What's this about?

[First-light]

Have you checked these for wear???

Piston Return Spring

HAHAHA, that can't be for real.

 

[DaveR]

Interesting that the two cylinders with the lower compression are next to each other. Is there a chance that there could be a weak head gasket or crack in the intake port thats opening up after it gets warm?

The inner cylinders are the first to heat up which is normal to these engines. But whether that's a possibily or not, I don't know...

when you did the compression test and found the 2 low cylinders, by any chance did you squirt oil in the those two and retest to see if you were losing the compression past the rings or top end?

No... just did the test and returned the plugs, all were fine

Hopefully it is the module or a couple of bad plug wires?

Good luck sometimes bad things happen to good people and at the end of the day you will know more about your boat than you wish too.'

Alan

I'll be checking the module next... and I can write a book about all the things I know about the boat and wish I didn't....

Have you checked these for wear???

Piston Return Spring

Yeah, but I had a little trouble getting them out through the spark plug holes...
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[First-light]

it seems you stated the problem happens when you are running, stop, then throttle back up. have you fine tuned your low speed adjustment and acheived the highest possible idle speed at a given throttle screw setting?

have you checked the status of your accelerator pump? those go bad and will cause a symptom much like you are explaining.

edit, if you still have "breaker" type ignition, replace with breakerless.

 

[DaveR]

if it was a bad compression problem or valve, etc, it would just get bad mpg's and run like shit all the time, you would have to adjust your idle high to keep from stalling all the time. your compression is fine, imo. besides if you had a compression or valve problem is would be obvious by the way the plug looked. ignition control module keeps coming to mind, for me, solid state electronic components are sometimes little bastards that test ok, then when there hot they run like shit. which distributer set up do you have, it's probably the pertronix, if it is I have a clymer for it.

Not sure the make... will check next time I am at the boat

it seems you stated the problem happens when you are running, stop, then throttle back up. have you fine tuned your low speed adjustment and acheived the highest possible idle speed at a given throttle screw setting?

have you checked the status of your accelerator pump? those go bad and will cause a symptom much like you are explaining.

Carb settings were done by my mechanic that rebuilt them. What / where is an "accelerator pump"... is that a part of the carb?
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[First-light]

Not sure the make... will check next time I am at the boat



Carb settings were done by my mechanic that rebuilt them. What / where is an "accelerator pump"... is that a part of the carb?
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which carb do you have?

the accel pump is found by removing the top half of the carb and finding the thing that looks like a mini toilet bowl plunger, what it does is it provides the engine with a shot of fuel to compensate for a off idle throttling, which requires a extra fuel. if your not getting a good shot of fuel, then it will stumble and sputter when you throttle up, you said the carb was recently rebuilt, if so the AP should have been replaced, they are very inexpensive, again, this is just something to look at, I still lean more tward ignition fault, mech fuel pump/quadrajet combos are know to be very reliable.

a easy way to test your AP is to look down the throat og the carb and manually pump the throttle on both carbs, it should provide a shot of fuel that comes out in a even strong spray, both carbs should be the same.

 

[DaveR]

Marcus, thanks for the clarification... I will look into that.
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[AKULA683]

Originally Posted by Gil Marlin
Have you checked these for wear???

Piston Return Spring

HAHAHA, that can't be for real.

Did you see the other parts on the site? Adjustable power band, Cross drilled brake lines, Engine oil bypass kit. Priceless!

 

[OILAGER]

My experience with symptoms on accelerator pumps have been the carb falling on its face while accelerating and then smoothing out to a normal RPM range. I would think it should do it all the time, not only after it's been ran a few miles.

I would take another look at the color of the spark plugs on the lower compression cylinders and see if they are burning a different color than the others. I assume you have raw water cooling which makes it difficult to see if you are burning/using water in the combustion chamber by checking the reservoir.

I'm no expert on boats but I've had enough mystery cooling/acceleration/idling issues the last 30 years with automotive based engines to make me want to torch the next one that I might encounter.

 

[Lou W]

Replace this and all will be well.

Kuhneutson Valve - $65.99 : KaleCoAuto, Hard to find automotive items!

 

[drdiesel]

You need to get it to miss again, try to keep it running but not clean out! Than have your rubber coated pliers ready and pull spark plug wires one at a time! find which wires dont change the way it runs, leave them off. After you've done all eight what ever is off of the cap is your starting point. At least you'll know its ignition, those particular wires, plugs, or could very well be the ign. control mod. Is there a ballast resistor on the ign circuit?

 

[Gil Marlin]

Replace this and all will be well.

Kuhneutson Valve - $65.99 : KaleCoAuto, Hard to find automotive items!

I just ordered some premium turn signal fluid from them...

 

[DaveR]

My experience with symptoms on accelerator pumps have been the carb falling on its face while accelerating and then smoothing out to a normal RPM range. I would think it should do it all the time, not only after it's been ran a few miles.

I would take another look at the color of the spark plugs on the lower compression cylinders and see if they are burning a different color than the others. I assume you have raw water cooling which makes it difficult to see if you are burning/using water in the combustion chamber by checking the reservoir.

I'm no expert on boats but I've had enough mystery cooling/acceleration/idling issues the last 30 years with automotive based engines to make me want to torch the next one that I might encounter.

Yeah, I'm about ready to do some torchin'..... the plugs all looked good, no diff from one cylinder to another.

Replace this and all will be well.

Kuhneutson Valve - $65.99 : KaleCoAuto, Hard to find automotive items!

.....

You need to get it to miss again, try to keep it running but not clean out! Than have your rubber coated pliers ready and pull spark plug wires one at a time! find which wires dont change the way it runs, leave them off. After you've done all eight what ever is off of the cap is your starting point. At least you'll know its ignition, those particular wires, plugs, or could very well be the ign. control mod. Is there a ballast resistor on the ign circuit?

OK, that's worth a shot.... thanks.

I just ordered some premium turn signal fluid from them...

Yeah?....... now go buy a boat and use it up ....
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[brokeass boater]

Air+Fuel+Spark-all at the right time. Whats missing? A choke stuck closed = no air.(dealing with a warmed up motor here yes?). Run the boat till failure. Lift flame arestor. Verify choke opening up at temp. If choke o.k, now have someone at the helm and push the throttle a couple times. looking down into the primaries, got a good strong supply of fuel? If o.k its a spark issue. No need changing parts until you know what direction to head.

 

[Gil Marlin]

David, I feel for you and I don't have anything to offer as just about everything has been touched upon. I was just trying to add a little levity here.

 

[DaveR]

David, I feel for you and I don't have anything to offer as just about everything has been touched upon. I was just trying to add a little levity here.

....

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[ALUMINATOR]

David, I read this and didn't see if you tried switching the fuel lines. Both times this happened wasn't it after you hit some rough water (wake)? I do hope you find it soon and it is an easy fix!

 

[brokeass boater]

O.k. David, I saw on one of the other threads you may have idea of what your dealing with that motor. I been checking on your progress waiting to here somthing good. It seems that you and I been stepping on the same stones this past month with a some what simular motor issue. Like I stated in a previous post theres alot of this "motor dies when warm" " motor wont run above 1500 rpms" on other boating forums and not many come back and share what they found.

 

[DaveR]

O.k. David, I saw on one of the other threads you may have idea of what your dealing with that motor. I been checking on your progress waiting to here somthing good. It seems that you and I been stepping on the same stones this past month with a some what simular motor issue. Like I stated in a previous post theres alot of this "motor dies when warm" " motor wont run above 1500 rpms" on other boating forums and not many come back and share what they found.

Based on a discussion with another long frustrated boat owner that just figured his problem out and solved it, I believe mine is the same, and it's an overheating coil due to poor original manufacturer wiring using non-tinned wire... of course that was 30+ years ago. So I am going to re-run the wires to my ignition switches tomorrow, then take it out over the weekend and see if that was it.

Of course, while I'm at it, I'll be changing out those damn piston return springs too...
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[Albiebac]

edit: Ha, ha, looks like we posted at the same time.

I had the same problem, and FIXED it this weekend, after 3 years of chasing gremlins! I've already PM'd David, so he's going to look into it, but for anyone else, this was my issue.

BTW, I tried anything and everything mentioned is this thread and all other threads (including my own) on the internet, I thought it was a fuel issue.

Symptoms:

• Motor runs perfect at idle.
• Motor bogs down after 20mins to 1-2hrs of running, only can go <1500rpms.
• After time, it will run fine again.
• Coil is noticeably very hot to the touch

Cause:

• Not enough current available to 12V+ lead of coil, too much resistance in the line.

Fix:

• Replace 10 gauge ignition wire running from starter to helm.
• Replace ignition switch.
• Replace coil wire running from helm to coil.

Side note:

Skipjack/Volvo did not use tinned wire on their engine harnesses, therefore one or more of the leads had corrosion, I did not bother to identify the one with the bad mojo, all I care is the problem is solved!

Good luck everyone else,

Eric

 

[DaveR]

Thanks again for your input and for sharing what ended being your long sought after solution. Hope you have a long period of worry free boating accompanied with great fishing....

As I mentioned, I will be doing as you suggested and will post up whether or not it works equally as well for my problems.... which seem to be pretty much the same.

Tight lines

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[piperca]

I hope this works out for you, but if you are going to delve deeper and address the distributor module, let me know. I have a brand new module, still in it's box, laying in a drawer on my boat. If it is the same one as yours, you can use it to troubleshoot; if it works out, I'll sell it to you for less than you can find one. I'm starting to feel a bit like a parts store ... lol

 

[brokeass boater]

you can check wires in question with a multimeter before replacing. I might have suggested to you to check the coil with same meter. I lost the secondary side on mine. when you replaced the coil did you replace it the correct coil for your ign. system? resistor vs no resistor

 

[DaveR]

I hope this works out for you, but if you are going to delve deeper and address the distributor module, let me know. I have a brand new module, still in it's box, laying in a drawer on my boat. If it is the same one as yours, you can use it to troubleshoot; if it works out, I'll sell it to you for less than you can find one. I'm starting to feel a bit like a parts store ... lol

Sure, I'll buy yours if I can pick it up in the AM from the Piperca Parts Source near me, and presuming it matches what I've got.

Got any more good parts that I need just laying around there bubba ?....

Thanks for the offer.... let me know.
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[brick_haus]

Any backfiring? Black smoke? Backfiring through the carb would indicate a lean condition (fuel supply prob.). Black smoke would indicate a rich condition (needle and seat problem). Otherwise I would suggest that you check for vacuum leaks next. With the spark arrester removed and the engine running, cover the carb air intake (venturi) with a wadded towel and stop all air from entering the carb. The engine should immediatly die. If it doesnt, your carb gasket may be the culprit or a loose or disconnected vacuum line. To determine if you have a vacuum leak in the intake manifold or its gasket, get a can of brake cleaner and carefully spray it directly onto the gasket, all around the perimiter of the manifold and around the carb base. If there is a vacuum leak there your engine RPM will surge due to the brake cleaner entering through the leak and igniting in the combustin chamber. Be careful and good luck.

 

[Vigilant32]

Diagnosis is where good mechanic makes their money.

It is easy to replace stuff but can be difficult to find the correct remedy, imho.

You might want to give Kiwi Dave a call, he is one of the best inboard guys on the coast.

I for one wonder if you are running out of fuel in the carb bowls. If the accelerator pump is weak, or float bowl seat has some junk in it, you will not keep the bowls filled and the engine starves for fuel, runs rough, no power, etc....

Did you replace the impeller after you dry ran the motor? If so, did you pull apart the heat exchanger to remove any broken pieces? Hot dry motors tend to loose power and run rough.

Good luck, I hate gremlins in the engine room..

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