Honda XR250L Mods Part 1 of 3 by Rick Ramsey on 4Strokes.com

4Strokes.com Honda Technical: Modifying the XR250L By Rick Ramsey - Part 1 | Part 2 | Part 3

Page Jump Links: Carburetor & Jetting | Exhaust System | Air-Box | Gas Tank

XR250L Modifications
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So you just bought a brand new XR250L. Have you noticed how heavy it is? Have you noticed that it doesn't have much punch? Are you afraid to ride hard trails with it because the tires won't make it? Well, all of these thoughts occurred to me too so I did something about it.

The objective was to remove as many parts as I could from my 1991 Honda XR250L and still keep it street legal. My friend Gordo wanted to convert his but with shorter suspension that he could occasionally ride on the street. We both got what we wanted. My bike weighs 23 pounds less than when I started and has DOT approved tires that can be used on the street and off-road with some confidence. Gordo's bike weighs about the same as mine and has dirt tires on it. Gordo uses his bike in the desert and in the woods. He doesn't plan to do much street riding, but he's legal in most areas and can ride on the street if he needs.

Gordo and I have "49-state" model bikes. We don't have an over-aggressive DMV in our state, and we can get by on a lot less than people in other states. If you think that some of the things we've done might not get by your DMV, then don't make the changes. There are more than enough things to do legally. If you are making a pure off-road bike, then have at it. Where I knew about the California-specific differences, I mentioned them. I'm sure that I didn't catch them all.

The following sections describe in detail how we modified our bikes. Many parts from the XR250R ('86-'94) will fit the XR250L. These parts are sometimes lighter and/or give better performance than the XR250L parts. We used standard XR250R parts whenever possible. Working only on week nights, we each took less than a month to do all the initial work. We rode on the weekends to check our work. The biggest time delay was waiting for parts to be delivered. Cost is not mentioned much, but rest assured, neither of these project bikes was cheap. Gordo had a NASA budget, while I had a Kitty Hawk budget, so sometimes I didn't spend as much on mods as Gordo did.

Carburetor & Jetting

The accelerator pump carb on the XR250L looks like it has potential. Pumper carbs can be jetted to get rid of that nasty four-stroke hesitation on the bottom and give good power on top too. However, the non-pumper carb from the XR250R is ultimately a better performer because it is designed for more air/gas flow. The needle and seat on the pumper carb are designed to make the bike EPA legal (lean) and are the biggest impediment to performance.

But, if you want to stick to the stock pumper carb, there are a few things you can do. The carb is jetted too lean. If you do any of the intake or exhaust mods, then it will be way too lean. Install a 125 or 128 main and a 40 or 42 pilot as a start (sea level jetting). While you have the float bowl off, remove the pilot adjusting screw. Be careful with the spring, metal washer, and o-ring. Heat the end with the small ear on it, and the ear will fall off. Reinstall the screw before remounting the float bowl. The pilot air screw can now be adjusted throughout its range.

There are too many hoses on the California model carb. If you don't need to be EPA legal, remove the purge control valve and canister and two extraneous hoses. Consult pages 1-22, 1-27, and 5-10 in the service manual to see which hoses to remove. Seal the holes in the carb body with short lengths of hose that have been plugged with Shoe Goo or something similar. You can seal the carb body directly if you trust yourself.

Besides hoses, there are two other differences between the California and 49-state carbs: the part numbers are different for the throttle slide and carb top. I don't know the extent of the physical differences, but I would guess that the slide cut-away is different, and the carb top has a throttle limiter.

The XR250R and XR250L carb bodies are nearly identical. The complete XR250L carb was derived by drilling out the extra channels that were already cast into the standard XR250R body. Extra hoses were added, and a different float bowl, choke mechanism, and jets were used. The similarities and differences are summarized below:

Main jet:
Pilot jet:
Pilot air screw:
Float bowl:
Accelerator pump:
Float bowl vent:
Float bowl overflow:
Emissions hoses:
#125 long hex head
#40 raised thread, large aerator holes
tall, main jet access
lever on carb body
push/pull cables
1 hose
2 hoses
#122 short top hat
#38/40 raised thread, small aerator holes
limited adjustment (ear)
short, no main jet access
remote via cable
none on 49-state model, 2 on Cal model

XR250L Modifications
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If you want to replace the XR250L carb, you might be able to get a used "take off" carb from XR's Only. The XR250R carb is a perfect fit because the carb bodies are identical. You will have to use the choke lever on the XR250R carb body and discard the XR250L choke cable. The XR250R carb is most definitely recommended if you do any of the intake or exhaust system mods.

Exhaust System

The XR250L exhaust is somewhat restricted. The exhaust header from an XR250R is about 3 mm larger in diameter, and will bolt right up to the engine. Gordo and I both installed XR250R headers. However, the XR250L tail piece/muffler will not mate with the XR250R header because the diameters are different. You have the following two choices:

If you use the Honda muffler, you may want to change to a large diameter muffler insert from an '85 XR350R. Alternatively, you can use the insert in the XR250L muffler by grinding off the weld. Good luck, the weld is plenty deep.

I installed a '90 XR250R muffler with the large diameter insert that I removed from my now-ruined XR250L muffler. My bike seems peppier and revs out better than it used to, and it's still plenty quiet. I can install a small diameter insert to make it even quieter. The XR250R muffler is about 1.5" shorter and one pound lighter than the XR250L muffler.

Gordo installed a SuperTrapp Racing series muffler with 8 discs, and it was very noisy. He had an insert made to fit inside the hollow middle of the SuperTrapp. This insert adds another layer of fiberglass insulation and quiets the bike considerably, but his bike is still noisier than mine. Gordo talked to the guys at SuperTrapp, and they told him they were planning to make a Street/Trail Series muffler for the XR250L. This version will be the 4" steel muffler with integral "S" bend like they make for earlier model XR's. Lastly, Cobra makes an aluminum muffler that fits the stock XR250L header.


The stock inlet air tract is too restrictive.

Remove the inlet air duct by drilling out the two pop-rivets that fasten it to the top of the air box. These pop-rivets will be difficult to drill out unless you can keep them from turning. Grind them off if necessary but keep the air box from melting by applying water to the rivets as you grind.

Remove the internal metal brace by drilling out the pop-rivets on each end of the brace. Grind the middle off at the welds and leave the metal plate mounted in the air box, so you don't have to mess with holes in the back of the air box. Don't let the plastic melt; apply water during drilling and grinding operations.

Replace the stock air filter with a K&N air filter. You can use the large capacity air filter for the XR600R, if you remove the metal brace from the air box. The larger filter is a tight fit and the stay arm must be bent a little, but it works. You can make a longer stay arm fastening loop from 1/8" welding rod and then the stay arm doesn't need to be bent.

Remove the breather canister from where it is mounted on the left side of the frame by the shock reservoir. Remove the mounting tab from the frame. Disconnect all hoses from the canister. Remove the hose from the crankcase vent tube and install a K&N crankcase vent filter directly on the crankcase vent tube. Remove the hose from the left front of the air box and plug both ends of the plastic tube on the airbox with Shoe Goo. Remove the hose from the bottom of the air box and replace it with an XR250R air box drain valve.

Gas Tank

The stock tank is steel and will dent permanently if you fall on it very hard. IMS and Clarke make replacement plastic tanks.

The IMS tank holds 3.5 gallons and comes in white or XR flash red (orange looking). The red/orange tank is semi-transparent and is exactly the same color as the seat and red/orange XR fenders. The tank mounts on the stock donuts at the front and has a trick metal bracket at the rear. You use the stock petcock. IMS provides a plastic non-locking gas cap (unlike the Honda 49-state metal locking gas cap). The tank does not feel any wider than the stock tank; most of the extra capacity is obtained by drooping the front and raising the top. The upper triple clamps just kiss the tank at full lock. The tank does wobble when you press with your knees.

Clarke makes a 4.0 gallon tank with a very solid mounting system; a threaded rod passes through a pre-existing hole in the frame and the front of the tank. The tank is narrow at the back, like the IMS tank. I tried both tanks and liked the Clarke tank the best.

Modifying the XR250L By Rick Ramsey - Part 1 | Part 2 | Part 3

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