# Stihl Km55r Carb Problem



## mikel m14 (Jul 27, 2009)

It's been awhile since I've been on here but I'm back for now.:wave:

Okay got a stihl km55r with zama carb. Put a carb rebuild kit about a month or so ago. Ran ok for a few hours after kit put in. After using the stihl about two weeks ago, that night fuel leaked directly out of the fuel tank onto my garage floor. I tried the primer bulb yesterday and very little fuel is going into the primer bulb. Also I see really tiny bubbles pushing out from the nipple that the hose connects to. I started taking the hose that connects to the primer bulb but line has built up back pressure causing fuel to spray out, got some in my eye. I was thinking that there is a problem with the check valve but would like a second opinion. Thanks


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## geogrubb (Jul 28, 2006)

mikel m14 said:


> It's been awhile since I've been on here but I'm back for now.:wave:
> 
> Okay got a stihl km55r with zama carb. Put a carb rebuild kit about a month or so ago. Ran ok for a few hours after kit put in. After using the stihl about two weeks ago, that night fuel leaked directly out of the fuel tank onto my garage floor. I tried the primer bulb yesterday and very little fuel is going into the primer bulb. Also I see really tiny bubbles pushing out from the nipple that the hose connects to. I started taking the hose that connects to the primer bulb but line has built up back pressure causing fuel to spray out, got some in my eye. I was thinking that there is a problem with the check valve but would like a second opinion. Thanks


It could be the fuel cap is not venting. Have a good one. Geo


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## mikel m14 (Jul 27, 2009)

geogrubb said:


> It could be the fuel cap is not venting. Have a good one. Geo


I unscrewed the fuel cap off and there wasn't any change. Sorry I forgot to mention that earlier when I posted.


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## paulr44 (Oct 14, 2008)

Most likely one of two things.
1. Fuel hose is rotted - it happens, look for cracks (bend the line if need be to inspect it). Part number is 4140 358 7702
2. Inlet needle valve in carb. is no longer seating, allowing fuel to be pushed through carb.

In either case, the natural vapor pressure of fuel will cause it to migrate wherever it can. We test carb. inlet needles, tank vents and lines to .8 bar (12 PSI). Carbs needn't hold quite that much, but that's the new-unit benchmark.

Primer won't work right if system is sucking air through fuel line, so this is what I'd lean toward. Primers have their own check valve, so even if the inlet needle valve is stuck in the open position the primer would still work reasonably well.

Would suggest you not store any fuel or fueled equipment in a garage unless it's detached. Have seen house fires from people working on cars in their under-the-house garage, it's not pretty. Of course, no fueled equip. near furnace or water heater for same reason.


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## mikel m14 (Jul 27, 2009)

I checked the fuel hoses and the fuel filter. All look good. Will double check on the inlet needle valve. When I press the primer bulb I have a small fuel leak on the primer body between the brass hose connection and the plastic of the primer body. I believe this is where the fuel slowly leaked out that night. I took apart the carb to make sure all was good. I did get it to start briefly and primer bulb filled up a tiny bit with tiny air bubbles.
My local stihl dealer said that the carb is $100 for the C1Q-S97, alot higher than what I thought.
My garage is detached about 30 yards away from my house.


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## paulr44 (Oct 14, 2008)

Well then, the primer may be the issue. In any case, the carb if it's an S97 it's not $100 (unless it's been on someones shelf for a few years, the prices came waaay down about 4 - 5 yrs. ago which left some of us with seemingly overpriced carbs on the shelf). The carb number changes to 4140 120 0619 and should be in the $30 to $40 range. Given the carb cost, proper operation and not having fuel on your floor I'd change it out.

The primer bulb itself can be changed, and is about $2 to $3 through Zama. If bubbles are coming from the cover mating areas where the diaphragm fits on either end of the carb, I'd replace the carb.

One more thing, did you change the fuel filter? I always replace the filter when rebuilding or replacing a carb as they can be plugged or allowing fine dirt through. Filter is 0000 350 3506, although a ...3502 will work too.

Carb list is attached.


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## mikel m14 (Jul 27, 2009)

I change the primer bulb out a month or two before putting in rebuild kit. I don't see a way to fix where it's leaking at because it's where the brass connection(hose) meets the plastic of the primer body. The tiny bubbles that were coming up inside the primer bulb were coming from the check valve.
No I didn't change the fuel filter but will pick one up and will go ahead and replace the fuel lines since I haven't never replaced them.
I'm glad you posted that about the carb prices. I had went to that stihl dealer(in my town) for the rebuild kit and was expecting spending around $15. Well it was $50 for the rebuild kit and $100 for the carb. I was floored and told him to keep the rebuild kit and of course I didn't get the carb either. I did get the rebuild kit for around $10 off ebay. Well I called where I originally bought the stihl(15 miles away) and just got a price of $32.10 for the carb. So I will definately be going this route. Thanks for the replies guys!
So is 30 year tech still around here?


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## mikel m14 (Jul 27, 2009)

Well I picked up the new carb, fuel filter and fuel lines, total was just over $46. Paul your spot on on that carb #, model of carb is C1Q-S186. 
I tried just changing out the fuel lines and fuel filter with the old carb to see if there was a difference but there wasn't. Then I took the old carb and took it back apart and checked on the inlet needle, double checked everything else as well. Reinstalled and still no change. I did get it to run before and after taking the carb apart. The primer bulb still didn't have much fuel in it even when idling.
So I then put the new carb on pressed the primer a few times and the fuel filled up to halfway in the primer bulb. While idling, primer bulb filled up like normal. Now it is running great!


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