Big Bore Q's

[fndaway66]

First off I would like to thank Eric for the Big Bore job he did on my kids RM85. I have'nt really started it yet but am trying to get an idea about jetting this thing when I do. The bike is has a:
*FMF Fatty pipe and silencer
*Stock jetting 125 main, 50 Pilot, 2 turns out on airscrew and needle clip in the middle.
*In California

Should my final outcome be richer or leaner? Help!!

 

[elf]

Do you need special jetting in california? :laugh:

I have a ktm 144 which I know is different from you bike but in my case I had to go leaner on all the jets. the main went from a 190 to a 162. Big difference! I think eric recomends starting with the stock jetting and see how it works and go leaner in small increments till its running good.

 

[fndaway66]

Thanks elf.

I figured I would have to go leaner.

 

[MikeS]

In our RM Big Bore we stayed stock on the main and 48 Pilot using race fuel.

 

[fndaway66]

Mike S.,

This is where I'm at jetting this thing.

Main 120.....Stk. 125
Pilot 52.......Stk. 50
Needle clip at Stk. #3
Air Screw Stk. 2 turns out

* 1/8 - 1/4.....good (pilot/air screw)
* 1/2.... good (clip position)
* At 3/4 to WFO I'm still getting hesitation, blurb, blurb, blurb!!! (Main)

Should I go any leaner on the Main (#118)? I'm kind of afraid of blowing this thing up! Also when shifting at high speeds it blurbs! Any help would be great!

 

[Bodge]

What color is the pulg after a full throttle run?

 

[fndaway66]

It's hard to run it at full throttle when it goes blurb, blurb, blurb!!!

Other than that the plug looks good. Can't see down inside where it counts, but overall it looks good.

 

[elf]

Mike S.,

Should I go any leaner on the Main (#118)? I'm kind of afraid of blowing this thing up! Also when shifting at high speeds it blurbs! Any help would be great!

Dont be afraid to try the 118, there is a very small difference from that and the 120. There is no way your going to wreck your engine with that small of a change. You may find you need to go even leaner than the 118.

 

[bclapham]

i would go to the 115 and try it- sometimes a bigger jump makes a bigger effect thats much easier to notice- if itd really bad you wont run it for more than a few secs anyway.

 

[fndaway66]

Thanks for all the reply's guys. This is where I'm at on the jetting.

Pilot - 52
Air screw - 2 out
Needle Clip - #3
Main - 115

Bike sounded great at 1/4, 1/2, 3/4 & WFO. I will look for a 118 main tomorrow to try. Is it OK to run it rich from 1/4 - 3/4 throttle then lean on the main? This seems the only way I got the blurb out at the top end.

Thanks again, Kurt

 

[elf]

If it was too rich with the 120 and runs good with the 115 I would just leave the 115 in. Sounds just about right. You can try the 118 if it makes you feel better, but with warmer weather just around the corner it will probably run better with the 115.