Hi guys I recently got my bike out and rebuilt the carb and replaced the clutch etc. So I am having some trouble dialing in my carb which is a M74B got any advice? I know the basic instructions:

1.Turn High Speed Needle in until it lightly seats
2. Turn High Speed Needle Counter-Clockwise 2 Turns
3. Turn Low Speed Needle in until it seats
4. Turn Low Speed Needle Counter-Clockwise 5 Turns
5. With Spark Full Advanced Adjust Low Speed Needle by turning it clockwise one click at a time until it misses, then back it out 5-10 clicks.
6. With Spark Fully Retarded should continue to run, but slower.
7. Adjust High Speed Needle for best as needed.
8. Adjust Idle between 900 and 1100 rpms.

One last thing when they say "5 turns" or "2 turns" do they mean a full revolution like 360 degrees or 180 degrees? I have been turning it 360 degrees for each "turn". I'm trying to get it running good tomorrow we are going to have some nice weather after a lot of rain for weeks.

Thanks!

 

They are refering to complete 360* revolution of the needles.
Those are reccomended "base line" settings, and adjustments are needed from there.
Those carbs are notorious for air leaks around the throttle shaft "thru" hole.
Scott

 

I set the low speed like that , but on the high speed cracking the throttle was the indicator. If it spit back when cracking throttle, open the needle more until you can rapidly advance the throttle with no lag or spitting. All this done with hot engine and full timing advance. Linkerts were a bastard for catching fire on startup sometimes. Generally if it kicked back or spit without starting, there was a flame at the throttle shaft that needed to be blown out.
Ron

 

When I make it go richer it seems to backfire while leaning it out seems to make it die when advancing the throttle rapidly. Yeah I know about the flame in the carb, yesterday when starting it up without the carb air cleaner flames shot out 3 feet.

 

Might need a touch richer on the low speed screw. This helps in mid range transition between the low and high speed. There's a very narrow sweet spot where it all works, but the slightest hint of an intake leak will throw a wrench into the setting of the carb. A sloppy throttle shaft will cause major grief, as one example or float level not in the right range. Get everything right and that crude carb actually works pretty good. Back in the day, I eventually went to an SU and later to a Zenith Stromberg off of a Volvo. Worked like a charm with a jet and needle swap.
Ron