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:
Item
|
XL250
|
XL350
|
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: Ported and piped 412cc
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.
Powroll:
3.5 slide
6F8 needle
230-26- main jets
P5-159 needle jet
20 pilot
no air jet.
WB
166 cut to 5mm height (2-stroke style needle jet)
Some threads with usefull info over at www.oldrice.com: