Lots of good advice on the fuel flow issues, and apparently you have that one licked. Now get to the running issue. Back in post #1, you said you turned the screws to 1 1/4 turns. That is not a bad place for the AIR screw (on the side), but the FUEL screw (on the bottom) should be in the 5/8 to 3/4 turn range. The fuel screw pretty much gets "set and forget", then fine-tune your mixture with the AIR screw.
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Carb rebuild catastrophe!
- Thread starter Mr.Vroom
- Start date
Mr.Vroom
Forum Apprentice
Thanks! I had just set it to what the manual suggested! It's running very well right now. I got it going up to 9000 rpm. Now its time for a sync and a tune. But do I tune it before or after I get the carbs synced?
I have always synchronized the carbs first, then tweaked the settings.
My theory on that is: if a carb is unsynchronized, it may be closed enough that it won't be contributing to the power output. With the carb closed, you could tweak the screws all day long and not see any difference. Synchronizing the carbs is a mechanical process, not a mixture. You are ensuring that the carbs are all open by an equal amount, so any tweaking to the mixture SHOULD be seen/heard in the way the engine runs.
Yes, you do need some ballpark settings to get things going in the first place. For stock carbs, airbox and exhaust, the fuel screws are usually in the 5/8 to 3/4 range. As a 'rule', the air screw goes to about double the fuel screw setting, but I richen it up a bit for easier starting for the tune session. I usually start with the air screw about 1 turn out, but it will end up between 1 1/4 and 1 1/2 turns out when you are done.
My theory on that is: if a carb is unsynchronized, it may be closed enough that it won't be contributing to the power output. With the carb closed, you could tweak the screws all day long and not see any difference. Synchronizing the carbs is a mechanical process, not a mixture. You are ensuring that the carbs are all open by an equal amount, so any tweaking to the mixture SHOULD be seen/heard in the way the engine runs.
Yes, you do need some ballpark settings to get things going in the first place. For stock carbs, airbox and exhaust, the fuel screws are usually in the 5/8 to 3/4 range. As a 'rule', the air screw goes to about double the fuel screw setting, but I richen it up a bit for easier starting for the tune session. I usually start with the air screw about 1 turn out, but it will end up between 1 1/4 and 1 1/2 turns out when you are done.
Mr.Vroom
Forum Apprentice
Wish I would've seen this earlier! I've been spending the whole week trying to tune the carbs. While the bottom end power is now smooth, there is lots of popping and backfiring when decelerating from higher rpm, and the bike struggles to rev out in the higher gears. I'm fairly new to carb tuning but I believe I need some bigger main jets? Or do I lower the needle position? Does anyone know where I can find a tuning guide. I had found one but forgot to save it.
