Honda Twins banner
1 - 9 of 9 Posts

·
Registered
Joined
·
10 Posts
Discussion Starter · #1 ·
Hi guys! I recently put together a bike out of spare parts the motor has good compression the spark is strong it starts first kick and it will rev up and down and idle fine but then it’s as if someone is pulling the throttle without me touching anything it just keep revving and revving until I hit the kill switch and if I do open the throttle while it’s doing this, the motor bogs down, the slides aren’t getting stuck up, the cables aren’t sticking and I can’t find an air leak. I have NO idea what I’m doing when it comes to VM carbs. I’m thinking it might be an air leak so I took the boots off and siliconed them to the head, the carbs are tight in the boots. I can’t attach a video but I do have one. Thanks in advance!
 

·
Registered
Joined
·
3,205 Posts
Are the slides in the right way around?
 

·
Premium Member
Joined
·
7,865 Posts
There is a sticky for tuning the vm carbs in the 350 section.

there is no place on your motorcycle where silicon is suitable for use

give us some more info on your carbs

what jets do they have
what throttle
what air filter
what carb boots
have you synched your carbs
have you synched the throttle cables
is your ignition properly tuned
does it advance and retard properly

i can think of about a dozen things that can cause your issue
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #5 ·
Are the slides in the right way around?
There is a stud inside of the body that falls into a slot and makes sure the slid is in the right way, i set static timing, can’t check the advance without it idling warm, the carbs and cables have been synced. Should the slides be all the way shut or should there be a small gap like a few thousands to allow idle? This is the same bike, I’m not sure of the jet size I have to pull a bowl and Check.
 

·
Premium Member
Joined
·
7,865 Posts
Do you have a left and right side carb?...or are they both the same side? If you have left and right side carbs then it’s possible to swap slides between them and run them backwards. If you have two lefts then it’s not...

if you don’t know what your jetting is, it will be difficult to help you. Where did you get the carbs? Have you ever seen them run properly on a cb350?

bench setting the slide idle stop is described in the sticky...drill bit method. Short answer is yes... there is normally a very small opening to the slide once it’s dialed in.

taking shortcuts and tuning carbs don’t typically make a good combination. You may be better off finding a set of OEM carbs than trying to make the VM30s work
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #7 ·
Do you have a left and right side carb?...or are they both the same side? If you have left and right side carbs then it’s possible to swap slides between them and run them backwards. If you have two lefts then it’s not...

if you don’t know what your jetting is, it will be difficult to help you. Where did you get the carbs? Have you ever seen them run properly on a cb350?

bench setting the slide idle stop is described in the sticky...drill bit method. Short answer is yes... there is normally a very small opening to the slide once it’s dialed in.

taking shortcuts and tuning carbs don’t typically make a good combination. You may be better off finding a set of OEM carbs than trying to make the VM30s work
See that’s what I thought maybe there’s a right and a left but I’m not sure how to tell, I bought a few cb’s in boxes and piles of parts the VM’s were brand new in a box never were mounted. I used the drillbit method to get the carbs synced!
 

·
Premium Member
Joined
·
7,865 Posts
Post some picks showing carbs, intake boots, filters and cable routing

VM carbs are used on hundreds of different bikes with thousands of jetting combinations.

even the ones sold to work on cb350s frequently don’t have jets anywhere close to what’s needed

first thing I’d do from what you said so far would be to look at idle speed stops
What size drill bit did you use?

i use the smallest one I have then adjust from there
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #9 ·
You may be better off finding a set of OEM carbs than trying to make the VM30s work
At this point I’d trade them for a set of stockies

I used a 1/16 still bit to sync them.

They fit in the boots tightly, I have a smoke machine maybe I’ll try to tape them up and fill them.
 

Attachments

1 - 9 of 9 Posts
Top