[fatcaaat]

So I'm trying to dial my TJR motor in and it exhibits some interesting symptoms. I can start it up really easy, even in the coldest weather. It will idle without choke after 10 seconds...and it was 45 degrees out.



After about two minutes, the bike revs cleanly. Go take it for a ride and once it starts warming up, it stops running well..particularly in the 1/4 throttle range. Runs fine WOT.



it idles perfectly smooth. I'm guessing the pilot is too big? Once the motor warms up, the 1/4 turn low speed becomes too rich and causes the stuttering and such.



Offbase or what? Any input is appreciated.

 

[mexicanyella]

Sounds to me like too rich on the pilot circuit, as you say. It is happy on cold starts off the choke because the rich mixture is what it wants until the motor warms up, then it runs like crap at lower speeds.



The "up to 1/4 throttle" thing...I guess try a few leaner pilots and see how that clears up, but that seems like a pretty big amount of range overlap for the pilot circuit...although if it's REALLY rich...



I had to do some slide cutaway surgery once to fix an idle-to-midrange transition, on a two-stroke, but that would be getting ahead of yourself until you try some different pilot jets. Also, I never hear anyone talking about trying different slides or cutaway profiles, so I don't know if I was ahead of the curve or behind it on that one. It did work, though.

 

[boonacka]

How does it act when you cut it off after a good warm up and try to start it up again?



Wouldnt 1/4 throttle be in the Needle range?

 

[mexicanyella]

Yeah, that's what I was getting at; 1/4 throttle should be about where it's getting out of the slide cutaway and into the needle, for mixture control.



The 'caaat has probably jetted a few more carbs than me, but I'm going to type this anyway because it makes me feel knowledgeable, helpful and important:



pilot screw, pilot jet opening=idle to about 1/8 throttle



slide cutaway=1/8 throttle to about 1/4 throttle



needle clip setting, needle taper=1/4 to 3/4 throttle



main jet opening=3/4 throttle to wide open





Have you tried leaning out the metering needle by one clip slot to see what happens?



EDIT: I just realized, from reading another thread, that we're talking about one of those Yoshimura carbs here. I don't know that anything I've said here has any relevance now; my bike carb experience is with basic round-slide carbs only.



Does red boldface italics make that stand out enough to be noticed, do you think?