will not idle down

[sataniclumberjack]

1977 xs650 Engine idel issue. Not sure if this is a clutch or an engine problem or a carb problem. When I enguage the clutch at a stop light or where ever the engine idle is climbing up to about 3500rpm. This seems to do it especially when it has been running and the engine is hot. Even when i am rolling and completley let off the gas and enguage the cluth it still does this. I dont belive the carbs are getting stuck open. When bike is cold engine runs fine. The only thing i have notied is there is a small oil leak in the head gasket. But very small just some seapage and compression is still good. I checked the cluth friction plats and springs. All in good shape. Carbs we tuned and synced last summer about 600 miles ago.
any input will be helpfull at a complete loss with this one
thank you

 

[wherearewe]

Advance could be hanging open.

 

[retiredgentleman]

Check for air leakage around the rubber carb maifolds, and the carb bodies as well. Old seals on the carb butterfly shaft can allow air inleakage.

Mixture screws need to be adjusted correctly.

Another thing that caused my bike to have a high hovering idle, was a bad O-ring on the BS38 needle jet. If you have not checked them, better have a look, and replace them.

 

[sataniclumberjack]

thank you for the input i will check those issues out.

 

[trance]

Could be that your idle is just agjusted a bit high.

 

[jd750ace]

You should always set your idle speed adjustment on a thoroughly warmed up engine, or it will be fast when it IS warmed up.

 

[XSLeo]

Do you have and know how to use spell check?
When you pull the clutch lever you disengage the clutch not "engauge" it. When you release the clutch lever you "engage" the clutch. Note the spelling.
Proper spelling will help us understand what you are saying and help us help you better.
On your high idle you got some great advice, heed it.
Leo

 

[sataniclumberjack]

sorry about that xsleo. new to this whole bike world. and jd750ace this is new problem on the bike it has been fine for about 600 miles or so since i purchased the bike it just stared doing this with no adjustment to any thing

 

[jd750ace]

You said your tune and synch was last summer/600 miles ago. Did you just tune and synch what you got without disassembly? How did you prep the bike for winter storage? Did you use a fuel stabilizer? Did you drain the carbs, or did they set wet?

 

[gggGary]

have you had the tank off, moved cables, handlebars etc.? Is the throttle stop arm contacting the idle speed screw?

 

[5twins]

I'd say you need to service the advance unit and the advance rod. Pretty much all that I look at need it. Servicing these items is not mentioned in the manuals so most haven't been done since leaving the factory. The last one I looked at was all dry, half rusty, sticking, and only had one spring. Needless to say, it wasn't working very well, lol.

 

[sataniclumberjack]

jd750ace. i personally did not sync the carb's it was done when i bought the bike and for the winter it was stored in a heated garage and i fired it up about once a week for 10 to 15 min to keep the fuel moving through it.
ggggray i have had the tank off nothing seems to be binding up and the stop arm is making contact
5twins i did pull of the advance cover and it was very cruddy so i cleaned it up not sticking any more have not been able to test ride yet it has been and will be raining out for the next couple days i will let you know if that works if not i will just order a new one don't think there that expensive. and if that don't work on to cleaning the carb's and checking o rings
thanks again for all the input from everyone its been a big help

 

[wherearewe]

Actually the advances are quite expensive. An OEM one is about 200 bucks. You would be best too buy either a non-oem from mikes or consider investing in the electronic advancer that has just been released by Pamco Pete. On the other hand, sometimes a proper service does the trick.

 

[gggGary]

Yup if you keep mechanical advance, pull your rod out and polish it, use light grease reinstall, you aren't done till the weights snap the advance back. (at certain points cam positions)

 

[payaso13]

I had same problem...idle creeps up at stops...and ordered pamco kit with rod and new advance with springs...solved that...I'm sure like others have already said service your advance and rod.

 

[ANLAF]

The pilot jet is important for the idle, so its ok you saying its a 77 engine, but (like I discovered on mine) the carbs might not be 77.

First, though, is your bike stock or have you made some changes?
Then, correctly ID your carbs and the jet sizes (while you're in there, ID the float needle position, #1 is the blunt end of the needle and #5 towards the sharp end).

Once you have that info we can look at matching up the jets to your carbs to your set-up. I have had some great advice from 5twins (the main man, and I will step aside if he jumps in).

The carb ID is important, too, for float height, but lets concentrate on the idle. Retiredgentleman is right to suggest air leaks - and they pop up at the most obvious places because we don't tighten-up clips when the carbs go back on after cleaning (etc, etc).

So, back to the pilot - I have 76/77 BS38s (sounds a match for yours). I have pods and straight-through exhausts so I upped from stock to 27.5 and wow! what a difference. Idle was terrible before (for no apparent reason starting to race, then settle, then be different almost ever time I dropped off the revs) now it hits idle every time.

If this helps we can take it forward from there - it might be just to eliminate the carbs as the source. There is also the possibility you haven't got your exhaust headers seated quite right as well as the other suggestions above. There are things we can work through.

By the way, what wisdom I have is the received wisdom of the guys here, I am just a passer-on-of-stuff that I've learnt and had fun doing so and putting the bike together.

Anlaf

 

[sataniclumberjack]

well got the bike back to running order. pulled the carbs and cleaned them. new o rings and synced them back up. also cleaned and serviced the advance. so far seems to be running good put about a hundred or so miles on it, and no problems. so it must have been one of those two issues.
ANLAF yes the bike is 100 percent original stock. according to the person i bought it from i am the 3rd owner. i also identified the carbs as 77 which surprised me they were the correct year but awesome for me i guess. any way thanks for all the help and input from everyone it was greatly appreciated.

 

[ANLAF]

Good news - enjoy the riding.

Anlaf