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| Care & Feeding of an Alcohol Two-Stroke Racing Engine By
Jon Fitzpatrick Jon Fitzpatrick is the owner of FTZ Performance, Inc. a top micro-midget motor supplier and builder. Their motors have won features at the NMMA Nationals 4 times and the Tulsa Shootout 5 times since 1989. I met Jon at Tulsa this year and asked if he would supply us with the following tech article. You can reach FTZ Performance at 573-334-5439. I've been meaning to do this tech article for some time now. Because of the increasing influx of new people in the two-stroke micro classes, I see a real need for a set of guidelines concerning the major cause of engine failure; burned pistons. Many of these new people have limited experience with two-strokes or they have worked with karts or bikes. This article is meant to help the new and not-so-new racers that seem to have more than their share of problems finishing races. I have seen many of these "bad luck" types heed the following advice and run 30-40 races a year without burning a single piston. I hope that this info can help you have a fun and successful season. The motors supplied today by the top-name micro builders are not "hand grenades" They are designed to run hard and finish races. Many chronic problems concerning burned pistons arise from incorrect installation or plumbing or just lack of maintenance. Any good running engine needs a steady supply of both fuel and cool water. You can buy a good dog but you will also have to feed it! Here is something to consider, a micro motor has the hardest life of any race engine I know of. The load put on by the chassis and the length of the races at wide open throttle makes for an unforgiving situation if something not correct. The well meaning advice given you by your kart or bike racing buddy may put a hole in your piston and you , watching from the infield. Racetrack advice in general is risky business, so beware. Burned pistons are the most common form of engine failure in micro's. I will separate the causes into two categories Piston Heat and Fuel Starvation. Piston heat: Methanol (as well as gasoline) motors build up tremendous piston and combustion chamber heat when under a severe load. Such as when you're really hooked up for several laps. People try to point to one single cause such as the ignition, lean jetting, compression, but actually all of these factors can combine to push the heat over the limit. Also, add to this list; rpm, load, water or head temperature. What happens is the hot piston and combustion chamber will heat the compressing fuel mix and explode it. This is called pre-ignition or detonation, depending on whether or not ignition has started. Improper head shape is a major cause. It is not as simple as just compression. Lowering the compression can actually worsen the situation if the head shape is wrong. One of our major priorities has been developing "forgiving" head shapes that maintain good compression for top power. For now we will assume the head is suitable. With this is mind, anything we do to cool the top-end and piston will provide us with a greater safety margin. We recommend keeping the water temperature below 120-125 deg. This will require a large radiator in hot weather. You can richen up the jetting and cool the motor down, but the power will be depressed. I recommend that it be mounted in the back of the cage behind the drivers head, avoid small water fittings (under 5/8"I.D.) and tight 90 deg. elbows in the water lines. Be sure the water hose from the head runs to the top of the radiator without dropping down any more than necessary. This allows any air in the system to travel freely to the top of the radiator. Remember the water pumps on these motors aren't very forceful, so make it easy for the water to circulate. We now carry a real nice digital LED water temp gauge which allows the driver to monitor the temperature from 0 degrees Far. up. A cool running methanol motor will show a wet spark plug with little color on the end of the body or the center which will be mostly white. This is a very "safe" condition and it will run a long time. This is not to be confused with a white plug from a four stroke showing a lean or hot condition. A hot motor's plug will show black or gray/black with rich jetting. If you burn a piston with cool water and reasonably rich jetting the cause is probably Fuel starvation; Interruption or lack of fuel flow. Methanol under pressure pre-ignites very easily if it is very lean. I don't know of any fast competitive motor that will tolerate running out of fuel under full load. |
What happens is the fuel level in the carb will slowly drop causing the mixture to become very lean, causing detonation or pre-ignition. It would be nice if it would just quit....It will, but it usually takes out the piston when it does. These are some common causes: Stopped up fuel filters, pumps and carbs- Keep those puppies clean! Change or clean the filters after a week or two. Paper element filters are notorious for clogging up. Use only filters with a nylon or metal screen (and not too fine either). Methanol and Castor oil will tend to clog up a very fine element. Clean the filters with brake or contact cleaner or Gumout. Also remember it can take a few minutes of running to get all the air out of the fuel line after the fuel line has been removed, so try to run the air out before you go full tilt. Methanol gums things up worse when it is allowed to sit and absorb moisture. For years we have recommended "flushing" the motor by running a gasoline & oil mix through the pumps and all- This takes about 5 minutes, your fuel system will require cleaning less often and it helps keep rust off your very expensive internal engine parts. Clogged fuel tank vents; We recommend putting in a fitting in the top and a 1/4" hose running to below the tank to prevent spilling in a flip. Vented caps are bad about stopping up. Check that your fuel line cannot be pinched or kinked and is routed fairly low in the car to feed the motor easily. We have known several 250 motors over the years that will not always get enough fuel from a single fuel pump. With the addition of a second pump, fuel pressure at wide-open throttle usually triples, while pressure at idle is up just a fraction. Crankcase pulse and wave activity is very unpredictable and sometimes even a hopped-up pump does not get a good sharp pulse at every rpm. A second pump (pulsed from a different location) is cheap insurance to maintain consistent fuel pressure. Keep the pulse line 4 to 6 inches long - any longer and you weaken the pulse at high rpm. We discovered not to mount the pump(s) solid as this can make them pump too much or not enough. Isolate the pumps from vibration by hanging the pumps or wrapping in soft foam. These are only two of many causes for burned pistons, but I believe they are responsible for most of the problems new guys have with a good professionally built motor. Very often the cause is something simple. I will admit there are more exotic reasons such as air leaks, failed water pumps, ignitions gone haywire, but these are not as common as some people think. Your motor builder should be able to help you diagnose these if you can't. I will add that I have seen some very bad carb designs and also motors built so poorly that they wouldn't stay together if you poured fuel in with a garden hose. This is unfortunate, but it is usually fairly simple to fix. Okay, this also has to be included as a reason; It is the situation where somebody gets "greedy" and just plain leans the jetting down too far, trying to squeak out the last horsepower. This person should be made to write the following -100 times on the chalkboard: "You have to finish to win"- This might help! If it doesn't... just shoot them. Oh, here is another tip: Make sure the throttle is opening fully..Otherwise the needle will restrict fuel flow out the needle jet. Adjust your throttle stop so that you can just barely pull up the throttle cable at the carb top while holding it wide open. Please keep in mind, there is more than one way to do the same thing and you can find exceptions to any rule. But you can also find examples of guys that don't work on their car and still do well. Don't ask me to explain luck! I try only to offer advice that I have proven to myself during 25 years tweaking on two strokes, 11 years building micro motors for a living and a zillion alcohol dyno runs. I won't try to confuse you with theories or guesses... Now here is something I have learned for sure: If you do your homework .......your racing luck will improve. So feed your "race dog" with enough fuel and cool water and it will likely give you a good hunt! Back to FTZ Tech Page |