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Cleatus

JD Jetting / fuel screw issue

16 posts in this topic

Hello,

I recently installed the JD kit/O-ring and A MSR fuel screw on my:excuseme: 07 YZ450

When I tried to start it with the choke it would not start. It started right up with the hot-start and I had to hold the hot-start on until it warmed up or it would die. Rode it up and down the stret and it had great response.

Now the issue -

I set the fuel screw at 1.5 out as a starting point. Idled it up pretty high and started to turn the screw in looking for the stumble. It revved like crazy the farther i screwed it in. When I wack the throttle open to test for responde it dies when it is out past about 1 turn. It seems to have the best response at about .25 to .5 turns out. It has the stock pilot jet wich is smaller than the one in the JD kit.

Also- The screw has a very vague bottoming feel.

Should I go 1 smaller on the pilot?

Thanks

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did you compare your msr fuel screw to the stocker, ive read on here that somtimes there has been defective screws, thats somthing to look at. also you can call jd they will help you out. Im sure someone on here has to have a better answer than me.

bump

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Yes, they looked similar.

I have always understood that the idle should slow down as you turn the screw in, but just the opposite is happening. This is making me think that maybe I am on the rich side of things, but this is strange because the jet kit only comes with a richer jet than I already have.

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Hello,

I recently installed the JD kit/O-ring and A MSR fuel screw on my:excuseme: 07 YZ450

When I tried to start it with the choke it would not start. It started right up with the hot-start and I had to hold the hot-start on until it warmed up or it would die. Rode it up and down the stret and it had great response.

Now the issue -

I set the fuel screw at 1.5 out as a starting point. Idled it up pretty high and started to turn the screw in looking for the stumble. It revved like crazy the farther i screwed it in. When I wack the throttle open to test for responde it dies when it is out past about 1 turn. It seems to have the best response at about .25 to .5 turns out. It has the stock pilot jet wich is smaller than the one in the JD kit..

When the MSR fuel screws are new they need a little help of turning in and out a few times before it seats..

The MSR screw when new needs to turned in and in and out and in and out.... Untill it seats all the way.

The MSR screw is rough going in when its new, so you need to turn in and out and in and out and in and out.... Then it will seat

Also- The screw has a very vague bottoming feel.

Should I go 1 smaller on the pilot?

Thanks

The problem is the MSR fuel screw.... you need to take it back out and check to make sure the o-ring, washer and spring are in, some times the o-ring doesn't seat all the way so just turn the screw all the way in until you feel it seat and then back it out 1 1/2 to 2 turns out.

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you said your kit came with a new pilot jet mine didnt but its for a diff bike, what do you have in there right now, you might want to basicaly start over on the instructions and just double check everything when i put mine in by the instructions i didnt have to change anything. again if you dont get a good answer on here just give them a call.

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+1 skeeter i didnt even think about that i almost mixed those up on mine when puting it back in I had to look at the manual after scratching my head for ten mins.

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+1 skeeter i didnt even think about that i almost mixed those up on mine when puting it back in I had to look at the manual after scratching my head for ten mins.
It will do all kinds of crazy things (pilot screw not seated all the way or o-ring kinked in sideways)..

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I will check to make sure everything is in there right. I recall a spring and o-ring but no washer.

PJ is stock, 46 I think. Kit comes with 48.

Burned in the jetting forum suggested that the aftermarket fuel screws are not machined to the same specs as the stocker and oftien make them too rich. This sounds like what I have going on if it's not the o-ring.

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it will take 5 mins. to prove that right or wrong just put the stock fs back in and see if anything is diff.

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I will check to make sure everything is in there right. I recall a spring and o-ring but no washer.

PJ is stock, 46 I think. Kit comes with 48.

Burned in the jetting forum suggested that the aftermarket fuel screws are not machined to the same specs as the stocker and oftien make them too rich. This sounds like what I have going on if it's not the o-ring.

Exactly Ive done it before, take it back out and if now washer its on the bike some were. The o-ring may be stuck up inside which is ok, but take flash light and look up there to make sure.. Just turn the carb side ways

O-ring first in the carb

washer second

spring last

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just fyi it should be from the screw side it should be spring, washer then oring

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just fyi it should be from the screw side it should be spring, washer then oring

Perfect BRYAN..:thumbsup:

That will do the trick, the pilot screw is very sensitive.

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Will do.

Thanks for all the help. I'll keep you posted on what I find. It's too late to start it tonight but I will take the screw out and see what I find.

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Today I switched back and forth between the factory and MSR fuel screw several times to try and get a feel for what is happening.

They act basically the same. The bike idles higher from 0 - 1.5 turns and slows past 1.5 turns out. I can screw it all the way in without the idle ever slowing or getting rough. Is this right?

When I wack the throttle very fast on the stand it dies, but has very good snap and response whern riding without bogging.

Should I just leave it, or get a smaller PJ to try to get it to respond normally to fuel screw adjustments?

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When I wack the throttle very fast on the stand it dies, but has very good snap and response whern riding without bogging.

So, do you race it on the stand? Thought so. The bike uses different ignition timing in neutral than in gear, for one thing. If it responds well in gear underway, then it runs as it should, I would say.

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