08 YZ450F with DRD full system shooting fireballs

[mdkcrf250r]

I just installed a DRD full system on my 08 YZ450F and even with the spark arrestor screen in I'm shooting some good size fireballs out the pipe. I believe the jetting is stock and it ran good with the stock exhaust on it...I'd imagine after ditching the restrictive stock muffler that I'd be running lean now but the fireballs are convincing me otherwise. I havent changed the jetting because i dont know which way to go yet...DRD system is brand new btw no cracks in the header, and a brand new exhaust gasket installed when pipe was mounted...Any ideas?

[mdkcrf250r]

Anyone?

[William1]

Your fireballs are decel back fires, correct? If it is pops and not explosions, it is normal with a more open pipe however:

Make sure you have no exhaust leaks.

You can try a small slow air jet or a needle the has a one or two size richer on the straight diameter.

Make sure the fuel screw is set right. Opening it to reduce this is like peeing in the ocean. There will be some effect, but it is minimal. The slow air jet and needle are like a BP leak.

[picapacapopo]

Opening it to reduce this is like peeing in the ocean. There will be some effect, but it is minimal. The slow air jet and needle are like a BP leak.

AHAHA! That made me LOL pretty good!! ????

[mdkcrf250r]

Your fireballs are decel back fires, correct? If it is pops and not explosions, it is normal with a more open pipe however:

Make sure you have no exhaust leaks.

You can try a small slow air jet or a needle the has a one or two size richer on the straight diameter.

Make sure the fuel screw is set right. Opening it to reduce this is like peeing in the ocean. There will be some effect, but it is minimal. The slow air jet and needle are like a BP leak.

Yeah they are decel pops that shoot flames but its also doing it on the stand revving it up decently high and chopping the throttle just like most of the flame pop videos on youtube. So you're saying the needle (the straight part) is too lean? Someone told me the needle was too rich and when the throttle is chopped it creates a lean condition that ignites the unburnt fuel. Does that sound right? and how far should I go with the air jet? One size smaller?

Thanks for the response.

[William1]

What the bike does on the stand means nothing after all, you did noit but it t just sit there on the stand, right?

How is the bike when actually ridden?

Decel pops are caused by a too lean mixture that will not burn in the cylinder and that accumulates in the exhaust, When enough accumulates, it burns.

You can jet your bike so that when ridden, it runs great or you can jet it so when it is on the stand, it does not pop.

[mdkcrf250r]

No I rode it too and it definitely pops on decel more than usual but I couldnt tell if it was fireballing but I assume it was...I'm pretty sure I have stock jetting in it now which is 160MJ, 45PJ, NFLR needle, clip in position #3, 55 Leak Jet, and fuel screw 2-1/2 turns out. What needle would be richer? The micro fische only lists them as "needle ap" with no i.d. as to which needle is which. What is the slow air jet? Is that the leak jet? Should I go up one on the main and pilot too? Sorry for all the questions and thanks for the help.

[William1]

'....more than usual....' ok, more of the story. So this is a new issue. What did you change? Bad crash? Something had ot of happened. Let's not jet away some other problem.

[bob450]

try turning your fuel screw out, but i don't like going out more then 3.5 turns out. if you need to go out more then 3.5 go up 1 on your pilot jet. You also might want to contact drd and see what jetting they recommend running with that set up and your location.

[mdkcrf250r]

'....more than usual....' ok, more of the story. So this is a new issue. What did you change? Bad crash? Something had ot of happened. Let's not jet away some other problem.

No I mean more than it did stock. I literally did nothing other than install the drd full system. No crash or anything. Nothings bent, new exhaust gasket installed with new pipe. Bike ran great with stock exhaust, I installed the full drd system and it pops more than it did with stock exhaust, and pops fireballs which is new to me.

[William1]

That is normal. A stock muffler muffles much of those pops and backfires.

You have a race pipe. Whe n being raced, the bike is eaither flat out or the brakes slammed on. When just riding about like 99.9% of the world does, you will get all the popping and backfiring.

You can jet away the pops at the expense of performance and running quality. Your choice.