Installed JD Jet kit... now my WR400 spits flames...

Popping on decel with white brothers e-series exhaust.

Prior owner installed 170 main jet. Haven't checked actual size on pilot jet. It's supposed to be 45. I'll verify tomorrow. I have on size above and below the stock pilot jet to play with.

how the dyno time go?

i ended up on my 444 project 47hp- 39ft lbs at the tire.

the bike had a pretty flat power band.

had a 168 in it to start i could tell it was running awfully lean all over the place.

jetted it to a 170 and it got a little better.

after about 8 pulls on the dyno and drilling my 170 out to a 184 the bike has perfect, flat air fuel ratio.

i need to spring for some "real" exhaust...the stock, bashed up header i have along with the 8" cut down muffler dont help the bike a bit.

i came across a nice ti- slip on a buddy had sitting on a shelf in his garage, im thinking after i froze the header and got rid of the dents and figure out the muffler not only should it make a little more power down low but will quiet it down considerably.(its REALLY loud).

i think that will do til my birthday(as i found a really nice full leo vince mx/sm system for my bike) as i planted the ness info where my girlfriend may pick up the idea. :thumbsup:

good luck on the dyno...its a fantastic tool to have available.

If it was me, I'd simply go a 1/4 turn richer on the fuel screw.

If that didn't do it, go to a 48 pilot, and re adjust fuel screw.

Like others have said, it is NOT the main doing that

Dyno day is tomorrow.

For now, I'll take it up a 1/4 turn and then a 1/2 turn to see if it eliminates the issue. I cleaned my air filter as well as it's been a few rides, maybe it's leaning out the mixture as well (less air = rich though... hmmm, this probably will make it worse, haha).

We'll see how it goes going forward.

Absolutely positive you have no exhaust leaks? Fold a towl over the muffler end and listen for a leak.

Next, do teh fuel screw set up:

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

I went out to 2.5 turns and it still had popping on decel. I'm pulling the pilot jet now to see what size is in there, and then go up a size if it's the stock 45. I'll try that at 1.5 turns and go from there. Hopefully I can get a proper idle out of this thing!

I just noticed you have added an FMF system. Here's a little story from about a month ago: I was helping a friend out with his 06 WR450. Brand new FMF Powerbomb and Q4 exhaust. His stock exhaust system was pretty battered up and he decided to spring for a full FMF system. Well, the frigging thing would pop like a Mofo on decel. Addressed all the likely scenarios - jetting, leaks, ACV circuit - no joy. I don't remember why, but I put the stock header back on with the Q4 pipe and the popping stopped. SONOFABIATCH! It turns out, the bend of the PB header was not quite optimum and when mated to the Q4 and torqued down, would lift the header ever so slightly off the gasket in the head. A new gasket wouldn't fix it, but two gaskets (the old one and new one together) did. Also, the two pieces (header and muffler) came together a little better.

So, just for shits and giggles, slap on your old header and see if it's still doing it.

Old header is in the trash.

I'll just post my dyno sheet from tomorrow and we'll discuss. If all it is is popping on decel, I can deal with it. It's those hills climbs that I gotta sweat!

Ya know, the more I think about it... the more I think you are probably right. The exhaust fat was quite snug. Doubling up on gaskets might help though...

I'll do some experimenting after the dyno day, if needed.

hope you didnt pull slide out to change needle,if you did sounds like throttle plate in upside down,hole goes towards the bottom,pull carb back from front rubber and look,bike will shoot flames and only run with choke

hope you didnt pull slide out to change needle,if you did sounds like throttle plate in upside down,hole goes towards the bottom,pull carb back from front rubber and look,bike will shoot flames and only run with choke

Yep, that is not the case. Runs without choke, only flaming on decel.

Okay, so I went ahead and doubled up on crash gaskets, and cranked the beast down. There is no way there is an air leak in this beast, maybe an ultra minor barely existant one inbetween the header and muffler, but after my white brothers setup I guarantee this is leaking far less, if not leaking NOTHING.

I've played with the fuel screw. I'm going to tool around more with it to see what's going on. It's been my experience thus far though that it isn't the problem here...

Where would I look next? Valves?

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