Honda CRF50 jetting guide, will work on chinas aswell

[motoXXX]

found this guys ,it will help you learn too jett your bike right well it sure helped my learn/understand how to rejett a bike

some of the stuff that it tells you i never even knew haha...

Here's a link which may be easier to read then on here...
XYZ – Domain Names for Generation XYZ®




HONDA CRF50, XR 50, Z50 1992-1999
Purchase these from your Honda Dealer.

Stock Main Jet Size #58
60 Main Jet #99101-187-0600
62 Main Jet #99101-187-0620
65 Main Jet #99101-187-0650
65 Main Jet #99101-187-0680
70 Main Jet #99101-187-0700

Jetting with stock displacement engine and bolt-on mods:
Stock jetting is appropriate for most applications. Increase Main
Jet size by 2 during break-in.
Jetting with 75cc and smaller engines: Increase Main Jet by 3
sizes. Move needle clip down one position. Stock pilot jet.
Jetting with 76cc and larger engines (larger carb recommended):
Increase Main jet by 4 or more. Move needle clip down one
position. Stock pilot jet.
JETTING BASICS
It is the responsibility of the owner to determine
proper jetting for their engine.
These jetting specifi cations are designed as a rule of thumb. They are
in no way absolute. Variations in air density, specifi c gravity of fuel, altitude
and other engine modifi cations play a large part in jetting. Newly
built engines need rich jetting during break-in. Do not jet for power
until an engine is broken-in.
Plug reading may not work. Revving the engine while it’s sitting in the
garage doesn’t work. Other than Dyno testing, the steps below is the
simplest way you can jet your engine.
1. Find a gentle slope that you can ride in 2nd or 3rd gear. Look for
something that will put a reasonable load on the engine. This will be
your “dyno”.
2. A basic outline of which jet is active at a particular throttle setting:
Pilot Jet = 0 to 1/4 throttle. Needle = 1/4 to 3/4 throttle. Main Jet = 3/4
to Full Throttle.
● Changing the Main Jet size won’t affect how your engine idles or
runs at 1/4 throttle.
● Engine RPM isn’t what determines which jet is active - throttle position
does.
3. Make the recommended jetting changes. Always start rich and
work leaner.
4. Start and warm up the engine, then ride your ‘dyno hill’. Any point
where you feel the engine stumble or hesitate indicates a tuning problem.
Note the throttle position and modify the corresponding jet (1/4 to
1/2 throttle = needle. 3/4 throttle or more = main jet).
5. Only change jetting by 1 step at a time, and 1 circuit at a time (don’t
change needle and main at the same time). Re-check after every
change.
6. Once the engine runs smoothly throughout, you’re jetted!
If you ever notice an abrupt loss of power, or
engine sounds change, shut it down.

 

[unit_mx]

A sticky I reckon , very help full. I wish I new this ages ago!

 

[Flarry]

Yer this is what i need, my bike needs to be jetted so bad.

 

[wogtaz ryder]

Same!! ^^^ only with my keihin carb runs like crappp? but with me el cheapo 19m? works a treat..

 

[50freak]

Jetting is next on my long list of mods haha.

 

[Cactus Jack]

Excellent info ... Note that they state final jetting to be the sole responsibility of the owner/rider !!!! That's pretty hard to get most people to understand ... the second factor is that once you have an engine tuned to run spot on when the throttle is rolled on and it revs cleanly throughout the rev range and peak revs out cleanly up top ... then it's tuned to perfection ... and altering any setting will be a backwards step ... That INCLUDES ... trying to tune out any bog or hestitation that occurs if the throttle is slammed to full suddenly from idle or low revs in neutral or in gear ... The symptom is caused by the clown on the bike not understanding that the fuel supply thru the jets dies in the ass as the vacuum drops instantaneusly when the slide is lifted too suddenly ... It has NOTHING to do with the jetting , float level or anything else ... IF an engine is hesitating or bogging after being tuned to run properly when the throttle is twisted at a sensible rate ... then the problem is that the carb is TOO BIG to suit the riders ability ... and the ONLY answer is to fit an accelerator pump carb ... or go back to a smaller more forgiving carb ...