Topic: High idle after taking air box off 1979 cb750f

[Scott fowler]

Hello im new to this site, im a pretty good metal fabricator and decided to build a cafe racer. I found a great running 1979 cb750f and decided to use it as my base. The bike ran great when i brought it home but now it runs at 4000 rpms at start up. The only thing i have done is remove the air box and modified the exhaust. Is there anything i might have done to create this problem?

[flybox1]

yes, youve altered the intake and the exhaust, which ultimately alters the air/fuel ratio.
if you want it to run like it did, put it back the way it was.
if you want it to run correctly with your chosen mods, you'll have to make jetting changes.
Runs on a dyno are your best bet to getting it right. 
This is a forum for SOHC Hondas, if you have a 79F, its most likely DOHC, and this thread should move to the Other Bikes section of the forum.

[robvangulik]

If  and when it is a DOHC 750, it's almost impossible to get it to run right with those CV carbs  without the standard airbox.

[Retro Rocket]

Hello im new to this site, im a pretty good metal fabricator and decided to build a cafe racer. I found a great running 1979 cb750f and decided to use it as my base. The bike ran great when i brought it home but now it runs at 4000 rpms at start up. The only thing i have done is remove the air box and modified the exhaust. Is there anything i might have done to create this problem?

Well yes..!!, you removed the airbox and cut the exshaust....