I have a 2000 FLSTC with 7300 miles. I didn't ride last year so this winter I drained the old gas, put in new plugs, new gas and started it up. When I got the rpm's up it would spit and backfire. I took the carb off, tore it down, cleaned it with carb cleaner, replaced the accelerator pump diaghram which was cracked really bad. I also replaced the tank filter. Again I put in new gas, new plugs and statred it up. SAME thing, the choke has to be out some, if I push it in it stalls and high rpm spitting and backfiring. I also sprayed water at the intakes thinking maybe a vacuum leak but nothing. Does anybody have an idea? It ran great the year before at Sturgis. Thanks for your help, Slabman

 

you didnt spray carb cleaner in the pump diaphragm seat I hope ... a lot of newby's at my dads shop (He rebuilds carbs) tend to want to clean the whole carb with carb cleaner and that seat needs to be dry and clean of anything that is going to eat the rubber boot ... I have seen that boot go bad and cause a ton of problems .. also seeing as you seem to have enough knowledge to pull the carb apart did you check everything else ( I.E. the float ,needles ,ect.) ... is the ignition system working correctly ( is it advancing and retarding the timing correctly ) ... just somethings to look into ... i am a auto tech but most of these same principals apply to bikes an engine is an engine just little diffrences ... and carb engines are even easier ... I would get a rebuild kit for the carb if you already havent and check and replace everything you can ... then if it is still doing it after the carb is tuned I would check the ignition ... normally you would check the ignition first but you already found problems with the carb so I would start there ... other than that good luck

 

By "tearing down the carb" did that mean removal of everything or just enough to spray some cleaner in? If you didn't go through at least two big cans of cleaner, you didn't use enough! Did you also get al the little air passages in the body of the carb? Did you maybe put the needle valve (the little "guide" the jet needle passes through) in upside down (speaking from experience)? VOES hooked up & working properly? Sounds like something still plugged to have to choke it to run. Next time just put some inhibitor in the gas tank and run it through prior to storage.

 

that stabil stuff works well to ... my father has a yamaha 4 stoke outboard that has the new carbs with the small epa approved jets and they get clogged all the time cause the boat sitts for a few months at a time ... if your bike is going to sit drain the gas in the carb bowls and lines and put stabil in the tank ... works for are boat and its very tempermental about old gas

 

This happened to me yesterday. It would idle fine and run at low rpm, but at lightly higher rpm, it was backfiring and poping out of the exhaust. If it was a plugged carb, it would probably backfiring out of the intake, so I tried changing the sparkplugs and it was immediately fixed.
My plug were almost new, but I had them out the day before, and I must have cracked the porcelain on one of them. It is very easy to do, and you can't see it on the plug, but it it will backfire and run like sh**.
They're cheap, so give that a try.

Stubby

 

there is a simple test to see if the plug is cracked just take a test light and hold the light near the plug and go area the edge of it ... if you see it kinda lighting up ... means the plug is grounding on the cyl. and not inside one the electrode ... but yeah plugs are cheap ... just something to try if your board and the auto parts store is a distance away ...