Well I know this is a somewhat dated thread, but I wanted to share my experience with the decel valve. -Just in case it could help someone searching later...
I was getting a bad stumble after closing the throttle. I've heard someone else describe this perfectly somewhere... Basically, the engine would rev up without a problem, but when I closed the throttle it would stumble down below the idle speed and sometimes even die. If it didn't die, it would soon catch back up to idle speed and be fine. I was also experiencing some erratic idle after a good hard run, then sitting at a light type of scenario. It seemed once the engine was all hot and bothered, she'd have trouble breathing... At first I didn't think the problems were related, but they were. Also was getting decel backfires. You know, the Grrrrr, grumble grumble, POW, grrrrrrr, POW POW.... type of decel pops... (you should hear me do it in person!!)
I read some about the decel valve & decided it was worth a shot. It's easy to get to & remove. All I did was remove it, shot a good bit of Brakleen into the orifices, both the carb side & cap side, hit 'em with compressed air, cleaned & inspected the diaphram, & reassembled. My idle issues are gone!! I still have the decel POW, but not as bad. I honestly think that's a muffler to headerpipe leak, which will get attention soon... Maybe...
The moral of the story: DO NOT OVERLOOK THE DECEL VALVE

What's the decel valve?

LANCER wrote on 05/31/10 at 04:22:01:

Cool, looks like an oxy/acetylene torch cleaning kit, which would probably work also.

LANCER wrote on 05/31/10 at 04:22:01:


Thanks....now that I've read about the technique from the Carb Master, maybe I'll now not be afraid to use that carb jet cleaning tool that's been sitting in my tool drawer for over a year.

Reposting from Rubber Side Down! / Re: "Thoughts on pops, backfires during decel" on: 07/17/13

I got rid of 95% of the backfiring by changing the spring in the TEV to a shorter spring. The length of the stock spring has two negative effects on the valve's operation.  
Having measured the pocket that the spring resides in, I came to the following conclusions:
1. There was not much room for the diaphram to move or open during the high vacuum present at full throttle, thus limiting the enriching effect the valve is supposed to provide.
2. The stock spring was stronger than necessary and was closing the valve too abruptly during the low vacuum present at deceleration, thus the backfire.

Instead of cutting the stock spring, I chose to find a shorter one. I'm satisfied with the first spring I chose, a #90 spring I bought at Ace Hardware. Listed below are the dimensions of both springs:

                                 Stock         #90
Free length      1.400 in.         0.715 in.
Wire Diameter      0.032 in.         0.035 in.
Outside Diameter       0.483 in.         0.597 in.

My bike is a 2002 model with just under 4000 miles. I installed the #90 spring at around 2800 miles. The bike is stock with one exception: a previous owner drilled out the baffle. The bike is much more pleasant to ride, and I would recommend this modification before I changed anything else.

My bike doesnt backfire except when you shut it off and the last charge is thrown into the exaust. always comes with a laugh and a slap on the ass afterwards haha.

I must be the odd man out, I happen to like the backfiring. Seems to fit right in with the character of the bike (at least in cafe racer form).