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Fuel flows into engine


Steve McMahan's Avatar
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01-29-17, 01:48 PM   #1  
Fuel flows into engine

Hey:

I have a Craftsman LT2000 riding mower with a 20 HP B&S engine. Originally, the riding mower did not have a fuel cutoff valve. It has one of those carbs that has that electrically operated plunger, screwed into the bottom of the float bowl. When I noticed the fuel was going lower on the tank, I found the fuel in the oil and fixed that issue. I purchased an inline valve to fix it and that seems to be working.

But my question is, how is it suppose to work? I've verified the float is working, stopping the fuel before it reaches the top of the float bowl with a good needle valve. The float is plastic and does not have fuel in it either (it floats in water). The fuel is physically higher than the carb, so it exerts pressure on the float and needle, but somehow, it is getting past that and into the engine.

Of note, the fuel cap on the tank had what looked like someone forgot to put it back on before mowing the yard and it cut a gash into it. Just giving you what I know. Thank you for advice on fixing it; I would rather like to fix the issue because I could forget to turn the fuel off!

 
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01-29-17, 02:24 PM   #2  
I think the electric solenoid in the carburetor is supposed to rely on the ignition key to open it, and then shut it when you turn the engine off . . . . the primary purpose being to prevent backfiring of a little additional fuel entering the hot engine after it's been turned off.

 
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01-29-17, 03:04 PM   #3  
Thanks, good to know. I thought it might be connected to the fuel leaking in. I haven't checked to see if it is working.

 
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01-29-17, 05:11 PM   #4  
That solenoid won't have any bearing on the problem. Your needle/seat is leaking or the fuel pump is leaking through the pulse line. One or the other. Unless this is a single cylinder (don't know what engine you have)... then the o-ring between the carb housing and the plastic assembly with the float on it may be leaking.


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01-29-17, 06:08 PM   #5  
Thanks for the help. Here's what I did. I put the fuel line on the carb with the float bowl removed, and as I manually moved the float up and down, I was able to easy stop the fuel flow. So, I thought the needle and seat were good.

I have a single cylinder and don't see a fuel pump. If the needle was good, what else could it be and how could I test it? Everything is great while I have it running. The problem is afterwards as the fuel in the tank slowly drain into the engine.

 
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01-29-17, 08:03 PM   #6  
Does yours have the walbro carburetor or the nikki carburetor? It is one of only two things. Either the needle and seat is not sealing, or if you have the nikki, the o-ring between the carb body and insert is leaking. There is no other place for this failure.


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01-29-17, 08:54 PM   #7  
How do I tell which one it is? Would disassembling the float bowl and coating the seal with Vaseline create the seal I need? Also I noted that the float assembly fit into an o-ring cavity in the carb body. Would also coating that seal help? Thank you.

 
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01-30-17, 12:26 AM   #8  
You have a nikki, I can tell by your last post. Take the float assembly out and replace the o-ring right where the inlet needle goes through. Problem solved. Coating with vaseline won't fix anything.


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01-30-17, 11:29 AM   #9  
Do you think that one o-ring is available or do I have to purchase a complete rebuild kit?

 
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01-30-17, 04:05 PM   #10  
It's available.
..............


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02-02-17, 03:20 PM   #11  
I have one on order. Will let you know how it turns out. Thank you for the advise.

 
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02-06-17, 07:01 PM   #12  
Ok, so I replaced the bowl gasket which included a new o-ring to seal the float mechanism. As part of this service, I've installed a fuel shutoff valve after the tank and before the fuel filter.

I moved my garden tractor to the rear of my yard, requiring me to drive around the block to reach it. As I did, about every 45 seconds or do, the engine should act like it ran out of fuel, losing some RPM, before jumping back to life as though nothing had occurred.

I did check to make sure the new shutoff valve was working, it is flowing fuel without obstruction, and also checked the fuel filter, also flowed through very well. Before I reassembled the carb, I did verify the float settings, by eye, and the distance where it closed off the fuel seemed about right.

Once I had it where I wanted it, I let it run for about 10 minutes without any occurrence of the previous issue. So, what am I missing? Any ideas are appreciated.

 
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02-07-17, 03:08 AM   #13  
Just an observation but when the Float and Needle are seating properly, the Fuel Bowl "O" Ring really has nothing to do. The fuel level in the Bowl should never get so high as to require a gasket unless the engine is tilted or tipped significantly.

It still sounds like your engine is being periodically starved for air, like the fuel cap vent is blocked.

 
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02-07-17, 11:41 PM   #14  
The o-ring I mentioned is not the bowl o-ring, it is the one that seals the fuel inlet against the carb body.

The periodic stalling is probably a fuel starvation issue. Could be related to flow of fuel through the needle inlet, clogged fuel filter, pinched/collapsed fuel line, etc...


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02-08-17, 10:40 PM   #15  
The kit I purchased came with 3 rubber parts. The bowl to carb "gasket", and 2 o-rings. One I recognized as the o-ring that seals the plastic float structure (I don't know what it is called). I don't think that is creating or causing the problem.

As I mentioned before, the fuel cap was damaged when I purchased this; it had a gash near the top. So, I sealed the cut with silicon and thought I saved the cost of a new cap. But now I am wondering if in fixing it, I actually plugged up the vent. So, I'm going to try driving it around with the cap very loose and see if that does it.

One other question I have: does the needle seat against the plastic part or is there suppose to be some seal tucked there? The carb on my tiller had a red seat inserted into the place where the fuel comes out. This carb doesn't have that. The diagram from B&S doesn't show enough detail to indicate if it has one.

What is your experience?

 
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02-09-17, 10:37 AM   #16  
It seals against the plastic.

If you plugged the vent (sounds like it), it can definitely cause the problem you were having with the periodic stall.


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02-09-17, 07:59 PM   #17  
i didn't look that close, but can I adjust the float level by bending the tab? I know that is common on older car engine carbs. Just wondering.

 
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02-10-17, 12:53 AM   #18  
No, the tab is plastic and made int he correct position.


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02-10-17, 03:49 PM   #19  
The o-ring I mentioned is not the bowl o-ring, it is the one that seals the fuel inlet against the carb body.
I had Kawasaki Tech update training today and this was specifically mentioned as a source of fuel entering the crankcase, along with the regular culprits, float and needle valve.


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