While it's true that many engine manufacturers recommend the use of no-lead gas, it has been generally recognized that leaded regular gas is a better choice when examined under a microscope, look like tiny sponges. These round "sponges" add a cushion around all bearing surfaces and aid greatly in cooling of the ring-piston area. I understand that lead compounds also help hold two cycle oil in a more unified suspension.

There are several 2 cycle oil manufacturers who recommend only leaded regular gas. The problem with leaded regular gas is that it is not regulated by the E.P.A. for additives like no lead gas is. There are several refiners adding alcohol or methanol to their leaded gas. These additives "stretch" the product and usually work fine in automobile engines.

Methanol is very bad for our 2 cycle engines for several reasons:

1. Methanol attacks some plastics causing them to swell and crack i.e. fuel tanks, pumps and tubing.
2. Methanol causes diaphragms in carbs to grow hard and brittle thus decreasing their pulse action.
3. Methanol causes Tygon brand tubing to get soft and ductile so it stretches and weakens.
4. Methanol can break down in a carb and leave a white or red sandy substance in the screen on the fuel pump side.
5. Methanol runs HOT!

The whole picture comes down to this; plain regular leaded gas is still best to use, BUT if you can't get a non-methanol added regular gas go to no-lead regular (this should stir some controversy). (How could Mark know in 1984 how rare leaded regular would become or what the EPA would mandate being added to unleaded gas by 1996!--RDN)

Let's talk a little bit about carburetors. I realize that when you read this we'll have long been in the flying season but I want to talk about some general maintenance on these carbs. The following will be good for just about any carb whether it be a Walbro, Tillotson, Zama or TK. A carb that is allowed to sit inactive for a time can develop "gum" or "varnish" inside. Fuel mix evaporates over a period of time and leaves oil and fuel additives in carb jets and seats. Running an engine dry will not stop this because you can never run all the fuel mix out, in fact running an engine dry will speed up the evaporation process.

Start with a clean (and well ventilated) work surface, a clean coffee can or other suitable container filled with plain gas, paper towels, thin straight blade screw driver, small Phillips driver (only used in some cases), a small needlenose pliers or tweezers. We'll work on the fuel pump side first since this is easiest. The fuel pump side is the cover that is the closest to the fuel inlet barb (sometimes the inlet barb is attached to the cover itself).

Fuel pump covers are cast aluminum or plastic. Most Walbro carbs have a single screw through the fuel pump cover while Tillotson carbs use a screw in all four corners. Remove the screw or screws and carefully lift the pump diaphragm and a gasket, lay them on a clean piece of paper towel.

After you take off the pump diaphragm and gasket, inspect them both. Drop the fuel pump cover in your can of clean gas and let it soak. Do not use any solvent stronger than gas. Carefully blot the diaphragm and gasket dry. Check the diaphragm for holes or thin spots. A good way to do this is to lay the diaphragm on a slide viewer or any cool diffused light source. Don't lay it on a hot light bulb (I use a microfiche or microfilm viewer). The diaphragm should lay flat with no parts curled. If any flaps or edges are curled, get a new diaphragm kit.

The next step is to remove the metering diaphragm cover. The metering cover is usually pressed steel with a screw in each cover. The four screws in the metering side are usually smaller than those in the fuel pump side.

The metering cover will come off easily but use caution in removing the gasket and diaphragm. Some of the metering diaphragms will be loosely attached to the small fulcrum beneath. When this is the case, gently hold the diaphragm by one corner and slide it off instead of lifting it off.

Place the metering diaphragm and gasket on the towel next to the fuel pump gasket and diaphragm. The differences in carbs become evident at this point. Walbro carbs will have a thin flat plate held down with one or two oval head screws. This plate is the circuit plate in your can of gas and place the gasket on the towel. Tillotson carbs by the whole use "squashed" welsh plugs and no circuit plate. There is a way to remove welsh plugs but I recommend that you leave this kind of repair to a trained 2 cycle shop. Fortunately in model airplane application welsh plug removal will be very unlikely.

The last part of our disassembly is removal of the metering fulcrum, lever, spring and needle. Loosen, do not remove the clamping screw over the fulcrum. Before you do anything else, lightly place your finger over the lever so the spring will not fly. Now that the clamping screw is loose, take your tweezers and slide the fulcrum out of the carb body.

Remove the lever, spring and screw. Turn the carb upside down and let the needle drop out. Drop the needle, fulcrum, lever and spring in your can of clean gas. Unscrew the high and low adjusting screws from the carb body and soak them and the carb body itself.

Now go have a beer...

Beer done? Good, now fish all the stuff out of the can of gas and place it on a paper towel. Look at the main needle tip, it should be smooth with no grooves or gouges. The appearance of grooves means you should go right to a qualified service technician, because you have a seating problem. Place the needle back in its' seat, position the spring in it's depression and slip the fulcrum and lever in place. Tighten the clamping screw and check to be sure the top side of the lever opposite the needle is flush or even with the carb body. The use of a good straight edge is helpful. Bend the lever up or down to achieve this. Once adjusted, push on the lever to be sure the needle opens and closes freely.

The rest is simply a reversal of the disassembly procedure. I should add a few notes, as you install the diaphragms and gaskets. The metering side gasket goes against the carb body while the fuel pump gasket goes against the pump cover. Turn all screws down tight, but no superman moves or you'll strip a thread for sure. Never use anything stronger than plain, clean, fresh gas as a carb cleaner. There are check valves inside the carb that can be damaged by any stronger solvent. Never blow high pressure air through a carb, as this can also damage a check valve. Pushing a wire through any holes in a carb is the quickest way to the NEW carburetor store.

I know I'll hear from some of you concerning the part about setting the inlet needle lever with the carb body. It is true, the carb manufacturers have exact settings for this lever. I recommend you still set this lever flush with the carb body because it is not practical for you to buy a company tool kit with setting gauges. I'm sure you wouldn't notice a difference in performance for the matter of 1/64th of an inch or so.

I hope I have made these instructions clear. My purpose was to help you to some basic carb checks and cleaning. Should you have any particular problem or questions, get advice locally or write to me. Remember supply as much information as you can with your question.