Please help! Random Increasing Idol!!

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Pedal2metal

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Hi all, I have searched and didn't find a answer to my question below. But I NEED HELP!
: )

I recently got a 1980 xs650 special (i absolutely love this thing) and Random times at Idol usually when warm the idol will increase out of nowhere. (It will keep increasing till it blew up if I let it)
If I am driving it and pull in the clutch the idol seems to start increasing also. If I come to a stop with the clutch in sometimes the idol will start revving to the point I either have to let the clutch out to bring the rev's down, or turn off the ignition to it does't explode!

Its hard for me to think its the carbs because when it does it, I can let out the clutch to bring the rpm's down and then they stay down. If I give it a little gas, it will usually start climbing up and up and UP!

i have sync'd the carbs, got new carb boots, cleaned the carbs.
I have also had a guy that works on older bikes look at it and it seems to be a mystery.

Any info would greatly be appreciated!!:banghead:

Thanks,
James
 
Next time its revving up, give it some choke. If it calms down then you likely have an air leak somewhere. The choke adds extra fuel and evens out the mixture and she calms down. Its not the solution, but a quick way of checking.

I had the same exact problem.

Another thing, I had my idle set a bit to high, and when warm it always runs a bit faster than cold. A high idle and bad throttle shaft seals lead to too much air and high revvs at the lights . Even stayed high when I changed gears.

Dont wear out your clutch at lights calming it down, will only cause other problems.
 
I guess I will order new throttle shaft seals and also needle jet o-ring, I hear could be the issue.. When its hot and I spray carb cleaner all around it, I dont get ANY raise in idol. So I am curious how there could be a leak. I will try the choke trick, that is a good suggestion. And it doesnt do it 100% of the time. One stop light it will, next 5 it wont and so on. If i let out the clutch and bring the rev's down, they will stay down. Could it be the electronic advance messing up? And I hope it isnt leaning out and going to burn a hole in my piston.
: (
I will order seals now...
Any other suggestions out there?
 
Hi,

Have you taken the diaphrams out? Mine had tiny holes in the diaphrams and it caused the idle to increase sometimes, sometimes it wouldnt... usually worse when it was hot.

Do your inlet manifolds have the barbs on them? If so it could have an air leak there.
I have seen people spray carb cleaner to check for leaks and found no leak, I know it sounds bad, but I used to POUR water onto the inlet to check, if the idle changed I knew there was a leak, often the carb spray cant get to all the places that there could be a crack or air leak.
Alternateively, pull off the carbs, clean then REALLY well and then check the o-rings, seals, etc (diaphrams, etc)
 
Thanks Pristic, I did take the diaphrams out and one was bad so I replaced them both.

Barbs on the inlet manifolds? I will have to look, but not exactly sure what you mean?
I just ordered the throttle shaft seals, and will take them apart again and clean really really well once the seals are here...

I hate waiting for parts!!!!
 
Where did you get the diaphrams? Did you install them the right way?
Did the idle increase before you installed them?

If you had a leak and replaced one diaphram, then you would most likely need to adjust the carb balance...

Here are some instructions on installing diaphrams
http://jbmindustries.com/Yamaha650.html

By barbs I mean the little 'nipples' with a cover on them. they stick out of the inlet manifold (eg if you weer trying to use a manometer to balance the carbs this is where you would attach it) ill find a pic...

This one has no barb (http://www.mikesxs.net/product/41-4850.html)
This one HAS the barb (http://www.mikesxs.net/product/40-4850.html)

Cheers,
Peter
 
Actually you said its when warm and on idle and also that it keeps going up... I think it could be related to the pilot circuit (see the jdm link at the bottom there is a picture)
Does the throttle CLOSE all the way when its warm?
If you push the linkage down by hand does it drop the idle?


Might be best for some of the other forum members to help as carbs can be tricky.

Peter
 
I had the same problem, one thing to also check is your throttle cable. If it's getting bent or caught up it can increase your throttle. When running turn your handle bars left to right and back slowly and see if your throttle changes at all, you may have a routeing problem.
 
The idol did increase same as it does not before the diaphram change. Changed the in hopes it would fix it. And the inlet manifolds do have the barbs. I will double check the caps on them and maybe pour some water :)
I don't think it's a cable routing problem, and the linkage does return all the way.
I have even checked it by hand when the idol goes up and it's down 100%.

And are you referring for the pilot "outlet" #13 in the diagram?
And what could be wrong with it?
 
Auto-correct on my phone butchered my last post. The idol had the same problem before changing diaphrams. I was hoping that would solve it, one was messed up.
 
Did you replace the orings on the float valve bodies? they get hard and leak fuel. do you still have a vacuum petcock?
a leaky petcock diaphragm can feed fuel to the left cylinder.
How did you do the synch?
Is the bike running great otherwise?
 
James,

I'm not sure if this is the problem but I had something similar happen to me that ended up being my advance weights were sticking. I removed the advance rod, greased it with moly grease and then ordered new springs from mikes to place on advance weights. Again I'm not that experienced as others on here but that was my issue.

Andy
 
It may be a lean condition without an air leak.
The mix needle set to the lean side and/or the float level set too low.
example: the racing you experience when the last of the gas leaves the chainsaw or weed eater.
 
I ordered a carb rebuild kit and it comes with the float valve and o-ring.
Also ordered the butterfly seals. My mix screws are STUCK!!! Won't even turn. Tried to free them with pb blaster and they are froze. So I also ordered new mix screws so I can force the old ones out.

Bike runs awesome besides the creeping idol.

The weedeater running out of gas analogy makes perfect sense. Very similar what I am experiencing.

Could it still be the advance if its electronic and not mechanical?

Thanks,
James
 
Pedal2metal said:
They guy that had It before me replaced the petcock. I am not sure if its vacuum or not?
Click to expand...

A Vacuum petcock will have a hose going from a carb intake barb (this is where the hoses go for the sync) over to the back of the petcock body. The valve is closed under atmospheric pressure, and is opened when the engine produces vacuum. A syringe that fits the tubing is a handy test piece for these. You can pull vacuum on the valve with the syringe inserted in the hose, and see if it bleeds off, and assess the valve's fluid tightness.
 
Be very careful with the mix screws better they are stuck than the slot stripped out...

That was the missing key to my mind, good chance you have one pilot circuit plugged and you are idling on just one side. If so the idle speed screw is turned in too far, any any slight bobble gets the slides to start lifting and it goes racing off. I just sold my running BS34 equipped bike but the idle screw should only be about 1/4" through the bracket. If it's screwed in much past that something's wrong with an idle circuit.
IMHO He wasn't much of a mechanic if he would try to sync carbs without having idle screws available.
 
ace79xs650 said:
James,

I'm not sure if this is the problem but I had something similar happen to me that ended up being my advance weights were sticking. I removed the advance rod, greased it with moly grease and then ordered new springs from mikes to place on advance weights. Again I'm not that experienced as others on here but that was my issue.

Andy
Click to expand...

+1. I've read in a couple of other places that if loading the engine against the brake brings the revs down and they stay down, it's the ignition advance. If the revs drop and then pick up again when you pull in the clutch, it's the carburation.

Regards,
 

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