I know this subject has been beat to death but I need help with 30mm Mikuni carbs on my cl350. I know basically how the jetting should be done. Short history: got the carbs jetted like this: needle jet 159P5, jet needle 6F5 clip in center slot, slide 2.5, main jet 135, secondary jet 27.5, air jet 2.0. Bike is stock bore, electronic ign, cl pipes with shorty open mufflers, pod filters. When I put the carbs on, the bike would not run on main jet. Jetted up in steps to 180 mains and now is a little rich on top end but running pretty well, however it is missing and running lousy right off idle to about 1/3 throttle. I have raised the needle and changed the secondary jets in steps all the way up to 40's and still runs lousy (cutting out and spitting). I don't know what else to do except changing the needle jet and needle, but I don't have cubic dollars to throw at this project and would appreciate any advice.
Geezergen
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put some cb750ko carbs on it and it will run perfect straight away
that said you do need to make sure all is well with the ignition
what brand e ign do you have
process of elimination dictates testing with points ignition back on the system because they work perfect without issue this is a known
the mikuni vm carb while it can be set up to run quite well at wot and higher rrevs
well it was never designed as a four stroke carb and it is simply impossible to get them to work anywhere near as well as an oval venturi keihin as far as ridability and throttle response
what kind of exhaust have you got on that turd
you need loooong pipes baby shorties will only work on a nitro motor running wot all the way up the hill
short pipes rob every bit of exhaust scavanging untill up near redline and then it doesn't loose as much but short pipes create the same effect as having too much back pressure
that said you do need to make sure all is well with the ignition
what brand e ign do you have
process of elimination dictates testing with points ignition back on the system because they work perfect without issue this is a known
the mikuni vm carb while it can be set up to run quite well at wot and higher rrevs
well it was never designed as a four stroke carb and it is simply impossible to get them to work anywhere near as well as an oval venturi keihin as far as ridability and throttle response
what kind of exhaust have you got on that turd
you need loooong pipes baby shorties will only work on a nitro motor running wot all the way up the hill
short pipes rob every bit of exhaust scavanging untill up near redline and then it doesn't loose as much but short pipes create the same effect as having too much back pressure
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here ya go you must have the bleed type needle jet for good response
if it was me i would copy this entire setup
including the 2.5 cutaway slide
your welcome aLL I DID WEAS A GOOGLE SEARCH
https://www.caferacer.net/forum/technical/15910-cb350-mikuni-vm30-jetting-results.html
I EVEN COPPIED THE TEXT FOR YOU OUT OF THIS LINK
if it was me i would copy this entire setup
including the 2.5 cutaway slide
your welcome aLL I DID WEAS A GOOGLE SEARCH
https://www.caferacer.net/forum/technical/15910-cb350-mikuni-vm30-jetting-results.html
I EVEN COPPIED THE TEXT FOR YOU OUT OF THIS LINK
Well it's been a long road, but well worth it. This old girl is finally running great after 4 weeks of testing, tuning, and waiting to receive jets a few times over. I've got some jetting numbers to share to feed the hungry baby birds out there who seek to run a bleed type needle jet. Keep in mind, these numbers work for MY bike in MY conditions. Perhaps it will get you in the ballpark and save you some cash.
Bike:
1972 Honda CB350 twin
Generic 12" shorty mufflers, freshly repacked, with additional baffle inserted before muffler</u> for a bit of backpressure and less raspy pop
NEW Mikuni VM30's and K&N pod filters
Fresh points at proper gap, condenser, plugs, valves checked, correct timing, clean and smooth timing advancer, good compression
87 octane fuel w/10% ethanol
![Image]()
Conditions:
Typical hot summer, sea level.
Jetting:
Main Jet:Large Hex 200
Emulsion tube/Needle jet: BLEED TYPE 176 series P-8
Slide: 2.5
Pilot jet:30
Needle: 5F3, lowest (richest) clip setting
Air Jet: 0.5
Air Screw: 2.0 turns out
So far I've got a few hours of spirited riding on this combo and it feels great from idle to redline at all throttle positions. Plug has a slight cardboard color so far and I'll keep an eye on it. The bike can idle for an extended period and still have a clean off-idle response. I'll eventually try an even richer needle to get the clip settings closer to the middle, but let's enjoy it for now. Hope this helps.
Bike:
1972 Honda CB350 twin
Generic 12" shorty mufflers, freshly repacked, with additional baffle inserted before muffler</u> for a bit of backpressure and less raspy pop
NEW Mikuni VM30's and K&N pod filters
Fresh points at proper gap, condenser, plugs, valves checked, correct timing, clean and smooth timing advancer, good compression
87 octane fuel w/10% ethanol
Conditions:
Typical hot summer, sea level.
Jetting:
Main Jet:Large Hex 200
Emulsion tube/Needle jet: BLEED TYPE 176 series P-8
Slide: 2.5
Pilot jet:30
Needle: 5F3, lowest (richest) clip setting
Air Jet: 0.5
Air Screw: 2.0 turns out
So far I've got a few hours of spirited riding on this combo and it feels great from idle to redline at all throttle positions. Plug has a slight cardboard color so far and I'll keep an eye on it. The bike can idle for an extended period and still have a clean off-idle response. I'll eventually try an even richer needle to get the clip settings closer to the middle, but let's enjoy it for now. Hope this helps.
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1,631 Posts
ONE VARIABLE IS THE CAM INVOLVED ALTHOUGH IT WONT MAKE MUCH DIFFERENCE IN THE JETTING
1971 or so honda ditched the higher revving cam for a slightly milder grind to make the bikes more easy to lug down like a harley
for sure 1970 or earlier is what is called the fat cam which is only fatter in the way the casting has a thicker center section
the cam lobes are actually generated from a significantly smaller dia base circle and hence the need for matching rocker arms with more reach
i am using the fat cam grind and love it,it has lots of torque from 4000-on up but i turned 2.2 lbs of iron of the crankshaft
1971 or so honda ditched the higher revving cam for a slightly milder grind to make the bikes more easy to lug down like a harley
for sure 1970 or earlier is what is called the fat cam which is only fatter in the way the casting has a thicker center section
the cam lobes are actually generated from a significantly smaller dia base circle and hence the need for matching rocker arms with more reach
i am using the fat cam grind and love it,it has lots of torque from 4000-on up but i turned 2.2 lbs of iron of the crankshaft
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1,631 Posts
i use a clear hose attached to the float bowel drain to observe the actual level
in fact i ride with them on the carbs
i route the hose up the side of the carb u bend it straight down so water cant get in
makes for a quick diafgnosis check if out riding and having fueling issues
on the vm mikuni as well as the keihins you want the level to be at least 6mm below gasket
if you have a pamco in there yank it off and put the points back in you have to or you could go mad chasing a carb problem that is really an ignition issue
the pamco is good unit but they fry easy from simple little wiring snafus
in fact i ride with them on the carbs
i route the hose up the side of the carb u bend it straight down so water cant get in
makes for a quick diafgnosis check if out riding and having fueling issues
on the vm mikuni as well as the keihins you want the level to be at least 6mm below gasket
if you have a pamco in there yank it off and put the points back in you have to or you could go mad chasing a carb problem that is really an ignition issue
the pamco is good unit but they fry easy from simple little wiring snafus
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