The 250R Carburetor

Having carburetor problems on your ATC250R? You've come to the right place. I've got a few suggestions to help the 250R owner with his (or her) carb problems. Carburetor problems are just as mysterious as electrical problems to many backyard mechanics. It can be viewed as an aluminum can of surprises if you don't understand the basic concept of engine carburetion.

I will try my best to make this as simple as possible. Many of these concepts are stretched into bare-bones, first grade style explanations. So here are the basics of 250R carb troubleshooting.

First everyone should have some idea of how what it is and how it works. Honda used Keihin brand of carbs on all the 250R's. The Keihin company is still alive and well today (visit their website). The carburetor controls the amount of fuel and air entering the combustion chamber.

It is a finely tuned system, built of aluminum, plastic, rubber, and brass, and relying on cleanliness as well as proper adjustment to function properly. Here's a basic explanation of the 250R carburetor. The Honda ATC250R is equipped with a slide carb. This means a cable, the throttle cable to be exact, operates the slide up and down. Thhis provides the rider the ability to obtain the proper amount of engine power depending on thumb throttle position.

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The Basics

The upward motion of the piston in the combustion chamber draws air through the throat of the carb which essentially creates a vacuum. A small, yet precisely sized hole leads from the throat to the bowl of the carb. The bowl is essentially a reservoir of gasoline at the bottom of the carburetor.

250R carburetorThis miniscule hole is located inside a jet, a brass part which can be removed for cleaning or resizing. The opening in the jet happens to be the means of evening out the pressure inside the carb. It does this by allowing a fine amount of gas to be drawn upward from the carburetor bowl. Basically it acts as a brass straw.

The fuel which is sucked into the throat of the carburetor is mixed with incoming air from the airbox side of the carburetor, and cast into the combustion chamber where it will be ignited by the spark plug at just the right time.

It sounds quite simple but it is really a marvel of engineering. All it takes is a mal-adjusted screw, a little bit of dirt, or a leaky seal and this little machine called a carburetor will not do as it was designed. I have listed a few of the basic carburetor troubleshooting tips but by no means is this an all inclusive listing. It is meant to be a guide to help with the most common 250R carburetor problems.


Let's look at some of the more common issues. Flooding, or too much fuel when not needed. The float valve may be set too high or stuck in a lower position thanks to dirt or varnish from old fuel. Fuel starvation is the exact opposite situation.

This will cause lack of power and a dimished running capacity for yiour engine. Again can be as simple as a stuck float in the bowl of the carb or possible a clogged jet. A faulty or leaky bowl gasket can also cuse this to occur. Idling problems are usually caused by a clogged pilot jet.

250R carb adjustmentThe pilot jet leads into the bowl of the carburetor. All jets in the carb can be cleaned with carburetor cleaner and compressed air. There are also commercially available jet cleaners that can be fed through the jets for stubborn debris. Lack of power can also be a symptom of an air leak.

It is important that there is a tight seal between the carb and the intake side of the combustion chamber. High idling is another common occurrence. This can be caused by the slide being stuck or improper setting of the slide in the first place. Fuel air mixture is set using the air screw.

Past experience has led me to turn the screw all the way in until it bottoms out, then back off approximately 3/4 to 1 full turn. This setting is not set in stone, but a guideline, you may need to adjust.

If you attempt to disassemble your carb in any way. Be sure to have a clean work area before you start. Cleanliness is key and organization is vital. Old fuel is bad fuel since it breaks down over time. And carburetor cleaner is cheap, just make sure you use it in a well ventilated area.

I hope this 250R carb guide has been of some help and shed some light on the aluminum mystery can.

Carb Q & A in the Forum

1986 250R carburetor setup

1986 250R carburetor setup

Does anyone have a setup procedure for the 1986 ATC250R carburetor? Looking to start from scratch.

Re: 1986 250R carburetor setup

There's some 250R carb info posted here: It doesn't look like a procedure to set up from scratch, but maybe it will help you with something.

Re: 1986 250R carburetor setup

The 250R carburetor page is a good read, but I was hoping for a step by step 250R carb setup starting from a pile of parts on the workbench. I know it's asking a lot, but I was hoping for something.

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Other Carburetor Information

Just when you thought you knew it all... As for other three wheel ATC websites I usually recommend the DMOZ as all the websites contained in their directory are supposedly reviewed by humans who have knowledge of the category to which they are responsible. You may find additional 250R carburetor information as well as techniques for troubleshooting and adjusting.

I have also listed some 250R parts here. These suppliers have rebuild kits as well as miscellaneous carb parts.

And use the buttons below to share the glory of the legendary 250R... Keep on Ridin'...