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1982 CB750C - High Idle after touching throttle

2858 Views 8 Replies 6 Participants Last post by  CBF
Hey all, I received the a set of carbs from eBay, cannibalized the original set and set up the new one on the bike.

Fired up instantly, few pops, but smoothed out after adjusting the rod with black knob at the "bottom" of the carbs.

Problem is, when I touch the throttle, it hangs at 3.5k- 4k RPM, and won't go down, choke kills the bike after a few seconds, so that works.

I've made sure there's a bit of slack on the throttle cable, and the others as well. No leaks, but it does smell rich. The Primary Screws have all been equalized to ~3 turns out. Compression is great hovering around 135 (all 4).

This is my first carb rebuild, and at first I actually misplaced the primary and secondary jets, but that has since been fixed.

Any ideas? I've asked over at the CB750 forums as well.

I know the bike runs well, carbs are the only issue. Should I just scrap 'em and get a set of:

  • Murray's Carbs (Mikuni VM 34's)
  • Dynoman's (CR 31)
  • Cycle X's (Mikuni RS)

and move on from the horrid CV carbs?
1 - 1 of 9 Posts
Seat and carbs are off, but pretty much stock all around.
Exhaust is a 2to2 with the older Mac slip ons, as I've been told.

View attachment 105366
Seat and carbs are off, but pretty much stock all around.
Exhaust is a 2to2 with the older Mac slip ons, as I've been told.

View attachment 105366
Did you fix it?
Sounds like you need to sync the carbs, or have a leak at the intake boots.
Try doing a bench sync first, would not hurt. (Make sure the butterfly valves close properly.)

You said you renovated the carbs, did you take out the plates for the butterfly valves? The edge of the plates are slightly angled and it´s possible to put them in the wrong way.
I am very certain the source of the problem is either Boots or butterfly´s.
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