Looking for some guidance from those that know, on carb tuning.

Story is, the 110cc machine wouldn't start. Cleaned the carb twice, still no joy. Compression test was very low, so split the motor, new head unit (valves lapped in), rings and piston installed. The compression went from 50psi (!) to what seemed to be 75, although the new head unit has what I believe is a decompression valve so I'm not sure if the 75 psi figure is a good comparison. Bit disappointed but decided to try and start it up and it does start. It's actually quite easy to get it started (choke on, start, choke straight off) and it'll run so drive now. I'll have another look at compression, probably get a leak test rig made up, and may even buy a new engine to tear down the old one again for learning and for spares, but that'll take time and in the mean time, it's been so long out of commission for the wee lad and I want him to have a go for a while.

But the idling is where I'm flying a little blind. The way it's sitting just now, it idles really high. If I try and decrease the idle screw, or the mixture (fuel) screw it stutters and may shut off. Granted, compression may be contributing but i just need to do the best I can for now.

The carb has a mixture screw on the fuel side. All the videos I've looked at online seem to have air screws. The standard seems to be fully seat the mixture (air) screw, back off a couple of turns, set a reasonable idle and then start to screw the mixture in to richen it, for max rpm and iterate on from there.

However my question is, if it's a mixture screw on the fuel side, is the process the reverse? Set two turns back from fully seated, and then slowly unscrew to increase the rpm and then adjust the idle and iterate from there.

When I put it into neutral it revs very high and in gear the revs drop so the clutch I assume it partially engaging so it needs dialled down a bit.

Picture of the carb adjustment screws added for info. Any thoughts and help very welcome.

Happy New Year to all

Ally

 

Get the engine warm, set the idle stop screw (cross head) nearly as slow as it will go without stalling then screw the mixture screw in or out about 1/6 of a turn, if revs drop, turn the screw the other way, keep going 1/6th of a turn at a time and blipping the throttle between adjustments, until revs start to drop, back off a bit until revs start to drop t'other way, then set the screw midway between. I go for slightly on the rich side, or you can get a stutter on acceleration. Re-set the idle stop screw to suit it now.

 

Thanks for the help. I’m sort of on that track. Might need another look at the inside of the carb. Home schooling has started again!!
Cheers