Warm engine dies

[bones774]

I've been stumped by this since i removed boat last season. When I cold start the motor it starts fine, runs at idle fine and revs up fine, sounds great, leading me to believe there is nothing wrong with the motor, once it gets hot it sputters and stalls, it can be started again with difficulty but dies almost immediately, with spark arrestor removed i can see raw gas spitting up thru carb throat when it sputters to a halt. I replaced rotor and cap previously, checked for gas in the throat(i can hear it squirt when i press accelerator), I just checked for water in gas(at the filter) with a special paste and no indications at all. When I did remove my fuel separator the filter was only half full and nothing spilled out when i unscrewed it, i'm not sure if that is normal or not. Keeping in mind it only happens when warmed up could it be the fuel pump? Any safe way to test the flow? Any other suggestions? I'm at the boat location for the next few days so any suggestions I could test almost immediately.
Thanks

 

[bones774]

Re: Warm engine dies

any ideas?

 

[wellcraft-classic210]

Re: Warm engine dies

Possiblities seem to be related to fuel and spark delivery. A few ideas;

Have you looked at the spark by hooking up a spark plug note its color cold & hot / yellow is bad -- blue is good.

Are the plugs wet or dry ?

The electronic control module could be acting up under heat / I suppose the coil could act up as well. The coil is specific to thunderbollt ignitions/ as in not interchangable with auto coils

When is the last time the motor had a full tune & the carb was cleaned /rebuilt.

Edit-
Fuel pressure can be measured with a gage. If you have pressure at he carb you willl have flow if thier are no obstructions. Flw can be sen a th venturis insidthe arbbarrels. You may want to rig one up & leave it their while the engine warms up. Debris can settle & then clog fuel passages after running the engine a while.

You may also want to monitor vacuum on the manifold and do a compression check.

The experts here may also have some thoughts

 

[bones774]

Re: Warm engine dies

I put plugs, rotor and cap on the middle of last season, carb unknown and i've had boat for 3 years.

 

[Don S]

Re: Warm engine dies

Is the choke opening up when warm? If it's still closed, it will die at idle because it's flooding out.

 

[bones774]

Re: Warm engine dies

yes the choke is opening, the engine will die even if it is revving higher than idle, at higher revs it also becomes impossible to keep it running, then engine shudders, coughs and spits up thru carb. Been doing some archive search and been reading about coils possibly acting up when warm, is that a possibility? Any good diagnostics? How about that half filled fuel separator, is that the way it should be?
The engine runs so good when cold, it idles, it accelerates thru RPM and runs steady, this is very frustrating. Even my neighbors heard me start the other day and said "it sounds like he fixed the boat", then it dies.

I really appreciate all the help and i'm determined to get this thing fixed.
Thank you all.

 

[wellcraft-classic210]

Re: Warm engine dies

Electrical components can definitly act up as they expand from heat -- the inner connections can fail. Your electroins ignition module and coil coulld bot be suspect for this type of failure. Other than swapping them out I am not sure of a good test for the intermittent issue you have. ( Intermittent circuit opens are a pain-- Short circuits are nso much more exciting )

Spark strength by color as mentioned above may give some indication but its not the only possibility. Perhaps the experts can add to this I have heard of the electronic ignition module and coils acting up when warm but have not seen one personally.

As far as fuel --You should be able to visually see these things--
Does your accelator pump squirt fuel after it dies.
Do the venturis deliver fuel until it does?
Not sure about the 1/2 full fuel filter thing but if your getting fuel its probably not a problem.

 

[bones774]

Re: Warm engine dies

yes the accel pump squirts after it dies.

 

[wellcraft-classic210]

Re: Warm engine dies

Ok so thier is some gas in the carb.

If you can see fuel coming out of the venturis as the rpms increase ( these don't supply fuel at idle ) monitor that until it dies. If that's working its very likely not a fuel delivery issue. You may want to Verify that & then start working the electrical issues if it's oK.

How about that spark color ? That is step 1 of the electrical debug. If thats blue on a grounded plug the coils is delivering a strong spark.

The more checks you make the quicker you will get to the issue.

 

[joewithaboat]

Re: Warm engine dies

My money is on a bad coil or module.
Id buy both, change one at a time. Either way its not a bad thing to have a spare of each on-board.

 

[bones774]

Re: Warm engine dies

I had to leave the boat house for a day so i will resume tomorrow, 1st thing spark check.
Thanks

 

[joewithaboat]

Re: Warm engine dies

Just a heads up, i have had a coil with a nice strong spark when it was cold that got weak as the coil got heat soaked.

good luck!

 

[Luhrs28]

Re: Warm engine dies

I think those symptoms could indicate a vacuum leak. When the choke is partially closed that causes the mixture to be rich enough to cover for a vacuum leak so you don't notice it. Then when the choke butterfly is wide open the vacuum leak is enough CFM that it interferes with sucking the fuel through the jets.

I would get the engine at least 75% warmed up but where it will still idle, then spray all over every intake gasket and intake hose connection with either carb cleaner or WD-40. You'll hear the engine change speed if the spray is sucked in anywhere.

 

[bones774]

Re: Warm engine dies

Update-

Could an overheating engine go into shutdown mode for self preservation?
My neighbor came by and noticed very little outflow of water during my test procedure, after shutdown i removed the one big hose coming from the water pump and it was dry, i looked at one of the smaller hoses going to risers and it was just full of steam, i checked a lower petcock and very hot water came out. Which hose can i remove to test the inflow of water from the outdrive? and will that be an underlying cause of shutting down?


Thanks

 

[Rob the weekend warrior]

Re: Warm engine dies

I have the same problem. My problem only happens at idle- at off-idle it runs great, I idle down and its like I turn the key off cranks and cranks nothing, nada-as it gets cooler it will start firing but wont "catch" until it gets about 30 degrees cooler. temp gauge works and runs right up to about 160 but never gets hot. I have to wait for the motor to cool and then it starts right up like nothing happened. I talked to a speed shop and they suggested that it was the coil, but I tested for spark, and had good spark. I then got the mallory troubleshooting leaflet and dist is good. Good spark when warm. Went to carb, had it rebuilt-ran it, same problem, figured maybe as the intake air gets warmer engine goes to the rich side, checked plugs-BAM-BLACK! but not caked up. Cleaned them leaned the carb out (quadrajet-3 turns out=real lean) ran it, same problem! pulled plugs-white! checked spark, good spark. Accelerator pump will spray fuel-checked that, checked fuel pressure-good, opened carb checked float level-good, new float. Okay, heres the funny thing-advanced the distributor about 4 degrees and the problem seemed to go away-will let you all know after running this afternoon. I thought AH-HA it must be a broken spring on the manual advance dist-nope, all good, free and well lubed. I dont know-im gonna try running it a few degrees advanced and see-it cranks hard but runs smooth. If this solves it, I will just order a high torque starter and always run 91 octane.

 

[dingdongs]

Re: Warm engine dies

was it good when you pulled it out the water last year.ie did not run up a sand bank etc.get impellor sorted .could pull drive completely and stick a hose straight up hose through gimbal housing to see if its gonna circulate whilst running.maybe no vanes left on impellor and there all sitting in and around thermostat housing now.some good investigating is now in order .

 

[bones774]

Re: Warm engine dies

No, i had the same problem at the end of the year when i pulled the boat, figured i'd fix it now in spring.

 

[ktbarrentine]

Re: Warm engine dies

How much water supply do you have going to your muffs? Or are you using a drum/tub? On the fuel side, have you ruled out a bad fuel pump diaphragm? This will cause raw gas to enter the air horn of the carb while the engine is running. Ok cold/choked, but floods when hot. Check the sight-flow tube from the pump to the carb...should be dry. FWIW, this was my smoking gun for the very same symptoms.
KB

 

[bones774]

Re: Warm engine dies

I have a regular hose connection going to the muffs. Have not diagnosed the fuel pump diaphragm. The sight-flow tube looks dry, have not seen any fuel flowing thru that.

 

[Rob the weekend warrior]

Re: Warm engine dies

okay was on the water today. I feel that it is the distributor. I thought it was the coil so I bought a new one. Same problem. Replaced with old coil-same problem. Ran it around a bit (with the old coil), throttled to idle-dead. Felt coil-normal heat, felt intake-normal heat, coolant gauge @165. Felt dizzy-WOW SMOKING HOT! reached into the good old ice chest, grabbed a miller light and a block of ice and threw it on ol dizzy, and BLAMO within 5 mins the ice was all gone and we were heading back to the dock! Dunno if it is the module or what but I know its in that dizzy. Either that or I gotta get a water jacket for the dist. I did pull a wire from a plug and set a new plug on the intake to check for spark, and I had a little-very little, and apparently not enough.