honda xl 250 mikuni jetting

[Davy123]

first race on the xl today ...ok on the straights ..shut off into corner,open throttle to come out corner farts and bangs and misses..had to slip the clutch to and rev the guts out of it get it past the farty bangy point...i run a 38mm mikuni with...
 
6F8 needle

250 main jet

P6-159 needle jet

30 pilot jet

the inlet port is 38mm ,bigger valves, big cam, bored to 298cc
what jetting  do you guys use on yer honda xl sideports any help/advice would be good ..cheers

[LWC82PE]

What valves and cam are you using? I am looking for a 305 kit and by the sounds of it, any capacity around 300 you need bigger valves and a different cam so i need ideas on what to get. I was going to use a bigger Mikuini too but not sure what size.

[Davy123]

i'm using stainless valves, 30mm exhaust and 35mm inlet with a needle roller cam and roller rockers...

years ago i raced a C&J XL 298, standard valves,megacycle cam,mild porting,bigger header and supertrap...worked well with a 34mm mikuni .

i've a good little used 79mm piston kit if your interested..

Davy..

[LWC82PE]

I have a few more questions but i will PM them

[matcho mick]

6F4 needles slightly richer allover,might help?,what the slide #?,

[Davy123]

mick...slide is 2.5...but i stripped  carb and the air jet in the belmouth was blocked solid so i took it out..no wonder it got worse as it got hot  ..better to run without so i've been told..

[bazza]

will try and find my jeting on similar 305cc,use 36mm Mikuni.
I cut away top half of the shield on needle jet and smooth as for last 20 yrs,it got rid of the slight hesitancy when fanging on throttle,some notable tuners query that but worked on that motor

[Davy123]

BAZZA.. did you cut about 5mm off the needle jet?

[matcho mick]

 

[Swiss]

Davy,

How much did the air jet help out when you cleaned it out?  Have you got it running better now?

Swiss

[Davy123]

Hey swiss...seems to run a lot better ,but not tried it on the track yet..also the cam chain tensioner bolt had stripped the crankcase !!! so cam timing off,advance off,points off ..surprising it ran at all , all fixed now ready for week on sunday to try again,maybe get a better result than 8th 

[bazza]

yes Davy about 4mm-seems weird but worked on my bike for 20yrs

[Davy123]

Bazza..seemingly Powroll did that in the 70's ...i'll see how bike runs next time before i try it ..

[bazza]

could only find some old notes (after all i did last jet in 1998) 36mm Mikuni
started with 30 Pilot went to #40
started 310 main went to 330
Not sure what needle but ran at the bottm,so no help there.
Baz

[Swiss]

The Mikuni 2-smoke carbs had the shield at the top of the needle jet.  Most of the 4-strokers either specified needle jets without the shield or cut them down. 

Swiss