This is a bit of a long post but I want to describe what I have and what I've done and get some advice. I've got a problem and have been looking at several threads and Google to try a get a clue. It seems to be common but the fixes are all over the map. After a little warm up I get gas spitting back out of the carb when opening the throttle. It's like a back fire but there's no fire just a rather forceful ejection of fuel. I found out when troubleshooting another problem. When cruising the bike will almost die but only for a second or two then go right back to running. My air filter was gas soaked too but I've read a little gas in the air filter is normal. Hard acceleration seems fine and the bike doesn't stall when idling.

Bike details - I just got a 2003 Sportster 1200c with 7400 miles. Has a Vance and Hines exhaust. Test drove the bike just for a few minutes and it ran well but was out of inspection and the original front tire was very dry rotted. Got it inspected, new tires and fluids changed. Mechanic commented saying "It really needs to be hot to run well," which didn't alarm me since this is my first Harley. What do I know?

I've read a lean condition can cause the spitting and that the new exhaust can contribute to a lean condition. I've also read the carbs like different jets and the idle mixture needs to be adjusted from factory spec. (air/ fuel mix adjustment still has the factory plug.) With that low milage I suspect ethanal (terrible stuff) has started causing trouble from siting too long. The inside of the tank looks clean and I removed the cap to rule out a clogged vent. The carb has never been off the bike and I assume it needs a rebuild and I've read the intake seals may be leaking too.

Before I start tearing the bike apart is there anything I need to do to troubleshoot before I do? I have an ultrasonic cleaner and a carb kit ready to go assuming it'll be needed. I'm a car guy and have no problem removing a carb and rebuilding it but bikes are new to me.

Any help is appreciated.

 

I have the same issue on my dads 85 tour glide classic with a cv40 carb ..and the carb is new . . HELP!

 

well, if it runs well and the plug color is good, pay no attention to it.
that could well be a normal thing. when the intake valve closes, there is a small reversion of flow, throw in reversion from the exhaust, if bad enough, will add to the issue. it you ever looked down the throat of a carb at WOT, nothing but a vapor cloud and if laminate flow across the opening is great enough, could pull the fuel out the carb. been there done that on my bsa salt machine, would actually soak my pants and the fuel would burn like fire on the skin.

 

Given that the bike isn't running great, I removed the carb for a rebuild, accelerator pump showing signs of leaks anyway. After removing the factory "don't mess with this" plug, I found that the idle mix packing didn't have the o ring. The washer and spring were there... Hmm. Some screws are a bugger to get off. I ground down a #2 Phillips to fit better but had to get pliers on one.

On ward.

 

The velocity emulsion time was green!

 

And there was no gasket between the body and the top.... This thing may have had a vacuum leak from the factory. I suspect that may have impacted the slide too.
Lot's of black residue on the slide and the body. After a 20 minute bath in the ultrasonic cleaner, ready to reassemble.