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New full system pipe and now backfiring

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Hey guys need your help/expertise -

I have an 08 KLX 450, have done the jetting kit and AIS block off, and the bike was running like a dream. However, this year I put a full sustem Pro Circuit T4 Pipe on it and when I started it up, instantly (within 4 minutes) the header was glowing red, the coolant started to boil, started to shoot flames out the back and it would back fire when I "quick reved" (quick throttle bursts) the bike.

Running too lean right? Well, I rejetted again went from 165 main jet to 170 and the pipe did not glow anymore and no more coolant boil. However, when reving I still see flames and it still back fires!!:banana:

Any thoughts on next steps?

Do I need to raise the needle one position?

Fuel / Air screw positioning?

Thanks in advance.

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Hey guys need your help/expertise -

I have an 08 KLX 450, have done the jetting kit and AIS block off, and the bike was running like a dream. However, this year I put a full sustem Pro Circuit T4 Pipe on it and when I started it up, instantly (within 4 minutes) the header was glowing red, the coolant started to boil, started to shoot flames out the back and it would back fire when I "quick reved" (quick throttle bursts) the bike.

Running too lean right? Well, I rejetted again went from 165 main jet to 170 and the pipe did not glow anymore and no more coolant boil. However, when reving I still see flames and it still back fires!!:banana:

Any thoughts on next steps?

Do I need to raise the needle one position?

Fuel / Air screw positioning?

Thanks in advance.

I run the 170 main with a 45 pilot,stock header with a KX silencer fuel screw 1.5 to 1.75 out. I had a 48 pilot in it and it overheated and the header got red pretty fast. The fuel screw adjustment in conjunction with the pilot are crucial. With the 48 pilot I run the fuel screw all the way in and the bike would ideal real fast run the scew out past three turns and would still run good. I put the 45 pilot in ran the screw in until it wanted to die backed it out until it idled high and smoothed out. Turned the idle screw down and it now runs like a beast. Happy trails

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I am far from an expert, but from what I have read(from Eddie) and experienced first hand is what ever the bike does while on a stand or in neutral means nothing. Every bike will or can be made to backfire(shoot flames) in that situation. The only important reading is with the bike in gear, moving down the road.

Also header will glow red pretty quick, not a real big deal unless you continue to leave it running for 10 minutes idling, bikes are meant to move to get airflow.

How does it run in gear? Slight bog giving it throttle? Crisp acceleration giving it throttle?

I don't think your main jet is the problem , 165 or 170, pretty healthy jets and they only work at closer to full throttle.

When I put on my full system, I had a lean bog off ildle--bad--I changed the pilot to a 48, fuel screw at 1 1/2 turns out and the o-ring mod.....bike runs perfect....also a 165 main, but that was not the cause of the bog.

Hope this helps with a small piece of the puzzle. :banana:

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My .02 has nothing to do with jetting. Mine is dialed in now but when I first started playing with it mine shot flames too.

The problem was an exhaust leak! I forgot to change the $1.50 copper crush gasket where the pipe goes in the head. The stock gasket is married to the stock pipe. When you changed the stock pipe for the pro-circuit, did you pry the old copper gasket out and replace it? Mine was smashed into the head pretty good.

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42 is stock

Hate to disagree with you Romey...cuz like a Canadian...You're smart...but the 45 is stock...at least on my skoot it was 45.

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Hate to disagree with you Romey...cuz like a Canadian...You're smart...but the 45 is stock...at least on my skoot it was 45.

They are all different my 08 came with a 42 stock.

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They are all different my 08 came with a 42 stock.[/quote

Really?!? That seems odd to me...especially considering it is a 50 state model. I am in Canada but mine is an import from the US. HMMM...learn something new everyday.

I'm still gonna disagree with Rome though...just for the hell of it.:banana:

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My Alberta machine came with a 45.

After the pipe conversion it required a 42 as per JD jetting.

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They are all different my 08 came with a 42 stock.[/quote

Really?!? That seems odd to me...especially considering it is a 50 state model. I am in Canada but mine is an import from the US. HMMM...learn something new everyday.

I'm still gonna disagree with Rome though...just for the hell of it.:lol:

I thought you Canadians knew it all. LOL :banana:

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They are all different my 08 came with a 42 stock.[/quote

Really?!? That seems odd to me...especially considering it is a 50 state model. I am in Canada but mine is an import from the US. HMMM...learn something new everyday.

I'm still gonna disagree with Rome though...just for the hell of it.:lol:

Again DIRK......not feelin' the love! :banana: Seriously though mine has the 42. With a 34,000X micron microscope you can see the stamp :banana: I'm thinking maybe they change the pilot depending on regional location? Maybe elevation? Beats the heck outta me.....DIRK, what's the latest on the scoot jetting?

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So here is the update. I did change the head pipe gasket but that does not seem to be the problem as the back firing and popping is still going on when decelerating. Again this is when it is just on the stand, I have not taken it out for a ride yet, but I will and see if it changes anything.

Question on these new Pro Circuit / FMF slip fit pipes,,,,,It seems strange to me that the pipe is just metal to metal at the mid pipe connection. And when examining mine it appears there is a very tiny gap at that connection. Do you think this may be the cause?

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So here is the update. I did change the head pipe gasket but that does not seem to be the problem as the back firing and popping is still going on when decelerating. Again this is when it is just on the stand, I have not taken it out for a ride yet, but I will and see if it changes anything.

Question on these new Pro Circuit / FMF slip fit pipes,,,,,It seems strange to me that the pipe is just metal to metal at the mid pipe connection. And when examining mine it appears there is a very tiny gap at that connection. Do you think this may be the cause?

I filled mine with high temp silicone at the slip joint and no leaks yet. It seems to bake on if you use the red RTV. I was also a little leary of no clamp, no press fit....it would seem better to use a gasket, but......

Also, use a very small bead, as the slip fit is tight enough to take up the slack and spread it out quite a bit. I applied the bead around the end of the muffler, so as to allow it to drag the silicone down the entire interface between the two. IMO applying it at the end is important, and mine seems to work well.:banana:

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Dirt Bike mentioned in their KLX jetting article to check your hot start cables are properly attached and not pinched. This causes all kinds of lean type problems and is very common. Might be worth a try?

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