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Talked to thumper racing about jetting and plug problems

By lewichris,
in WR400F/426F/450F

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lewichris

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Ok Guys i just talked to a guy at thumper racing to ask him about my plug problems. What he said was:

1. Our bikes only rev to 8500RPM and the YZ Revs to 11,000.

2. That the reason my plug is so black and sootyafter a few rides is because of the yz timing.

3. He also told me that the needle needed to go from the 3rd clip to the 2nd.

I think that is what he said to try first. how much truth is there to this. I have ever taken the carb off before. So i am a bit scared. With the main and piolet jets if i just un screw them will they come out. I want to make sure they are clean. Also is the needle easy to move. Guys i need help here. I am half tempted to go back to wr timing and get rid of this problem. So if you all can help me i would appreciate it.

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Dodger

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Hey lewichris;

"Don't fear the reaper!", er, i mean "don't fear the flatside!!", yeah, that's it.

The carb is very easy to remove, just undo your throttle cables, your TPS, losen your carb boots, (hint: I tuck the air boot back agains the frame to get it out of the way.), and pop the carb out. All the jets are easily accessable, and simply unscrew them to replace. For the needle, pop off the top of the carb with your alen keys, undo the slide screw, and you'll need a needle nose pliers to "gently" pull the needle up and out.

Slim answer, but hopefully that gets you on your way.

Dodger ?:D

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racemile

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Lewichris,

Check my sig, Thats the position I am using. My ride pulls great. The FCR is easy to work on. The jets unscrew, and, to use another suggestion, When you change the clip position you are putting it in the second position from the top of the needle. When you pull the needle the clip will come out with it. put the whole assembly in a clear plastic bag and close the bag. Use your needle nose to move the clip while BOTH are in the bag and the bag is closed. The last thing you want to do is try and find that little tiny clip so you can go ride. Access the jets from the bottom of the carb and access the needle from the top of the carb.

Sorry to be so detailed, I just remember how nervous I was when I first tore into my carb. I had never done it before either.

Race

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racemile

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Lewichris,

One other thing, make sure you unhook the TPS at the electrical connection. The manuel says bad things happen if you unscrew the TPS from the carb. Dont know if thats true or not. Just a suggestion.

Race

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SFO

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Originally posted by YAMAKAZE:

Dude,

The black plug is NOT because of the YZ timing...It's Fat Jetting, most likely in the Pilot Circuit.

I think the guy you spoke with at TR needs his Head Space and Timing Checked.....

Bonzai ?

Headspace and timing?

You take me back to the gulf with talk like that!

My favorite weapon, the browning 50.

The wr ignition has its rev limiter set at 10.5k.

The yz ignition is set at 11.5k.

I ran both ignitions on the dyno and found the rev limiter on each.

The power is long gone by the time you hit it though.

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SFO

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If the blue wire mod would have been known when I did this I would of tried it.

I only had the grey wire mod done.

The power curves were identical though with the exception of the different rev limiter settings.

I don't think I would want to have a 11.5k rev limiter though, maybe I am wrong.

These are only my experiences that I am sharing.

I would love the chance to be edified.

I do know the wr does not have a 8.5k rev limiter.

So I'll bite Mark, what is the blue wire all about again?

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Mark_Cantrell

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SFO,

I came off way too cocky. Sorry. The blue wire connects the neutral detect circuit. This we are sure of. After that, there is conjecture. One effect is that it seems to reduce the rev limiter. Another is it is reputed to make it easier to start, usually described as a weaker spark. More likely it changes the timing to idle better.

Since the only 'known' difference between the WR and YZ CDI is the presence/absence of the gray wire, I don't think the YZ rev limiter and WR w/grey wire cut rev limiter are any different, both at 13,500. I just went to a couple of dyno charts for the 250F (fmfracing was one) and they all ended up at 13,500.

Side note: I called the guy that makes the Vortex in Australia. All of standard programming for the Vortex is set to 13,500 because 'that is what the factory CDIs come programmed as.' We could call and ask him what the blue wire does. If I had a tach, I'd go out and try it right now. I'll try to borrow one tomorrow and try it both ways. Sorry, I have a WR so gray and blue neutral, gray and blue in gear, gray and no blue, no gray or blue, no gray and blue in gear, no gray and blue in neutral. Damn, maybe just a couple of runs.

Someone has some 'splainin to do. Some tuner is bound to be able to clear this up.

Good luck,

mwc

p.s., I do know my rev limiter sounds different when in gear and in neutral. It is a buzzing up and down, maybe .5s frequency in neutral and just cutting out in gear.

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Taffy

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....yes but you run a bike on the dyno in gear mark otherwise the rear wheel wouldn't turn.

someone get that F****** monkey out again, marks got some work for it!

Taffy

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SFO

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Originally posted by YAMAKAZE:

All of this is very interesting, but has absolutely zero bearing as to why the plug on his bike is black......

running down rabbit trails again....

Bonzai ?

Head space and timing MARINE!

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armourbl

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MARINE,,,Uuuuurrrrrrrrr, Ooooooraaaahhhhh. KILL! Sorry, had a flash back...

I never met another Marine that could breakdown and assemble the .50 cal faster than your's truly. My only braggin rights I guess, among many cool experiences, list is too long.....

ben

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Taffy

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chris

just take it one step at a time. make it your mission on this occasion to do the needle ok?

it'll give you more confidense and anyway we're always saying to do one thing at a time so this would be good.

the list of tools are 10mm socket for seat and tank and rad flaps are cross head screws. #4 allen key for the carb at the front and the cross head for the rear. you can just put the #3 allen key in the top of the carb bgy twisting it and pulling the carb around.

remove the top, use the #4 key down in the middle of the top of the slide and by holding the needle through the back of the carb whilst lowering the slide with your left hand on the right throttle grip-you will make the needle pop outthe top of the slide.

the clip bit is the easiest part.

have all the tools ready and i'm sure it'll go well.

Taffy

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