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Message started by ralfyguy on 09/25/09 at 10:50:59

Title: Need help with idle
Post by ralfyguy on 09/25/09 at 10:50:59

If some of you guys could help me with this little test, I would appreciate it. I am trying to track down my inconsistent idle problems. Trying to figure out if it's the petcock. I sucked on the vac line, but nothing comes out as it should. However I have problems with the idle. Let's say first stop at traffic light it idles normal around 1,200. Drive off to second, idle could be at 1,500. Drive off to third traffic light, it about dies. Drive off again idle could be around 1,000. Drive off again idle is normal. This goes on all the time, not necessarily in that particular order, but it does it only when warmed up. So I keep messing with the mixture screw, needing it to turn it more lean, but will get more of a flat spot at about 1/4 throttle. It needs to be a 2 1/4 turn to run good, but idles crappy. Turn it to 2 turns out idles better, but has that flat spot. I haven't changed the setup in a year, and last year it ran perfect like this. Now that I have to go leaner, it could mean that the petcock might have a tiny leak, so a little gas gets through the vac line into the carb, thus messing up the setup.

Now my question is if some of you guys could try what I did:
While idling, pinch the vac line where it curves up near the speedo cable and see if the idle goes up about 100-200rpm and the idle gets more stable on mine then too. IMHO it shouldn't make a difference to the idle doing that. I wanna make sure it's the petcock for sure before I buy a new one.

Thanks for any input.

Title: Re: Need help with idle
Post by justin_o_guy2 on 09/25/09 at 10:56:23

If you suspect the petcock isnt delivering fuel, put it on Prime. That bypasses the diaphragm. Now, if the diaphragm is obstructing flow, then that test will not work out. You can see if its delivering fuel by pulling the line off the carb & putting it in a gas can, Maybe pull the fuel line off & poke a long one on, so you can sit a gas can down & make it easier. Fire it up. It'll run quite a while on the gas in the bowl.
I suspect crud in the carb, tho.
Maybe you could drain the bowl into a glass & see what kind of crap comes out. May want to drop the bowl & have a look.

Title: Re: Need help with idle
Post by Serowbot on 09/25/09 at 11:17:11

make sure that the vac line is securely clamped at both ends and not cracked... this would cause an intake leak...
if not that,... my guess would be a sticky slide in the carb,... go in from the top of the carb, pull the slide out and clean off residue from the slide and the cylinder....

Title: Re: Need help with idle
Post by ralfyguy on 09/25/09 at 12:31:56

The bike runs great other than the idle, so it must be delivering fuel. I got a new hose and clamps on it. I sucked on the end that hooks to the carb and stuck my tongue in it, and it keeps the vacuum, but I have a faint smell of gas there, but maybe because I am close to the carb and the bowl vents there. Could it be the o-ring on the idle mixture screw causing a vacuum leak? I am ging to drop the bowl and check for dirt, but I still am curious if pinching the vac hose is causing a higher idle on y'alls bikes. :)

Title: Re: Need help with idle
Post by Routy on 09/25/09 at 13:59:14

Raftguy,

Just for you, I took a little ride to warm it up to a perfect idle, then I pinched the vacum line,.......and I cannot detect any difference in idle when the line is pinched. But I notice you sure can feel the pulsing of that piston thumping away, when squeezing that hose.

IMO, if the hose is good and clamped tight at both ends, and the diaphram is not leaking, there will be no difference.

Title: Re: Need help with idle
Post by ralfyguy on 09/25/09 at 14:05:29

Thanks for doing that. I appreciate it. That's what I thought. Since this is a new hose and clamps, that means my petcock is going out. I feel the hose pulsating too. Just don't know why it has to be warmed up for that to occur.

Title: Re: Need help with idle
Post by Routy on 09/25/09 at 15:06:36

But seems like if you were to disconnect the hose from the diaphram, and block it, then run on prime, that would eliminate any problem in that circuit. If you still have the problem, and you are sure there are no other vacum leaks, then its time to attack the carb.

You can check for vacum leaks by spraying wd-40 around the carb intake area, and note any RPM change.

Is there any chance you have a valve too tight ? But if it runs good above an idle,....not likely I guess.

Title: Re: Need help with idle
Post by Digger on 12/11/09 at 21:47:07

70636E647B65777B020 wrote:

...... While idling, pinch the vac line where it curves up near the speedo cable and see if the idle goes up about 100-200rpm and the idle gets more stable on mine then too. IMHO it shouldn't make a difference to the idle doing that.....

If you've got gas entering the intake manifold via the petcock's vacuum line, this can cause an uneven idle as you will then have an intermittent and uneven rich condition.