# Carb air inlet leaking fuel, Stihl BG75 zama carb



## ls3c6 (Aug 4, 2011)

Don't have any running problems with this machine, prime a few times and always have had to wait for it to warm up... if I don't pulling the throttle causes it to bog.

Once warmed up RPM is good and it runs properly, but recently when turning it off I get fuel dripping from the air filter & housing.

I disassembled the carb and cleaned it, diaphram looks good, removed the needle and inspected while cleaning... nothing looked amiss, pressure was relieved when I disconnected the fuel lines.

what's wrong???


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## geogrubb (Jul 28, 2006)

ls3c6 said:


> Don't have any running problems with this machine, prime a few times and always have had to wait for it to warm up... if I don't pulling the throttle causes it to bog.
> 
> Once warmed up RPM is good and it runs properly, but recently when turning it off I get fuel dripping from the air filter & housing.
> 
> ...


The problem is a clogged fuel cap, as the engine runs there is a vent in the cap that lets air in to compensate for the fuel leaving and a check valve in the carb to control pressure returning to the tank, with age some things get dirty, so pressure builds and when you shut it off pressure in the tank forces fuel to the weakest point. Simple soulution, loosen the fuel cap before you shut it off. Have a good one. Geo


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## ls3c6 (Aug 4, 2011)

OK i disassembled the cap and ensured no air block, started no prime after off for 3 hours will see if leak is gone


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## geogrubb (Jul 28, 2006)

ls3c6 said:


> OK i disassembled the cap and ensured no air block, started no prime after off for 3 hours will see if leak is gone


Now you will have another problem and no one will know the cap was destroyed, the primer bulb will probably crack next. Get a new cap, or you will end up trashing a good piece of equipment. Have a good one. Geo


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## ls3c6 (Aug 4, 2011)

OK well it has nothing to do with the gas cap, even with cap removed and machine stored horizontally... gas still dripping while off into the air filter housing, onto the filter and then onto the ground. Can see fuel when removing filter and looking into the throat of the carb. Primes/starts/runs/idles properly.

what next?


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## geogrubb (Jul 28, 2006)

Since the fuel tank is below the carb the only fuel available to flow out of the carb would be that in the primer bulb unless in your neck of the woods water flows uphill. Maybe the check valve in the primer is failing. Have a good one. Geo.


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## ls3c6 (Aug 4, 2011)

Ok I replaced the fuel cap and did the complete carb rebuild with RB66, set the L screw which seemed best about 1.25 turns out and set the idle to 3000rpm, it runs about 8200rpm WOT.

I removed the muffler to check for carbon and noticed some vertical scratches on the piston in the skirt area, yet it starts/runs fine so not to worry?

Also does someone have a BG75 diagram for the carb and associated gaskets? Mine doesn't have a gasket between the carb and plastic block... not sure if there's supposed to be one?

Doesn't appear to leak now, but still when started cold I have to let it warm up for 30-45 seconds before pulling the throttle or it bogs down.


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## geogrubb (Jul 28, 2006)

ls3c6 said:


> Ok I replaced the fuel cap and did the complete carb rebuild with RB66, set the L screw which seemed best about 1.25 turns out and set the idle to 3000rpm, it runs about 8200rpm WOT.
> 
> I removed the muffler to check for carbon and noticed some vertical scratches on the piston in the skirt area, yet it starts/runs fine so not to worry?
> 
> ...


There should be gaskets behind the carb. While it is running spray/dribble some brake parts/carb cleaner behind the carb and along the mating surfaces, if the engine tempo changes you have an air leak. Have a good one. Geo


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## usmcgrunt (Sep 16, 2007)

Have you tried adjusting the High (H) screw a little counterclockwise (to richen) to eliminate the bogging problem? Here is a link to the adjustment procedure.Hope this helps.

http://www.zamacarb.com/tipspage.html


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## ls3c6 (Aug 4, 2011)

nice! on mine #8 is between #6 and #7 instead of #6 and #9, i'll put it in the right place...

what about the bogs on throttle first 30-45 seconds of running though, it starts easy... is this a problem?


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## ls3c6 (Aug 4, 2011)

it does not have a H screw and the bogging only occurs when pulling the throttle the first 30-45 seconds running when cold, after that throttle transition is perfect and it runs WOT no problem until i'm finished using it.


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## 2cyclefanatic (Apr 22, 2011)

sounds like my BG72-its pretty much the same blower you have (literally). mine bogs down unless you let it warm up.i've adjusted it numerous times, but i still have to let it warm up. its normal from what i see.


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## ls3c6 (Aug 4, 2011)

Still leaking gas from Carb while off about 5 drips per day what now  primer bulb retains fuel while off and starts and performs fine grrr


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## Rentahusband (Aug 25, 2008)

Seems like the needle is to blame. The tip may not be seating 100% I would replace it.


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## ls3c6 (Aug 4, 2011)

I put a new needle in with the rebuild kit


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## Rentahusband (Aug 25, 2008)

I usually twist a piece of steel wool into the seat area, polish it up real good and blow it clean. It does not take much of a speck to keep the needle from seating 100%. Maybe remove the needle and reassemble it.


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## geogrubb (Jul 28, 2006)

ls3c6 said:


> I put a new needle in with the rebuild kit


If you replaced the metering lever with the new kit I always suggest using the original unless it was very worn as it has the proper height setting, however if you are not the original owner of the blower that may be a problem introduced prior to your ownership. I have the same blower and it also takes a little while for it to realize it is time to wake up and go to work. Have a good one. Geo


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## ls3c6 (Aug 4, 2011)

I replaced the needle due to my concern for the fuel leak, maybe an issue with the seat though? Where can I get a cheap replacement Carb?


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## ls3c6 (Aug 4, 2011)

Disassembled again, paid close attention to the needle seat... everything looks in order. Runs beautifully but still leaks through the throat and down the air filter housing when off 

so frustrated now. just have it tipped so all the fuel dumps into the engine now!


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## Rentahusband (Aug 25, 2008)

Have you checked ebay for a cheap carb? 
Did you remember the spring under the metering lever? Would probably leak more than 5 drops a day without it though. Just a thought.
Feel your frustration!!!


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