Jump to content
Sign in to follow this  

carb help

Recommended Posts

I just bought a 02 xr 250. Hadn't been ridden for 2 years. Doing all the typical maintenance although never owned a 4 stroke before. I put new plug, air filter, cleaned the carb and put a moose kit in it. Still working on forks, sprockets, ect. but had to start it. Let it warm up, it idles good and sounds good at high rpm, but when you punch it, falls flat on it's face. If you don't let off it will die. Manual says middle notch on needle. Should I try lower notch? What jet runs middle rpm? I would appreciate any help. Thanks

Share this post


Link to post
Share on other sites

If you didn't remove the fuel screw when you cleaned the carb, you need to do that. A blocked fuel screw passage and pilot jet will make it fall on its face as soon as you crack the throttle.

 

When you cleaned the carb did you see what jets are in it currently and what clip position the needle is in? Post those.

Share this post


Link to post
Share on other sites

Yes, the kit was very complete. All jets and screws included. The main jet was the same. I believe 132 which is what the manual says. I couldn't read the other ones. Needle was in the middle. The only adjustment screw (not sure the proper name) is 1 3/4 out and I messed with it while it was running. I've had 2 strokes do this as well. Don't remember what was wrong. We're at 3500 feet but that's where I bought it. Should I buy other jets? Which one? Thanks for your help

Share this post


Link to post
Share on other sites

"but when you punch it, falls flat on it's face".

 

If that mean you open the trottle quickly , its normal on a XR250 with a carburator without accelerator pump.

Running the idle circuit richer can make it better but only a carb change (with accelerator pump) can fix it.

Share this post


Link to post
Share on other sites

I'm not questioning your knowledge, but if I would have brought a new xr in 02 and it wouldn't rev up quickly, I wouldn't have brought it. Are you sure I can't change jets? Thank you guys

Share this post


Link to post
Share on other sites

"but when you punch it, falls flat on it's face".

 

If that mean you open the trottle quickly , its normal on a XR250 with a carburator without accelerator pump.

Running the idle circuit richer can make it better but only a carb change (with accelerator pump) can fix it.

 

 

I'm not questioning your knowledge, but if I would have brought a new xr in 02 and it wouldn't rev up quickly, I wouldn't have brought it. Are you sure I can't change jets? Thank you guys

 

I've owned maybe a dozen XRs during the past 35 years.

The carburetor is sized to provide top end power and at low engine speeds there will not be enough air speed past the jet to pick up enough gas if the throttle is opened too wide for the engine's speed.

Whacking the throttle at idle with the engine in neutral is not a riding situation and will always cause an engine  bog. Being in a correct gear while riding usually avoids the problem.  Honda attempted a fix in 84 with twin carbs and progressive carb linkage but went back to a single carb in 86.

 

As posted a carb with a AP covers the problem but adds another circuit to the carb that is susceptible to fouling (I have one of those carbs :thumbsdn:).

Share this post


Link to post
Share on other sites

I'm not questioning your knowledge, but if I would have brought a new xr in 02 and it wouldn't rev up quickly, I wouldn't have brought it. Are you sure I can't change jets? Thank you guys

Its not that the engine will not rev quickly , its just the first moment when you open the throttle quickly at low revs .

The negative pressure at the Jet resposible for the fuel supply fail to be low enough for sufficient fuel and the engine run a short moment very lean and powerless.

Thats physics and can not be compleatly cured without AP.

 

@Chuck , whats your problem with the AP in your carb ?

I run a TM36 in my XR280 for more then 10 years , a TM40 in my XR440 and double TM34 in my Twin carb XL636 .

Never a Problem with the AP.

Share this post


Link to post
Share on other sites

my '02 xr250 doesn't bog at all no matter how wide I open the throttle at any rpm. try adjusting your fuel screw. what size pilot jet is installed?

Edited by washxr250

Share this post


Link to post
Share on other sites

I couldn't read the old pilot and didn't look at the new. It was a moose kit and I will take it apart and look. I thought the fuel screw was only for idle?

Share this post


Link to post
Share on other sites

I've found that fine tuning the fuel screw helps with off idle bog on my bike and my brothers wr250f which has an accelerator pump, he sometimes complains it bogs, and my bike doesn't even when lugging and just rip the throttle wide open.

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  

×
×
  • Create New...