CT Racing have tested methanol fuel extensively over the last five years and have learned how to set up engines and carburetors for most ATV applications. The following is a list of tips that every methanol fuel user should be aware of.
Preliminary Facts Regarding Methanol
Methanol fuel is generally harder to set up for than gasoline, therefore CT recommend its use for experienced tuners only. If you are not proficient in jetting carburetors and evaluating engine performance then it is best to gain these experiences with gasoline first.
Methanol fuel is recommended for short duration racing only such as drag racing or short sprint racing, you will consume twice the amount of alcohol fuel for any given horsepower output when compared to gasoline, so the range of your fuel tank is basically cut in half.
Because methanol is “hygroscopic” meaning it absorbs water, it requires special handling procedures. The number one piece of advise is to buy only as much fuel as you will use in a week, and buy the fuel from a reputable vendor who stores the fuel in sealed metal drums.
It is preferable to store methanol in a sealed metal container. Plastic is OK for short term storage only, but put the container on wood, not on the ground. Be sure to keep your container sealed at all times.
In addition to attracting water, methanol is corrosive to metals, gaskets and seals. In four stroke engines it is recommended that you use a “top lube” or methanol fuel treatment in order to combat corrosion. Many motorsports oil manufacturers make products specifically for treating methanol fuel systems.
For two stroke applications CT recommend Maxima 927 pre-mixed at 28:1, this will combat corrosion and sufficiently lubricate the engine. Check with the oil manufacturer before mixing your favorite oil with alcohol.
Methanol must be drained from the fuel system at the end of the day every day. This is especially important in the coastal climates. Because fuel tanks and carburetors are ventilated to the atmosphere the methanol inside will absorb water and corrode costly fuel system components.
Once the methanol has been drained from the entire fuel system you will have to put gasoline into the carburetors and run the engine. We use a radiator overflow bottle filled with pre-mix, attach a hose from the bottom of the bottle to the fuel fittings on the carbs. Start the engine and run it for two or three minutes, leave the gasoline in the fuel system until the next ride.
Engine and Fuel System Set Up
Because alcohol fuels burn so much cooler and slower than gasoline CT recommend that you increase the compression of the engine to maximize performance, there will be little or no advantage to running methanol on a stock compression ratio. We suggest first checking your cranking compression and then consulting your engine builder before running methanol, some engines will tolerate less compression than others.
Advance the ignition timing. Your results may vary depending upon compression ratio and the sophistication of the ignition system. Proceed carefully and document the timing change by measurement, either by degrees of crank rotation or by millimeters before top dead center.
Minimize flow restrictions between the fuel tank and the carburetors. Remove the petcock from the fuel tank and cut off the filter screen and the reserve stand pipe. Remove any in-line fuel filters or petcocks, use as large a fuel line as you can fit over the fittings on the carbs and petcock.
Check the operation of the slide, make sure that it opens all the way to clear the bore of the carburetor, this is particularly important with modified or bored carbs.
Put taller gearing on the machine. In our experience a methanol equipped ATV will pull a one tooth larger countershaft sprocket. If you run a 13T on gas try a 14T on alcohol.
Procedures For Tuning Methanol
Even if you are an experienced tuner, you will want to read up on your particular carburetor design before you proceed with methanol testing. Some of the best information is available in the manufacturers shop manual for your particular machine, most manuals have excellent carburetor sections, and all of the procedures for tuning gasoline will apply for methanol, just the jet sizes will be different. For aftermarket carburetors we suggest getting the Sudco/ Mikuni tuning manual (CT part# TL-002-999 $30.95), this book has some good general information that applies to Keihin as well as Mikuni products.
When you initially set up the carburetor for methanol err on the side of rich. Alcohol fuels generally have a wider air/fuel ratio tolerance for good power, methanol will make excellent power from a correct air/fuel ratio up to a rich condition, there is no need to “lean her out” in search of power as you would with gasoline.
Methanol fuels are less tolerant of a lean air/fuel ratio than gasoline and will detonate violently. Fortunately methanol detonation or pinging is quite audible, so if you hear any “rattle” you must stop immediately and richen the carburetor settings.
Tune from the bottom up. Dial in the slow circuit and air screw first, then the needle and clip position, then the main jet, and the power jet last. Don’t change the main jet if you have a problem at part throttle/ low speed.
Some words about the power jet. The power jet is essentially another fuel circuit in addition to the slow and main circuits, the power jet is throttle position sensitive and generally only comes in from 3/4 throttle and up. Many power jets have a screw type adjuster on them so you can vary the amount of fuel they deliver, turn the screw out from seated in order to increase the fuel fuel flow. The power jet will allow you to keep the slow and mid throttle settings clean/ correct and still allow enough fuel flow for wide open high rpm power.
The useful range of the power jet adjuster found on a CT alcohol carb is 1/4 to 3 turns out from seated.
When you test the methanol jetting be sure to make several passes before you settle on a particular main jet size and power jet setting, it will take a few passes for the engine to come up to operating temperature, if it doesn’t detonate on the first run it may do so on the third or fourth so proceed methodically.
The main jets supplied in a CT alcohol carburetor are sized according to the number drill index, therefore the smaller the number scribed on the jet, the larger the hole will be.
If you are running into a lean condition at wide open throttle (WOT) and you are getting no results by enlarging the main jet, you have reached the fuel flow limit of the needle and nozzle combination. (i.e.) The clearance between the needle and nozzle at WOT is too small to feed the larger main jets. The next step is to sand the last 14mm(9/16″) of the needle to a smaller diameter, this will increase the area of the needle/nozzle combo and allow the potential for more fuel flow through the main circuit. This should put the large main jets you tried earlier back into the useful range. Put the needle in a hand drill, take a piece of sand paper and carefully sand the last 14mm of the needle to the same diameter as the very end of the needle just before the final bevel.
CT Racing 11805 E. Slauson Ave.
Santa Fe Springs, Ca. 90670