Mik 42 jetting? w/dyno afr

[fxstbob]

This is a baseline run which looks to be lean from 3800-5200. My question is what to do to correct this, raise needle or bigger main jet.



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[axtell]

when you run full throttle the needle is "out of play".......you need a bigger main jet.  Ron

[Valley]

larger main, tune your main first, then fine tune your mid/needle.

[fxstbob]

Thanks for the replies. That's kinda what I thought, but the afr going richer above 5200 rpm had me confused.

[FLTRI]

Depending on what the "other" cylinder's AFR is, you may be right where you want to be.
For example I always tune off the rear cylinder to begine with on carbed bikes. I do this due to it usually being the leaner of the 2 cylinders....depending on the exhaust system this varies.

Then I check it against the front and usually find it richer than the rear.

Rarely do I find the front and rear the same AFR.

Some tuners simply probe the front pipe, tune to 13.5, or whatever and call it done. If they were to check the rear cylinder, 80% of the time the rear will read considerable leaner. ie: 14.5-up especially in the mid rpm range.

I tune the rear to about 14.0 in the mid rpms which will produce 12.0-13.0 in the front.

That said, if the graph is from the front cylinder, the rear prolly will be way leaner, however if the graph is from the rear the front very well could be 12.0-13.0 in the same rpm range.

This is why carbs are such a compromise compared to EFI, and why mfgs have had to go to EFI to meet mandates.

[Valley]

Depending on what the "other" cylinder's AFR is, you may be right where you want to be.
For example I always tune off the rear cylinder to begine with on carbed bikes. I do this due to it usually being the leaner of the 2 cylinders....depending on the exhaust system this varies.

Then I check it against the front and usually find it richer than the rear.

Rarely do I find the front and rear the same AFR.

Some tuners simply probe the front pipe, tune to 13.5, or whatever and call it done. If they were to check the rear cylinder, 80% of the time the rear will read considerable leaner. ie: 14.5-up especially in the mid rpm range.

I tune the rear to about 14.0 in the mid rpms which will produce 12.0-13.0 in the front.

That said, if the graph is from the front cylinder, the rear prolly will be way leaner, however if the graph is from the rear the front very well could be 12.0-13.0 in the same rpm range.

This is why carbs are such a compromise compared to EFI, and why mfgs have had to go to EFI to meet mandates.

Well put fltri,and sooo true!   

[fxstbob]

That would explain why my rear muffler (cycle shack slip-ons) is taking on a yellowish hue.
I don't know which cylinder the readings were taken from, but I believe it is a little lean.
At 80-85 mph, 4th gear, wot, then roll off about 1/8 turn, it seems to run smoother and accelerate a wee bit stronger.