Jetting Test


Ya know Taffy, I almost think you should write a jetting test we could all take and then we could all see if we have any CLUE as to how to do this for ourselves.

I know I am lost, but, I keep reading.


Then you could sell this whole thing to yamaha to include in their manuels, I could take the computer terminal out of my garage and start regrowing all the hair I have pulled out.

Who knows, If I ever get the logic then maybe I could apply it to the other bikes in the collection!!

Oh happy day!!!

did you read that thread on what everybody does for a living? :D

i've got the "thickest" job on the thread!

now there has to be a moral in there somewhere :)


Taffy, I have a DRZ400 E and have Tried to gain the results that you have had with your Yammie, with some success. I installed a 38 pilot, paj screw 1/4 turn out, 160 maj, ps 1 1/4 turn out, EFM needle #2 clip but had to go to a 170 main jet to get rid of stumble when snaping throtle open from 1/2 to full open like in the middle of a hill when I have to back off for a sec. I would like to know your fealings on this. You can email me at if you would reather. Ervin


drop the needle to clip 1. if that improves it, which it should, you will need to buy another needle as you will have no more clips left.

if you ride above 4,000ft get the EMN, if not the EMM. EFM c1 is = to EHMc2 = EKMc3 = EMMc4.

but i ran EMM c3 at sea level. so i suggest before you buy the new needle you try this.

first fit a 160MAJ for more fuel at max rpm. then lower the MJ to 160 on an open pipe and 152 on anything quiet. the EFM will be even better then. if you still can't get away with EFMc1 then you need EMM.

as for the pilot circuit, well you know by now what we recommend there!


Taffy, I have the 160 MAJ in and I'm very happy with the throtle response from 0 to 1/2 but was curios as why I had to increase main jet size to get rid of stumble in the 1/2 to full range.

170mj 160maj efm#2 38pj 55pjscrew 1/4 turn ps 1.5

flooding a bike has the habit of making people think they're better off. the acceleration is blunted by jetting up.

you'll only learn when it's flooded and you're on your third plug and the kickstart is worn out and your a sweating, heaving, dripping pool on the floor!!!


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