Have you balanced them?
First do a bench balance, then hook them up to a vacuum gauge and dial them in.
First do a bench balance, then hook them up to a vacuum gauge and dial them in.
1982 CB750C - High Idle after touching throttle
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:
and move on from the horrid CV carbs?
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 - 9 of 9 Posts
A vacuum leak or a leak on the rubber intake boots at the head can cause it to hang.
I have not, is there a video you recommend?Have you balanced them?
First do a bench balance, then hook them up to a vacuum gauge and dial them in.
Do you have a Clymer or Haynes service manual for your bike?
Its detailed extensively there
Its detailed extensively there
check the ignition timing. if it's electronic and the gap is too small or it's a bit advanced they can hang onto the advance which makes rpm and that stops them returning. don't just assume it's a carb problem.
if its smelly it might also be lean - poor combusiton smells much the same.
if its smelly it might also be lean - poor combusiton smells much the same.
The CV carbs should work just fine if you kept the intake and exhaust system stock. Guessing your intake and exhaust system is far from stock in which case, yep, regular old cable slide carburetors would greatly simplify carburetor setup.
If this is your first carburetor repair you didn't exactly select the easiest first motorcycle to work on, single cylinder bikes don't need carburetors balanced, they just need to work, 4 cylinder bikes have more then 4 times the complexity.
Best luck with your project.
If this is your first carburetor repair you didn't exactly select the easiest first motorcycle to work on, single cylinder bikes don't need carburetors balanced, they just need to work, 4 cylinder bikes have more then 4 times the complexity.
Best luck with your project.
Seat and carbs are off, but pretty much stock all around.The CV carbs should work just fine if you kept the intake and exhaust system stock. Guessing your intake and exhaust system is far from stock in which case, yep, regular old cable slide carburetors would greatly simplify carburetor setup.
If this is your first carburetor repair you didn't exactly select the easiest first motorcycle to work on, single cylinder bikes don't need carburetors balanced, they just need to work, 4 cylinder bikes have more then 4 times the complexity.
Best luck with your project.
Exhaust is a 2to2 with the older Mac slip ons, as I've been told.
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?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
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.
1 - 9 of 9 Posts
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