Xr250L Carb Mod That Really Works

[crzmonk3]

I dropped off my 1992 XR250L carb at my local Honda dealer and one of the techs said that for $10.00 he can modify the pump accelerator on my carb. He showed me the before and after results and normally the small L shape jet at the inlet of the carb will spit out a 4" fuel squirt. After the mod it now shoots out about 5 Ft of fuel almost in a straight line? I installed the carb and man! this thing really works, I no longer need to used the choke just jive some gas, the engine sound much better and the throttle respond is excellent. Very minimal power gain but the throttle twist is much crisper. He performed this mod in less the 10 min!

He did say that the return spring was cut almost in ½ and that the accelerator shaft stop was folded down to increase the travel.

My question is: who many of you know of this trick? And what exactly did he do to my carb? Is it just me?

[Ferd]

I did the exact same things to mine the day I bought it...Saturday... I just bought a 94...All the mods are on the side of the carb, you dont even need to take it off although the spring is a bit tricky...I now can have the bike idling and twist as fast as possible to full wide open without a bog or sputter...

[Meridian_Rider]

I just purchased a 94 XR250L thats in great shape but it has that annoying throttle hesitation. What exactly do you do to the accelerator pump and spring to get a faster throttle response? I assume that you want to get the pump to pump earlier (instantly) and possibly deliver more fuel?

[XR_RON]

? Yes please explain the mod. will it work on XR"S as well?

[Meridian_Rider]

This apparently is a mod for a accelerator pump carb, Like the one on the Xr250L. The regular XR250R doesn't have an accelerator pump so this mod wouldn't apply for you, unless you've swapped out carburetors.

[AdrianC]

Ferd, please tell us what the mod is.

I recently bought a '92 and it has that hesitation off idle. I checked, adjusted and cleaned everything I could think of. It idles fine, starts second kick from cold, runs well, but isn't as responsive as I remember my old '86 XL250 being.

Thanks,

A.

[Ray_Stedronsky]

OK fellas, I think I have this figured out....

No pics because the digital camera scrambled it's brains when I rolled downhill with it in my fanny pack after unsucessfully jumping a stump last week.

Anyways.....get your bike into good light and slowly open the trottle. Watch how the mechanism works on the right side of the carb.

What you will see is that as the throttle opens, a small spring (up at the top of the linkage) pulls back the arm that contacts the accelerator pump. (the acc. pump is the small brass rod with the black rubber accordian boot protecting it....it leads down the a flat diaphragm in a housing on the bottom of the carb next too the float bowl)

As the arm rotates it pushes on the rod and this pushes on the diaphragm squirting fuel into the carb intake.

Now...if your bike was like mine (a 94 XR250L) you'll see a gap between the tab that touches the acc pump rod and the rod when the throttle is closed (0ff) all the way. So the throttle must be rotated a ways before the acc pump ever comes into play. You'll also see that the weak little spring stretches....stretches...and stretches some more before it gets enough tension to rotate the arm that makes the acc. pump work.

So...to fix it.

First get a good set of needle nose pliers a clean garage floor and some patience. Observe how the spring is fitted into the linkage...take a digi picture if you're forgetful. Remove the small spring.....removing it is the EASY part.

Study the spring and observe how the two ends are hooked and how they are oriented to each other.

Take a pair of small wire cutters and cut about 40 per cent off the spring. Use the pliers to bend the last coil after the new cut to form a hook oriented in the same way at the old one.

Replace the spring. This is WAY harder now because the spring is shorter and has to be stretched to get it to go on.

If you shoot the spring off the bike more than twice remember than when cursing the curse word comes BEFORE the other words (This is the reason for the clean floor...so you can FIND the spring after it launches) If you're trying to do this outside on the dirt or in the grass you're gonna be very angry.

I was able to work the spring back on with the help of a very small screwdriver to stretch it back over the rear part of the linkage. You have to do this to understand what I mean.

OK.....now open the throttle and you'll see that the spring now pulls harder on the acc. pump linkage and the pump rod gets shoved down earlier and farther than before.

Next you can take the "play" out of the system by gently bending two tabs. One tab is at the top of the linkage and contacts the arm that works the acc. pump linkage. As you close the throttle, this tab pushes the acc. pump linkage forward. You can bend that tab back to the rear of the bike to decrease the play between the acc. pump linkage and the acc. pump rod.

You can also bend the tab that contacts the rod down just a bit to take the play out of the system.

Whew.......long description.

It bloody well WORKS though...

I had a slight hesitation after carb and airbox mods that no amount of fiddling with the pilot air screw would fix.....this took care of it and the bike pulls much better from slow speeds and off idle.

No real Power gain just a big improvement in throttle response. Probably at the expense of a bit of fuel economy....but that's probably negligible.

I didn't pull the carb off to see how far the acc. pump squirts fuel now but the motor is happier and that's what it's all about anyway.

Enjoy

Ray Stedronsky

Davis, CA

[XR_RON]

Your right,I should pay more attention.I seen some free horse power and thought,well.....

[DougBi]

Ray-I, for one would like to thank you for your effort/evaluation. I've been following this thread hoping to get an answer as to how to accomplish this mod. As soon as I have time I think I'll give it a go.

You da man!

[Meridian_Rider]

Thanks for the write-up Ray, I went out and did the spring mod right away and the results were exactly what I was looking for. Removing the seat and right side cover made it pretty simple. I also tied a thin piece of string to the rear hook in the spring. Once the front of the spring was hooked back onto the accelerator pump actuator, it was a simple matter of pulling back on the spring with the string and hooking it onto the throttle pivot. The added benefit of the string was that it kept the spring from going flying during installation. Cut the string after its all hooked up.

My only concern is , does this extra shot of gas wash down the cylinder walls possibly causing premature cylinder wear? Just a thought.

[Ray_Stedronsky]

I'm not enough of an engineer to know for certain, but it would seem to me that any fuel would vaporize right away and get burned as long as the engine is running.

Rolling the throttle on alot with the engine off will certainly have raw fuel running into the intake tract but I can see that being a problem with a running engine.

Ray

[Ray_Stedronsky]

Hey Meridian,

Great idea about the string. I wish I had thought of it before I wore out the knees of my Levis searching for the dratted spring.

Ray

[yofrankie]

This mod is almost exactly the one I did I my old crf250x

If you search for a dude called vonbeard he gives a nice explanation with photos

My old crf had a initialization / bog due to a gap between the spring end and the stopping mechanism. It took a ten cent rubber o ring and about 4minutes to fix

I did also switch out the stock bowl for a boyesen and those two mods made a huge difference

[Jeffery2]

So I looked at this tonight, the spring looks easy enough.  I wish there was one I could buy that would just go on there, but anyway, I'm going to try cutting the stock one.

 

What cam are you talking about bending?  What does it do?

[Celoufran]

Hi,

I love how this thread is still relevant even in 2020. I just tried the mod on my 1992 Honda XR250L and man does she run good now! I can full throttle it from idle and she doesn't bog up at all. Again, thank you Ray for the write up!

[Mike Wex]

On 9/26/2020 at 4:18 PM, FazeCelou said:

Hi,

I love how this thread is still relevant even in 2020. I just tried the mod on my 1992 Honda XR250L and man does she run good now! I can full throttle it from idle and she doesn't bog up at all. Again, thank you Ray for the write up!

True in 2021 as well.

[cdahl383]

Might have to give this a try on my 1996 XR250L I just picked up this weekend.  Sounds pretty easy to do.

 

[Oil Baron]

I did the pump mod a long time ago and I have played with the jetting a lot.  Recently, I went back down to a 40 pilot and 125 main.  One turn out on the screw @5000’ with the late xr250r needle at the middle notch.  It’s been running and starting better than ever especially on slow trails lugging the motor.  Over the weekend we did a three hour singletrack.  It ran great except when jumping logs.  There it died out and was difficult to hot start, was flooded.  The pumper is hard to clear when it’s flooded cuz you squirt more fuel when you open the throttle, especially with the pump modded.  It still runs stellar everywhere except jumping logs.  

It has the slosh baffle, but I’m thinking the original 1991 all plastic non-adjustable float may be the problem.   I’m actually thinking about putting my like new CRF230F carb on it (which was replaced with a pwk) even though it’s a couple mms smaller, but jetting would be an unknown onto the 250 motor.

@ramz