Topic: carbs, cb750

[wilminduke22]

i have a cb750, bored out to 850 with k&n filters and a straight through 4-2 exhaust. it runs great at low revs, up to 3 1/2 thou rpm, but then dies when under load. any suggestions as to setting up the carbs pls. ps, standard carbs, new boyer electronic ignition and new coils fitted.

[ekpent]

Have you done any jetting yet ? What size jets do yo have now and needle setting.
  Member Lucky seems to have a formula.  Lot of it is experimentation as different engines require different tuning.  Sounds like you need help in the mid-range area where needle height may help as well as a larger main.

[lucky]

i have a cb750, bored out to 850 with k&n filters and a straight through 4-2 exhaust. it runs great at low revs, up to 3 1/2 thou rpm, but then dies when under load. any suggestions as to setting up the carbs pls. ps, standard carbs, new boyer electronic ignition and new coils fitted.

Can you tell us more about the bike?

Year?
Stock carbs.
Do you know what position the clip is on,on the slide needles? Count from the top.
Mixture screws,number of turns open?

FACTS so far.

Pod filters.
4 into 2 exhaust, Mufflers?

Can you please check the timing with a timing light and see if the advance unit is advancing the timing?

[wilminduke22]

standard carbs. 105 main jet. needle on middle setting. air screw 1 turn out, have tried 2 turns out also. k&n filters on and straight through exhaust. hope this is enough info

[wilminduke22]

1973 engine with 850 cc top end. brand new boyer ignition and coils

[farmertom]

Let's assume the carbs are 657B or 086A type...
http://www.hondachopper.com/garage/carb_specs/carb_specs.html