High Idle after Carb-Cleaning.

[Megalomaniac]

I'm working on getting an 81 XS400 back on the road after neglect from the P.O and sitting for a winter. From what I can tell the Carbs are BS34 IIIs.

Prior to the cleaning the bike would idle high and die if throttle was given while the choke was out.

When I cleaned I found gunk/junk in most of the carb passages (dead bugs, dirt, ect).

Now with the carbs cleaned it idles and can be revved, but it rests the idle at 3000rpm even with the idle screw backed fully out and the sync-screw adjusted to even (have not sync'd carbs yet).

On my test runs I haven't bolted up the air filtres yet, will running it with no air filtres and cut off exhaust cause a higher than normal idle?

Assuming the PO didn't tangle with the jet sizing? (Waiting for mufflers to come to fix the chopped exhaust)

Will bolting on the filtres and exhaust bring the idle back down or do I need to go back into the carbs?

 

[Sesty]

did you take the diaphrams out and clean the choke plungers and passages? Cant hurt to clean them again as you wait for the exhaust.

What is the your jetting now?

check for airleaks around the boots and at the throttle seals

dont bother to sync the carbs till you get your mufflers and filters

 

[Megalomaniac]

How do I check the jetting sizes?

Pulling the jets and looking for numbers or do I need feeler gauges?

Right now though I'm mostly of the opinion that if I'm opening the carbs again I'll replace all the jets with known good jets of the correct sizing.

 

[xschris]

No air filters and mufflers will cause all the things you stated. After you instaled proper mufflers and air filters, sync the carbs with a manometer.

 

[razornightman]

Vacuum leak or running too lean

 

[Megalomaniac]

Fixed this ages ago, guess I should have followed up.

Fix was the following:
-New Carb Boots, Vaccuum Leak. But it still idled wonky, RPM was lower but still a would "run-away"
-New Exhaust, I went with a 2-1, the P.O. Didn't cut the pipes equally at all and it seemed like the different lengths were causing a weird idle.