K, so here's the deal.  Every other day someone asks for the stock specs or what carb people have adapted to their XL. 

I had some time to kill so I searched the forum for pretty much everything and anything to do with the 250 and 350 carbs, and this is what i came up with.  I know there's more people out there with mikuni carbs on their XLs (myself included) and more advice on setting up the stock carb.  Lets here it! 


Honda XL250/350 Carb Conversions


The general consensus is that the stock carb, when set up properly, is very adequate for every day use. There are, however, some of us that like that teensy bit of extra zip.

Setting up the Stock Carb

The stock settings are as follows:




Model (Keihn) '72-75; 645B

'76, '78; 074A

'74-'75; 699A

'76; 075A

'77-'78; PD01A

Main Jet '72-75; 120

'76, '78; 125

'74-'75; 130

'76; 125

'77-'78; 115

Air Jet N.A. N.A.
Slow Jet 45 '74-'76; 48

'77-'78; 45

Initial Pilot Screw Setting 1 1/4 '74-'76; 1 1/4

'77-'78; 1

Needle Jet Clip Position 3rd Groove '74-'76; 3rd Groove

'77-'78; 4th Groove

Float Level 24mm (.945 in.) '74-'76; 18mm (.709 in.)

'77-'78; 14.5 mm (.571 in.)

Idle Speed 1,200 rpm 1200 rpm


For the most part, these settings are very accurate. The only thing that is commonly changed would be the Needle Jet Clip Position. The setting was fairly rich from the factory. To cure the rich setting the needle clip is RAISED one position, to the fourth slot (lowering the needle).

If you are having issues with carburation, be sure the tank, petcock, and carb are all clean and make sure that all of the jets/settings are correct. If you're still having problems or you want a little more oomph, read on!

Adapting a Mikuni Carb to the XL

The most common choice for an aftermarket carb on the XL is the Mikuni VM, usually a 36mm or 38mm for the 350 and a 32mm or 34mm for the 250, although some have used as big as 44mm carbs on modified engines. The following is a compilation of what different people have ended up using on their XL's and how they set them up.

Carb: 36mm Mikuni

Name: smokndav

Engine: cammed 412cc with Xlint exhaust

q6 needle jet

6fj40 needle

35 pilot

for some reason did not get the main (220-230 range?)


Carb: 38mm Mikuni

Name: nh141

Engine: Stock 350 with 1.75 in OD header

Slide 3.5

6F8 needle - clip in the middle position

P5 needle jet

30 pilot jet (35 might be a better choice)

180 main jet - this will probably change when I get my 85mm bored and Web cam engine done.


Carb: 36mm Mikuni

Name: aircanjk

Engine: Stock '75 350

3.0 slide

P5-159 needle jet

230 main

6F8 needle

40 pilot


Carb: 38mm Mikuni

Name: overbore

Engine: 412cc w/megacycle AB cam. Pipe is open w/reverse cone meg

Series 159 P-5 Needle Jet

6F 9 needle

30 pilot

280 main jet

3.0 slide.

clip on needle is in richest position.


"Jetting Kits" from back in the day (thanks Swiss!)

Carb: 36mm Mikuni

Engine: Stock 350

Bill Bell: 3.5 slide

6F8 needle

220 main jet

P5-159 needle jet

35 pilot jet

2.0 air jet.

Jerry Branch:

3.0 slide

6F5 needle

230 main jet

P4-? needle jet

30 pilot

no air jet.

White Bros.: 3.0 slide

6DH3 needle

220 main jet

P8-166* needle jet

35 pilot

no air jet.


3.5 slide

6F8 needle

230-26- main jets

P5-159 needle jet

20 pilot

no air jet.


166 cut to 5mm height (2-stroke style needle jet)




78 CT70 74 TL125 76 XL175 72 XL250 75 XL250 74 XL350 75 XL350 78 XL350 80 XL500
and a buncha other junk.....



















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