Custom build surges at idle

[sunblock]

Hello, First time posting here.

My father in law has built one awesome xs650, but is having trouble getting it to idle properly. The entire motor has been rebuilt and custom intake manifolds where made. They each come out and bend about 45 degrees to the outside of the bike and are steel. The carbs are secured to these with some heater hose and hose clamps. Now the bike runs ok, but when sitting at idle it likes to surge up and down like it has some type of air leak. Could the design of the intake manifolds contribute to this any? is there something common we should check before tearing the motor down again ? I have some pics on my phone I will try and get posted.

 

[Sundie]

when sitting at idle it likes to surge up and down like it has some type of air leak. Could the design of the intake manifolds contribute to this any?

At idle? No, or very unlikely. You probably have a vacuum leak somewhere, or unbalanced carbs. Search for "manometer" in the forums on how to make a cheap carb balancer.

 

[sunblock]

cool thx, I have a vacuum carb sync kit for my cb750, I guess we should try that 1st. Here is a pic :

 

[Sundie]

yeah - i pretty much guarantee those are out of sync, and will go out of sync every 1000 miles.

 

[sunblock]

yeah - i pretty much guarantee those are out of sync, and will go out of sync every 1000 miles.

Just due to the vibration? would that cause them to keep going out of sync ? I didnt see the bike before it came apart but I was thinking the stock manifold had a lot more rubber than metal.

 

[sunblock]

any thoughts? Is this just a problem from excessive vibration or am I missing something else ?