Oh the fun - Carbs, Air filters, oh my

josephjhaney · Sep 10, 2019

So, I got the "lets make this thing run right finally" bug after tearing apart the carbs on an xs650 special that my daughters boyfriend just got, and cleaning them. I have had a carb/cyl that hasn't been quite right since I got the bike 5 years ago, and it's just gotten worse. I just did the shotgun, and while that seemed to help, it still wasn't quite right. So now comes the strange part, just for kicks, I went ahead and put individual air filters on instead of the airbox, and bam, it seems to be running gangbusters now, I haven't taken it for a ride yet, but all 4 seem to be firing. Why do I say seem? Well......

The front left one which this winter had a stuck float, is actually cold to the touch when it's running (the air filter top) while the other three are warm, and gas is building up on the filter. Now I found this very odd, since I've never seen this before, add to this that on that same side of the bike, there is gas dripping from the exhaust under the left foot peg, and I can't seem to trace that gas to anywhere other than the pipe, and, here is the fun part, when I turn the bike off, and just let the key on, it doesn't drip, so it's not a fuel line/gas tank leak, but somehow leaking only when the bike is running. So, my next steps are-

I'm pulling the carbs off this Friday, and replacing ANYTHING that doesn't look right, cleaning them all, and putting them back on, I'm also going to replace the plugs while I'm at at. I can't imagine this won't fix it, but in the event it doesn't what would be next? Oh, and is there any reason if it runs better with the new air filters I should go back to the stock airbox? (The bike has voodooo 4 into 2's, installed, so I'm thinking the stock airbox should have gone when they were installed anyway).

I know it's a lot, but I'm down the rabbit hole now, so off I go!

Joe

Fire-medic · Sep 10, 2019

Take a close-look at that carb pilot jet, they are very small orifices, and it needs to be clean/clear to flow gas, so the engine will fire on that cyl (all cyl's) at tick-over. It's common that at idle, your exhaust pipe where you have a blocked pilot jet won't fire, because the gas isn't getting through the pilot jet, but when you rev the bike, and the pilot jet is no-longer controlling the gas, the cylinder fires, and the bike revs normally, but when it drops-back to idle, the cyl stops firing again.

josephjhaney · Sep 17, 2019

I took the carbs off, and thoroughly cleaned the idle circuit. The front left (as you are sitting on the bike) fuel/air ratio screw wouldn't come the whole way out of the carb, it came loose to where I could feel it was backed out the whole way, but it wouldn't pop out of the hole. I blew though the hole, shot sea foam through the jet and it came out where the valve was, so it's passing fuel, but i didn't get it the whole way out. Any ideas on how to remove it if it won't pop out? I even tapped the carb with it facing down to let gravity do the work, with no luck.

Joe

Fire-medic · Sep 17, 2019

Maybe try a small piece of wire into the hole in the carb venturi? If you've de-gummed things, it should be able to come-out fairly-easily. I once had one stuck and turned it over to my friendly machinist, he gave it back to me clear, and the threads chased.

I'm no machinist, but one I tried myself, I drilled-out the hole with a small bit, where I wasn't cutting-into the threads, deep-enough to reach close-to the bottom of the threaded hole. The tip of the brass jet was protruding-into the throat of the carb (venturi, just above the butterfly) and I used a deep socket, like a 7/8", to push-out the brass tip, and the drilled jet fell-out the other side.

sdt354 · Sep 19, 2019

josephjhaney said:
I took the carbs off, and thoroughly cleaned the idle circuit. The front left (as you are sitting on the bike) fuel/air ratio screw wouldn't come the whole way out of the carb, it came loose to where I could feel it was backed out the whole way, but it wouldn't pop out of the hole. I blew though the hole, shot sea foam through the jet and it came out where the valve was, so it's passing fuel, but i didn't get it the whole way out. Any ideas on how to remove it if it won't pop out? I even tapped the carb with it facing down to let gravity do the work, with no luck.

How about a blast of air down PJ 1 to get the A/F needle out? Gas dripping from the exhaust sounds like the float is still hanging or a needle/seat issue possibly.
It's a guarantee that all will be perfect if you box them up and send them to Danny. He's the carb go to guy here.

josephjhaney · Sep 19, 2019

Yes, I've heard that, and it might come to that. My next step is to put the cops on the bike I got a while back, since there is no reason not to, and see if that helps.

Joe