Dirtbike Carburetor 101 Part Two!

Welcome back everyone,

At the end of the last class we ended with the carb sitting on the bench and the intake port in the head plugged to keep out dirt & small critters. Now let’s pull off the vent hoses and turn it upside down on the bench like this.

Take note of the pilot mixture adjustment screw that I have labeled here for you. I will be giving you a tip about it later in the lesson so be ready to refer back to this picture if you need to. Please remember these are not in the same place on all carburetors. I have seen them on the top and on the side depending upon the make and model. Some late model machines have them hidden under aluminum caps to keep you from tampering with them, but if you have a real problem you can remove the caps to repair it. Just be sure to replace them especially if you have to pass emissions inspections in your state. As usual I recommend you consult your handy dandy service manual for your motorcycle just to be on the safe side, because some carbs have more than one aluminum plug and you don’t want to remove the wrong one. Trust me I know….

Of course this bike has none of those annoying issues so let’s go ahead and take the screws out of the float bowl and look inside.

EWWW!

Now I am a fairly environmentally conscious guy, I grow organic veggies, the shop that I work in is powered by solar electricity, drive reasonably efficient vehicles etc. but you will never convince me in a million years that today’s gasoline is good for the environment. Once the lead was removed there really was not that much left to improve. There is no way  fuel that will rapidly break down into this toxic and corrosive sludge as fast as the fuel made in this day and time, can possibly be good for the environment. Just think of what it is doing to your vehicles as they sit in the driveway right now.

Let me get out of rant mode and get on with the lesson; here’s a shot of it with the float removed. You should be able to push the pin out to one side with a small punch and lift the float and float needle (float valve) out of the bottom of the carb.

So when someone tells you the float is sticking this is what they are talking about. Sticking floats are usually caused by either a piece of trash getting under the point of the float valve, or if the motor has been sitting by gasoline evaporating, and gluing it into place with a coat of gunk like you see here.

In this next shot I have removed the jets and the mixture adjustment screw. Even if you have a service manual handy, before removing the mixture screw, turn it all the way in slowly and count how many turns it takes to go all the way in. Write the number down somewhere, and then remove the screw along with the spring the washer and the o-ring that are in the hole under it.

You’ll probably have to dig for the o-ring using a piece of wire or a small pick like I did above.

At this point all of the metal parts are ready for a good long soak in the parts washer or carburetor cleaner until tomorrow. In fact the longer the better. Gather up some supplies.

If you have an air compressor and a parts washer you may not need the spray carb cleaner. If you don’t have a compressor it is mandatory even with a parts washer or a dip bucket of carburetor cleaner. For this bike I did pick up a carburetor overhaul kit. If your o-rings are all still in good shape and you can get all of your jets spotless you may not need it, but it is often difficult to clean the idle jet good enough to work again even with all of the right tools. If it’s my own bike, and I am broke that week, I might chance it, cause hey it’s part of the price I pay for this hobby. If it is your bike, you are getting new parts, because if it does not work, then I would be working on it for free and that would just piss me off. You would probably be upset at me too.

Here’s a teaser shot of everything laid out on the bench after cleaning, be sure to come back for the next lesson!

exploded view!

Click here to continue this lesson!

3 responses to “Dirtbike Carburetor 101 Part Two!

  1. Pingback: Dirt Bike Carburetor 101 Part 1 (how to clean a single cylinder motorcycle or atv carb) | Life on 2 Wheels (& other stuff)

    • Dear readers, I cannot vouch for the accuracy or legitimacy of the service manuals at this guys website but decided to allow his comment in case you wanted to check them out for yourself. Just remember I am not responsible for the contents of any external links..