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09speeddemon

01 yz426

12 posts in this topic

Ok guys i messed with my air fuel mixture screw cause it was popping a lot on deceleration now once it gets hot it will not start. what do you guys recommend for the setting of this?? i live in central California and the bike has a fmf power-bomb header and a fmf quite core can. Also what jetting??

Thanx guys

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Ok guys i messed with my air fuel mixture screw cause it was popping a lot on deceleration now once it gets hot it will not start.

There is no standard single setting for the pilot screw, and the fun of owning an old FCR carb is that today's setting may not work tomorrow. But one thing I've warned against over and over is not to diddle with the pilot screw to get rid of exhaust backfire until after you A) get the bike running right (regardless of the popping), and :banana: be certain the exhaust is not the cause of the popping by leaking air (and frankly, old FMF pipes are pretty notorious for that).

Start by reading this thread again:

http://www.thumperfaq.com/jetting.htm#PJ

What jetting are you running now?

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I put a adjustable zip ty racing fuel screw in... im not sure on the jetting im going to pull it apart this week.. The bike was starting great before i changed the screw. i cant see anywhere the pipe is leaking....

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When you changed the screw, did you remove:

  1. the original screw?
  2. a spring?
  3. a brass washer?
  4. an O-ring?

When you installed the new one, did you:

  1. Put the spring on the screw?
  2. the washer on the screw?
  3. the O-ring on the screw?
  4. The screw assembled as above until it gently bottomed, then back out 1.75 turns?

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I've heard from a lot of sources even when you are jetted right and everythings in tune you'll get some popping on decel... just the nature of the beast, its not FI by any stretch of the imagination :banana:

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When you changed the screw, did you remove:

  1. the original screw?
  2. a spring?
  3. a brass washer?
  4. an O-ring?

When you installed the new one, did you:

  1. Put the spring on the screw?
  2. the washer on the screw?
  3. the O-ring on the screw?
  4. The screw assembled as above until it gently bottomed, then back out 1.75 turns?

Yes everything is correct on that end of it. The turns out i tried 1 turn 1 1/2 and 2 turns ill get it started and warm it up and try it at 1.75 turns out...

Thank you for the help guys

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I've heard from a lot of sources even when you are jetted right and everythings in tune you'll get some popping on decel... just the nature of the beast, its not FI by any stretch of the imagination :banana:

I know there will be some but this sounded like a machine gun going off! I thought about putting a newer carb on anyways but i have to save up the money first

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lol mine is the same way right now, trying to get it sorted i have a feeling ill be diving into the valves soon :banana:

You may want to check your TPS, hot start button/tubing, and double check no air leaks from the airbox or intake boot.

and if its lean, shouldnt you try going in from 1 1/2? say 1? factory suggested is 1.75 but thats with their needle and stock equipment... once you add/subtract things you may end up quite a bit different

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and if its lean, shouldnt you try going in from 1 1/2? say 1? factory suggested is 1.75 but thats with their needle and stock equipment...

No. The screw is not an air screw, as with most two strokes. It controls an emulsion of fuel and air, so backing it out makes it richer.

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It's the internal plumbing that makes the difference, not the position on the carb. Air screws can as easily be at the base as anywhere, the passages are just routed differently.

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