1977 115HP Warm Restart Issue - flames out on acceleration

Hi all,

I've got the following symptoms:

Motor starts and runs well from cold, no issues whatsoever.

After working the motor hard - towing kids on biscuits/wakeboarding etc, if I turn the motor off, I end up with a problem when I restart it.

The motor will restart no problem at all, and will go into gear and power the boat at low RPM - under about 2000.

As soon as I try and accelerate the boat beyond about 2000 rpm, the motor simply dies. There is no sputter/cough/anything - it's like someone has simply turned the motor off.

If I accelerate up to close to this rpm point, then ease off throttle to lower the rpm again, the motor will continue running at low rpm/idle no problem at all.

After a few minutes, this behavior clears itself, and I'm able to accelerate again past 2000 rpm. Occasionally, it sounds as if one or more cylinders suddenly decides to start firing.

I'm at a loss to what the problem is.

Taking major systems in turn:

Fuel - symptom exists even if I have someone squeezing the fuel bulb when the problem occurs. Fuel bulb behaves in a completely normal manner. Carbs have been cleaned. I don't see any way that fuel can be my issue given the motor runs great at all engine speeds, other than after a warm restart for a few minutes. Carb bowls have been emptied to check for water - none present, and a decent fuel filter/separator is fitted.

Compression - all healthy, around 115 psi. Motor has recently been rebuilt - this problem existed both before and after the rebuild.

Ignition - Because of a variety of other wear and tear issues, my motor has a pretty new stator/timer base/coils/spark leads and power pack. All components test fine according the cdi test procedures, but I'm doing the tests at home with the gear case etc in a bucket, not when the problem is occurring. The stator and timer base have been examined carefully and tested with an ohm meter a number of times, so I believe they are both in good condition.

I'm down to being suspicious of one of 3 things:

- Poor engine grounding. I went through and replaced the various grounding cables, as all were in poor condition. I guess I'm suspicious of a wire/connection failing or increasing in resistance when hot, then coming right when cool again. I have yet to take the boat out with the replaced ground connections.

- Spark plugs - these are a couple of seasons old, but look fine. I don't see how bad plugs could cause my issue, unless they had some kind of insulation fault that becomes apparent when hot.

- Power pack. Am I unlucky enough to have a couple of power packs fail in relative close spacing? I have definitely had a heat related power pack issue previously, but in that case, a single cylinder was dropped when the engine got hot. This was resolved with a new power pack.

Do my 3 suspicions sound logical? Or is there something else I should be looking at?

Nick.

My first thought is also a sticking timer base as per the statement by "fdrgator".

Carburetors do not go and come... If they're bad, they stay that way.
Powerpacks of the type you have are not able to be intermittent either... once bad, they stay bad.
Pumping the fuel primer bulb, acting as a manual fuel pump eliminates the fuel pump as a possible problem.

S/Plugs should be Champion QL77JC4 plugs gaped at either .040 (Hot Spark) or the revised gap setting of .030 (Long Life)..... What plugs are you using?

If your timer base checks out okay...... You state that your stator is "Pretty New". Check it anyway visually, closely, carefully, for a sticky looking dripping substance dripping down on the powerhead area. Should this exist, when the stator is hot... very hot after running, then shut down, the water drains out of the powerhead and all the heat rises to the flywheel/stator area which creates a AC voltage drop to the powerpack capacitor. If this dripping is present, replace the stator regardless of what reading you might get from it.

If the stator appears to be okay.... Remove the black/yellow wire (kill circuit) from the "M" terminal of the ignition switch. If this cures the problem, the ignition switch has an intermittent short... replace it. NOTE: You will not be able to shut down the engine via the ignition switch with this wire disconnected.

Let us know what you find.

Thanks for the thoughts.

I have previously ruled out the sticking timer base, but I'll check it next time I'm on the water - on land sync and link is all good.

Plugs are the Champion QL77JC4, gapped to 0.04 from memory.

I popped the flywheel off today to check the stator - all looks completely normal.

Next time I'm on the water I'll disconnect the kill circuit + check the timer base movement.

Nick.

Feels like loosing spark you say ??----Use a timing light to see if you can pinpoint which cylinder.

Just a bit of an update - I haven't yet tried disconnecting the kill wire, or using a timing light during the problem.

I did recheck the sync and link and discovered it was slightly out - have corrected it.

I took the boat out, and noticed the following - unfortunately my test session was cut short by a bad starter solenoid (my lesson for buying "generic" junk).

After a cold start and warm up, engine runs great.

I ran the motor for about 10 minutes at speed, then allowed the motor to idle for about another 10 minutes - so the motor was never off.

The acceleration problem was present after the long idle period - I could get to about 1900 rpm, then it just started to die. I could accelerate to just on the point it starts to die, ease off the throttle slightly to say 1700 rpm, then it would allow me to accelerate past the 1900 rpm problem to whatever rpm I wanted.

Keeping the motor "working" keeps the problem away - any length of time idling or off, and the problem returns.

Do those symptoms help any?

I'm suspicious of some kind of link and sync issue - the only other thing I've noticed is the plastic cam follower is well worn - not broken, but it is probably 40 years old. Have ordered a new one but it won't be here for a couple of weeks.

OK, bit of an update. Tried disconnecting kill wire, no change. Timing light didn't really give anything away either.

The problem mainly turns up when the engine is hot, and has been switched off, and then allowed to sit for a short time.

Upon restart the engine won't go past about 1800 rpm.

However, if I ease off before that point, then try accelerating again, after 1-3 attempts, the motor suddenly "catches" and will accelerate past that point.

Is there a possibility the carb floats aren't quite right? Ie, if, they were a little low, I'd be running a touch lean, and with a hot engine that might lean it out just too far?

Or am I describing a vapour lock/fuel boiling under vacuum and heat issue?

The problem exists ONLY after you shut the engine down. THis is when all the water drains out of the engine and all the heat transfers to the highest point of the engine..... the flywheel and the STATOR! The stator being the beginning of the IGNITION system as well as the battery charging system.

Check the stator for cracks as also check to see if there is a sticky looking substance dripping down on the powerhead area. If that dripping substance exists... replace the stator as that dripping will result in a voltage drop to the powerpack.

Stators in this condition will usually function fine when cold... BUT... when hot will result in weak, erratic, and eventually no ignition.

Let is know what you find.

Hi Joe, stator is in perfect condition. Flywheel has been removed to properly inspect the stator.