So I bought a 1999 LS650 off a kid with 9900 miles on it. He had it sitting for about 2 years. I took the carb off, gave it a deep clean to remove all the gunk, bought a rebuild kit to replace all the jets and needles, put in a new float and put it back on. Also put on a new battery and a K&N air filter in the stock airbox.

Bike started up like a champ. Was able to ride it to the motorcycle shop up the road for the Missouri inspection and it passed. On my way back I noticed it was having a hard time throttling. Rolling on the throttle just by a centimeter caused the bike to get really jerky as it sounded like it was misfiring.

One of two things will occur if I roll on the trottle a bit more past the centimeter mark:
1 - The engine dies/stalls out
2 - The engine revs up really quickly and I go shooting down the road

I was reading on some of the forums on here that it could have possibly been the petcock having vacuum line issues. Today, i put on the Raptor 660 petcock and sealed off the vacuum line on the carb. Gave it a cold start and twisted the throttle. The throttle response was good and spot on. I took it for a ride and about 5 minutes into the ride, the throttle started doing the same thing as mentioned above. The problem only seems to be happening once the bike has warmed up. I'm running out of leads as to what the problem may be. I've got a new air cut-off diaphragm coming in today that I'll put in and test again but I'm thinking it will have the same problems once it gets warmed up again (as the diaphragm in the carb looked fine to me).

Any thoughts or ideas, fellow Savages?

Maybe a sticky slide in the carb?

The slide needs to be squeaky clean - or it can hang up and cause issues.

Did you install the spring on the lower side of the carb slide needle...or on top?

Dave wrote on 05/22/19 at 07:59:58:


The slide is brand new and I believe I installed everything in proper order. I'll have to double check it when I get it apart and get back to you on that one. I rebuilt the carb about a week ago and have had so much going on personally its getting hard to keep track of everything. Woohoo!

Thank you for responding!

Okay, so I didn't get a chance to remove the carb and get it apart. The wife needed some stuff taken care of so the only thing I was able to do was get the new air cut-off diaphragm put in.

I started the bike and just let it sit idle. Again, the throttle response was spot on until the engine got warmed up. Afterwards, the slightest twist of the throttle would cause it to bog and die, or bog then rev up quickly.

I'm not sure that I'm running rich though, I have the air/fuel mixture screw turned 2 full and 1 half turns out which I believe is the factory setting.

Again, I can't thank you all for your input. I'll definitely be checking the slide once I get the carb apart hopefully tomorrow.

Are running the stock air filter?

I'd be suspect of the rebuild kit ,we've seen these with the wrong size jets many times .I would also change back to the original jet needle if you changed it,  unless you can be SURE the new one is actually the same .The stock needle is straight, if the new one shows any taper it's allowing to much fuel in and flooding the carb .which would allow the changes your seeing , it either floods and quits , or it manages to get beyond that stage and runs away.) and yes it could be a sticky slide as others said) or the new float not set to the proper height .  It will idle OK ,because that only involves the pilot jet . It is far better to just clean the stock parts and reinstall them unless they are damaged.

I'd put the stock jets back in as well.

ohiomoto and batman

Thank you for all your tips! I'm placing an order on partzilla for all the parts you two have mentioned. Once they get in and I get them swapped I'll follow up with how things go afterwards.

Thank you two again!