backfire on decell

[440challenger]

04 450r with mild motor. 11.5 1 je, stg 2 hc, full motorworks pipe(just repacked also).

Back fires on decell ,mostly ridding trails when in the meat of the power then letting off. Stock carb, open box with dynojet stg 2 jetting for under 3000 feet. im at sealevel. fuel screw is out 3.

I took the carb off checked to see if the pilot was clogged or any dirt was in the carb,nope crystal clear. Carb boots are on tight(no air leaks) . Since i have my fuel screw out 3 turns i was thinking of jumping up one on the pilot jet.

Am i on the right track?

[coryatver]

the main jet is either to rich or to lean

[4bidden]

I'd ignore the above post...you're on the right track.

[coryatver]

I just thought it could have unburned gas still in there from being to rich and backfiring or it didn't have enough gas so it back fires. When he said meat of power i take it it would be on the main jet circuit.

Why do you think you need to adjust your air screw. You should adjust it to the point that it idles the fastest. I wouldn't go much more than 3 turns out though without going up on the pilot but i think you need a different main

Popping on decel is a lean pilot circuit. If you are out 3 turns on the screw, you need to go up one size on the pilot jet and that will fix your problem.

[400exrider707]

Exactly its not a main jet issue. It's not popping when he's riding at the meat, it's popping when he lets completely off and he's coasting. This is usually fixed by adjusting your fuel screw, but since you're already at 3 turns out, it's time to bump the pilot one size, then readjust your fuel screw again.

Also I hope you realize that your jet kit numbers do not correlate to the numbers on kehein jets. The same numbers is a different sized jet.

A 180 main from dyno jet or the likes is not the same as a 180 kehein jet. Just an FYI.

[chad502ex]

TRX450R_Racer is right on!

:macho

Jet size chart

Width------Keihin # -- DynoJets # -- Mikuni #
0.0350---- 92.5--------- 92----------- 86.3
0.0360---- 95----------- 94----------- 88.1
0.0370---- 97.5--------- 96----------- 90.0
0.0380---- 100---------- 98----------- 91.9
0.0390---- 102.5------- 100---------- 93.8
0.0400---- 105--------- 102---------- 95.6
0.0410---- 107.5------- 104---------- 97.5
0.0420---- 110--------- 106---------- 99.4
0.0430---- 112.5------- 108--------- 101.3
0.0440---- 115--------- 110--------- 103.1
0.0450---- 117.5------- 112--------- 105.0
0.0460---- 120--------- 114--------- 106.9
0.0470---- 122.5------- 116--------- 108.8
0.0480---- 125--------- 118--------- 110.6
0.0490---- 127.5------- 120--------- 112.5
0.0500---- 130--------- 122--------- 114.4
0.0510---- 132.5------- 124--------- 116.3
0.0520---- 135--------- 126--------- 118.1
0.0530---- 137.5------- 128--------- 120.0
0.0540---- 140--------- 130--------- 121.9
0.0550---- 142.5------- 132--------- 123.8
0.0560---- 145--------- 134--------- 125.6
0.0570---- 147.5------- 136--------- 127.5
0.0580---- 150--------- 138--------- 129.4
0.0590---- 152.5------- 140--------- 131.3
0.0600---- 155--------- 142--------- 133.1
0.0610---- 157.5------- 144--------- 135.0
0.0620---- 160--------- 146--------- 136.9
0.0630---- 162.5------- 148--------- 138.8
0.0640---- 165--------- 150--------- 140.6
0.0650---- 167.5------- 152--------- 142.5
0.0660---- 170--------- 154--------- 144.4
0.0670---- 172.5------- 156--------- 146.3
0.0680---- 175--------- 158--------- 148.1
0.0690---- 177.5------- 160--------- 150.0
0.0700---- 180--------- 162--------- 151.9
0.0710---- 182.5------- 164--------- 153.8
0.0720---- 185--------- 166--------- 155.6
0.0730---- 187.5------- 168--------- 157.5
0.0740---- 190--------- 170--------- 159.4
0.0750---- 192.5------- 172--------- 161.3
0.0760---- 195--------- 174--------- 163.1
0.0770---- 197.5------- 176--------- 165.0
0.0780---- 200--------- 178--------- 166.9
0.0790---- 202.5------- 180--------- 168.8
0.0800---- 205--------- 182--------- 170.6
0.0810---- 207.5------- 184--------- 172.5
0.0820---- 210--------- 186--------- 174.4
0.0830---- 212.5------- 188--------- 176.3
0.0840---- 215--------- 190--------- 178.1
0.0850---- 217.5------- 192--------- 180.0
0.0860---- 220--------- 194--------- 181.9
0.0870---- 222.5------- 196--------- 183.7
0.0880---- 225--------- 198--------- 185.6
0.0890---- 227.5------- 200--------- 187.5

[440challenger]

thanks guys, i thought i had it right, just wanted to make sure.
Cant wait to get rid of that popping!!! :D

[ricksmx865]

Not to steal your post but im having the same problem on my 05

hmf slip on, lid off

i think i have a 190 main

hrc needle and a 50 piolet, 2 1/2 turns out

what do you guys suggest for me

thanks

[440challenger]

Went up to a 50 pilot (next size up) with the fuel screw out 3 turns. Still is backfiring the same ,very bad on decell.

Should i go even bigger?? what are you guys running? thanks!

[MAD450r]

How many hours on the build. My 04 is doing that I tried everything myself. Jetting wise. I finally had my mechanic look at it and it was time for a vavlejob. Just my experience I hope thats not whats up with yours. I did have 4 seasons on my 04 stock piston hrc cam and full sparks system. Last year it started poping at the end of the season, this season I cant even ride it. I should have it back within a few weeks. I had to save up for other work while its apart. Im changing my crank and whatever other parts look worn with it all torn down. Im going with +1mm ex valves. Going with chads piston to run 15:1 compression. I should have a new beast when I get all the cash together to finish ordering the other parts.

[warriorxcr1]

my guess jets for that setup at our level would be ..

188 main
50 pilot
Screw 2 3/4 turns out
Stock Needle on the 4th clip down

What needle and clip are you running nick?

I had the same problem with my shorty... had to run a 52-55 (winter) pilot and the 4th clip down on the needle to stop it.

Bump the needle down to the 4th clip, keep the 50, and get back on to let us know what happens!

[GIXXER1KR]

Mad 450 you will be happy with that piston hope you have him do the rest!!!;)

[440challenger]

I took off the exhaust ,put on a new crush washer,and hi temp sealed the joint..didnt need it but i still did it, no difference...

What size pilot are you guys running on your 04/05's with exhaust and no lid? Im actually thinking of putting the lid back on and cutting half of it out and see if that richens it up ...

[warriorxcr1]

what needle and what clip man?

[440challenger]

dynojunk , set to stage 2 at sea level

[440challenger]

well.... i messed with it, and its still doing it. I dropped the clip to the 4th position,still backfires. Went to a 52 pilot still backfires.

Hot start cable moves freeely, no air leaks... I took a 450r lid and cut half of it out, and with the lid, 4th clip down, 52 pilot, 3 turns out on FS its getting noticeably better.

Im thinking of just getting a HRC jet kit and try that for giggles :grr:

[MAD450r]

Thats what im running and with my sparks pipe I have to go up on the main. I forget what the clip is at sorry its been that way for 4 years. but now im running without the lid cut fully then I put a velcrow cover over it to help keep stuff out but it now pops on decel so I think im going up another on the pilot :(

just letting you know for the cost of the hrc i'd probly still go up one more on the pilot if your 3 turns out and you say its beter.

you seeling it get better means your on the right track. Good luck I miss riding. wish I'd heal already from my surgery.

[warriorxcr1]

i thought you were running no lid the whole time?

[440challenger]

I was running no lid. I just yesterday put an HRC style lid on to help richen it up.

[warr72]

Up your pilot one possibly two more sizes. If that don't help check your valves.

[binegar]

Hey man i had a problem like that every time i was coasting it was backfireing like crazys it was my Hot Start cable it was stuck open

[liljhall09]

mine does the same thing i think its my valves , they prob need adjusted

[awj8074]

Mine would pop if i was downshifting to slow down quick or crawling down a hill. I had to go back to the stock pipe after breaking the pipe off the bike one night riding and no popping with the stock but thats understandable. I never worried about it though its almost 5 years old and never a issue.