PDA

View Full Version : engine stalls at running rpms


ryangraham
07-19-2007, 01:38 AM
I have a PCM Ford 351 with Holly Carb. on an 86 Mastercraft 19' Stars and Stripes. The engine cranks perfectly, and it runs at idle speed (600 rpm) all day. The boat will come out of the hole and run at 3000 rpm for 30-45 seconds. Then the rpms fall off drastically. It seems that when the take is full of gas I am able to pull back on the throttle and prevent the engine from stalling. If the fuel is under a half tank, the engine will stall completely.

What I've done so far:
1. new fuel filter - the old one was fuel of crap and had not been changed in at least 8 years.
2. cleaned fuel screen between metal fuel line and carb - this screen was not very dirty. Just a minimal amount of tiny debris.
3. checked for debris in metal fuel line: none.
4. cleaned carb with spray cleaner.
5. replaced spark plugs.

If it's a fuel related problem I think it may be the fuel pump, or possibly the fuel pick-up in the gas tank. But the old fuel filter was full of gas and the engine can be restarted after stall......unless you open it wide up and let it stall. I did that today and it took us quite some time to crank it back up, and after a lot of throttle pumping - and no, I did not flood it. So it seems like the engine is being delivered fuel, but maybe just not enough at higher rpms.

Can anyone shed some light on this??????

My other thought is electrical: Are the points bad? Is the cap bad? Maybe the coil? I've contemplated changing over to a pointless - all electrical ignition system.

Does anyone think my problem is electrical????????

HELP!!!!! My wife and I got new wakeboards as wedding presents and we're dieing to break them in!!!! PLEASE, HELP!!!!!!!!!!!

-GRAHAM

454Prostar190
07-19-2007, 01:00 PM
Sounds like a fuel supply issue and the bowls in the carb are running dry because of lack of fuel supply. I had an old Mopar that had the same problem. New fuel pump fixed it. It does not sound electrical to me.

etduc
07-19-2007, 01:32 PM
I have a PCM Ford 351 with Holly Carb. on an 86 Mastercraft 19' Stars and Stripes. The engine cranks perfectly, and it runs at idle speed (600 rpm) all day. The boat will come out of the hole and run at 3000 rpm for 30-45 seconds. Then the rpms fall off drastically. It seems that when the take is full of gas I am able to pull back on the throttle and prevent the engine from stalling. If the fuel is under a half tank, the engine will stall completely.

What I've done so far:
1. new fuel filter - the old one was fuel of crap and had not been changed in at least 8 years.
2. cleaned fuel screen between metal fuel line and carb - this screen was not very dirty. Just a minimal amount of tiny debris.
3. checked for debris in metal fuel line: none.
4. cleaned carb with spray cleaner.
5. replaced spark plugs.

If it's a fuel related problem I think it may be the fuel pump, or possibly the fuel pick-up in the gas tank. But the old fuel filter was full of gas and the engine can be restarted after stall......unless you open it wide up and let it stall. I did that today and it took us quite some time to crank it back up, and after a lot of throttle pumping - and no, I did not flood it. So it seems like the engine is being delivered fuel, but maybe just not enough at higher rpms.

Can anyone shed some light on this??????

My other thought is electrical: Are the points bad? Is the cap bad? Maybe the coil? I've contemplated changing over to a pointless - all electrical ignition system.

Does anyone think my problem is electrical????????

HELP!!!!! My wife and I got new wakeboards as wedding presents and we're dieing to break them in!!!! PLEASE, HELP!!!!!!!!!!!

-GRAHAM

There is a possibility, you distributor, is not advancing. (You won't regret going to a new pointless distributor. Even if yours, is fine.) Have you rebuilt the carb? How old is it?

Up to 3000 rpm, your probably still on the primary fuel circuit of carb. Has the boat, been sitting? Check your secondary float valve, float,etc. Check your float bowl fuel level.

On a properly working Holley carb and properly timed engine, you should not have to pump,pump, the throttle.

sahara00
07-19-2007, 01:53 PM
I had a similar problem last summer. The boat would run all day at idle but as soon as any throttle was applied it seemed to run out of gas a minute later even though the tank was full. We checked everything and it ended up being the check valve directly on top of the gas tank, that prevents the fuel lines from draining back into the tank. Ours was just clogged with everything and it wasn't allowing enough gas to flow.

ryangraham
07-20-2007, 10:03 AM
All of this helps. Thanks everyone. I bought a new fuel pump, a new fuel line, and a couple other non-related items. I'm going to go through a couple checks and tests before replacing the fuel pump, but I think/hope it is indeed a bad fuel pump. Others (outside this forum) suggest it may be the gas tank is not venting properly. I'm going to check for that as well. I'm leaving straight from work today to spend as much time as needed this weekend to fix this problem. I've got to get riding!!! If anyone has anything additional, please let me know. Again, I really appreciate the input. I'll let everyone know how it goes.

Cheers.
-Graham

JimN
07-20-2007, 10:44 AM
If you want to check the spark/points/coil/ignition issues, hook up a timing light. If there's an interruption, you'll see it. Doesn't have to be an expensive one, either. Won't show advance but at least you'll know if the spark is consistent. Then, once you determine that, you can go on to the fuel issues.

Personally, I would start with the fuel system. Look at the fuel pickup and the chamber in the tank where it lives. I have seen all kinds of debris in there that would surprise you. Pieces of leaves, seeds, twigs, silicone, etc. Some of this stuff will drop out while the motor is at lower RPM but over time, it gets sucked in. If you find anything in the pickup (some have a spring in them), go to the anti-siphon valve next. Once it gets past the right angle fitting, it won't necessarily fall back to the tank.

Kellogg X45
07-20-2007, 01:24 PM
float level adjustment?

ryangraham
07-23-2007, 08:17 AM
SUCCESS!
I had to tear down most of the fuel delivery system, and half the credit goes to shear luck, and there is a chance I'm not out of troubled water yet, but my boat is back on the water and running better than ever! New wake boards are broken in perfectly. Thanks for all your help Robby!

It took a bit of trial and error, but what final got it was an error and trial. What I mean is, I broke the check valve off the top of the fuel tank, DOH! But this got me digging into the fuel tank itself. I was never able to get the wicking tube out of the tank to examine if it was clogged or defective, so I blow through the tube, felt a little pressure on it, then it cleared and I was able to blow more easily. Seems as though the wicking tube sock may have been pulled up inside the aluminum or maybe there was some debris in there. But maybe that wasn't the problem at all. I replaced the nipple of the check valve with a new brass fitting, and I decided to leave the ball seat, ball, and spring (the parts that create the actual check valve) out. The engine runs perfectly now. No stalls. I purchased an inline check valve that I can cut into the fuel line if I find it necessary to do so.

As a side note: I was able to confirm the issue was not fuel pump, carb, electrical, timing, or god knows what else by feeding the fuel line directly into a 5 gallon gas tank (the kind you fill up at the gas station). As soon as I did this, the problem went away. This isolated the problem to that gas tank.

Another thing: EZ Outs are worth their weight in gold if you ever snap off a small aluminum fitting ;-)

One last thing: www.skidim.com not only do they have a great selection of parts (just about everything you'd ever need) their people are absolute tops. Richard spoke with me over the phone about my problem and gave me tremendous insight and perspective on my boat. Thanks Richard. Send this company your business. They've earned mine!

Thanks for everyone's input on this forum.

-Graham
86 MC S&S, 351 Ford PCM

skibtlvr4evr
07-23-2007, 09:46 AM
I had bought new fuel cap and boat was dying after getting up and skiing, the gasket under fuel cap expanded (10% alcohol in gas) cut gasket back to metal gasket and now no problems.