Jump to content
Sign in to follow this  

XR4 jetting detail - fine tune pilot and screw

Recommended Posts

I finished grinding welds, drilling 3 holes in SA. no snorkel, with stock carb (52, 142, stock clip position, front mixture screw two turns out) New plug. I started bike. It was hard to start and gave a popping backfire at idle and wouldn't idle well. Turning the mixture screw out didn't help much. I put in a 55 pilot jet.

Started better, but needed choke for a long time. Didn't idle well. After it was warm, the back fire was less. As I turned the idle adjustment in and the mixture screw out a little at a time the RPM got better with every turn out of the mixture screw. I kept dropping the RPM with the idle thumb screw and turning the mixture screw out as long as the revs increased. I repeated this fine tuning until I maxed out the mixture screw (it fell out).

Do I need to go up one on the pilot? Will the main have any influence on the idle? Is this the right way to get the mixture screw and pilot fine tuned? Any advice is welcome.

I'm at 3000 feet, 65 degrees indoors where I'm working on it. We ride at 4000 and up.

Share this post

Link to post
Share on other sites

I'm sure others will chime in, but I'll tell you what I learned from hours of reading up on this exact subject... from what you are saying it sounds like you are still lean at idle - go up on pilot jet. I suggest you try a 58 or 60.

The correct procedure is to start with the fuel screw about 3 turns out and start turning it in until the idle rpms are maximized, then turn it out 1/4 turn from there and leave it.

The needle should be in the third (middle) position.

The main jet does not have any effect until you are open over half throttle. But, I would say you will be very lean on your main jet. Try a 160 or 162.

I am at sea level and currently running 60 pilot and 160 main jet. My fuel screw does not affect idle rpms (until 1/2 turn out, and then it reduces rpms) so I need to go down another size. I am going to try a 58 pilot this weekend and see if I can get the fuel screw to have the effect I described above. Oh, and I am running a Uni filter and FMF PowerCore IV-Q pipe.

I hope this helps you.

Share this post

Link to post
Share on other sites

here's a starting point:

0000 ft > 160 / 60

1600 ft > 158 / 58

3200 ft > 155 / 55

5000 ft > 152 / 55 (54 act., turn pilot in more)

6500 ft > 150 / 52 (53 act., turn pilot out more)

9800 ft > 148 / 50

adding one of these also help adjust the pilot screw:


see the order form (the xr4 carb is the same as the klr650)

i use mine all the time for adjusting for elevation changes.

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

  • Similar Content

    • By 661Bran28den661
      What’s up guys. Totally new here picked up an XR400R I live in the desert so I’m riding often and enjoy it. But I am having some issues with my  01 XR400R. I brought it out this morning for a putt and it seems to be choking up in the top of second. Like a bog an go bog an go. First seemed fine and third I didn’t make it high enough into the rpms to see. Before I brought it back to the garage. Yesterday I also changed the air filter back to an uni. I had seen the other one had a hole in it and the box was dirty gunned up and oily. I removed the airbox gave it a good clean out wiped everything down very well put a piece of screen over the snorkel Or where it used to be I should say. “Lightly oiled the filter.Also the spark arrester an tip for the bike it did not come with I ended up making one with a piece of flat steel and drilling holes. Whilst doing this. I found also a crack in the pipe. It almost sounds as like there’s a vacuuming or whistle? When revving.The first one I had made worked fine I had no issues. This one I am wondering maybe if it’s a cause of a little too much back pressure.So I’m assuming it’s either a Carb or exhaust problem. Or something that could totally be minuscule. Or major issue. Would definitely like some second opinions and any advice would be greatly appreciated. Thanks guys! 

    • By ddickinson
      My lanky 14 year old boy started showing an interest in riding MX/Off-Road so I sourced the best beginner friendly, yet dirt worthy, bike I could find: an Ol' Honda XR250R (2004). So far I've replaced a few clutch levers and perches with stock parts. That's gotten old and I'm looking to upgrade to an ASV or Torc1 type fold-able clutch/perch brake combo. Went to purchase online today and to my surprise there were no such parts listed for the XRs. I saw plenty of CRF/CRF-X choices and they seem to differ depending on generation. Obviously I can use nearly any perch/clutch combo as long as the two match; but I was wondering if anyone knew which of these levers was closest to stock? Also, will the first gen CRF250X brake lever work on the XR? These may be stupid questions to some; but I'd rather ask a dumb question than drop money on an ASV brake lever I can't use. Thanks for any help.

    • By TheLastByte
      Im currently in the market for an xr400r, and considering buying one that's had some heavy engine work done. The current owner claims to have bought it from a friend who's an XR enthusiast. The PO installed a big bore kit and high comp piston, as well as a xrs only pumper carb, rsw triple clamp, aftermarket clutch, street lights, and a whole bunch of bling.
      My main concern is the effect the upgrades will have on the engine's longevity. How much quicker will I be going through top ends with the setup on this bike as opposed to a stock setup, and should I be worrying at all about bottom end longevity as well? I wouldn't mind having to eventually redo the top end, but I don't want to deal with a race bike type top end rebuild schedule on an XR. 
      Is there anyone here who's running a bike similar to this one who can give some advice? 
    • By Ralph303
      I have a 2001 Honda XR400R. It has a whirring/grinding sound in the lower end and a vibration in the top end. I pulled the valve cover and everything looks good. Decompression lever looks to be in order. Anyone know where I should start looking or just rebuild the whole engine. Ballin on a budget, but really love this bike. It looks like it’s new otherwise. Oil was jet black and thin. Thanks in advance! 
    • By junglePIG
      Hi, I have an Xr250r with a buckled/ wobbling front wheel, after trying to true the rim i have broken a spoke.
      I am wondering if it is possible to lace any 36 hole aftermarket rim to the oem hub, also will i need to buy an xr250r specific spoke set. also could i take a 36 hole rim from another front wheel and lace that up???? thanks