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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.

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.

Does it blow out any black smoke when it chokes out?

Vid?

Scrubcadet10 said:

Does it blow out any black smoke when it chokes out?

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

<<Does it blow out any black smoke when it chokes out? >>

PTmowerMech said:

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

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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.

PTmowerMech said:

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

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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?

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.

seattlepioneer said:

<<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?

Click to expand...

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.

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.

Hammermechanicman said:

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.

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Funny you should say that. Because I finally got back around to this one like an hour ago. Was gonna adjust the valve because it was a little hard getting over the compression stroke. Pulled the plug and a cylinder full of gas shot out about 6 or 8 inches.
So that settle that. Off came the carb and a freshly rebuild one went on it.

The oil level didn't raise at all. So I cranked it up and let it run for a while. Barely a spit or sputter out of it. Which is surprizing. I'm not normally that good at rebuilding those nikki carbs. Guess I'm getting better.

If this keeps up, I might make a 3 by the end of summer.


P.S. I put a new pump on it also, and forgot to plug the air line into it, but it ran fine. LMAO... So what's the point of a fuel pump on a system like this, where the tank is mounted under the hood. (higher than the carb)

I do so many carbs a dealer who doesn't want to work on older residential mowers with fuel problems calls me the carb guy and sends me work. Folks won't pay his shop rate to remove, clean, rebuild, reinstall and test a carb on an older residential mower. He just replaces and uses OEM. Have you priced a Kohler or Briggs carb lately? Plus many are NLA. Probably 75% of my work is fuel system related. I have a small commercial grade ultrasonic cleaner that was expensive but it has paid for itself. Just look at how many threads there are every week on this forum that are fuel system/carb related.

PTmowerMech said:

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.

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Fix it proper BEFORE selling it. Or properly disclose the unique running problem prior to selling. I would NEVER let an engine like this go if I were to sell anything. All mine are 1-2 pulls every time, rain or shine and on time.

slomo

slomo said:

Fix it proper BEFORE selling it. Or properly disclose the unique running problem prior to selling. I would NEVER let an engine like this go if I were to sell anything. All mine are 1-2 pulls every time, rain or shine and on time.

slomo

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Oh yeah. I sell nothing with known problems. Unless the customer knows about it prior to the sell. But that's rare. I usually fix everything I know about before for sale sign gets stuck on it.

From your description of the solution it sounds like someone installed a gravity fed carburetor in place of the fuel pump version.

StarTech said:

From your description of the solution it sounds like someone installed a gravity fed carburetor in place of the fuel pump version.

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That could very well be true. But the engine cover was made with the holes for the fuel pump. everything looks stock. Who ever did the swap, did a bang up job.

I have a good mind to just remove the fuel pump and install a shut off valve. There's no real need for a pump on this engine. Unless there's something
i'm missing.

I have seen lots of mowers from the factory that should just be gravity fed with fuel pumps. Probably that way because they bought thousands of the same engine for different models. I put a shutoff valve on every gravity fed rider i work on. Not if but when it fills the engine with fuel.

Hammermechanicman said:

I have seen lots of mowers from the factory that should just be gravity fed with fuel pumps. Probably that way because they bought thousands of the same engine for different models. I put a shutoff valve on every gravity fed rider i work on. Not if but when it fills the engine with fuel.

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Say it again Hammermechanicman, fuel shut off's for everyone!!

slomo

Hammermechanicman said:

I do so many carbs a dealer who doesn't want to work on older residential mowers with fuel problems calls me the carb guy and sends me work. Folks won't pay his shop rate to remove, clean, rebuild, reinstall and test a carb on an older residential mower. He just replaces and uses OEM. Have you priced a Kohler or Briggs carb lately? Plus many are NLA. Probably 75% of my work is fuel system related. I have a small commercial grade ultrasonic cleaner that was expensive but it has paid for itself. Just look at how many threads there are every week on this forum that are fuel system/carb related.

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Hammer, you said you have an ultra-fabulous cleaner. In your opinion, does someone that cleans say less than 10 carbs a year need one? I get by pretty swell without. Do they really clean better than soaking in Diesel overnight then spraying with carb cleaner and rotting out with a nylon bristle? Then a dual way full action air blast? Worst case they go in the dishwasher. Your thoughts?

slomo

If only doing a few a year one like mine would not be cost effective. I used to use the Gunk and Berryman carb dip on 4 cycle carbs but not cubes as it ruins the check valves. I feel the US cleaner does a better job than soaking and spraying. I started with one like the HF one and it is slow to really clean carbs. I stepped up to one with more heat and a sweep function. Night and day to the cheap Chinese ones. I do about 2 or 3 carbs a week on average.
This is the one i have

Wow you went all out on that sucker. $850.00 is a serious tool. No wonder it works better LOL. The videos I've seen, guys always had to run them again several times to get them partially clean. Probably the cheap machines like you said. Think I will stick to my poor man recipe of cleaning LOL. Thanks for the heads up.

slomo