carb tuning question. and Choke question...

okay...i'm making inroads with this bike, so here is an update of what i've done so far pertaining to this problem:

when i got the bike, it had battery vent tubing in place of the vacuum line for the petcock. I pulled the make shift line off one side, and sucked it out of curiosity when I replaced it, and it was NOT airtight...by any stretch. So the manifold was obviously sucking in some extra air. Before any change was made, it was idle-ing within spec.

I replaced the leaky non-vacuum line with a real one, and the idle dropped below 1000 RPM. I'd have to give it a little throttle to keep going when stopped, or drive with the choke on.

I figured that this was because the PO had reset the idle with the extra air going into the manifold, so before starting the next day, i tightened the idle adj. screw a touch. It still idled low, but enough to not die.

Today, I changed the oil and did some random maint... i wanted to get the idle up to spec, so while i had the engine running on the centerstand to warm it up, i tightened the adjustment screw a little more. When it could idle without the choke, it idled right around 1200 rpm.

I finished my maintenance, and took her for a ride.... For the first couple minutes it was fine, but after a few minutes, when I stopped, the idle was very high.... like 3000 rpm. Releasing the clutch a little to pull it down did nothing. As soon as I pulled it back in the idle went up.

I'm wondering if I adjusted it with the bike too cold. How long should it take to properly warm up the engine? Should I ride the bike tomorrow, and just adjust it down when the problem starts?

What is this usually a symptom of?

My other question is in regards to the "choke." I realize that this is an enrichment circuit in the carb, but what exactly does it do? Mine does nothing until its almost entirely engaged, and then it has a very small area to adjust. If i engage it all the way, the engine races to around 4k RPM, but I can use it effectively as long as I take care how far I engage it.

Is this normal behaivor? Something tells me it isn't, but I don't really know what it does and how it works, so I can't really diagnose it.

Oh ya, one more thing. UNI foam air filters would require a re-jet right? The bike came with one, but I have no idea if it was rejet. I'm planning a carb cleaning as soon as riding season is over, but until then, i just want the bike safe and rideable. i ordered a stock air filter and I'll shove it in and see if it helps anything....


thanks in advance for the help

kellen

 

Yes set your idle when the bike is at normal temp, which should be when the idle has raced up to 3000. Take the bike for a ride to warm it up, (like we need a excuse to go for a ride), that's the best way to warm any engine up to make adjustments. A motor will not warm up properly just idling (it will if you leave it sitting half an hour or so). It is bad for a motor and can fowl you sparkplugs, to just sit idling for long periods of time.

Any carb tuning adjustments should be made with the bike at normal temp, 10 miles will do the trick nicely.

Choke puts more fuel in the mix.

Tune the engine (sync and mixtures) then try adjusting the choke again. Check for air leaks.

Some aftermarket filters, pods and modifications require rejetting. Try 1 size up on the pilot jet. Have a look at your sparkplugs to check for lean/rich problems. If your sparkplugs look fine jetting should be OK.

When tuned up does the bike backfire? If so rejet.

This is only if your new filter lets "too much" air through, this makes the bike too lean.

Have a search of these forums there are many posts like this and should give you a better idea of what to do.

Ask if you are unsure.

 

Some links:

Rejetting

Sparkplug reading

XJ Tuning