1973 TX650 Idling High

[BowlingSS]

The engine was completed a couple of weeks ago. Both carb were rebuilt with new shaft seals. It starts easy but the idle keeps going up. This is the first one I have rebuilt that has high idle like this one. New cables. The idle screws are turned all the way off. I took the carbs off a couple time to check everything. I did not find anything wrong. I replaced the carb rubbers. The seals were new but how do I check them to see if they are leaking. The seals looked new. Most places were out of the seals so I had to use a new source.
Thanks.
Bill

 

[DogBunny]

Have you checked the mechanical advance springs-- the springs on the flyweights. When you push the flyweights out, they should spring back when you let go.
To check the shaft seals for leaks, spray ether, or carb cleaner, or something similar at the shaft ends while bike is running. If rpm does not change, then seal is good.

 

[gggGary]

Can you lower RPM pushing the throttle arms down?
Check that the pistons are bottoming in the throat. possibility of wrong length, or some other cable issue.
Easiest seal test is to spray carb cleaner around throttle shafts and intakes. should see no RPM increase.

 

[BowlingSS]

Can you lower RPM pushing the throttle arms down?
Check that the pistons are bottoming in the throat. possibility of wrong length, or some other cable issue.
Easiest seal test is to spray carb cleaner around throttle shafts and intakes. should see no RPM increase.

Throttle arms can’t go any lower, the idle screws are backed out . I did push them down. Cables are new. I did spray carb cleaner around the seals. No increase.
Thanks Gary.
Bill

 

[Jim]

I'd also check the enrichment valves are fully closing.

 

[BowlingSS]

I'd also check the enrichment valves are fully closing.

What enrichment valves are you talking about? Mush be having a senior moment.

 

[Jim]

Aka.... choke.

 

[BowlingSS]

Aka.... choke.

When I put the choke on the idle does go down but still increases. I will check it closer. I did replace the left carb with another one and it still does the same. Maybe I will take both carbs off again and check the choke circuit closer.
Thanks Jim.

 

[DogBunny]

When I put the choke on the idle does go down but still increases

???
Did you check the advance springs?
Did you visually check that the pistons are going all the way down, and not binding in their bores?

 

[BowlingSS]

Advance springs are working great.
I just installed new pistons and rings on the motor build. I will double check the pistons.

 

[Jim]

I will double check the pistons.

Pretty sure he meant the carb slides and bores....

 

[BowlingSS]

Pretty sure he meant the carb slides and bores....

Haha

 

[wesleyonoel]

While checking the myriad of possibilities, maybe disconnect throttle cables from carburetors. Idle RPM on my '73 TX will occasionally climb after riding but can return to normal idle speed by pressing down on throttle shaft where cables attach. Idle speed will occasionally increase when handlebars are turned - particularly to the left. Cables were lubricated prior to installation but have not chased the nuisance issue any further.........kinda acts like a frayed cable inside one of the housings?..........Oooppsss, didn't mean to step on any toes - saw where gggary touched on these possibilities earlier......

 

[DogBunny]

Pretty sure he meant the carb slides and bores....

Yes. I only called the slides "pistons" because that's what Gary called them in post #3...
I had a small Keihin roundslide on a TS185 that would get stuck in the bore. Took me months to figure that one out.

 

[Wingedwheel]

https://www.xs650.com/threads/upgrade-ignition.69161/
This problem is chronicled here with no solution as of today. I feel it’s an issue with the advance but many people keep pushing me back toward the carbs. I can set the idle down around 900 and it helps but the bike won’t stay running at that idle speed I have a set to try over the next few days and will report back. I did wire the flyweights which negated the issue however that’s not a solution.

 

[Its been a long time]

Hmmm. If wiring the advance mechanism closed cures the issue that's a pretty conclusive diagnosis, I would say. Full strip down and overhaul including lubricating the advance rod should fix it? Perhaps needs new springs?

 

[gggGary]

Vacuum synch? It's a pain on the early bikes and usually hand over the muffler gets me close enough.
Has to be two stage first with the levers off the idle stop screws then again with the levers on the idle screws.
Many times the settings vary between gas tank off or installed.

 

[BowlingSS]

Hmmm. If wiring the advance mechanism closed cures the issue that's a pretty conclusive diagnosis, I would say. Full strip down and overhaul including lubricating the advance rod should fix it? Perhaps needs new springs?

How do you wire up the advance? I have not tried that yet. I did make sure it was lubed and it looks like it is working but I figured it will not hurt.

 

[Its been a long time]

How do you wire up the advance? I have not tried that yet. I did make sure it was lubed and it looks like it is working but I figured it will not hurt.

Maybe I misunderstood? You said "I did wire the flyweights". That's the flyweights on the advance mechanism, right?

 

[DogBunny]

Maybe I misunderstood? You said "I did wire the flyweights". That's the flyweights on the advance mechanism, right?

Winged wheel is the member who said he wired up his weights, not BowlingSS.