Short story, I NEED HELP! Longer story. Have a 750 we just picked up. starts right up but after 10 seconds just start going up, likes to run about 5250. checked valves, installed new boots from carbs to intake, cleaned out carbs, like i said she starts right up. Where should i be looking? After it cools down i am going to hook up my sync and see what it says. even with throttle cables unhooked and ideal back all the way out after 10 sec it just starts going up could it just be to much fuel? any thing would help and i really appreciate it in advance. Think i hit the wrong garage the first time.
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82 custom just will not ideal below 5000
- Thread starter HUCKIE
- Start date
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- Tags
- carburetors dohc
BB74
CB750 Enthusiast
Too much air is getting into the motor. Check for vacuum leaks.
Did you check the high idle screw? Spray some carb cleaner near the boot connections, if the idle changes, then it is a vacuum leak.
Maybe remove the carbs and give it a good once over to be sure all of the butterflies are working correctly and the mixture screws are in the correct spot.
Maybe remove the carbs and give it a good once over to be sure all of the butterflies are working correctly and the mixture screws are in the correct spot.
Motogrady
Motogrady
Good advice above.
But, on my 79, I had to pull and clean the carbs when I got it, like, 4 times.
Thing is, low rpm idle is controlled by the air screws.
And I've found, the passageways going from the tip of the air screws that dump the fuel into the inner sidewall of the carb body, are very, very small.
It took a guitar string, like a miniature snake, starting fluid, 100psi of air, and a lot of patience to get the hard, dried fuel out of them.
If you can't remove the air screw, and shoot some wd 40 or something like that in there, and see it come out of the little hole in the inside of the throttle body, right below the slide, it's clogged.
Air screws, a good place to start, gently all the way in, and back them out 1.5 turns.
But, on my 79, I had to pull and clean the carbs when I got it, like, 4 times.
Thing is, low rpm idle is controlled by the air screws.
And I've found, the passageways going from the tip of the air screws that dump the fuel into the inner sidewall of the carb body, are very, very small.
It took a guitar string, like a miniature snake, starting fluid, 100psi of air, and a lot of patience to get the hard, dried fuel out of them.
If you can't remove the air screw, and shoot some wd 40 or something like that in there, and see it come out of the little hole in the inside of the throttle body, right below the slide, it's clogged.
Air screws, a good place to start, gently all the way in, and back them out 1.5 turns.
I have sprayed and sprayed around the intakes, cleaned carbs time and time again, got new intake boots just for S&G. Took carbs back apart the other day, the only thing I did different this time is put a piece of scotch bright in each of the float seats and cleaned them up really good. Sprays goes everywhere, see thru all jets, did a valve adjustment even though all were still right in spec or on the edge. Bank is sitting in the frame, but I don't dare to go downstairs and try it since I didn't do enough to fix anything and don't want to be dis-appointed. I do thank you for ideas, just baffled. Maybe I should go try it.
Idle screw makes not a bit of difference until you go way in, and it is exactly the same without any pressure on the cables. Haven't tried again but last time was just like before, starts right up idles great for 15-20 seconds and then vroom right up to about 5000, blip the throttle goes up and back down to 5000.
