extremely high idle when starting

ok now that i have it running i figure its time to ask running questions..

when you start the bike up it will rev up to 6 or 7k rpm right away and wont come down for about 30-45 seconds or unless you twist the throttle a couple times..the intake boots are flexible and not cracked so its not leaking there.. the petcock vacuum line is gone i replaced it with an on off valve..i have bench synced the carbs. im not sure where to go from here..

 

what happens if you turn the idle screw out? your butterflies may be held open by the idle screw, causing the bike to be running with an open throttle.

 

the carbs were bench set..you can barely see through the butterflies its not the idle screw

 

i had the same thing tonight, one of the manifold clamps was hanging up the # 4 throttle linkage.
yours is kind of extreme but that's what a out of sync rack does. try to get a running sync.

 

ill check the clamps..but im gonna take it to a yamaha dealer and have them sync the carbs monday, i just dont have money to buy all the tools right now.

 

The dealer's gonna charge you more than the tools cost, if they do it right.

 

ok well i was all sorts of wrong....when you start the bike it revs straight up to 9k rpm and wont come down even if you blip the throttle. i need help quickly. ive turned the idle screw almost all the way out and no success...im completely lost..

 

Assuming you set the float levels, recheck them. Also check the fuel levels in the bowl with the clear tube method, but 9k is wide open, i dont think that is possible without the butterflies open, it takes a bunch of air to do that. The linkage for the throttle can get stuck too. I say pull the carbs and start over... and welcome to the prestigious club of "I have pulled the carbs x times and the damn thing still runs wrong." Methinks 9,000 rpm takes a lot of gas and alot of air...

 

From the chacal file, reasons for high idle:

- A lean air-fuel mixture condition, which can be caused by a variety of problems......vacuum leaks, plugged or too-small fuel jets, etc. Old or "stale" gas may also cause a lean fuel-air mixture to occur temporarily (until the fuel is used up!).

- A vacuum leak somewhere in the intake system.....intake boots, internal o-ring seals, etc.

- Mixture screws not properly set or adjusted.

- Vacuum piston sticking or stuck in a partially raised position.

- Idle speed screw set too high, or set to create a "proper" idle speed when the engine was cold (and thus results in a "high idle" once the engine reaches operating temps). The idle speed when the engine is cold should be modulated via the use of the choke (enrichment) control system.

- Butterfly valves opened too far; synch screws out of adjustment.

- Throttle cable wear, adjustment, or throttle lever brackets installed incorrectly or interfering with other nearby objects (cylinder head fins, etc.).

- Choke (enrichment) circuit is stock "open"....this can occur even if the choke lever is rotated to the fully closed position, if for some reasons the choke plungers are not fully closing (cable wear, cable adjustment, bent finger brackets, or installation problems).

 

yay back to taking apart the dreaded carbs...i would love to get the thing running right pretty soon

well as marvin the martian says "back to the drawing board..."

 

ok so it turned out to be the throttle cable adjuster was screwed all the way in holding the cable open. bike idles at 1k rpms and revs up and drops just like it is supposed to. havent gotten to road test it yet due to tags and past my 30 day window. but hopefully by the weekend ill make it to the license office and get it all taken care of

the exhaust is blowing a light blue almost white smoke im assuming it had to do with the marvel mystery oil the PO put in the gas to free up the dirty carbs..so i drained the gas out and i will get the gas can out and pick some new up on the way home from work tomorrow

 

Better hope that's the reason, because usually blue exhaust means burning oil/"blowby"... =need top end rebuild.

 

well the plugs didnt have any wet oil on them neither did the pistons when i shined a light down in there...it didnt smoke before i got everything back in synch, and set. i dont think its blow by or burning oil..the bike only has about 5k miles on it from factory. the bike was running rich before i rebuilt the carbs. and the PO told me he added the mystery oil to the gas after i left because he was trying to get the bike to run better....if it does need rebuilt it will be ok ill run it for the rest of the season and keep an eye on the oil level, and just rebuild the whole motor over the winter..usually if a motor is burning oil the plugs would have oil residue on them at the very least..

and the exhaust really isnt that blue its more white than blue...but you can smell a faint oil burn smell..kinda how your weed eater exhaust smells

 

If there is indeed Marvel oil in your gas still that will cause it. A two stroke XJ, must be one of a kind. An XJRD perhaps.

After a tank or two just be sure to monitor you oil level.

 

oh it was indeed in there lol i put the gas in my weed eater and it ran like a top