Strange hesitation problem

"I have an older boat, a 1980

"I have an older boat, a 1980 Invader with a Mercruiser 260. When I drop it in the water and start it up it runs like a dream, especially for an older boat. After a couple of hours though, it can't build power when I accelerate hard. It stutters and misses and after a long time can build up the RPM, and once the RPM are up it runs smoothly. At first I thought it was a fuel starvation problem. The fuel pump was replaced 5 years ago and there aren't enough hours on the boat to suspect that. I've replaced the fuel lines, had the carburator rebuild and checked the tank for sediment. I began suspecting electrical and replaced the plugs, plug wires, distributor cap/rotor but problem persists. I am pretty certain the problem is temperature related because if I shut the boat down for an hour it runs just fine again for 45 minutes or so and then the problem returns. The only other clue I have (which may not even be related) is that when the engine is hot it tends to stall at idle when switching into neutral.

At this time I am suspecting the distributor itself. Its about the only thing left, and at 28 years old I'm wondering if the springs that govern spark advance have become weakened and are affected by temperature when the engine is fully warmed up. I'd just replace it and give it a whirl but the location of the distributor requires that I drill a hole to get the distributor out and patch the fibreglass afterward. Any thoughts as to what else it could be or how to determine for certain would be appreciated."

"advance can be checked with a

"advance can be checked with a timing light. you may have a coil problem. have you replaced it? notice the tach acting up? try disconnecting. the stalling is usually shift cable related. any binding causes the interupt switch to stay engaged too long, and kills the engine. you could check the distributor shaft for axial play. this would cause the timing to wander a bit if running points. usually not a problem for electronic ign."

"the shift cable/ interupt swi

"the shift cable/ interupt switch could be causing your accel. problem too.when the problem occurs, look and see if the switch is centered. the shift cable lies on the exhaust y-pipe so temp could have effect."

"First timer here. I have a m

"First timer here. I have a merc 140 (181 cid) around 1985. I was having similar problems with hesitation along with problems starting. I am ordering the electronic ignition conversion and getting the high performance coil. I am going to also order the standard kit in case it does not work. I am in Ohio, so the boat sits for long periods and seems to be a standard practice of replacing points. The last coil I bought the top screw just broke off, so I am wondering on the quality of my local dealer. (No, I did not over torque it) Appreciate the good forum responses here and I have added this site to my favorites. I will check the shift cable/interupt as well. Curious if anyone knows if there is a real benefit of going with the better coil or if any issues/problems over using the standard replacement coil?
Thx.. Jeff"

"I thought of the coil but fig

"I thought of the coil but figured its not the problem since the behaviour only occurs under acceleration. Is my thinking flawed? The tach operates just fine. Advance is fine with a timing light but that's in my driveway and not under load.

But...I'm intrigued by this shift cable/interrupter switch. I didn't know there was such a thing (I grew up with cars, not boats!). Its been a few months since I had it in the water, but I vaguely recall being able to gun the motor without problem in neutral. If my memory serves me correctly, would that tend to confirm the shift cable/interrupt switch being the problem?"

"[b]"would that tend to co

""would that tend to confirm the shift cable/interrupt switch being the problem?"

Nope,... That would be irrevelant....

1980,... Is this a Point fired motor, or Electronic,..??

Is the Fuel Tank Vent restricted,..??

How long ago was the Carb rebuilt,..??

Changed your Fuel Filters lately,..??"

"point fired
fuel tank vent i

"point fired
fuel tank vent is fine I think, how would I check?
carb was rebuilt 6 months ago, after the problem appeared and made no difference
changed water filter several times, filter at the carb changed last year, also made no difference."

Wouldn't hurt to put a fue

Wouldn't hurt to put a fuel pressure guage inline just before the carb.Have someone watch it while this is happening. 5 or 6 lbs pressure is good.

"Wow, thats a TON of informati

"Wow, thats a TON of information. I want to thank everyone as this is more valuable input in just a couple of days than I have gotten from months of asking questions of people who actualy get paid to fix my boat!

I'm developing an action plan focusing on the ignition system first since almost every piece of advice I've had on the fuel system is something I've already done. I won't be able to make progress on this for another six weeks or so because where I live it won't be above freezing for at least that long. When I do get into though, I'll post the results here so that everyone sees the final answer (assuming I find it!)

Also, once I know what the problem is, I will satsify those who are looking for murder and suspense by destroying the guilty parts in some gruesome fashion!

Thanks once more everyone.

Dave"