Jungle Jim
ArboristSite Member
Think I've got a carb issue on this saw but need some help.
First some history: when it runs it runs good! It worked fine for years then gradually became fussy to start & keep running. Lots of fooling with high / low / idle adjustments, venting tank, waiting for cool down, etc. It would have spells where it wanted to lock up, break my hand ... other times would pull just fine. Eventually it started to dump a little fuel into the air filter. This got worse and worse until one day all it would do was flood and the saw became useless. At that point I let it sit nearly a year with fuel in it. Fast forward to recent weeks when I actually needed it. [Farm & firewood saw -- cuts / bucks about 3 cords annually (since 1984). It has a new Stens electronic module, always runs premium fuel / Stihl mix.] In spite of the neglect it did grudgingly start and ran a few minutes roughly with much coaxing on the trigger, until it flooded its air filter, then never started again.
I only 'sort-of' know what I'm doing so please bear with me. OK, probably a carb issue so I put in a kit branded Rotary which was a very close match to rebuilt the carb. I do have the Tillotson service manual. Still can't get the saw to run. Depending on the control lever setting, it will either start, then starve OR not start and flood, or maybe pop, then flood. I've adjusted the control lever many times and have become expert at taking the carb apart.
Regarding the control lever, the Tilly manual says to set it level with the floor of the metering chamber. OK, that nets start & starve. It will pop, run fast, and quit and the plug is dry and no gas leaking from the carb. Any setting below the floor of the metering chamber = same result. OK, at a setting 1/32" above the floor of the metering chamber it will flood (wet the air filter) and not even fire. At a setting 1/64" above the floor it will start then starve. There's only 1/64" left to play with between these extremes. Can it be that fussy about its setting? I've put carb kits in this saw before and never had such trouble. Also after a few pulls it is liable to try to lock up, become hard to pull, like hydraulic lock. I am using the settings of 1 turn out on both the high and low screws. I have pressure tested the inlet needle and it will easily hold 10 lbs or so indefinitely. With alternate pressure and suction on a tube to the fuel inlet you can feel things opening and closing.
The carb was disassembled and soaked in fuel mix, then blown out with compressed air. When I first disassembled it the metering lever was set quite high; apparently it ran ok for some time like that or the setting changed somehow. The screen under the needle had a little debris which I cleaned out and the old needle looked just fine. I've tried both the old and the new with the same results. There was a tiny amount of debris under the welch plug. Everything seemed to blow thru OK. Yes I do have the gaskets & diaphragms on correctly and the old ones looked OK. The only thing I didn't fool with is the main jet as there was not one in the kit, but did blow through it. I'm not sure if there's a check valve it there or not. No carb cleaner used, just fresh mix.
One thing I'm not sure about is the butterfly in the venturi. I had it apart and did not remember which way it went: there is a little notch in one side of the plate and it can go either of 2 ways. The notch can line up with the low speed nozzles or be opposite them. I did the former but it's not clear on Tilly's sheet. Could this make a difference, hmmm.
OK, I've considered that there might be some other issues with the saw and have checked things out. Here's the list. Everything from the fuel tank to the carb is OK, venting, filter / hoses clean, no dissolved foam, no water, etc. Using fresh fuel mix in a clean tank. The exhaust system is clean; port, muffler good. The intake boot and impulse hose are good and fit tight. The carb is mounted directly to the intake book with boot sleeve intact but no additional gasket (supplied with kit but interferes with impulse hose fit), no vacuum leaks. The saw has good compression. The spark is good and plug is correct. The flywheel key is OK. If there is any play in the crank bearings I can't feel it. Have not tested the crank seals. The entire starter assembly has been serviced OK. Locking up is not from that and not ignition timing. With the plug out the flywheel will turn freely but you can feel the magnet pull slightly around TDC. The coil gap is the business card setting around .032". The entire engine has been flushed out internally (per HarleyT). The saw will leak bar & chain oil just sitting but it doesn't seem to be getting into the crankcase.
Thoughts anyone? Thanks --Jim
First some history: when it runs it runs good! It worked fine for years then gradually became fussy to start & keep running. Lots of fooling with high / low / idle adjustments, venting tank, waiting for cool down, etc. It would have spells where it wanted to lock up, break my hand ... other times would pull just fine. Eventually it started to dump a little fuel into the air filter. This got worse and worse until one day all it would do was flood and the saw became useless. At that point I let it sit nearly a year with fuel in it. Fast forward to recent weeks when I actually needed it. [Farm & firewood saw -- cuts / bucks about 3 cords annually (since 1984). It has a new Stens electronic module, always runs premium fuel / Stihl mix.] In spite of the neglect it did grudgingly start and ran a few minutes roughly with much coaxing on the trigger, until it flooded its air filter, then never started again.
I only 'sort-of' know what I'm doing so please bear with me. OK, probably a carb issue so I put in a kit branded Rotary which was a very close match to rebuilt the carb. I do have the Tillotson service manual. Still can't get the saw to run. Depending on the control lever setting, it will either start, then starve OR not start and flood, or maybe pop, then flood. I've adjusted the control lever many times and have become expert at taking the carb apart.
Regarding the control lever, the Tilly manual says to set it level with the floor of the metering chamber. OK, that nets start & starve. It will pop, run fast, and quit and the plug is dry and no gas leaking from the carb. Any setting below the floor of the metering chamber = same result. OK, at a setting 1/32" above the floor of the metering chamber it will flood (wet the air filter) and not even fire. At a setting 1/64" above the floor it will start then starve. There's only 1/64" left to play with between these extremes. Can it be that fussy about its setting? I've put carb kits in this saw before and never had such trouble. Also after a few pulls it is liable to try to lock up, become hard to pull, like hydraulic lock. I am using the settings of 1 turn out on both the high and low screws. I have pressure tested the inlet needle and it will easily hold 10 lbs or so indefinitely. With alternate pressure and suction on a tube to the fuel inlet you can feel things opening and closing.
The carb was disassembled and soaked in fuel mix, then blown out with compressed air. When I first disassembled it the metering lever was set quite high; apparently it ran ok for some time like that or the setting changed somehow. The screen under the needle had a little debris which I cleaned out and the old needle looked just fine. I've tried both the old and the new with the same results. There was a tiny amount of debris under the welch plug. Everything seemed to blow thru OK. Yes I do have the gaskets & diaphragms on correctly and the old ones looked OK. The only thing I didn't fool with is the main jet as there was not one in the kit, but did blow through it. I'm not sure if there's a check valve it there or not. No carb cleaner used, just fresh mix.
One thing I'm not sure about is the butterfly in the venturi. I had it apart and did not remember which way it went: there is a little notch in one side of the plate and it can go either of 2 ways. The notch can line up with the low speed nozzles or be opposite them. I did the former but it's not clear on Tilly's sheet. Could this make a difference, hmmm.
OK, I've considered that there might be some other issues with the saw and have checked things out. Here's the list. Everything from the fuel tank to the carb is OK, venting, filter / hoses clean, no dissolved foam, no water, etc. Using fresh fuel mix in a clean tank. The exhaust system is clean; port, muffler good. The intake boot and impulse hose are good and fit tight. The carb is mounted directly to the intake book with boot sleeve intact but no additional gasket (supplied with kit but interferes with impulse hose fit), no vacuum leaks. The saw has good compression. The spark is good and plug is correct. The flywheel key is OK. If there is any play in the crank bearings I can't feel it. Have not tested the crank seals. The entire starter assembly has been serviced OK. Locking up is not from that and not ignition timing. With the plug out the flywheel will turn freely but you can feel the magnet pull slightly around TDC. The coil gap is the business card setting around .032". The entire engine has been flushed out internally (per HarleyT). The saw will leak bar & chain oil just sitting but it doesn't seem to be getting into the crankcase.
Thoughts anyone? Thanks --Jim