right one, buy it and stick it in a safe place.

You might have to do some research in the US to start the quest. For example I found that a Bosch HEI Mod for a Falcadore worked fine on a Land Rover 3.9 V8 (with original Lucas distributor). I know there might be subtle mapping differences but if you can get it close you should be sweet.

Cheers