Will a new CDI fix the WR stutter

I too have the stuttering just as WR450SM did, only when riding slow under minimal to no load. However, I have continued to play with my jetting and it seems to of been minimized to the point where it is barely discernible. I know this makes no sense when looking at the data. My goal with jetting changes were only AP related, which is all the more confusing to me, as we know the AP has (darn well ought to) no effect at steady throttle. So here is my misguided and hare brained conjecture. If... at small throttle openings, most of the air velocity moving through the carb are at the bottom, is it possible... that some fuel is being sucked out of the AP nozzle, causing an occasional overly rich condition? I know the YZ's do not exhibit this condition but, I found the stuttering to become less of an issue the larger a leak jet I ran. Currently I am using a Merge adjustable one on the bike. As I said, these are all thoughts from a deranged and disturbed mind.

I too have the stuttering just as WR450SM did, only when riding slow under minimal to no load. However, I have continued to play with my jetting and it seems to of been minimized to the point where it is barely discernible. I know this makes no sense when looking at the data. My goal with jetting changes were only AP related, which is all the more confusing to me, as we know the AP has (darn well ought to) no effect at steady throttle. So here is my misguided and hare brained conjecture. If... at small throttle openings, most of the air velocity moving through the carb are at the bottom, is it possible... that some fuel is being sucked out of the AP nozzle, causing an occasional overly rich condition? I know the YZ's do not exhibit this condition but, I found the stuttering to become less of an issue the larger a leak jet I ran. Currently I am using a Merge adjustable one on the bike. As I said, these are all thoughts from a deranged and disturbed mind.

I wonder what you'd see with a vacuum gauge.

I wonder what you'd see with a vacuum gauge.

On a thumper you'd see wild gauge needle swings, probably cause the gauge to fail rapidly.

One way to potentially test my probably poor theory/guess would be to try it with a plugged leak jet, maybe a 40, then a 70 then a 90. If... with a larger leak jet, the problem lessens, my guess could have something to do with it. But my knowledge of the FCR combined with those that know much more than I do feel it is not carburetion. Just today's observations were surprising.

I too have the stuttering just as WR450SM did, only when riding slow under minimal to no load. However, I have continued to play with my jetting and it seems to of been minimized to the point where it is barely discernible. I know this makes no sense when looking at the data. My goal with jetting changes were only AP related, which is all the more confusing to me, as we know the AP has (darn well ought to) no effect at steady throttle. So here is my misguided and hare brained conjecture. If... .

The same jetting with both closed and open leak jets has not been an issue on Honda's and KTM's that are ridden as dual sports on roads.

This is a Yamaha WR issue most of the time. The jetting needs to be correct on any of the bikes, but clearly the replacement ignition solved the problem when WR450SM's jetting was near perfect and was misfiring.

----He has an air/fuel meter strapped to his handlebars to confirm that this was not a fuel richness problem from the accelerator pump circuit or any other source.

James

I too have the stuttering just as WR450SM did, only when riding slow under minimal to no load. However, I have continued to play with my jetting and it seems to of been minimized to the point where it is barely discernible. I know this makes no sense when looking at the data. My goal with jetting changes were only AP related, which is all the more confusing to me, as we know the AP has (darn well ought to) no effect at steady throttle. So here is my misguided and hare brained conjecture. If... at small throttle openings, most of the air velocity moving through the carb are at the bottom, is it possible... that some fuel is being sucked out of the AP nozzle, causing an occasional overly rich condition? I know the YZ's do not exhibit this condition but, I found the stuttering to become less of an issue the larger a leak jet I ran. Currently I am using a Merge adjustable one on the bike. As I said, these are all thoughts from a deranged and disturbed mind.

I remember having this discussion before!

The interesting thing that the guy from Zip Ty said was that my problem is not a needle problem at all. He was certain that it was an accelerator pump issue.

How do I fix this problem with AP adjustments?

I already have a 45 leak jet and the AP arm o-ringed, but I have not changed the pump timing screw setting or taken the airbox out to watch the spray pattern (if it hits the slide or not).

The guy at ZipTy was wrong, no nice way to put it. You are at (or nearly at) steady throttle. The AP has no effect on small or gentle throttle changes.

If you change the emulsion tube to any design other than what you have now, your needle may also have to be changed. did you try a new stock on tube for your carb?

I should have asked the Zip Ty tech guy for his theory on why the AP would effect the steady throttle condition. My mind went to some sort of siphonig effect where fuel was pulled through the AP system, but I think it was just false hope:confused:

I still haven't really dialed in my AP system, in fact I have a RD adjustable leak jet cover that I have not even put on yet....maybe one day, for now I am enjoying riding the bike...not just working on it.

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