I have checked the mixture, bike starts first time, runs well, idle good.
when i back off the thottle it backfires a little, and at 70mph, the occasional cough from the carb. Plugs colour is a eggshell or very light tan.
I am running a OEM carb with 2 into 1 Vance and Hines, with a K&N filter.
I have read that you can upgrade the needle to one from a Sportster, but what year?
What do i need to do to sort this slightly annoying problem.
I live in the country, and the bike scares the **** out of horses most times, but when it coughs back in the carb, horses and riders get really pissed.
Any help guys.
Dee

PS I dont want to changed the Carb to a Mikuni etc.

 

your plugs seems okay, but you might be running a little lean considering the K&N and 2-1 pipes

if the carb is truly stock like you say, you probably have a 175 main and 40 pilot... you could probably use at least a 185 and 45

also, you gotta dig out the air/fuel adjuster underneath and make some adjustments, afterward

 

Agree with all that was said above, I use a 46/185 on most stock bikes, thqts will give you a good baseline

 

Another option would be having yours Performance Tuned by Dale at Killer MC Products. A lot of positive feedback on his carbs has been posted here in the Evo section as well. I ordered one 4 weeks ago. I'll post results as well once I receive & install it. You can read more about it on his eBay auction: http://www.ebay.com/itm/270620924203...84.m1423.l2649

 

You could chase your tail around and round looking to cure this and we will share your pain, but diagnosing elusive problems over the internet is not easy! There comes a time when a visit to an expert can pay dividends, as he may well put his finger straight on the problem and sort it in no time. So don't spend too much time annoying the local horses, go and get it fixed!

 

This is the needle http://www.cv-performance.com/cvp-n65-needle/
Here is a good article on CV carbs http://www.nightrider.com/biketech/hd_cv_mods.htm great site lots of good info.
Running a K&N filter and 2 into 1 exhaust with stock carb setup will make your engine run on the lean side as already mentioned. It's not ideal to keep running like that IMO. That being said I think you should have the carb re-jetted and tuned. As far as your problem of little back firing and carb cough up at speed. Other than the carb being the problem, you could have vacuum/intake leak or a faulty V.O.E.S.
good luck

 

An air leak in the exhaust will also cause popping when decelerating.
John

 

It's a lean thing most likely,check all your exhaust flanges for a leak.
The needle you want is from an 1988 XLCH I think it's an N65C but check it first.I use this needle in a CV carb.
All my engines burble on decel,they're basicially registered race engines, It's when the carb goes back on the pilot ,makes sense as if it don't burble it's too rich FOR ME. Don't give a toss what others do.Burble good bang and explode bad.
Ever heard a race engine that don't burble on decel.
Anyhoo sounds lean somewhere to me.
Cheers hth.