Engine Stops after 30-40 mins

[JXP]

Hi All

I am new to the forum and I have C&C 34 1978 boat with the A4 engine with the crank handle on the front of the motor.
I can start the engine on the first time and it runs very well for 30-40 mins then it starts struggling and if try to increase the speed it doesn’t like it, if I lower the speed it slows but still struggles shortly after stops.

I have replaced the fuel / water separator filter and the fuel pump.
I removed the fuel from the old filter and gas looked great, the temperature gauge needle is showing between 140 - 160.
But my problem is still exactly the same.

[ndutton]

Welcome to the forum and welcome to A4 troubleshooting. I have a two-tiered test for you to perform based on your report:

1. Try running the engine with the fuel fill cap open, well past the normal 30-40 minute shut down point. If the problem disappears we know it is a tank vent blockage. If it shuts down again . . . .
2. Immediately upon shutdown test for spark. There are several threads on the forum describing the test, most recently this one.

Please report back with the results and we can proceed further.

[JXP]

Reporting back on tests

Removed gas cap and ran engine in gear at 1460 rpm it ran for 52 mins in total.
It started struggling at min 33 to 52
During the run water temp was 178 , consistent white vapour it had smell and was warm to the touch and lots of water through exhaust, oil pressure steady at 40 to 42.

Not sure if I performed the spark test correctly, never done one before.

Engine stopped I push in my ignition switch ( other wise my points burn out I am told)
I went under the stair hatch pull lead off the 1st plug in front of the row removed the very hot plug attached the lead cap to it and cranked the engine handle anti clockwise or to the left I did not see any spark crank 3 or 4 times total.
The spark plug had some black residue on it, I haven’t checked the rest of the spark plugs.

[ndutton]

Negatory - - the engine must be cranked the same as trying to start, ignition on, starter turning. The hot spark plug suggests you have spark however meaning this is probably a fuel related problem.

Practice doing the spark test anyway so when you do it for real you'll know how and know what to expect.

[JXP]

Rerun of problem

I will re run the tests today and post results thanks for info on spark test I wasn’t sure how to do it

[ndutton]

I suggest doing the spark test as you start the engine for practice then again immediately upon shutdown. You'll probably need a helper to operate the starter while you observe for spark.

[edwardc]

... You'll probably need a helper to operate the starter while you observe for spark.

Or get one of these remote starter switches from Harbor Freight.

https://www.harborfreight.com/12-volt-remote-starter-switch-35448.html?cid=paid_google|*PLA+-+All+Products+-+Lower+Sales+Items|New+Products+-+%281%29+Price+%3C%2410|35448&utm_source=google&utm_medium=cpc&mkwid=sqnzgLe7k|pcrid|318476002950|pkw||pmt||pdv|c|slid||product|35448|&pgrid=63088204786&ptaid=pla-295570145486&pcid=1654049980&gclid=EAIaIQobChMIwM37lMqq4wIVi0sNCh3VPAWcEAQYAiABEgL8SfD_BwE

[JXP]

Results of second test run

This time I left on the gas cap and the engine run was 1 h and 2mins and it only started to struggled in the last few mins of the run .

I performed the spark test with ignition on and got a blue spark.

Any thoughts on what I could try next?

[Dave Neptune]

JXP, you stated the plug had a black residue. This leads me to think you are just to rich and after a while (updraft carb!) the engine just floods out. Once it sits the excess fuel evaporates out of the engine and repeat.

Check all 4 plugs and if they are black or sooty check to see that the choke is fully open. If an open choke is confirmed you have a carb problem. Your blue spark and dirty plugs lead me to this.

When you were running the engine at 1450 were you in gear or not?

Dave Neptune

[JOHN COOKSON]

When the engine starts to "struggle" shut it down and put finger on the stuffing box.The stuffing box should be close to the water temperature the boat is floating in.

TRUE GRIT

[JXP]

JXP, you stated the plug had a black residue. This leads me to think you are just to rich and after a while (updraft carb!) the engine just floods out. Once it sits the excess fuel evaporates out of the engine and repeat.

Check all 4 plugs and if they are black or sooty check to see that the choke is fully open. If an open choke is confirmed you have a carb problem. Your blue spark and dirty plugs lead me to this.

When you were running the engine at 1450 were you in gear or not?

Dave Neptune

It was in gear during all engine runs

[JXP]

Changed the coil

Engine run in gear for 30 mins sputtering and I tried the choke as per manual. It didn’t change with a bit of choke. So I checked the fuel tank pickup tube and blew it out but nothing came out and the screen was clean.
Next I changed the coil, and re-ran the engine in gear it ran perfectly for 2h 36m, I thought i found the problem, then the engine suddenly stopped.
Back to the drawing board.

[Peter]

do you have points or electronic ignition?

Peter

[JXP]

I have points

[roadnsky]

ANOTHER TACK

Here is another thought.
This is a quote from Don...

"There is at least one other item that behaves in this manner (fails from heat and cures itself when it cools), which is a faulty connection in the primary ignition circuit (some electricians call these faulty connections cold joints, I suspect because they only work when they're cold).

Please skip this paragraph if this is more than you wanted to know, but I am told by normally reliable experts that an electrical circuit sees a weak connection on the verge of failure as a localized zone of high resistance which translates into a small amount of heat build-up.
As the heat builds up, the expansion created by the heat eventually causes the connection to open up (minuscule though this heat and expansion is, remember that a connection in this condition is on the virtual edge of failing anyway, even without the heat and expansion).

To keep things simple, before chasing the entire primary circuit which runs from the large battery terminal on the starter solenoid, through the ignition switch and back to the positive terminal of the coil, you could simply connect a jumper wire from the large battery terminal on the starter solenoid to the positive terminal of the coil.
If the engine never shuts down as long as that jumper wire is installed, you will have confirmed that the primary ignition circuit is a cold joint in it someplace.

If the shutdowns continue with the jumper wire installed, you can check the remaining short section of the primary circuit which is between the negative terminal of the coil and the points.
Sometimes the conductor in this short wire develops a cold joint where it passes under the distributor cap or at the terminal of the coil or at the points themselves."

IMPORTANT NOTE: Installing the jumper wire between the starter solenoid and the coil is the very same thing as turning on the ignition switch, so you cannot leave that wire installed except when running the engine or you willburn out the coil or kill the batteries.


You can read the entire post and thread here...