[inspector54]

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1977 Wing with carb troubles

Bike came to me with an idle issue. It won’t idle down from 3000rpm if you just touch the linkage in will drop to 1000 rpm touch the throttle and its back at 3000 rpm.

In my attempt to curt this I have done the following:

*Checked the timing belts
*Cleaned advanced unit
*Check the compression 155 +/- 5psi good
*Set valves .004 in
* Set timing split method
*Rebuilt Carbs, Air jets were in wrong locations. I didn’t split the plenum
*Cleaned and assembled the slide and cap
* Installed the Needle “washer” fix.
* Installed new manifold tube O-rings.
* Attempted to sync carbs but with the idle problem I couldn’t get it done.

Everything seems to look and function as it should.
So what did I miss?

 

[exavid]

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It sounds to me like you have some binding in the carb linkage, might be one of the throttle cables. It could be worn throttle shaft bushings sucking air but I really suspect there's something loose in your linkage or throttle cables. I'd test it by removing the cables from the carbs and see what kind of idle you get then. Operate the thottle by hand without the cables and see if it behaves differently. If it behaves that way you may need new cables, you probably do, you'd be surprised how much better a bike handles with new throttle and clutch cables. If it still acts up you need to pull the carbs and inspect the linkage carefully and look at the throttle plates to see if one of them is hanging up. One other common problem with not dropping back down to idle is a CV slide hanging up and not fully seating.

 

[inspector54]

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Thanks, I'll let you know what I find...

 

[inspector54]

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bump

 

[dingdong]

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Afraid you're going to have to get the carbs synced somehow. That is more than likely the problem.

 

[exavid]

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You really can't sync the carbs at 3000rpm. You can try but even if you do when you drop the idle back to normal you'll see a lot of error in sync because sync is important only in the lower rpms. Bad sync can cause the engine to resist dropping back down in rpms when you close the throttle but the largest effect of sync on operation occurs at idle and initial application of load to the engine. Carb sync should be the last thing to do when setting up the engine and carb parameters. Spark, cam timing, and carburetor operation has to come first or you'll just end up chasing your tail.

 

[Broke Winger]

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I'm with Paul on this one. Something is binding in the throttle linkage.

 

[sandiegobrass]

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exavid wrote:

....Carb sync should be the last thing to do when setting up the engine and carb parameters. Spark, cam timing, and carburetor operation has to come first or you'll just end up chasing your tail.

Agree up to a point.. pilot screws (idle drop or "colortune") should be the last after carb sync

 

[DBohrer]

imported post

inspector54 wrote:

1977 Wing with carb troubles

Bike came to me with an idle issue. It won’t idle down from 3000rpm if you just touch the linkage in will drop to 1000 rpm touch the throttle and its back at 3000 rpm.

In my attempt to curt this I have done the following:

*Checked the timing belts
*Cleaned advanced unit
*Check the compression 155 +/- 5psi good
*Set valves .004 in
* Set timing split method
*Rebuilt Carbs, Air jets were in wrong locations. I didn’t split the plenum
*Cleaned and assembled the slide and cap
* Installed the Needle “washer” fix.
* Installed new manifold tube O-rings.
* Attempted to sync carbs but with the idle problem I couldn’t get it done.

Everything seems to look and function as it should.
So what did I miss?

 

[DBohrer]

imported post

I would check the throttle return spring, it might be disconnected, loose, stretched or such.