Starts and idles but stalls when opening throttle

[dankamus]

My bike was running fine but had been idling a little high. Somewhere in the 1800 to 2000 rpm range. I finally decided to just turn the idle adj. knob to bring it down to around 1500 rpm. It ran normal for about three miles or so then started to slowly drop in rpm at a stop until it would stall. So I turned the idle adj knob back the other direction. Then it would idle at 3000 rpm. I tried to turn it back down in tiny increments. At this point it would only idle at 3000 rpm or stall if I turned the knob one way or the other. I managed to get it home and the next time I tried to start it, it was hard to start and then finally got to a good idle but will stall when I give it throttle.

I couldn't have guessed a well running bike would start running like garbage just because I adjusted the idle. I've turned that knob before w/o any problems. Any ideas?

[Atesz792]

Maybe a new intake leak? Spray some WD-40 around the intake boots with the bike running, if the rpm changes, you have a leak.

[robfriedenberger]

Im suspecting bad gas?  How old is your gas and did you fill up any where that wasn't a busy gas station?

Try draining off the carbs?

[dankamus]

Man, I forgot about the old spraying WD-40 or carb cleaner around the vacuum tube and intake trick.

Gas isn't really that old and I think I got it from a pretty busy station. I've been having problems with this thing ever since I got it so I'm starting to think it's a lemon. We did have a report of some bad gas in this area not too long ago though so it won't hurt to try some fresh fuel. Hopefully that will sort it out.

Thanks for the tips!

[yamahonkawazuki]

when was last time carbs were cleaned?, ( curiosity of mine )

[dankamus]

Well... to try to give a brief history. This bike has had problems like this off and on since I got it. First it had gas leaks because the floats would stick open... cleaned. Then after I fixed that one float would stick shut... put in carb kit w/new needle valves and seats, cleaned. Floats continue to stick shut. Then I realized the gas tank had been coated with sealant. Crappy sealant or crappy job putting it in i don't know, but it was leaching into the gas an gumming up the carbs... clean, repeat. Got the tank problem sorted out. Floats stick open AGAIN some time after. I assumed it was just some left over gunk from old tank (even though I'd cleaned thoroughly after fixing tank issue)... cleaned.

At this point it ran great for several weeks. It had been idling high all that time (~1800-2000) but after the troubles I'd had I hesitated to adjust the idle. After getting more confident that it was finally running good again I adjust the idle and bam, gremlins are back again.

I'm tempted to give it a good soak, but I've read elsewhere that a good carb cleaner aerosol should be all you need and that soaking is pointless. I'm going to clean it again and check for intake leaks and bad gas I guess.

[bombsquad83]

I'm guessing you used the K&L economy rebuild kit instead of OEM when you replaced the float needles and seats?   Those things are crappy.  I had zero luck with them.  Then I went to OEM replacement needle valves and seats, adjusted the float height using the clear tube from the drain method, and no problems since then.  I also replaced the vacuum petcock with a manual one to eliminate fuel flow issues.

[dankamus]

I originally went with the K&L. Can't remember now but I think I ended up replacing the K&L w/OEM seats and needles after having so many problems. I've been seriously tempted to replace the vacuum petcock w/a manual like you did. It's a shame the stock petcock is so bad. I finally ended up taking the cover to the inner diaphragm off and slightly extended the spring inside so that it actually seals when there is no vacuum applied. Working so far... I think.

[jsyzdek]

When I got my bike last year, it didn't have much power. And when I opened up the throttle, it would have a 1-2 delay before it would start actually reving up. It was my first bike, had no idea what to expect.
Anyway - after a few months of riding just a couple of miles here and there, it finally started losing all the power and would idle, but wouldn't run. Opening up the throttle would kill it, choke kept it running for a couple more minutes, but finally it died completely.

Diagnosis? There was half a gallon of water in the gas tank. And it was mixing well with the gas because it held a lot of ethanol in it. Separated the water layer away (I'm a chemist  ), put the gas layer back in, and after running it on idle for a couple of minutes (until whatever was in the carbs got burnt out) it turned into a completely new bike.

In order to avoid water precipitation in your tank, try to keep it full whenever you leave it alone for a while, just so there is less air moving in and out as the temperature swings day & night.

[dankamus]

Keeping the gas tank full is definitely something I'll try to do. Can't hurt with the humidity here in Louisiana.

So I'm guessing you had a spare separation flask laying around? hehe.