Stihl 045AV Chainsaw Blowing Fuel Thru Carb - HobbyTalk
  
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  #1  
Old 09-15-2007, 06:37 PM
wvslatepicker wvslatepicker is offline
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Stihl 045AV Chainsaw Blowing Fuel Thru Carb

Hi,

I have an 045AV Stihl chainsaw, electronic ignition. When I try to start it, it attempts to hit, but stops immediately. After a number of pulls, fuel can be seen in the carburetor area. If you take the air filter off, you can see fuel on the surface of the carburetor where the air filter attaches.

It is piston port and I am getting 130 PSI compression. I installed a new carburetor kit - gaskets, diaphrams, needle, etc.

I checked the exhaust for obstructions and it is fine. I also removed the flywheel and checked under the rotor. It appears as though the primary coil was not set in correctly (it had obviously been replaced or worked on) and it had worn a place on the inside of the rotor on the inner edge part. I set the stator plate in the middle of the adjusting slots, replaced the spark plug cap and installed a new spark plug. It is getting spark when I pull on the starter.

After all this, it is behaving as though I had done nothing. I am familiar with 2-stroke engines on motorcycles, but not this type of carburetor. Seems to me that with the compression I am reading, whether it starts or not, the fuel should be going into, not back out of, the engine.

Any thoughts, suggestions, etc. would be greatly appreciated.

Thanks, Mark
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Old 09-15-2007, 06:46 PM
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30yearTech 30yearTech is offline
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Have you had the cylinder off?

It might be time to remove the cylinder and inspect the cylinder, and piston as well as the wrist pin bearings and or connecting rod for excessive wear or play.
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Old 09-15-2007, 11:22 PM
wvslatepicker wvslatepicker is offline
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I looked through the intake and exhaust ports. Did not see anything alarming in there. I figured with 130 PSI, the piston and rings were OK. What I really do not understand is why the fuel actually get blown out the intake side of the carb.

I did not notice any obvious play in the crankshaft and based on the compression reading I got, I did not figure to crack the case unless I just had to.

Mark
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Old 09-15-2007, 11:50 PM
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hankster hankster is offline
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How much fuel on the carb. It is not uncommon on ported engines to have some blowby.
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Old 09-16-2007, 07:49 AM
wvslatepicker wvslatepicker is offline
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A pretty good amount it seems to me. A small "puddle" on the area under the carb. It gathers on the lip where the cover goes on.
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Old 09-16-2007, 09:00 AM
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Quote:
Originally Posted by wvslatepicker
I looked through the intake and exhaust ports. Did not see anything alarming in there. I figured with 130 PSI, the piston and rings were OK. What I really do not understand is why the fuel actually get blown out the intake side of the carb.

I did not notice any obvious play in the crankshaft and based on the compression reading I got, I did not figure to crack the case unless I just had to.

Mark
You can still have good compression with worn or bad bearings on the wrist and or crankpin this can cause the piston timing to be off. This is just a suggestion as you seem to have covered most everything else. Many times you can get a good idea of the condition of the cylinder and piston from the intake and exhaust ports, but sometimes you just have to take it down to see. A nick in a port or a broken piston skirt may not be visible from the outside, but can cause excessive blow back through the carburetor.
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