66mm bore CB350 VM30 Jetting

sandman28

Been Around the Block
CB350 fresh rebuild. 66mm bore (wiseco pistons) 2:1 exhaust ("hooker headers" scrambler style)
Timing is good, compression is good (slowly getting a little better as it runs some and rings seat)
VM30's with pod K&N style filters (oiled)

sorry for another jetting question.... been reading all over about jetting and tuning these carbs for a CB350. Cant seem to find much info for them with over bored cylinders though. anyone have some experience ? Im in the 145-155 range for main jets right now and 40-55 for pilot. Just want to make sure im in a good range and dont need to be much richer because of bigger bore. Idle plug chop with 145 main and 45 pilot looked a bit lean. thanks.
 
sandman28 said:
Idle plug chop with 145 main and 45 pilot looked a bit lean.

Jetting isn't really something you can get right the first time. It's dependent on a lot of variables. You said 145/45 seemed a little lean so try something a little bigger. There's a shop called 4into1motorcycleparts on eBay and they've got CB350 jets for ~$5 each with free shipping. Getting it right is going to be a lot of trial and error.
 
thanks, tuned alot of carbs on 2 stroke builds so I know it takes time and patience. obviously trial and error, but if some people give some feedback it makes the process a little easier and speeds it up, thats the idea. Theres TONS of info on VM30s for stock CB350's ... just seeing where people land generally with 2mm over
 
thanks xb33bsa , thats what I figured but afraid of running too lean. hopefully have sorted out all the small stuff and will able to FINALLY rider her tomorrow and begin final tuning process .
 
remember it is also a factor of where in the rpm band you are lean

the main only really effects top end wide open over 3/4 directly

the pilot only the first bit of throttle and a air correct jet can tweak the pilot size so you need to know if you have one installed

the throttle slide jet needle and needle jet effect from about 1/8 throttle till over 3/4

in combination with the pilot and main
 
Also, on the VM series of carbs, the main jet number is largely irrelevant until we know your needle jet size and type.
 
just got back from first ride. need to better adjust the clutch.
right now the VM's have 145 main jet, 3.0 slide, needle is 6F5, P2 needle jet, 2 air, 45 pilot,
seems to be running OK from first impressions on a short ride, throttle very responsive through low end to mid range, returns to perfect idle at stop.never really took it over 4-5k or above 45mph. checked head temps with "lazer" on top fin and right behind spark plug when I got home, both were below 250.
I live right in the city and I was encountering rush hour traffic so Im gonna wait til later and head outta town a little bit to see how it feels and do a proper plug chop(s)
 
I've got the same kind of pistons as you at 67.5mm. Was trying to figure out what jetting to use. So you're somewhat good with your current set up then?
 
I've got a 350 with vm30 and k&n air pods. i'm also at sea level.

best setup i have arrived at so far is 150 main, 50 pilot, 2.0 air, 6F0 needle. strong punch all the way to redline. but seems to have trouble idling.. braking hard (especially when descending an incline) can cause the engine idle to stumble enough to quit.

i'm going to try a 40/45 pilot and see if that helps stabilize the idle. but i think this is the best setup i've gotten to so far.
 
if you are having issues on a incline or during hard braking make sure you float level is set to the max height

or min fuel level in the bowl

range for a vm30 is 86-94 thou or 22-24 mm so set for 94 or 24

you are probably experiencing fuel slosh over also that pilot seems awful big

what needle jet do you have?
 
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