• Enter the March CB750 Supply gift certificate giveaway! It's easy... Click here, post something, and you're entered into the drawing!

Advice on syncing carbs

Jarrett_Honda

CB750 Member
Messages
29
Reaction score
0
Points
1
Location
Spokane, Wa
I get my carbs within 2 cmhg of each other which I believe is close enough. The bike idles between 1000 and 1200 rpm.

The bike is able to stop and start easily while the bike is warm. Once the engine cools I have trouble starting the bike without increasing the turns in the idle adjustment screw.

How do I adjust the carb to where the idle screw would be in the desired setting to provide enough air to start?

Everytime I make a change to the carbs the idle would drop or rise in which case I would adjust.

My timing is good
Electronic ignition
Compression good
New jets and clean carbs
Fresh fuel
New coils and spark plugs


 
You don't, you are fighting physics there and no way are they going to change for you and just like everybody else on the planet.

You set those things up for hot idle and leave them alone for cold starts. Your hand on the throttle and choke are what you use at cold engine time. It's a learned bike skill.

A cruise control (throttle lock device) can be handy for that to hold the throttle open a bit more when cold if you can find one.

The later DOHC has a fast idle cold linkage setup but thinking the SOHC does not have that.
 
Last edited:
You don't, you are fighting physics there and no way are they going to change for you and just like everybody else on the planet.

You set those things up for hot idle and leave them alone for cold starts. Your hand on the throttle and choke are what you use at cold engine time. It's a learned bike skill.

A cruise control (throttle lock device) can be handy for that to hold the throttle open a bit more when cold if you can find one.

The later DOHC has a fast idle cold linkage setup but thinking the DOHC does not have that.
Thanks. I guess I figured that it was too warm to be using the choke. It's 80°F plus here right now.

 
Stone cold engine at 80 degrees would be the difference in choke for say just a few seconds or maybe just the start only then off; to like cold and 40 degrees, or choke on and for up to a minute in varying amounts.

Cars do the same, the choke will often be on at cold even if 80 degrees, it just gets used for the actual start then and quickly pulls off, it stays on much longer the colder the ambient temperature is. Even the modern computer ones do the same but they often idle high like the old school fast idle did, mine do right now around 15-20 seconds, and much longer time period in the winter. Then the idle drops down slowly to the normal hot idle speed. At the same time the idle is higher than normal the injectors are feeding richer than normal. The software has the control for that in it.

YOU are the software on an old bike....................
 
I'm constantly adjusting my idle. As the engine warms, and the oil warms, I slowly turn the idle down when I'm at red lights. It always requires 1/8 to 1/4 turn up when I'm cold starting it.
 
That sounds about normal, it is a carburetor there is no electronics to adjust air into the engine like an Idle air control valve or iac like on a fuel injected vehicle, the motorcycle will start like that when cold no matter what you do it's the the nature of carbs.
 
Post #2, the physics haven't changed and never will.

Insistence on setting cold idle speed over and over is silly.
 
Back
Top