Your carb has been apart twice by the mechanic and it looked good to him, but did he run the carb cleaning tool through all the jets and every passageway ?
The carb cleaning tool is a little kit if speciality wires made for the very purpose of running through jets and passageways, which at times is the only way of clearing them of built up carbon, grit and fuel residue.  There is no way to eyeball those passageways, you must run them with the wire.  If your mechanic did not do that then he did not complete the job of cleaning the carb.

It is a fallacy that a big single is destined to backfire simply because it is a big single.  Do you think the owner of a BMW 650 would be satisfied with that answer from a dealer ? Or KTM or Honda 650 owner ?  Nope.
They do have fuel infection systems but that is just a better version of a basic carb.  If their FI system malfunctioned do you think they would backfire ?  Yep.  And would the dealer simply pass it off as "it is just the nature of a big single" ?  Not if they want to keep their business.  They would fix it.  
We are such a small portion of the market that many Suzuki dealers just blow us off because they do not care or because their mech's no longer know how a carb works and how to fix them.

DavidOfMA wrote on 11/26/12 at 05:11:36:

Thanks.  I don't know if the mechanic at the dealership actually cleaned the TEV or just eyeballed it. I'll get a carb cleaning tool (there's a link here somewhere) and when I have had more practice with carbs (by cleaning the spare carb I have), I'll tackle this one and see if I can resolve the issue by cleaning the carb as  you suggest. If not, then at least I know it's not the carb.

While you have the carb apart on the bench, keep everything on a perfectly clean surface,... pretend you are doing brain surgery or something.  
-- I used to use a towel, but a t-shirt works better because t-shirt material has very little lint compared to terry cloth.  One bit of lint trapped in a jet will add a lot of frustration.
-- Doing everything on a large cloth also helps to keep small pieces in front of you, rather than bouncing and rolling into black holes, never to be seen again.

Another way to get inner surfaces of complicated mechanical devices (carbs, for example) clean internally is to do it ultrasonically.  These gadgets are cheap now, and can be used for all kinds of things besides carbs.  I use mine for cartridges cases, gun parts, jewelry, dirty switches, piles of small fasteners, glasses, etc.  Here's a newer version of the one I bought a long time ago, and it is on sale at the moment:

http://www.harborfreight.com/25-liter-ultrasonic-cleaner-95563.html

LANCER wrote on 11/26/12 at 03:55:35:


Exactly.  Every cylinder on every motorcycle of any type ridden by those viewing this discourse has a carb, cylinder head, exhaust header, and muffler.  (this statement excludes FI systems)  
-- Single, twin, triple, four, or six cylinders makes no diff.  
-- It's just more noticeable on an LS650 because of the size of of the cylinder involved, and, since it has but a single cylinder, the burbles and pops seem more dramatic because of the time between exhaust pulses.

This might be slightly off-topic, but it involves a single and afterfiring. I have a Yamaha Majesty scooter, 400 cc single, fuel injected. When I took it to the Rocky Mountain Park earlier this year, I noticed at high altitude it also would afterfire and "grumble" on deceleration. I didn't happen to notice the altitude at which it started happening, but I am guessing above 8000 feet. I started browsing through its service manual, and it has an air injection system which injects air into the exhaust very near the engine any time the pressure in the exhaust goes negative (below ambient) with the idea of burning any unburnt hydrocarbons in the exhaust. I can only speculate that at high altitude the pressure differences were small enough the air injection didn't work, and the resultant unburned stuff could afterfire. The LS650 has no such injection system (and if it did folks would complain and remove it), so has no way to avoid the afterfire.

Quote:


Thanks!

Man,, I wanna see the tool, but IM not loadin that whole catalog over it..

KInda sorta looks like a cuttin torch tool.

I have a selection of fine wire, NO, Not Wine, Wire,, & can generally find what I need just layin in the shop, on a shelf, by the radio. Some are pointed, some blunt. A trip to the hobby shop for what they call Control Rod , or PIano Wire,, Great stuff, so hard it can break if bent too far too quickly, & heating it & letting it cool slowly only makes it more brittle,,
I havent tried a quench to anneal step, one day I may need to. Heck,, Im just gonna, today,, I have a small torch I use for soldering thatll do it,,

Anyway, that stuff comes in sizes smaller than a straight pin,or up to approaching 1/4",, 3 foot lengths, great stuff to have in a shop.,

$10.00 worth would get an assortment that'd surely cover the needs of carb passeges & youd have stuff long enough left over for projects.