86 Maxim X 750 high idle when warmed up

Suspected an air leak so I checked

Intake boots. No cracks
Vacuum line on carb 2 to the petcock. Airtight
Found a couple loose Allen bolts to the motor and clamps to the carb. Tightened
Sprayed wd40 on intake while running at normal rpm. No change


Still high idle on being warmed

So I then,

Removed the carbs and all the intake boots
Boots looked good but found 2 crappy O rings on cylinder 3 and 4
Replaced o rings and cleaned up intake metal on engine

Still high idle!

This is a new to me barn find. I took the carbs in and had them rebuilt and reassembled
Before I ever fired the bike
It does run smooth and starts perfectly when slightly warmed.
Carbs have NOT been sync'd. ( I did do a bench sync before I installed them)
Nor have the air mixture screws been set. The tech said he set them to a flat reference but the y should be tuned once installed and running

I'm going to take the whole bike back Monday for carb setup , sync and valve clearance check

I use the choke to start it cold. Once it is idling nice with no choke before it get hot, if I push the choke lever out, the motor revs up to redline. ??? Most chokes I've operated on a warmed up carb motor will stumble and kill the motor!

Any last areas I should check for "leaks" before Monday?

Also, the airbox boots are not on very tight, just sort of snugged up against the intake side of the carb. That should not make much difference I would think?
'

 

choke is not a choke it is an enrichment circuit which dumps gas into the carbs to get bike started and will rev quite high if left on mine will go up to 4k rpm.
I never let it go to any higher.

get the airbox boots clamped properly. if leaking you are not using the airfilter and will make a differance with the cv carbs

Idle needs to be set after bike is fully warmed. ride it for 10 minutes set Idle to 1100rpm to 1200 rpm max spec is 1050 rpm.

leak in your wallet for going to a mechanic

 

What are mixture screws set at? 2 1/2 turns out to start and is the throttle cable got enough slack?

 

Thanks for the insight on the enrichment circuit!

I've never had CV carbs before, only the slider with needle style. So your saying the carb to airbox seal (or lack of) can cause high idle? Interesting.

The bike idles cold fine where the idle screw is set right now. So reducing the idle speed a bit now then fully setting it to 1050 when hot is my next step

The throttle cable slack is set to about 3-4 mil of slop before the linkage starts to move.

The things I learn!

I believe the guy that rebuilt the carbs said he set them to a base value. Which I assume is 2 1/2 turns.

 

2 1/2 turns from lightly seated is the starting point

 

Normal idle speed should be set when the bike is fully warm. My bike idles low until it is fully warmed up. By the way, if I add choke with the bike running it stalls out. Probably not a good idea to try for a final idle setting until the carbs are synced. I'm also assuming the valves are in specs. If you want to get the pilot screws properly set you will need a color tune plug. With the colortune plug installed close the pilot screw until you get some white flames (lean), then open until the white disappears. Repeat for all cylinders. Install new plugs and take a 20 mile ride. Remove the plugs and look for a light tan color on the insulation. If still white, open the pilot screw about the width of a dime. Repeat this procedure on all cylinders. Take another ride and repeat the procedure. Continue until you get a nice tan color on all plugs. It took me several rides over a couple of weeks to get mine set properly. My pilot screws are set anywhere between 1 3/4 and maybe 2 1/4 turns open.

 

Excellent info! I did lower the idle after it was warm and it made quite a big difference. Drops down after a second or 2 but your right. It's now sync time then adjust the pilot screws. It's running a tad lean but feel 100% that it's a carb adjust issue and NOT an air leak. My guys at Mots told me to bring it in once I installed the rebuild carbs for final set up. The bike only has 18k kilometres on it but I want then to check the valves as well. It ran pretty sweet last night for my 20 mile test run. I can only imagine how nice this will be after the final tweaking. Hard to believe it was an abandoned bike sitting on a field 4 weeks ago!

 

Congrats! That does NOT look like a field bike. The x is a special beast when set up properly. Better focus on grip exercises cuz she'll pull the bars out of your hands!

 

My avatar is a pic of the bike after we dragged it out of the field. Yes dragged. The wheels were seized. Lots of hrs but she's almost done. Even out of sync and out of tune, it runs nice. Very smooth on and off the throttle.

 

Make sure to check/ adjust valve clearance prior to your running synch.