wont idle without choke

[blukrom]

Hey Guys,
First off ive been lurking around the site for almost two years while ive been building my bike. Havent posted but have been able to find every answer ive been looking for...... until now.. lol
Anyhow, i have a 78ish xs built from scratch,with PMA, Pamco and VM34 carbs. Had it running a few weeks ago, got it to idle, synched the carbs and all seemed pretty good. The only thing wrong was I was have trouble off idel. loud sucking sound and it would want to die. I could get it to rev but with lots of throttle work. Now the Bike starts and runs with the choke on but nothing else. It will run with both on or just one side. the minute i take it off choke it dies. also when it is running with the choke it vibrates so much it walks across the garage on the center stand (is that normal?) I followed all the directions for cam chain and valve adjusment, thinking maybe that haad something to do with it. Timed it the best I could with the choke on. But no matter what i do nothhing seams to help.

Help!

Thanks

 

[retiredgentleman]

I suspect the pilot circuit is plugged up in the carbs. You're using the choke to suppy fuel/air, when in fact the pilot circuit should be doing that job. That rich mixture is not good for the engine, so best to get the pilot cicrcuit inspected.

Information on VM carbs can be found in the "Tech" section.

 

[5twins]

Do you have those VMs jetted according to the baseline that has been established and proven to work with the 650? If not then you're lucky it starts at all.

 

[blukrom]

Yes, jetting should be good. I ordered the carbs from 650central and mike asked specifically what pipes and intake. He pre jetted them at purchase.
I will check the pilot circuit next.
Thanks

 

[grizld1]

Jetting should be good, should it? Remember, the baseline jetting supplied by MMM is a starting point from which to tune; all Michael can do at a distance is to make a very well-educated guess at what your particular setup will require, and the rest is up to you. Personally, I've never seen an aftermarket carb or jet kit that didn't need to be worked with, and what you're seeing is not at all unusual. Read the VM Carb Guide and the tuning guide that Michael supplies.

 

[5twins]

Besides documenting all your current jetting (in case you need to make changes), you'll want to verify float and air screw settings. These are aftermarket high performance carbs and the settings aren't always spot on from the factory.

 

[blukrom]

Good point on the base jetting. I will go through the guide and see what I come up with. I don't know why carb tuning is such a struggle for me. It's like a black art.

 

[5twins]

Well, with the VMs, you've certainly jumped in the deep end of the pool, lol.

 

[blukrom]

Lol... We'll I guess it's the best way to learn to swim... Lol. Or give up and take up gardening. Lol

 

[grizld1]

Tuning a VM is simple, IF you don't take short cuts, and IF you pay attention to secondary effects of component changes. Read, think, do. I don't have anything to offer on the subject that I haven't written fifty times already.

BTW, do you have any idea how many others have asked the same question in one form or another? Ignoring the existing resources of the board is not a way to look smart. 'Nuff said.

 

[blukrom]

Thanks guys. I thought I had read the guide griz wrote well. But went back. Read it again. Read it again. Spent some time with it yesterday and made progress. Need to spend more time but good progress. Thanks for the help.