Idle too high

[Bobby Joe]

http://youtu.be/rii-IZ1eUDk

I finally got my 1971 CB500F running again, but the idle is way too high. Correct me if I am wrong, but shouldn't it be near 12-1400? It appears that something is sticking. I can adjust the idle screw and bring it down, but hen I rev it, it gets stuck again. I still need to sync my carbs, but the air screws aren't making THAT large of an adjustment. Ideas? Feedback?

 

[fresh_c]

Cables sticking?

 

[Bobby Joe]

They shouldn't be. They are brand new...first time using them. And the throttle appears to be popping back all the way

 

[Bobby Joe]

It may be the slides. They were synced bit it looks like the adjustment screw and set-nut came loose...

 

[Bobby Joe]

Should the bottom half of the butterfly be touching this stud??

 

[edukaycheon]

If you know the carbs aren't synced I would definitely do all that I could before trying to troubleshoot something

 

[Bobby Joe]

Sync them before bringing the idle down? ...Ok...

 

[mydlyfkryzis]

Being out of sync is what keeps the idle up....a couple of the carbs are high throttle, a couple low....the imbalance makes for a strange idle.

There is a procedure for syncing these. I don;t have it for yours, but the NH750 requires you to use a vacuum gauge and a specific order. Get a manual for your bikeor you will spend a bit of time fighting the linkage. Syncing is not woththe air/fuel screws, but with the throttle linkage across the 4 carbs. on most 4 cylinders, there is a "primary" carb that moves exactly with the linkage, and you sync the other three to that primary. Maybe someone here has worked on your model and can give you specifics.

 

[Bobby Joe]

Yeah, I have that on my old laptop...need to get some stuff from there before it totally dies. I think the left carb with the choke control is the main one. I'll go ahead and research that more before going around in circles. Thanks

 

[trek97]

They shouldn't be. They are brand new...first time using them. And the throttle appears to be popping back all the way

New cables are shipped bone dry. You need to lube them before install.

 

[Bobby Joe]

I lubed the cables and followed procedure to sync carbs according to the SyncPRO tonight. According to the tool, carb 1,2, and 4 are pretty close. However, 3 is WAY HIGH. Well...the only adjustments I have available are the idle screw and the air screws. So I turned the air screw for #3 both ways...no change. I almost backed it all the way out and went to the stopping point. I am guessing I need to get a super small wire and maybe clean out the air screw holes (none of them were showing a change on the manometer.

Ideas?

 

[mydlyfkryzis]

You do not sync carburetors with the air screw. There is a procedure for aligning the throttle shaft.

It is in section 2 of the common service manual. you use the Base Carb for the reference. On my 1991 NH750, the base carb is Carb 2...Yours is probably the same.

 

[Bobby Joe]

I actually reread your previous comment and tried responding on Tapatalk, but I guess it didn't work. A buddy at work told me the same thing today. And thinking on what was happening last night, I noticed this issue, but lack of knowledge made it so I didn't connect the points. I got to get some female to female connectors to extend my fuel line so I can move the tank out of the way and give this a shot.

I think I need to take my carbs off and look at #2 again tho. Last night, I shut off the petcock and ran until the bike does on its own. No fuel leaked out. Left for work this morning, no fuel leak. My wife came home and it leaked so much during the day that she said the entire house smelled like gas!!! This is with a brand new petcock! I need to double check the new bowl gasket as well.

Lots of work ahead of me!

 

[Bobby Joe]

Just some updates. I did get the carbs synced. I think I found a new carb leak a few days later. I also made adjustments to the slides rather than minor tunes to the air screws. That was the key. The bike was still idling high, but the carbs were synced.