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1977 115HP Stalls occasionally under load after restart

nicklanigan

Contributing Member
Hi all,

I've been gradually restoring and repairing this motor, which I don't think has had much looking after ever.

My remaining problem is a stall under load, which only occurs occasionally, and only after a warm restart where the engine has been off for a few minutes.

In such a scenario, the engine will start just fine, but as the throttle is opened, the engine will rev up, but then quickly slow and stall out completely. The engine can be restarted, and it will idle fine, but will stall out again as the throttle is opened. If I'm fast enough and back off the throttle, the engine will keep running and return to idle. Most of the time though, the engine dies.

In this situation, I've re-primed with the primer bulb, and managed to get going again.

There is occasionally a slight hesitation as the engine rpm increases in normal use - almost as if the engine has to overcome some hurdle - once beyond the hurdle, all is fine and the problem won't repeat, unless the engine is shut down again for a few minutes.

I've also had two occasions in the last couple of weeks where altering the motor trim seemed to cause problems - once was at full speed - I tweaked the trim and the engine slowed right down, and a second time where I was coming into shallow water and raised the motor to have the prop just under the surface. In the second scenario, the motor stalled and couldn't be restarted in that position (I know it's not a great position for the carbs).

So far, I've replaced all the fuel lines, the primer bulb (with OEM), fuel connectors, filter and water separator, and the fuel pump. (old pump was leaking, so had to go anyway). The tank vent is fine, and I've run off a separate fuel tank as a test - same problem. Plugs are relatively new, compression is all fine. Power pack is also new as old one failed. Fuel is good.

My next fix will be to rebuild the carbs, which would seem to be most logical source of the problem given everything else that has been done.

I guess my other potential problem remains an air leak in the fuel system somewhere, but given the engine runs great, and restarts great, I don't think this is the case.

Any other ideas I should be considering?

Nick.
 
Last edited:
An update on this - pulled the carbs off last night - lower float bowl had a nasty brown liquid in it, as well as fuel.

I guess at some point water had gotten in.
 
Hi all,

An update on this one.

I've rebuilt the carbs, which were in great condition, aside from the rusty stuff in there.

So, carbs are back on, which has definitely helped in terms of general motor starting/running (many of the o rings/washers were in poor condition).

However, my stalling problem under power remains. It only happens after the engine has been running and then shut off. Most of the time, restarts are great, but occasionally I get the stalling issue.

I took a close look over the weekend - as the throttle is advanced, timing is advancing until it hits the stop, and the engine rpm increases appropriately.

Opening the throttle any further though, the engine quickly stalls out. So, the engine is running just fine until just the point the timing is fully advanced, but then stalls.

My next thoughts are to check out the "sync and link" settings - my current thinking is that the maximum spark advance needs increasing, but this can only be proved by the "sync and link" setting procedure.

However, I struggle with why this only occurs after a restart?

Anyone have any insight into what might be happening?

Thanks,

Nick.
 
Caution------Do not adjust spark on a whim.------------------Maximum timing is set at the factory and generally needs no adjustment for the life of the motor.-------Do more trouble shooting on this motor.
 
It's been a while on this one - the hot restart problem has plagued me.

I've searched the internet far and wide for a resolution - it seems to be a fairly common problem, but one that very rarely has a solution found. There are a world of suggested problem components - be it electrical or fuel related that could be the problem. None of these suggestions fixed my problem, although they did fix many other issues I had.

Ultimately, my hot restart problem came down to either worn piston rings, or piston rings allowed to rotate because of worn piston ring locator pins.

I eventually had a ring rotate and catch on the exhaust port, breaking the ring and damaging the piston.

Upon opening the engine, two pistons had ring locating pins completely worn away, and another piston had pins worn about 75% though.

Replacing all this as part of a rebuild has finally cured my hot restart problem.

My theory on why:

With the engine running, the cylinder is cooled by the water supply. Once the engine is stopped, the cylinders heat up from residual heat, and expand, losing the seal with the piston rings.

Restarting the engine starts the cooling process again, but this takes a few minutes to shrink the cylinders back to the size that they seal against the rings again.

Until they cool and shrink again, the compression and vacuum cycles fail, resulting in engine problems. The problem is probably the crankcase vacuum required so fuel doesn't make it to the combustion chamber.

I could be completely wrong on my theory, my certainly the engine rebuild fixed my problems.

Nick.
 
Post # 1 said that " compression was all fine " on this motor !------------I guess it was not.-------What are the compression numbers today ?
 
Yeah - compression was ok when cold or warm - around 95 on all cylinders.

In hindsight, I never tested it when hot - I could never had gotten the motor hot enough at home and didn't think to take a compression tester out on the water. Normally the problem occurred during a session of wakeboarding when I've stopped the motor to get the kids back on the boat between turns.

Other potential source was a "stuck" ring - not sure of correct terminology, but some of the rings seemed to be frozen in the ring groove and weren't springing outwards.

120 on all four now.
 
Compression of 95 obviously is no good.------That is why I always say ---" post the numbers " -------Poor quality oil and fuel will jam the rings with carbon.
 
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