Adjusting a CV Carb

[glider.]

Many people are under the assumption that to properly adjust the idle mixture on a CV carb that you just turn it open 3 turns and that's it.

There's much more involved in adjusting the idle mixture on a CV carb.

First off warm the engine up completely and make sure the enricher is fully off.
From there after the proper jetting is achieved, the idle mixture screw should be lightly seated and then the mixture screw opened up slowly until the highest and steadiest idle speed is achieved. From there I like to close the needle just a very tiny bit to the lean side for a crisper throttle response.
You adjust the idle speed next and then re check the mixture setting one more time to get it optimized.

Generally speaking, if you have to open the idle mixture much more than about 3 turns, your low jet is too small and conversely if you open the idle screw much less than three turns, the low jet may be too large. The norm usually falls between 2 1/2 to 3 1/2 turns open for most bikes but again it depends on jetting here.

There's other posts in this area that will tell you how to check to see if your jetting is correct for your application.

 

[twooodogz]

What is the ideal rpm for idle speed?

 

[glider.]

950-1050 on most later model bikes that are fuel injected.

Carbed bikes can go a little lower but not by much.

 

[twooodogz]

ok sorry to be bothersome but where do I hook a digital multimeter to accurately read the rpm? I have done this on cars many times not so used to motorcycles yet. Grandfather always told me You're never going to learn any younger boy so I guess i better start now.

 

[glider.]

Don't think a digital multi meter would do the trick. You need a hand held tach dwell meter to do it.

 

[twooodogz]

Sorry I should have been more specific. My digital has the tach on it.

 

[glider.]

There should be instructions with your meter but they usually attach to the coil terminal.

 

[twooodogz]

There should be instructions with your meter but they usually attach to the coil terminal.

Sorry i never got back to you, but I got all excited went out to hook up my digital then realized it only went down to 4 cylinders.

So I found a friend with an analog that hooks to a plug wire. I dialed in the mixture screw the best I could then set the idle, went back and forth like that a few times and darned if it doesn't run better than it did when Harley rejetted it for me. I still think the main jets need a little tweaking but for now I am at least not puking gas out my exhaust while parked at a light.

 

[Fastlinnie]

950-1050 on most later model bikes that are fuel injected.

Carbed bikes can go a little lower but not by much.

Mr Data I could use your help Please/. I have a twin cam with carb. it is a 95 inch motor .branch heads and runs around 185 psi compression. 600 lift cam 248 dur. and cv 44 carb. it backfires out exhaust at full fuel. I have a 230 main jet and a 48 slow speed jet bike runs great and pull good but it still back fires out exhaust if I let off a little bit it stops back firing . I have tried smaller main jets and bigger too. the only way I can get it too stop is too install the clip on the needle all the way at the bottom . but fuel mileage is bad and mid range is a little jerky. I sure could use some help. Thank you.Fastlinnie

 

[HDDon]

Are you sure you're not hitting the rev limiter? That is an awful large main jet for a 95 inch motor.