331877 0036 G1, every 6 seconds

PTmowerMech

Lawn Addict
Joined
Apr 16, 2018
Threads
387
Messages
2,953
Every 6 seconds, all by itself, it chokes itself for a couple of seconds, then runs normal for another 6 seconds. Problem is, the choke plate never moves. In fact the linkage that normally moves the choke (just passed full throttle) isn't even close to touching. I can hole the throttle plate in place, and it never misses a beat. But on it's own, it'll choke itself every 6 seconds.

Fuel pump is pumping, no blockage in the fuel lines and I've installed a new filter.
 

StarTech

Lawn Royalty
Top Poster Of Month
Joined
Feb 19, 2020
Threads
75
Messages
10,105
Check the intake manifold for a bad o-ring causing air leakage. I had one last year that was acting simply except sounded one like it was sneezing.
 

seattlepioneer

Active Member
Joined
Jun 20, 2020
Threads
10
Messages
93
<<Does it blow out any black smoke when it chokes out? >>

Yes, it does. It seriously just like you choked the carburetor for a couple of seconds.

Doesn't that imply that it's being periodically flooded with fuel to cause that problem?

Just guessing, but if the fuel pump was increasing fuel line pressure periodically perhaps that might cause this kind of problem. Perhaps the fuel pump is supplying a little too much fuel pressure and that is reflected in the periodic flooding, with the flooding relieving the excess pressure for a few seconds. Can you temporarily eliminate the fuel pump and feed fuel by gravity as a way of testing that kind of theory?

I'm wondering if you could try partially pinching off the fuel line to the carburetor to see if that affects what's happening. Restricting the fuel line might reduce the fuel pressure and cause the engine to run normally if that's the problem. I might try putting a screw clamp on the rubber fuel line and gradually tightening it to see if that causes the engine to even out at some point.

A dirty fuel line float or valve seat that's allowing too much fuel to get into the carburetor some of the time?

And if others think periodic flooding of the engine might be causing this problem, you may need to spend a good deal of time with your engine to think of more things that could be causing the problem, and ways you can test those ideas to see if they are the actual cause of the problem.

I'm no Xpert. I'm trying to develop diagnostic skills on small engines that I don't have. So don't take these ideas too seriously. I figure perhaps I can develop some diagnostic skills by imagining possible causes of problems people are having and coming up with methods to test those theories.
 

Hammermechanicman

Lawn Addict
Joined
Jan 10, 2020
Threads
49
Messages
3,485
Yes, it does. It seriously just like you choked the carburetor for a couple of seconds.
When it does this can you watch the carb linkage? Does the throttle butterfly move? If so, how does it move and how much? Have you tried running the engine with the oil sipstick loose to relieve any excessive crankcase pressure?
 

PTmowerMech

Lawn Addict
Joined
Apr 16, 2018
Threads
387
Messages
2,953
Choking the carb, like you're explaining, is too much fuel & not enough air at the same time. Which is how you get the black smoke. So slowing down the amount of fuel going to the carb might be an easy test. I have adjustable fuel line crimpers that might do the trick.
 

PTmowerMech

Lawn Addict
Joined
Apr 16, 2018
Threads
387
Messages
2,953
<<Does it blow out any black smoke when it chokes out? >>



Doesn't that imply that it's being periodically flooded with fuel to cause that problem?

Just guessing, but if the fuel pump was increasing fuel line pressure periodically perhaps that might cause this kind of problem. Perhaps the fuel pump is supplying a little too much fuel pressure and that is reflected in the periodic flooding, with the flooding relieving the excess pressure for a few seconds. Can you temporarily eliminate the fuel pump and feed fuel by gravity as a way of testing that kind of theory?

I think you're onto something there. I removed the fuel pump all together and just ran a line from the tank to the carb, with a filter in the middle. And the flooding stopped. Thanks for the idea.
It seemed only logical once I realized that the 6 second flooding increased to 9 seconds when I increased the RPM's. Engine burning fuel faster, meant that it took more time for the engine to flood. If it was a carb issue, I think it would flood all the time. That's the usual case, in my short experience in doing this kind of work.

Gonna let her run for about 10 minutes, if there's no hickup's, I'll button it back up and get'r ready to sell.


This forum is awesome.
 

Hammermechanicman

Lawn Addict
Joined
Jan 10, 2020
Threads
49
Messages
3,485
If the carb needle and seat won't hold against the small amout of pressure a pulse diaphragm fuel pump puts out you have a carb problem. Is the tank located higher than the carb? Do you have a pressure tester? You should be able to hold carb upside down and it hold 7 psi applied to the fuel inlet. I think you are asking for a crankcase full of gas. A fuel pump should not affect the level of gas in the carb.
 
Top