LT-Z250 wont idle

[MPTonyT]

The bike is a 2007 LTZ250 that is completely stock. The bike used to idle fine and one day it just stopped. It will crank and run for a few seconds and it just seems like the kill switch is hit and it dies. If i turn the idle up to where i know its way to high then it will idle fine and if you keep the RPM's up it will never die.

I have had the carbs apart probably 5 times cleaning and such. I have tried the air fuel screw at 1, 1.5, 2, 2.5 and three turns and it doesn't seem to make a difference. Also when i adjust the idle it seems to take 10 to 15 seconds to change the RPM. Should i have to change the jets if the bike is completely stock?

Any help is appreciated, I have searched and it seems like everyone fixes the issue with the fuel screw and to me it seems like when i adjust mine it makes no difference. I'm no stranger to carbs and i hope its something simple im missing due to not being familiar with this specific quad.

[stunmai]

When I bought my 250 and had 'carb issues' I installed an inline glass fuel filter, and was puzzled at why the filter didn't stay half full like they normally do. Then after reading the plethora of petcock issue threads, I pulled the petcock (which is an over engineered vacuum valve design) and saw it disintegrating, also restricting the flow. Replacing it with a manual design Raptor valve cured my problem, don't even need much or any choke to start it now.

A week later, the same design petcock on my 400, the vacuum diaphragm let go, letting fuel run down the vacuum line flooding the engine. Replaced this one also with the Raptor. Hope this helps!

Fuel Petcock Mod (with pics)

[MPTonyT]

I did the test with the blocking off the vacuum line and setting the petcock to prime and it seemed to let fuel out and not make a difference. maybe ill order a petcock for a 660 and put it on here. i would at least gain a true off.

[muddbelly]

Mine did the same thing, it would start and run for about a minute and die.
It was the 'vacuum valve' petcock. I too did the service manual 'test', and that test showed nothing wrong, but upon removing the oem petcock and testing it with a vacuum pump, I could see that the problem was a 'very' slow leak in the diaphragm. I replace the oem petcock with an Yamaha Raptor 660 petcock, found all the info. and part numbers at this forum....check the stickies!

[ltz250kid]

my 2006 250z had some what of the same problem. mine would start up and idle for a 1 min and die. i put a HMF COMP. PIPE on it with a twin air, air filter. also re-jetted to the recommended 135 main for the pipe and it sits and idles every time

[MPTonyT]

Originally Posted by MPTonyT

I did the test with the blocking off the vacuum line and setting the petcock to prime and it seemed to let fuel out and not make a difference. maybe ill order a petcock for a 660 and put it on here. i would at least gain a true off.

Finally I was able to get the 660 petcock in there and there was no change. I ended up pulling the carb apart and replacing the current pilot jet with a pilot jet I had from my 660 (22.5) and it cleaned the idle up after turning out the fuel mixture screw to 3 turns and it will now idle just fine. Funny thing is that it still has the factory exhaust and intake. I would have never thought that I would have had to change the jetting.

[fastfarmer]

I changed my 250 air filter to a uni and it was running waay lean. I did the petcock mod(660) changed stock main jet from a 125 ,found a 145 mikuni main jet and put in there and changed pilot to.. These are soo chocked cause of epa, no wonder they run at all. I want to put a Lexx slip on it in the future..