Back fire in carburetor...

[Gugi47]

I was out yesterday first time this year, with my boat.
2001 Maxum 2100SR2 with 5.0 l engine.
The first 20-25 minutes everything was fine. Low speed full speed, no problem.
Then I have to slow down because some waives and try to speed up again, when some back fire start in my carburetor, lose power and engine stop.
Open the engine hood check see if everything is ok. Don't see anything wrong.
try to start again after 3-4 minutes, start up with no problem. Turn around and go back to the ramp.
From that point to the ramp, happens 5 more times. but after 3-4 minuter start and run for like 4-5 minutes then back fire and stop the engine.
Anybody have any idea what can be wrong?
Thanks for your time.

[mmwjr]

I’m thinking it’s time to rebuild the carb. Gunk in the bowl, sinking float, clogged passages, ...

[Gugi47]

Originally Posted by mmwjr

I’m thinking it’s time to rebuild the carb. Gunk in the bowl, sinking float, clogged passages, ...

That was my first guess.
When engine stop running, I try to restart but would not start. But will start after 4 minutes....and run good for 4-5 minutes. Like a timer.....

[mmwjr]

Ok before touching the carb run the boat to repeat the issue and check for spark as soon as I dies. Ignition sensor in the distributor is know for this same symptom. Easy way to do this is have a timing light set up in advance, when it dies crank and have someone hold the timing light trigger to see if it flashes. No flash it’s an ignition issue and you’ll then have to test the sensor.

[donald]

Good ,morning
Also sounds like a bad coil.
A bad coil will quit working then after a few minutes will start again and then quit again after a short while.
Just my 2c.
Don

[mmwjr]

Originally Posted by donald

Good ,morning
Also sounds like a bad coil.
A bad coil will quit working then after a few minutes will start again and then quit again after a short while.
Just my 2c.
Don

Yes Don that is a possibility which is why I asked him to determine if spark is going away then he will need to isolate between the coil and ignition sensor although it could be another electrical component but these are the most common.

[Gugi47]

Thank you guys.
I try here in home with water hook up and run the engine like in the water 3800-3900 RPM run great for 35 minutes, nothing happen.
Next time I go to the bay, I will take a ignition coil and the timing light with me.
I will let you know what i find.
Thanks again.

[jparsons121]

Don't run those RPMs on a garden hose flush hookup!

[mmwjr]

Originally Posted by jparsons121

Don't run those RPMs on a garden hose flush hookup!

Agree, first a hose cannot provide enough water flow but more important you will cause engine damage at those rpms with no load on the engine.

[Gugi47]

Originally Posted by jparsons121

Don't run those RPMs on a garden hose flush hookup!

Originally Posted by mmwjr

Agree, first a hose cannot provide enough water flow but more important you will cause engine damage at those rpms with no load on the engine.

I use a 55 gallon plastic drum cut to the height i need it.
Fill up with water and let the water on so coiling the water what come out from engine.

[donald]

Gugi47
As Mike said you can damage engine at those rpms without a load.
Also if use a 55 gal drum and put it in gear you wont be able to keep enough water in the drum to cool the engine.
Don

[mmwjr]

Originally Posted by Gugi47

I use a 55 gallon plastic drum cut to the height i need it.
Fill up with water and let the water on so coiling the water what come out from engine.

None the less there is no load on the engine as the boat is not pushing through water. At that rpm and no load engine damage can occur especially over 35 minutes.

[Phillbo]

I would never go above idle on the muffs.

[Gugi47]

I got it. Thank guys.

[Gugi47]

I end up to replace the exhaust manifold.
Buy new, but all I was need was a set of gaskets for the raisers. The one I take of have only 120 hours on them and never salt water.

[mmwjr]

Originally Posted by Gugi47

I end up to replace the exhaust manifold.
Buy new, but all I was need was a set of gaskets for the raisers. The one I take of have only 120 hours on them and never salt water.

The exhaust manifold is the reason for the backfire and loss of power?

If so I must assume the engine was overheating due to blocked coolant passages in the manifold and the over heating caused the loss of power.

[Gugi47]

The manifold have a 3 inch spacer and then the raiser.
One of the gasket let the water get in the engine when become hot.
The engine never pass 170-175F. Not from the time I got it.
Before I reinstall the manifolds, I replace the plugs, ignition wires, distributor cap, rotor and termostat.
Thanks for your input on this forum Mike. You are a great help here.

[mmwjr]

Good thing you caught it early before there was any engine damage.

[Gugi47]

Yepp.
Don't was mach. You can see inside of the manifold.
That explain how come was running for a well and if you wait to cool down will run again...
If I would know, I would not buy the new manifolds ($1200) nothing wrong with the old one.