RM-Z 250 Carb tuning


Elevation about 850

Temp 30-50F humid or dry conditions

Main 185

Pilot 42

Fuel screw 1 3/4 turns out

Starts fairly easy but won't stay running when the choke is in. Backfires and sputters when I keep the rev up (to keep it from dying). Fire comes from the pipe when we don't use the choke. Even holding the choke part way out makes it run better.

I took the carb apart, removed and blew out all the jets as I've done before with other Keihin's I have had. We cleaned the air filter and installed a new plug. I also cleaned out the hot start, and replaced the cable and ends. Those things made little difference.

This thing just seems to not be getting enough gas. Given the 42/185 jets, how could this be? I think they are substantially bigger than stock.

William1 and Burned, do you have any suggestions for me?

If you had the carb apart make sure you put it back together right. I've read countless posts where the plate was put it in upside down and now the bike only runs with the choke out!

"the square end should be down on that thin plate that goes on the head side of the slide"

Create an account or sign in to comment

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

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Similar Content

    • By Sammy_1101
      Hi Guys,
      So I recently bought a 1997 XR400. I've done some research into getting more power through some basic mods and rejetting the carbs. Though all of the ones I've found have been for post 98 XR400s so the stock carb set up is a lot different. Usually people are opening up the airbox, exhaust ect. ect. and Jetting their carbs up to 160/162 for mains around 60 ish (I think) for the pilot. However for the 97 model this is close to stock for the jets.
      So essentially what Im asking (Just to cut to the chase ) Has anyone got a 96/97 (maybe 98, not sure) XR400 and has done these similar mods, and what sort of jetting have to done as a result.
      Thanks in advanced, also its my first post so apologies if I havent done everything correctly.
    • By Jturn
      38MM Cast SmartCarb. Purchased a couple years ago for a yz250. Don't have the bike anymore, and it has been sitting around for about a year. Used, but in fine working condition. You can also purchase a different needle for different bikes, as well as rebuild kits from their website.
      Asking $250 shipped to continental United States. I can arrange other shipping options at the buyers expense.
    • By faizakhtar125
      Hey guys I just bought a bike last night. So the seller said the bike will turn on but then die. We didn't try it because it was really late at night and it was raining (seat was wet). But he said if you bump start it, it will turn on and ride. So what do you think the problem is? I just want to make sure it runs... I probably won't be able to bump start it till Saturday (rain)... It's a four stroke, and I know absolutely nothing about them. Thanks.
    • By knotduke08
      I know this topic has been discussed in the past, but I have not found any options available for the new 2018 bikes. I live and work for a new Beta Dealer (Auburn Extreme Powersports) in California, and we are having a difficult time mapping the RR-S bikes for full FMF exhausts. We have tried contacting Beta Support several times for this issue to no avail, and we typically are given the runaround when transferring to techs and secretaries. From what we can gather, the FMF flash is designed for the RR bikes, but not the street-legal counterparts. Every time we try to install the FMF map onto an RR-S errors occur, and the programmer screen goes virtually blank. We have heard through the grapevine that some are using the RR maps on the RR-S with success, but we have yet to try it, even on our own bikes for fear that it will permanently erase or damage the CDI. Any and all help or suggestions regarding this topic would surely be appreciated! Thanks, Ben.