Stop The Backfiring!!!

[speedy400]

I can not figure it out, I've tried everything. I know for a fact the main jet and needle are at the right spot. And the fuel screw is at 4 1/2 right now and it dosnt seem to make a diffrence, I tried the pilot up to where it dosnt even idle and it still backfires, a little less though. I even checked the needle just for something to try and still nothing. Colby from C and D racing suggested to loosen up my valves, but this has been doing this 1/2 of my fall and so far all winter(I've adjusted them since). I made sure the headers were nice and tight, and I'm trying that orange exhaust sealing goo tomorrow for the headers where it meets the head just to make sure. Any ideas are greatly appreciated!thanks -darren

[flyin#5]

what size pilots did you try? if its backfireing mostly at idle and when you let off the throttle it sounds like the pilots... but it could be an exhaust leak too... so try the goo stuff and tell us what happens.

[speedy400]

I've tried up to 50 pilot size-darren

[flyin#5]

get a trailboss:cool:

http://www.imagestation.com/picture/sraid93/pe6198281ea1b6af2a65884176dc31d0c/fa474a2b.jpg

you'll never have to worry about it running right... becuase... well that will never happen:blah:

jp around.. i think you must need to do something besides your jetting. do a leak down test. :confused:

[2004TRX450R]

Make sure there are no vacume leaks around the carb or intake boot. When you start modding the crap out of them they will pop on decel sometimes and there isn't much you can do. If it is excessive then there might be a problem. Make sure everything is sealed up good and maybe go up a size on your pilot.

[foleyit]

I was running originally with the FMF Powerbomb head pipe. And experienced the same problem. Take a look at the pipes where they sit inside the head's exhaust ports. The welds on the rings had give way, where it seats in the ports. I had re-welded mine and and then dremeled out down the welds. And that solved my back-firing problem. I eventually had run into some of other problems with the FMF pwr-bomb pipe. So I switched.

[cals400ex]

i noticed that when i get a good plug reading at idle, my seems to pop a little bit on deceleration. i have just came to the conclusion that is will do this. i guess it has to do with my pipe, cam, piston, etc. i run a 42 pilot jet at about 1.75 turns out with my air box lid on. most people i talk too say that i am too lean on the pilot, but i am getting a good plug reading, the bike starts good, and my stainless steel headers don't glow at idle. this makes me pretty sure that i am not lean at idle. with the lid off, the jetting will lean out a bit. i would also check for leaks at any carb connections or the boot that connects the carb to the head. i have also been told that make sure the top plat on the carb has a good seal in it so it doens't leak. you run dynojets or keihins?? whats the needle location??

[speedy400]

my jetting-
-175 dynojet mainjet(from my dad's DS650 kit)
-dynojet needle at the 3rd from the top with the washer under it
-45pilot right now
-4 1/2 turns out on the fuel screw
the plug is reading near perfect, a bit rich if anything(medium-dark chocolate color)
I'll check out that header connection when I get home, I'm doing a lot of welding in tech 2 right now so adleast I know that now and I can fix it easly if needed.

I'm almost positive the carb side has no leaks, I checked it over yesterday. I'll look at the top of the carb tonight also like you said. thanks a lot. It hasnt really been that big of a problem I just pull in the clutch when I decel and it dosnt do much anything. It's just annoying.thanks again...any more ideas?-darren

[cals400ex]

are you getting a nice brown color at idle, 1/2 throttle, or full throttle. i can almost bet that you pretty rich at idle. i don't use dynojet needles, so i can't suggest a position on the needle for you. i bet your big on the main too, but that is just from what i read since i don't use dynojets. i don't believe your ever suppose to go out 4.5 turns on the fuel skrew. i have been told that 2.5 turns is as far as your suppose to go out, however, i will go out 3 sometimes. i would try the fuel skrew at 2.5 or 3 turns out. you running an airbox lid??

[polabareus]

I just got a brand new 250ex a month or so ago and it popped on deceleration. I tried adjusting the carb but just could not get it to go away. Well, since it was new and under warranty I brought it in to the dealer and they adjusted the valves and that solved it. So with my problem anyway it was a combination of getting the carb adjusted right and getting the valves adjusted right.

[speedy400]

cals400, I also heard that but C&D racing suggested to me to turn it out that far so i'm hoping they're right... I've never really tested it at idle, then mid range, then top end, just after riding for a week I checked it. -darren

I'm going to go play with it and try and figure it all out now.

[Silverfox@C&DRacing]

he said that if turning it out 4 4 1/2 fixed it then you needed a bigger pilot, if I remember right.

[cals400ex]

yeah, that sounds right dusty. i think mickey was the one that said your not suppose to run it out farther than 2.5 if i remember correctly. however, if i have to go more than 3 out, i will pop in a larger pilot that i have laying around.
here is what i would do for your jetting:
first get the bike up to normal temp by riding it for a while. after it is up to full temp, let the bike idle for one or two minutes. don't give it any gas. shut it off and check the plug. you will have a plug reading from your pilot jet/fuel skrew location. if it is black, your rich. if it is whitish, your lean. i personally like my plugs a really really light tan color. i find it to perform best when my plug turns from a gray to a light tan right on the bend of the plug. if you have questions about how to get it right on the bend, let me know and we will get that straightened out later.
after that put the plug back in and take it out and ride it at 1/2 throttle for a good distance. don't let it idle and don't go past 3/4 throttle. just ride it around 1/2 throttle or so through all of the gears and keep it in fifth for a while. quickly pull in the clutch and shut it off as your moving. check the plug. take note on the color. this 1/2 throttle test will indicate if your rich or lean on the needle.
put the plug back in and take it out and floor it all the way through the gears. keep it pinned in fifth for a little while. quickly pull in the clutch and shut it off as your maxed out. check the plug and take note on the color. this full throttle test will indicate if your too big or small on the main jet.

by doing this it really helps me tune in my bike. you could have in a 185 mainjet and still get a nice tan color from normal riding. this is because the large mainjet is not a factor untill your at 3/4 to full throttle. if your confused, let me know and i will try and elaborate. good luck

[sprtrx300ex]

I am almost 100% sure that your problem is your exhaust. I had the same problem on my 400. Check where your Slip-on meets the header. I bet there is a leak. You may think that its tighten up ll the way and there is no way that there is a leak, but there probably still is. You will need to go to an auto parts store and buy axhaust sealent. Make sure you get the sealent, NOT the tape. The tape does crap. Check for black soot around the slip-on and header, and where the header meets the engine. Make sure everything is tightened up. If you notice even a little black around these parts, seal it up. I find that if you can get a "gel" type sealent, it works better then the "paste" type, which has a tendency to crack off. YOu may need to disconnect the silenser and spead some around, then put it back on.

Also, you sound really rich on your pilot! I have a 42 pilot and 2 1/2 turns out and Im still a little rich. I'm not sure of the exact jetting since ou have a bore kit, but I still think thats way to rich.

I'd buy a new plug, and put in a 42 with 2 1/2 turns out. Do a plug test at idle. See how it looks.

Like someone else said, make sure all your carb boots etc. are on tight. BUt like I said, i bet its in your exhaust.


I went through the exact same thing you have. Its annoying. Mine popped and then i sealed it up, and it completly stopped.

Good Luck.

[speedy400]

Originally posted by sprtrx300ex
I am almost 100% sure that your problem is your exhaust. I had the same problem on my 400. Check where your Slip-on meets the header. I bet there is a leak. You may think that its tighten up ll the way and there is no way that there is a leak, but there probably still is. You will need to go to an auto parts store and buy axhaust sealent. Make sure you get the sealent, NOT the tape. The tape does crap. Check for black soot around the slip-on and header, and where the header meets the engine. Make sure everything is tightened up. If you notice even a little black around these parts, seal it up. I find that if you can get a "gel" type sealent, it works better then the "paste" type, which has a tendency to crack off. YOu may need to disconnect the silenser and spead some around, then put it back on.

Also, you sound really rich on your pilot! I have a 42 pilot and 2 1/2 turns out and Im still a little rich. I'm not sure of the exact jetting since ou have a bore kit, but I still think thats way to rich.

I'd buy a new plug, and put in a 42 with 2 1/2 turns out. Do a plug test at idle. See how it looks.

Like someone else said, make sure all your carb boots etc. are on tight. BUt like I said, i bet its in your exhaust.


I went through the exact same thing you have. Its annoying. Mine popped and then i sealed it up, and it completly stopped.

Good Luck.


GOOD JOB!!!!!!!!!!!!!!!!!!
your right, yesterday I did just what you said, got some sealant and closed up 2 little holes where the header meets the slip on. Gave it 24 hours to set, rode it today.- PERFECT!!!-thanks everyone for the help,oh and the pilot is right at 45 and now the fuel screw should be just right at 3 turns out.thanks again-darren

[sprtrx300ex]

Awesome. Glad it worked out for you!

[cals400ex]

i assume you guys know there is suppose to be an exhaust gasket where the header meets the silencer if you are running a slip on??? i can't see how it would be possible for it to leak at the header/silencer connection with the gasket in place unless no bolts were holding it on.

[speedy400]

Originally posted by cals400ex
i assume you guys know there is suppose to be an exhaust gasket where the header meets the silencer if you are running a slip on??? i can't see how it would be possible for it to leak at the header/silencer connection with the gasket in place unless no bolts were holding it on.
I did not know that. Oh well It's all good now.-darren

[cals400ex]

it is # 8 in this pic:

http://www.servicehonda.com/hard%20parts/atv/trx400ex/trx400ex%20frames%20page.htm


glad you got it fixed though.