Wandering Idle Set Screw?

[rustyspoon]

Hey All!

Over the last couple of weeks, I've been very happy to be back on my bike for the season! However, I have been reminded of an issue that I had in the Fall but wasn't sure what to do with.

My idle set screw seems to be unbalanced; whichever side of 1500 RPM I set the idle to, the crew seems to slowly turn in that direction. If I set it below 1500 the idle will eventually drop below 1000 RPM, and if I set it above 1500 the idle will eventually climb to above 2000. When I say eventually, I mean over the course of about 200-300 km.

My first thought on how to fix this was some gasket maker (to add silicone to the threads and make it stick better) or the lowest rated Loctite. However, before I commit one way or another I thought I'd check and see if anyone here and any suggestions.

So. Any ideas on how to fix this issue?

[LAB3]

I'd be looking for a slight intake leak. My 450 acted much in the same way until I realized that the boots on the intake side of the carbs needed to slide forward a bit over the mouth of the carbs to properly seal.

[Nessism]

There is a spring that puts tension on the idle speed screw so it won't move in use. It sounds like you have a vacuum leak and/or a poor carb vacuum sync. Typically, vacuum leaks lead to a high idle when warm.

[rustyspoon]

It's interesting that you mention the carb intakes LAB3, as I was checking over it the other day and noticed that the boot on the airbox currently does not cover all of the metal of the carb intake. I'll have to fiddle with the airbox extension to get it sitting more evenly on the carb intakes.

I think I need to go looking for a spring as well, I do not have a spring on the outside of my carb assembly like Nessism mentioned.

The issue may be a mix of a missing spring and a poorly seated airbox.

Thanks all, I'll update here when I figure it out!

[chuck hahn]

Wont hurt to stretch the spring a little to ensure good pressure on the knob. Spray starter fluid at all the rubber joints and see if rpms go up

AND the clamps will stretch over time so if you got them as tight as possible and the starter fluid still ges past them replace the clamps.

[Nessism]

Here is the parts diagram for the carbs. https://www.partzilla.com/catalog/su...uretor-model-x

[rustyspoon]

Updates!

I do indeed have a vacuum leak, though only a small one. Spritzing the carbs down one after another with starter fluid gets me a 250 rpm increase for 5 seconds after hitting the outer left carb. My idle screw is adjusted to 1600rpm cold and idles as 2000rpm when warm. Honestly, it's been pretty nice as a temperature indicator, so I don't know if I actually want to fix it...

After about 600kms of riding all along the rev range, my idle screw has not moved at all. So while the spring will be nice I don't think it'll be a big deal. I've ordered the part indicated from the partzilla diagram graciously provided by Nessism and will install it when it gets here.

[rphillips]

Yes, like he ^^^^^ was indicating, it needs to be fixed. But like the rest of us, you do what suits you.

[Rob S.]

2k is too high to idle at. Fix it.

[rustyspoon]

Well alright then...

The leak has been fixed. I think. The carbs were reseated, and I used some liquid silicone to seal the edges of a rubber boot that was loose in the airbox and rotated really easily. No changes to the RPM when I used some starter fluid around the boots and carbs. But when I shot it into the airbox intake directly the bike bogged down for some reason? This confuses me and I would love some insight if anyone has any.

That being said, I am still finding that there is about a 500 RPM difference in idle when the bike is cold (just off choke) vs when the bike is warm (riding/idling for a bit). Is that a normal increase, or is that too much?

[tom203]

When not yet warmed up…but choke off…my 650’s idle is less than 900 rpm and you can feel it struggling. After some running, it will hold steady at 1200 rpm without complaint. After a good hot run, it’s still holds this idle. I set my idle stop screw to to this hot condition.

[rphillips]

I may be reading this wrong. But possibly turning choke "completely" off too soon. It's a gradual thing, after eng. starts keep it around 1K by decreasing choke a little at a time,, as eng. warms it will go up, decrease choke to keep it around 1K. If you ride down the rd. a few mi. and find idle too high, it sounds like maybe you took off before eng. was completely warm.

[rustyspoon]

More updates!

Spring came in and was installed. Adjusting the set screw took a little bit of time, but I managed to get it bang on 1200 RPM when warm. Went for a 2 hour ride yesterday and the idle stayed constant the whole way, no increase in idle when sitting in traffic or after riding hard.

Looks like this particular issue has been solved, thanks everyone for your help!

[Rob S.]

My $0.02 - I prefer an 11k rpm idle on my 11EZ. Just sayin'...