I recently bought a 2003 Sportster 883 custom. Runs great after the engine warms up. When I start her up I have the choke all the way out. I wait until engine starts to run faster in idle before pushing in choke. When I push the choke in and give her some gas(still in nuetral) I get popping and backfire. It eventually goes away after a ride awhile. It has been cold outside since I bought it. Prior owner put VH pipes(straight) one her and I'm not sure how to tell if it has be re-jet. Any help on these issues would be greatly appreciated.

 

Could be running lean.
When the engine is cold, the gas will condense on the walls of the intake, and you tend to run lean.
Carbs have to be tuned for cold weather, and then for hot weather when it warms up again.
I had an Alfa Romeo Alfetta 1.8 with four carbs and was a PITA to get tuned every spring and every autumn.
Love carbs, though. If it werent for our idiotic Euro norms I'd get a carb on my Superglide tomorrow.

 

Thanks for the reply, I didnt know carbs had to be tuned for weather. Is that something you do yourself or take it to the local greaser?

 

Well, if you know the particular carb and how to do it, it's not really difficult.
Otherwise, I'd say you bring it and watch closely hwo it's done.
Be careful, though: while some popping does really no harm, tuning the carb the wrong way and running lean for a long time may waste the engine.
When in doubt, run rich.

 

If you read the Owners manual it will tell you how to use the enrichener "choke" during warmup. After starting on full choke you want to lock the throttle on fast idle and go to partial choke. After a couple minutes of warmup, ride the first 1-3 miles on partial choke, depending on how cold it is.

 

Chances are it is lean when cold. Some adjustment in the air/fuel will correct that. Is it while you throttle on or deaccel?

 

A 2003 Sportster shouldn't have to be tuned for the weather if it's remotely close to a stock engine. Popping can be a sign of both toolean and too rich. In this case one might suspect it's lean with a pipes install and no rejetting perhaps? Has the air flow been altered with a hi-flow air cleaner...leading to an even leaner condition?An air leak at the manifold might be the cause as well. Try re-torquing the head pipesfirst. Check for other leaks. Check to see what jets are in the carb next.

 

Without access to the bike, and more details, I'm going to go with AF07. Given it is doing it on start up, cold, I'm "leaning" towards lean vs rich. To assist you in finding any vacuum leaks, take a can of carb cleaner, and spray it around the base of the carb and the intake manifold, if there is a change in the RPM, usually up, have a leak, and you can pinpoint it by short bursts of cleaner using the nozzle to direct it. I'm guessing, it wasn't properly jetted after the exhaust upgrade. Happens way more than it should.cHarley gave a good recommendation also. Instead of taking choke all the way off right away, do it gradually as bike warms up, see if that will help. DO NOT run lean as stated earlier. Lean = HOT, not a good thing in any engine, but 'specially in an air cooled. If you are not carb savvy, and have access to an indy, they can help you, and as99 mentioned, get your nose right over their shoulder, and suck up on the info. Good luck.

 

If it has not been done move the low speed jet up on size CV carb is stock If the LS jet is a #45 move to a #46 These are also called pilot jets Makes a difference on warm up