I need some carb. advice.



9 replies to this topic
  • Elevator_Eddie

Posted May 10, 2001 - 07:11 PM

#1

My bike runs good except when I snap the throttle open real quick the bike will stall.

I was told that this is a characteristic trait of all 4-strokes.
Is this true?

Does anyone have any sugestions?
Thanks

99 WR400, airbox lid removed, throttle stop trimmed, WB Pro Meg & tapered head pipe w/9 disks, YZ timing, DVP needle #4 clip, 178 main jet, 48 pilot jet, #200 main air jet, Sudco pilot air jet screw 1 1/2 turns out, pilot screw 1/2 to 2 1/2 turns out; no improvement.

  • MN_Kevin

Posted May 11, 2001 - 12:29 AM

#2

Accelerator pump has too mch stroke. HUGE, HUGE, HUGE, HUGE amount of posts on this already.

Look at my post, Carb Mods from 05/07/2001.

------------------
'99 WZ with ALL YZ mods, de-octopused, DSP Doug Henry airbox w/ velocity stack, FMF PowerBomb header, Stroker SX-1 silencer, SS front brake line, forked over by Pro-Action (and then fixed by me), OEM YZ tank, IMS YZ seat, carb mods by Jim Dean, Andy in OZ, & Sir "Taffy" from Jolly Old England, AMA, NESC.

  • Elevator_Eddie

Posted May 14, 2001 - 08:17 PM

#3

Thanks Kevin,

I've read your post & others, and tried delaying the accelerator pump by bending the forked tab that the push rod linkage rests against. I've tried delaying it from 1/8 to 1/2 throttle opening, then disconecting it completly, with no positive results.

Do you know what the throttle position should be at when the accel. pump starts to squirt?

The size of the main air jet port looks close to 2.3 mm, so I tested with the main air jet removed, but still no improvement.

I've also tried moving the jet needle clip position up & down, and noticed the difference in acceleration, but no difference when the throttle is snaped open quickly.

Maybe I should try a smaller size main jet, but from reading the posts here, the consensus is the 170 mj is the right jet for this combination.

I sure would like to get this bike running good so I can smile again.

Thanks for your help.

  • James_Dean

Posted May 14, 2001 - 08:37 PM

#4

Be sure to keep a fast idle and probably work with the clip in the #5 position.

The pump should start to squirt just after the slide clears the way. The measured gap is supposed to be .6mm. About 1/8-1/4 throttle.

The pilot screw is normally at 1 1/8 - 1 1/2 when the air screw is at 1 1/2.

The main jet could be increased to #175 considering you are using the DVP needle. The #170 is more popular for the EKN or EKP needles. The main air jet will not solve your problem.

-------------

There is still a limit to how hard you can snap it open at a low idle. The EKN (or EMN) needle will give a harder acceleration if that is what you're after.

James

  • Tree_Crippler

Posted May 15, 2001 - 06:36 AM

#5

I'm real close with my jetting.
48PJ
178MJ
DVP#5
100PAJ
Fuel screw 1 1/4
I need to mess a little with the fuel screw but it is getting there. I had it perfect in the cold weather but had to work on it in the 80 degree area.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • MN_Kevin

Posted May 15, 2001 - 07:04 AM

#6

Right or wrong, I was trimming the tip of the accel pump rod that acts on the diaphragm to reduce the stroke of the pump.

  • James_Dean

Posted May 15, 2001 - 10:52 AM

#7

Kevin,

Trimming the pump rod is not a good solution. This will delay the start of the stroke when you actually want it to pump early enough to help. There is a limit to how early and how short also. The short stroke needs to refill when the throttle is not completely closed. The ideal solution would be to alter the cam rather than install a stop screw or P-38 Lightning pump cover.

As an alternative, you may want to carefully drill and tap a bolt centered below the diaphram as a plug to stop the pump stroke at about 1-1.5mm. Use washers to set the bolt protrusion inside the cover. This was my first attempt, and it still works very well.

James

  • Elevator_Eddie

Posted May 31, 2001 - 06:59 PM

#8

Well, I tried the clip in the 5th position and the acceleration didn't seem as strong, and there was severe popping on deceleration.

When I rev it then let it drop back to idle, the revs stay high for about second or two then it drops back to idle.
Is this an indication of a lead mixture?
I've tried turning the fuel screw out, but could not get it to drop right to idle.

Oh! by the way, I made a mistake on my previous post. I have the 178 main jet.

Are some needles easier to tune than others?
I'm thinking about trying the EKN needle for harder acceleration.
Or maybe I should go back to the WR timing.

I like to play on the motocross tracks, but I'm not out to be the fastest guy on the track.
I'm just trying to adjust my bike to come out of the corners quick enough to make the doubles.

Any advice is welcome.
Thanks Eddie

  • Elevator_Eddie

Posted June 04, 2001 - 06:10 AM

#9

Well, I tried the clip in the 5th position and the acceleration didn't seem as strong, and there was severe popping on deceleration.
When I rev it then let it drop back to idle, the revs stay high for about second or two then it drops back to idle.
Is this an indication of a lead mixture?
I've tried turning the fuel screw out, but could not get it to drop right to idle.

Oh! by the way, I made a mistake on my previous post. I have the 178 main jet.

Are some needles easier to tune than others?
I'm thinking about trying the EKN needle for harder acceleration.
Or maybe I should go back to the WR timing.

I like to play on the motocross tracks, but I'm not out to be the fastest guy on the track.
I'm just trying to adjust my bike to come out of the corners quick enough to make the doubles.

Any advice is welcome.
Thanks Eddie

  • James_Dean

Posted June 04, 2001 - 12:04 PM

#10

The fast and unstable idle condition sounds like an air leak or low float level. Possibly a clogged carb passage.

You didn't remove the PILOT AIR jet instead of the MAIN air jet?

The pilot air jet should be a #75 or #100.

You have a carb setup that is commonly used (#48 pilot, DVP#4 or #5). Check anything that might be suspect.

James

[This message has been edited by James Dean (edited 06-04-2001).]




 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.