engine running poorly after warmed

[malibu215]

New to the forum here, appreciate any help.

I have a 1990 Malibu 215 euro F3 with a GM 350 (5.7L Blue water skier), serial # D379763. It has a quadrajet carb, mechanical fuel pump, conventional ignition.

It runs great when we hit the water. I will run it for over an hour, pull a couple skiers, etc. Once I stop the engine for a while and re-start it, it will run poorly by not accelerating with a load. It will die out if I continue to accelerate. I can rev it in neutral, with some sputtering. I will head back to the dock easing it to cruising speed. It will continue to get worse as I continue to drive, to the point that it is difficult to get it into gear without dying. I can always get it started, possibly requiring several pumps of the throttle. As it gets worse, it will not rev smoothly in neutral either.

I have been working this for several weeks, trying to diagnose the issue. Here is what I have done so far, with a test run after each step:

1. Replaced inline fuel filter and filter at the carb (had an issue with solids in the carb filter early last season)
2. Replaced ignition coil
3. Put Seafoam in the gas
4. Replaced spark plug wires, points, and condenser, tried to replace rotor but my new one snapped about a half mile out from the dock.
5. Checked and set the timing
6. Attempted to change fuel pump, but got the wrong part. I pulled mine apart while I had it off. Inspected the diaphragm, pressure tested the check valves.

Appreciate any help, let me know if I can clarify anything.

 

[HT32BSX115]

Re: engine running poorly after warmed

Howdy,


I don't see where you may have rebuilt or replaced the carburetor.
You may have contaminants in the float chamber or an intermittently working accelerator pump...


Also, if it gets progressively worse you may have a plugged or restricted fuel pick-up screen and/or sticky/restricted anti-siphon valve.


I would lose the "Seafoam" too, some will disagree with me, but that doesn't do much except maybe foul your plugs.


Regards,


Rick

 

[bigdaddypt]

Re: engine running poorly after warmed

I agree with Rick...SeaFoam is nothing more than mechanic in a can and won't fix your problems.

 

[bruceb58]

Re: engine running poorly after warmed

I also agree with losing the SeaFoam. I wouldn't give it the benefit of calling it mechanic in a can. Just can't figure how putting something in your gasoline that is half oil is really going to help you much and considering another good portion is just alcohol...just a very expensive way to buy a little bit of naphtha solvent.

 

[Bondo]

Re: engine running poorly after warmed

Ayuh,... I'm thinkin' the Carb is Junk... Definitely a fuel delivery issue...

 

[malibu215]

Re: engine running poorly after warmed

Carb was next on the list, I already bought the rebuild kit and haven't had time to get on it yet. I haven't gone through the carb for a couple of years.

The only thing I can't figure is that it seems to be heat related. If it was the carb, why would it run fine after it cools again?

Where is the fuel pick-up screen located?

I have never been impressed with seafoam, but some people swear by it. I can't figure?
Thanks for the help!

 

[John_S]

Re: engine running poorly after warmed

The only thing I can't figure is that it seems to be heat related. If it was the carb, why would it run fine after it cools again?

How hot is the carb after the heat soak? Did gas perk out into the manifold? The last time you rebuilt it, did you use the same style base gasket? Was the original one a thick 1/4" gasket? ie one that helps prevent heat transfer from your hot intake with exhaust crossover.

 

[malibu215]

Re: engine running poorly after warmed

Everything is pretty hot after heak soak, I will take a IR heat gun to it and check. I was noticing that even the flame arrestor is very hot, didn't want to touch it for more than 5 seconds.

When rebuilt, I used a 1/4" thick base gasket.

I am not sure what you mean, "did gas perk out into the manifold", or don't know how to check.

 

[John_S]

Re: engine running poorly after warmed

I am not sure what you mean, "did gas perk out into the manifold", or don't know how to check.

It can get so hot that the gas boils and overflows and runs down into the intake and runners. With engine compartment open, if you are quiet, you can hear it, or smell a stong gas smell.

Older q-jets were known for leaking well plugs. Again, gas running down in the intake.

 

[malibu215]

Re: engine running poorly after warmed

Any idea on how hot is too hot? I will check it this weekend and listen/smell for gas perking.
If it is too hot, how do I permanently fix it? A cooler running thermostat?

 

[bruceb58]

Re: engine running poorly after warmed

Let it idle for a little while before turning off and turning on your blower for awhile after turning off will help.

Just as a test, next time you stop, open up the engine hatch and lay some wet towels around the engine maniold around the carb to keep things cool. If the problem still occurs, probably not a vapor lock problem.

 

[malibu215]

Re: engine running poorly after warmed

Thanks for all the help thus far. I checked the temp on the carb, and it seemed normal, only about 120F. I did rebuild the carb, and it did not help.

Since I have replaced the entire ignition, I was beginning to think the problem was in the primary circuit/harness. I took the boat out, warmed it up and it began to sputter and run poor. I installed a jumper from the battery to the ignition coil (with an external resistor), and it fixed the issue.

There are two wires going to the + side of the ignition coil. My wiring harness shows a purple "resistor wire" coming from the alternator and a purple/yellow wire coming from the starter solenoid. Does anyone know if the resistor wire could be breaking down?

My two thoughts are the wiring harness or the alternator. Any thoughts?

Thanks for all the help

 

[bruceb58]

Re: engine running poorly after warmed

Use a voltmeter and measure the voltage at the coil when all of this happens. Also measure the battery voltage.

 

[Geko104]

Re: engine running poorly after warmed

Ok im new to the forum and this is my first post. I once had a clinker style ski boat that was fitted with a 6 cyl inboard petrol engine. It ran quite hot and a bit ordinary after about 20 minutes on the water. When i restored the old girl i put a jabsco type water pump in it and ran it via a vee belt form the harmonic balance pulley. This meant that the pump was going flat out, actually too fast, water was passing through the engine far to quickly for it to have enough of a cooling effect, and when i stopped the boat the engine heated right up. I fixed it by putting in a tap where the inlet is at the bottom of the boat so i could regulate the flow. Most skiboats have their waterpumps connected to a small pully on the flywheel on an inboard engine with low gearing. Mine was geared way to high. Anyhow i fixed that problem. Is it possible also that your fuel tank is not breathing?? after you shut the motor off have you tried taking off the filler cap to see if it makes a sucking sound? If it does then that will probably be your problem!

 

[malibu215]

Re: engine running poorly after warmed

Thanks for the help so far everyone. I did some more work after all of these exchanges and here is what I have found:
The problem is definately electrical. I found that if I jumped a wire from the battery to the coil (with an external resistor) the problem would go away completely and we could continue to ski all day. I think the problem is in the motor wiring harness, too bad mercruiser doesn't make my wiring harness any more.

Not only do they not make the harness, but the harness has a "resistor wire" that feeds the coil. I finally found a resistor wire that was for an older FORD that I was able to use. The resistance measured out the same as the one in the boat. I replaced it and thought the problem was fixed. I went out last weekend and we had the same problem. Luckily, I still had my jumper wire and we were able to enjoy the rest of the day.

I am planning to replace two more wires that are between the battery and the coil. If that doesn't fix it, then I am not really sure what to do.

If anyone has any tips, please let me know. Thanks

 

[cr2k]

Re: engine running poorly after warmed

Sounds like a bad coil.

 

[bruceb58]

Re: engine running poorly after warmed

Sounds like a bad coil.

How could it be the coil if it runs fine when he jumpers it?

 

[bruceb58]

Re: engine running poorly after warmed

You need to measure the voltage at the coil with the points closed. Also, have you checked your dwell to make sure it is at spec?

 

[malibu215]

Re: engine running poorly after warmed

I do not have a dwell meter, so I have not checked the dwell.
I checked voltage at the coil with the motor running at idle, I am not really sure if this tells me anything, but this is what I saw:
When idling, the voltage was ~9.9V (oscillated +/- .5v). The voltage stayed constant even when running poorly and missing. I connected my jumper wire with the resistor and the voltage raised to ~12V. If I jumpered straight from the battery without the resistor, then the voltage raised to ~14V.

Last time when I was out, my trick with the jumper and the resistor eventually began to not work. At that time, I had to jump straight from the battery to get the boat to run well. This and my voltage measurements are showing that the coil is needing a higher voltage to have a hot enough spark, but possibly my points have begun to burn over from the time running off the jumper at the higher voltage.

I am beginning to think I was incorrect on my assumption of power to the ignition system. Do you think I could have purchased a bad coil last year when I replaced it?

I am looking at upgrading to electronic ignition. I am not sure that it will fix anything, but I figured an upgrade never hurt. I see several options from $100 conversion kits to entire new ignitions for $400 (HEI or non-HEI). Any thoughts on the options?

 

[malibu215]

Re: engine running poorly after warmed

So I am still considering the ignition upgrade. From the research I have done, the best one seems to be the Delco EST ignition. I was looking at installation instructions, and it has a wire to connect to the shift interrupt switch. My boat does not have a shift interrupt switch. Is that only for outdrives, or will I need to install one?

If I don't need one, what do I do with that wire (ie. leave disconnected, connect to 12V)?