OzVMX Forum

Marque Remarks => Honda => Topic started by: Davy123 on August 01, 2011, 04:13:26 am

Title: honda xl 250 mikuni jetting
Post by: Davy123 on August 01, 2011, 04:13:26 am
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
Title: Re: honda xl 250 mikuni jetting
Post by: LWC82PE on August 01, 2011, 08:56:05 am
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.
Title: Re: honda xl 250 mikuni jetting
Post by: Davy123 on August 01, 2011, 08:00:28 pm
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..
Title: Re: honda xl 250 mikuni jetting
Post by: LWC82PE on August 01, 2011, 08:23:25 pm

I have a few more questions but i will PM them
Title: Re: honda xl 250 mikuni jetting
Post by: matcho mick on August 01, 2011, 10:42:48 pm
6F4 needles slightly richer allover,might help?,what the slide #?, :P
Title: Re: honda xl 250 mikuni jetting
Post by: Davy123 on August 01, 2011, 11:22:49 pm
mick...slide is 2.5...but i stripped  carb and the air jet in the belmouth was blocked solid ;D so i took it out..no wonder it got worse as it got hot  ..better to run without so i've been told..
Title: Re: honda xl 250 mikuni jetting
Post by: bazza on August 02, 2011, 05:30:24 am
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
Title: Re: honda xl 250 mikuni jetting
Post by: Davy123 on August 04, 2011, 06:35:02 am
BAZZA.. did you cut about 5mm off the needle jet?
Title: Re: honda xl 250 mikuni jetting
Post by: matcho mick on August 04, 2011, 02:58:04 pm
 :o
Title: Re: honda xl 250 mikuni jetting
Post by: Swiss on August 05, 2011, 06:10:02 am
Davy,

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

Swiss
Title: Re: honda xl 250 mikuni jetting
Post by: Davy123 on August 06, 2011, 03:19:11 am
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  ;D
Title: Re: honda xl 250 mikuni jetting
Post by: bazza on August 06, 2011, 08:19:11 am
yes Davy about 4mm-seems weird but worked on my bike for 20yrs
Title: Re: honda xl 250 mikuni jetting
Post by: Davy123 on August 06, 2011, 06:09:43 pm
Bazza..seemingly Powroll did that in the 70's ...i'll see how bike runs next time before i try it ..
Title: Re: honda xl 250 mikuni jetting
Post by: bazza on August 07, 2011, 01:22:11 pm
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
Title: Re: honda xl 250 mikuni jetting
Post by: Swiss on August 08, 2011, 12:08:28 pm
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
Title: Re: honda xl 250 mikuni jetting
Post by: bazza on August 10, 2011, 12:12:35 pm
davey your jetting is close to jetting in old US article
Title: Re: honda xl 250 mikuni jetting
Post by: Davy123 on August 10, 2011, 08:19:52 pm
Bazza... hopefully should be ok now..however i've a new 36mm mikuni on loan from a mate off his bored 350 and it runs fine..so 'll try that if no joy with my own carb..sunday is next race,hope the weather clears up its to rain for 3 days straight ...lovely scottish summer  ;D