I’ve been having issues tweaking the tune on my carb. It seemed to be gas level dependent which sounds crazy. Last night though I noticed that the fuel line has a little weep around where it connects to the carb. I disconnected it to investigate and found that fuel is constantly siphoning from the tank to the carb when the tank is more than 1/2 full.
How do you normally fix this? I guess I can’t do anything about the siphoning affect but does that do anything to the tune? I figure I could put a fuel tap inline but am curious about the effect when it is running (richer when the tank is full and leaner when low)?
The engine is a ROK TT and the Carb is a Tilliotson HL360 as far as I can tell. It has an integrated fuel pump in the carb if I remember correctly. Will this positive pressure on the fuel line change the metering?
It sounds like the metering needle inside the carb isn’t seating/sealing fully. Sometimes they will get a little gummed up if they have been laying for a while.
It acts somewhat like the inlet needle on a float carb, except it’s actuated by vacuum in the venturi. Inside the carb body there is an arm and spring that are used to adjust the amount of fuel that comes into the metering chamber.
That setting is measured in “pop off”. The reason I mention is because a popoff test would probably confirm the issue you have, as well as making sure everything is working correctly after you have cleaned, or replaced the needle and seat.
Sometimes carb cleaner will do the job to clean those up. You can do a stage further and very, very carefully clean the seat with a q-tip and a little toothpaste.
It sounds like you’re mechanically inclined, in which case I’d say go ahead and buy a full rebuild kit.
I’ve heard them referred to as “all position” carburetors. Notice in chainsaws, the carburetor is below the fuel supply. As long as the needle and seat are functioning properly, no fuel can get through. Needle seats seldom go bad, but needles, with rubber tips, go bad on occasion. Debris, where the needle seats, can cause them to leak. Gas can contain contaminants, that’s why I always ran a filter between the carb and the fuel tank. You’d be surprised what you find in those filters at times. A fulcrum arm, that is set too high, can also cause this, but if nobody’s had the carb apart, this is not likely. The fulcrum arm spring, if it’s broken, can also be the culprit. Not likely! How adept are you at taking a carb apart and putting it back together properly? With 30 years of experience, taking a carb apart, and putting it back together, became 2nd nature. lol