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HELP! Stihl 029 leak problem at the carb

Bob95065

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I rebuilt a Stihl 029 for a friend at work. He had me put a Meteor 039 P/C in it. I replaced the seals, impulse line and intake boot with OEM parts. The saw held vacuum and pressure with the muffler blocked off and a block off plate in place of the carburetor. Needle didn't move for an hour.

I put the carb on it and started the saw to find it idled like it had an air leak. I used a can of brake cleaner with a straw and sprayed near the base of the carb and found the leak. I removed the carb box cover, drove the studs out and used a metal bar with sandpaper to sand the mounting interface flat. I put a piece of sandpaper on my tablesaw and sanded the carburetor flat. I measured the rubber flange if the boot to find it was 0.110" and the outer metal ring was 0.080" so the rubber sealing surface is proud of the metal ring. I tried removing the outer metal ring and it still leaked.

I am getting ready to pull the carb then put a block off plate on either side of the carb with bolts through the mounting holes. If one of the plates had a barbed fitting I can do a pressur/vacuum test to look for leaks. I would use a piece of fuel hose between the impulse barb and fuel inlet. If the fuel pump side cover or metering side cover isn't sealing that would cause the leak I am experiencing when the saw is running.

Has anyone had this happen to them with a 1127? Has anyone tested a carb for leaks this way?
 

Shane¹

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I rebuilt a Stihl 029 for a friend at work. He had me put a Meteor 039 P/C in it. I replaced the seals, impulse line and intake boot with OEM parts. The saw held vacuum and pressure with the muffler blocked off and a block off plate in place of the carburetor. Needle didn't move for an hour.

I put the carb on it and started the saw to find it idled like it had an air leak. I used a can of brake cleaner with a straw and sprayed near the base of the carb and found the leak. I removed the carb box cover, drove the studs out and used a metal bar with sandpaper to sand the mounting interface flat. I put a piece of sandpaper on my tablesaw and sanded the carburetor flat. I measured the rubber flange if the boot to find it was 0.110" and the outer metal ring was 0.080" so the rubber sealing surface is proud of the metal ring. I tried removing the outer metal ring and it still leaked.

I am getting ready to pull the carb then put a block off plate on either side of the carb with bolts through the mounting holes. If one of the plates had a barbed fitting I can do a pressur/vacuum test to look for leaks. I would use a piece of fuel hose between the impulse barb and fuel inlet. If the fuel pump side cover or metering side cover isn't sealing that would cause the leak I am experiencing when the saw is running.

Has anyone had this happen to them with a 1127? Has anyone tested a carb for leaks this way?
Is the throttle shaft worn out? I have had that one bite me before
 

Brad Button

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Is the throttle shaft worn out? I have had that one bite me before
Brake cleaner is not a good thing to use. I have taken a brand new saw just out of curiosity and sprayed brake cleaner around the carb area and it showed an intake leak even though the saw ran perfectly. Shane was thinking the same as I was, the throttle shaft. If the carb is old it may be sucking air. The throttle shaft is brass and the carb body is aluminum so it will wear. If you are going to use anything to spray around for intake leaks I would use WD 40. Try known good carb and see what happens.
 
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