Slightly high idle when warm

Hey team,

Hope you're all well. I know, another thread about idle issues. I'm sorry in advance.

I've been chasing a small issue for a while now and am getting to the end of my tether with it. First a bit about the bike. '82 XJ650 Seca, engine number 14R-000219 (I think it's like the UK models, but sold in the Oceania region). It has a standard airbox with a brand new hiflofiltro air filter and an aftermarket 4 into 1 exhaust. I've had it for around 6 months and am working to get it back on the road.

The issue I'm facing is that it won't idle at 1100rpm when warm, even with the throttle control screw all the way out. It'll start with a lower idle when cold (requires some "choke"), but then when warm it wants to sit at around 1.7 - 2k rpm. Not super high, but not where I want it, and the fact that the idle control screw is all the way out at all times seems odd. I haven't taken the bike out on any rides. This has all happened on my driveway

What I've done so far:
- Set valve clearances to spec (Currently considering going all the way back to square one and checking these again in desperation)
- Cleaned and rebuilt the carbs with new throttle shaft seals (I haven't done the idle mixture screw seals and washers)
- Bench synced and checked the butterflies seat correctly
- Checked that the carbs have the correct jets (110 mains and 43 pilot)
- Replaced the intake boots
- Thoroughly checked for vacuum leaks using starter fluid with no luck
- Set float levels to spec
- Checked other things like sticky cables for throttle and enrichment plungers

What have I missed ??

Things I'm wondering/looking to trying next:

- Could it be that the idle mixture screws are too far out at 2.5 turns out? Could dialing all of these down effect idle rpm?
- I have a colortune. Should I aim for the leanest possible idle mixture? Could that be it?
- While I couldn't find evidence of this being the case, could there be air leaks past the idles mixture screw orings?
- Another thing I though of was the enrichment plungers, can they get to a state where they don't close entirely and end up supplying more fuel when they're in the closed position?
- Maybe I should do a compression check?

I'm open to any and all suggestions of where to go with this next. I dream of the day I can have the bike idle nicely where it should. Many thanks in advance.

Reagan

 

i would put a different source for fuel supply on the bike. make a small shop tank and get the bike warm then swap it to alternate fuel source. it is possible your supply from the petcock is restricting fuel at idle causing a high idle.the petcock can cause problems you might even try to put it on prime and make sure your fuel is flowing good.and then see if the fuel petcock is restricting the fuel. the bike will idle high when lean turn the mixture screws out.what does the color tune show?

 

you have to do a running sync, no doubt about it

 

you should replace the orings on the idle mixture screws, washers if they are rusted
idle mixture screws set them to 2-3/4 you do have a color tune you are looking for bunsen blue color close to where you get yellow/orange color.
the color tune is what gets set by the mixture screws if they are not is goog shape as far as o ring and washer as well as the circuit being clean you will be just wasying your time.

push down on the plungers see if idle drops

always do a compression test just so you know where motor is . it is best to evaluate motor first before anything else then safety Items then go for the cosmetics.

running sync will be needed then color tune again if you change anything bench sync again.

 

Legends! Thanks for your thoughts.

So I've actually been running the bike from an alternative fuel source for all this work, rather than from the tank. (Also working on restoring the tank), so I don't think low fuel levels are an issue at all. I've generally played with the colortune to set in at the lower end of the blue/white spectrum, but I think I'm going too lean on it, based on what XJ550H has said below. That could be the culprit right there.

Cool, will do! I did notice on closer inspection last night that three of the butterflies are closed up tight, while number 1 carb sits slightly open, so this absolutely could be a factor. Still not sure about that idle screw being all the way out though...

Cool, point taken on getting those orings replaced. Turns out it's quite hard to find the right size here in NZ, but I think I've managed to track down a source. I'll hopefully get those delivered and installed for the weekend.
It also sounds like I'm tuning too lean with the colortune. Not having a garage means I'm always doing it out in the daylight and seeing the colour gradient can be tricky. I'll keep at it and aim for that sweet spot.
Spent some time on testing the EC circuit and plungers last night and they appear to be making a good seal, so I think I can count that out as a factor.

Thanks again for all the input. I'll keep you all posted.
Cheers!

 

use a tarp as a tent to block daylight

 

What happened after that? Did that fix the idling problem?

 

he was here last month maybe he will reply