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Discussion Starter #1
Just installed a TTR225 header with DG oval exhaust on my 1998 TW. I'm at sea level. The TW had a 116 main jet and I bumped it up to 120. At both main jets, there was a lot of popping/backfires when I would release the throttle. I've bought the next two sizes up from the 120 (122 and 124 I believe). Does it make sense to be bumping the jet sizes up that much or am I missing something? Could it be exhaust leak?



Can any of you with pre-2000 bikes and have installed the DQ-O pipes let me know where you guys ended up as far as main jet sizes?



Thanks in advance.



Ken
 

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If it's idling and accelerating fine, leave it alone. You're gonna want the smallest jet that will maintain a good mix (check the plug) and smooth running. If you can find that, you'll get the least backfire. It's just excess gasses not getting burned in the cylinder. Pretty normal, but jets that are too big can add to that. Jets too small can give the same effect, but usually only with advanced timing.



If you were getting it with stock jetting as well, I'd say do a valve adjustment, and cam chain adjustment wouldn't hurt. A wasted spark system and valves hanging loose could easily set you up for that, regardless of jet sizes. A loose valve in this case would be a bad adjustment by someone else, or the cam chain really needs tightened to get it shut in time. I don't think there's any other reason for valves to go loose on this engine unless something's broken.



After that, look for exhaust leaks.
 

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Discussion Starter #4
Okay, so here is the update. I was at 120 and the bike would bog a bit around 40 mph WOT and backfire upon releasing the throttle. Pulled the plugs and it was pretty clean (not brown). I then went up to a 126 and it would bog down much faster and lurch and then backfire when the throttle was released. I'm thinking that I am going the wrong direction here. Perhaps I need to back down to a 118. I believe stock main jet is 114 and when I bought it, the bike had a 116. The bike does not have a spark arrestor. Would this cause the backfiring? I'm considering going back to the old exhaust someday.
 

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I'd try the 118, but there's still no reason not to get your valves right to be sure. 120 really seems like the most you'd ever need for an older carb unless you're doing intake work as well.
 

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Maybe I am full of it ~ but , I had the same popping on release of the throttle. I raised the needle and put the air screw out to 2 1/2 turns. It all went away.... purrs . Now mine is a 2005 so maybe its all different on older models... ??? But it was an easy fix for mine...................
 

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Like he said, jetting won't matter if you're not adjusted for the jet you have. Definitely play around with settings first.
 
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