I had a mild intake/exhaust port and muffler port done on my Husky 55 Rancher, advanced timing maybe 1/2 degree, if that. Put it all back together, re-tuned the carb to sound right and idle at 2700, rev at 12300. It starts and runs great at first, but once warm it wants to die when idling and then I have to choke it a little for it to start. This suggests to me that once everything warms up there isn't enough fuel at idle. What do I need to adjust to fix this? Run the low end richer?
I'm new to playing with engines, so open to any ideas or corrections. Thanks ???
RP
WAG try opening the L up to fed more fuel. Get good throttle response and then finish with I adjustment.
Might want to fatten your H too being she might be lean after mods.
How long has it been since the carb diaphragms were replaced? When you did the cylinder work, did you pressure test the crank case to test the seals? Is there a gasket between the cylinder and the case?
Some guys will put the cylinder onto the case without a gasket to gain extra compression. Trouble is should you choose to not use a gasket, the joint may leak. Dont use rtv on a saw.
If you have an air leak your going to have trouble getting the carb to stay tuned. One minute good the next off. At idle speed is usually where an air leak will show itself.
Once your sure that you dont have any air leaks then look to the carb; The low side of the carb handles the idle and transition to rpm. The H side is added fuel for max rpm power. Chainsaw engines will not accelerate off a lean carb. They need a richer idle in order to accelerate. Control your idle speed with the stop rather than the jet and open the low jet far enough for transition to occur without bog or hesitation.
Other than the standard checks for leanness, you could also check whether your porting or timing advance has caused the engine to run hotter. Also whether the ring is worn.
Both these could cause heat build up in the crankcase, which in turn could cause poor suction at the carb.
Joe
Step 1: compression test.
Step 2: try a known-good plug. Which are you running?
Then all the other good suggestions.
Thanks for all the responses! I used new gaskets for the rebuild, and the carb diaphragms are new. I don't have a compression tester, but just by turning the saw over it feels to have really good compression, better than before the rebuild. I had a Stihl that had an air leak, and this is running nothing like that. It runs great, just doesn't like idling long once hot, and once hot takes a little choke and several pulls to start up again. It sounds like my I or L screws need adjusted, I'll try that first.
RP
Maybe its now running hotter with your mods, causing a bit of vapor lock in the carb?
Quote from: RPowers on December 08, 2013, 09:16:02 AM
Thanks for all the responses! I used new gaskets for the rebuild, and the carb diaphragms are new. I don't have a compression tester, but just by turning the saw over it feels to have really good compression, better than before the rebuild. I had a Stihl that had an air leak, and this is running nothing like that. It runs great, just doesn't like idling long once hot, and once hot takes a little choke and several pulls to start up again. It sounds like my I or L screws need adjusted, I'll try that first.
RP
Adjust L first by fatten. Then I if needed for idle.
Also if this done fix it, did you replace the needle and fulcrum? If so did you adjust your fulcrum height? If not might need to raise it a tad.
Thanks Cut4fun,
I think raising the fulcrum might help fatten her up some. I meant to bring it into work (where I have a shop to use) today, but have been walking down the drive 1/4 mile to the truck due to snow and didn't feel like sliding down the hill with my chainsaw. In a few days hopefully I'll get to work on tuning her up.
RP