hey whats up everyone. Well i know this may sound kinda dumb but here we go. I have this engine was gonna use it for my truggy X2 but have been doing alot of 1/8th On Road lately and need a practice engine. Does anyone know what other on road heads fit on this engine? thx for your help in advance!!

I am in the process of changing the O rings in the carb and engine. I noted all the needle settings before disassemble, but on reassemble I noticed the mid range adjustment needle (the one your not supposed to move) has a hole through it. My noted installed setting is flush with the carb case.

Now for the Question. - I set the mid to flush but a half turn one way or the other and the hole lines up with the HSN as you look down the hole where the HSN installs. Does anyone know if the hole should line up or be offset?

It's hard to explain but if you look down the HSN opening should you see the hole in the mid range needle or not?

I hope someone can help.

yes..i sujest turn it all the way till you see it flush as possible then look down the hsn and see where the hole is then bring it back even with the hsn..you get wat im saying?

So, line the mid hole up with the HSN. Got it.

yep just turn it all the way flush(as far as the eye can see) then just look down the hole and fine tune it

huge Thanks

no prob

looks like at dead flush it's halfway between holes. So if you lean it to line up with the closest hole it seems to be to far in and the hole in the mid needle doens't line up well with the HSN hole. From flush if you richen until you get to the hole in the mid needle it lines up much better. So i say a good of thumb would be make sure it's dead flush then richen until the hole lines up.

This actually was the first i knew about the hole in the mid needle. I always thought the 2'oclock thing from the old stock vspecs applied and after getting the jx broken in i moved the settings to this and i've seemed to have a "run on" symtom since. I kept leaning the bottom and lowering the idle and it just seemed not to affect this at all. After checking mine, my needle was dead flush and no where near lining up with the holes. I can't help but wonder if that was the problem i was having. What do you guys think? Would the hole not lined up cause tuning issues? tia

The hole lining up does NOT matter. there is a reservoir bulb down there in the mid range needle. The stock setting for the mid needle is 3-1/4 turns form closed, (10'oclock).. When screwing the mid range or low speed needle all the way in to reset your needles always be sure to have the slide all the way open as the LSN will get stuck inside the MRN.


Really you should set your idle at 1-1/8 turns in from just closed and leave it. Then tune the top to clean out good, then tune the bottom to rip and idle. If it "runs on" on top your top is to lean, if it "runs on" on bottom, your bottom is lean. The MRN should be about 3-1/4 turns from closed, the HSN should be around 2-1/8 from closed, and the LSN should be around 3-1/2 - 4 turns from closed.. These settings are a good starting point and will have you close to a race tune. running a P4 plug. I use "running on" as a reference point to race tune. I slowly lean my needles till i get a slight "run on" then back it off an 1/8 of a turn.

not a day for me (sat.) weekend ,i decide to add outer fuel filter ofna large filter ,so i went to test it damn motor doesnt want to start it start for few secds. but it die all the time so i checked the p3 plug its busted so i try new plugs finally it starts but it die for few secs. ,so start again decide to give some throthle & finally touch the (dirt)ground after 10 ft.it die again so i tried to lean the hsn but no success i rich the lsn it start well so i did the 1st lap ,so on the straight way the idle sounds high ,this is my 1st time to experience this ,i just did the fuel filter on & the motor is out of tune any idea??is this really affect the motor i remember the fuel line from the tank to the engine is about 14 inchs. then i just add a large fuel filter & the motor is acting up

I checked the mid needle and at just about 1/16 richer then 3 1/4 the hole lines up perfect so i would say that was the goal with 3 1/4. On the idle screw when you say turn it in from closed do you mean looking down the neck and putting it closed and going in 1 1/8 from closed? thx for the help.

yep, take out the velocity stack to be accurate.

what is the factory setting for this jx21 ?,i missplace the box i m still in trouble tuning ,i just installed the outer filter & its acting up...........i checked the clutch system & just found out the 2 clutch bearings is shot hopefully this is the cause .

Ran my first 20min main with one pit yesterday!

Could have gone 11min easy with what was left in the tank.

MBX6
6mm restrictor
Dynamite 086 pipe/header
TKO ceramics
EBmods button
P3 plug
WERKS 30%

GREAT engine!

Getting ready to break-in a similar setup.
JX-21B01
EB Mods head button
O.S. Ceramic rear bearing
EB Mods 2041 pipeset
JX21 7mm carb restrictor
P3 glowplug, but may switch to P4 after break-in.
Will break-in on 5% nitro, then switch to 30% afterwards.