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Discussion Starter #1 (Edited)
Took the new (well, new to me) tw for a run today, up a few pretty steep hills, through the forest then back down. On downhill 2nd gear seemed to hold it best without riding the brakes too much, but at higher RPM I was getting what I guess I'd describe as mild backfiring... but not really a loud pop just mild pop-pop-pop. With a little throttle it goes away.

Anything I should check or is this pretty normal? '05 just over 2k miles. Valve adjustment maybe? Only had the bike since last week and LOVING it so far. We have a cycle shop in town was thinking about bringing it in for a full checkup, but I dunno, I'm pretty mechanically savvy and wouldn't mind saving a few bucks for my rear racks and other wish list mods.
 

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Valve adjusting and an oil change won't hurt..! So you can keep track on maintenance schedule of the bike without asking the PO when he did the last oil change or valve adjustment..!

lil backfire on a low gear on downhill sounds like mine..! Mine does that too..! I can only hear hear it if i concentrate very carefully..! even then i'm not sure it's really backfiring..!
I've ridden it nearly 4000 km after i got it and so far no issues..!
 

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A bit of quiet popping on decel is probably nothing to fret over. Does it respond to the throttle well and run good overall? Valve adjustment wouldn't hurt especially if you don't know the last time it was done. Same for the oil change and servicing air filter, chain, etc.
 

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Discussion Starter #6
Thanks for the replies. Overall it runs really well. Starts right up every time, idles fine, plenty of power & throttle response. Gonna go ahead and change the oil & check the valve adj, check exhaust, etc. Don't really want to dive into the carb yet as it runs fine overall, but this will be a good opportunity for me to get familiar with the bike mechanically anyway I guess. Appreciate the input!
 

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I've got a new bike and it back fired when decelling down steep hills. After about 9 months it graguly got worse. Old school, it would be the timing but that was 40 years ago. Nothing to adjust today, except the spark plug. I pulled it and closed the gap one size smaller. That made it worse. Then adjusted it one size larger. That made it better. Adjusted it one more size larger and no more backfire. Also noticed more power going up the hill.

Took the new (well, new to me) tw for a run today, up a few pretty steep hills, through the forest then back down. On downhill 2nd gear seemed to hold it best without riding the brakes too much, but at higher RPM I was getting what I guess I'd describe as mild backfiring... but not really a loud pop just mild pop-pop-pop. With a little throttle it goes away.

Anything I should check or is this pretty normal? '05 just over 2k miles. Valve adjustment maybe? Only had the bike since last week and LOVING it so far. We have a cycle shop in town was thinking about bringing it in for a full checkup, but I dunno, I'm pretty mechanically savvy and wouldn't mind saving a few bucks for my rear racks and other wish list mods.
 

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Stock California model TWs come set up lean and one can expect them to backfire as reported near sea level (Kernville).
Simply adjusting the mixture screw to about 2 to 2.5 revolutions from fully seated cured the backfiring by enriching the fuel mix slightly (they usually are found to be from factory set at 1.5 to 1.75 revolutions out). No need to tear into carb to change jetting for most TWs. Many here consider this one of the basic first steps when getting a TW right up there with setting the correct amount of oil in the forks.
This minor change should still permit the TW to operate well at higher elevations without being overly rich yet lessen the annoying but harmless backfiring on downhill decelerations.
 

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Good advice above.

Also, isn’t the coast enricher designed to control off throttle operation? Wouldn’t hurt to examine the diaphragm if you clean the carb. Picture from jbfla’s write-up...

 

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How slow were you trying to go? If you hold any standard down hill with too much pressure on it the engine will try to spin backwards causing it to backfire. In that case it would require a little more throttle. This may not be the issue but it is good to know. I was playing in a standard car in a very steep area one time and I tried to see how slow I could go on a steep downhill section in 1st gear. After it popped a couple of times I gave it a little gas and it ran fine. I had learned something new.
 

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This minor change should still permit the TW to operate well at higher elevations without being overly rich yet lessen the annoying but harmless backfiring on downhill decelerations.
You sure Fred, at the Sweet Water all I could hear was your bike farting (backfiring) going down into that dead end valley.
 

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Well, I did qualify by saying "lessen" , not "eliminate" the farting. We were after all descending from over 11,000 feet into the 10,000 basin and my 223cc TTR motor still had stock carb and settings for the 198cc motor.
Once home I did tear into the carb looking for the mysterious missing rubber plug as well as ultrasounding the orifices in the main jet holder. Runs better now but Betty Boop hasn't gotten that high since.
carb.jpg
 

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Well, I did qualify by saying "lessen" , not "eliminate" the farting. We were after all descending from over 11,000 feet into the 10,000 basin and my 223cc TTR motor still had stock carb and settings for the 198cc motor.
Once home I did tear into the carb looking for the mysterious missing rubber plug as well as ultrasounding the orifices in the main jet holder. Runs better now but Betty Boop hasn't gotten that high since.
View attachment 204461
That sure is a good exploded view. I wish they were that clear on all the web sites. I think that is more clear than the books, good job.
 

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also if you have an aftermarket muffler or modded stock muffler, then the decel popping will sound worse
 

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My 2017 backfired and popped a lot upon deceleration when I first got it. That is a classic symptom of a lean fuel mixture. As Fred stated, adjusting the mixture screw is an easy solution to the problem.
 

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I cannot take credit when due to others, in this case JBFLA did thise wonderful series of photos and help:
I saved it years ago to refer to when confused.

TK Carb Photos and Parts Identification
 
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Must have gotten lucky with mine. 2018 bone stock no adjustments on the Central Coast of California and it runs perfectly with no popping or backfire.
 

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The lean fuel mix backfiring on downhill compression braking can also be caused by minor vacuum leak in the hose , coupling, or fitting on that $20 intake manifold pipe ( 5lb-13584-00-00) & & $6 surge chamber plug ( 90338-08007-00).
Without the restraining clip my intake manifold pipe once came loose at the manifold's nipple causing vacuum leak and subsequent backfiring.
 
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