I can't for the life of me ...

[Marty]

Subject line says it all. I will simply throw in a few of the related details. Have a little (old) single cyl. 250 cc 2 stroke motorcycle. I replaced the piston and liner twice before it was even warm enough to ride this spring. After finally getting everything right, (and nearly $400) I started using AMSOIL 2 stroke oil at a recommended mix of 100:1. It ran very well all summer till last week. I have all my firewood cut for the season and had a bit of chainsaw gas (40:1) left over so I dumped the remainder (about a quart) into the tank of the motorcycle which I am guessing had about a gallon of the 100:1 mix gas in it. I had run an errand on the bike later that day about 12 miles. On the way back, I noticed the motorcycle steadily slowing down as I'm trying to give it more throttle. All of a sudden at about 30 or 35 mph, the back tire locked up and went into a skid. (I think thats what caused the skid marks in my underwear) It took a couple seconds but figured out it might be best if I squeezed the clutch which I did and coasted to a stop. What happened was that the engine locked up, locking up the back wheel. After I stepped back into the real world, I tried turning the engine over and it was TIGHT and hot as H***! I was about 6 miles from home and managed to get a ride, brought the truck & little trailer back and hauled the thing home. By that time, the motor had cooled off and was once again loose but wouldn't start. The following morning, it was reluctant but did start up. And made some god-awful noises so I shut it right back off. Due to lack of time, I didn't pull the cylinder off but I know the third piston and probably the sleeve are shot. I'm hoping it is one more time fixable but not gonna mess with it till late in winter. Details completed, what the h*** happened? Logic says it locked up due to over heating due to lack of oil. I can't understand why adding 40:1 mix with 100:1 mix would coz that? I think there is something very important that I should learn from this and need your help doing so... Thx

 

[Randy Hart]

Marty, First of all a person could get a degree in the science of oil ! I didnt.. But I have worked on two strokes for 24+ years and 16 of them were in a dealorship on saws, trimmers and mowers.. Every factory school goes into detail on what oil to mix and how to mix it.. And every school says the same thing about too much and too little oil in the mix ! Cut the oil too thin and it runs lean- Add that extra little bit left in the Qt thinking a little is good and more is better= another lean mixture.. Heavy on oil but lean on gas. I have seen it both ways when a guy adds Homelite mix 16/1 to his Husquvarna that runs at 50/1 it burns up.. And then run the 50/1 in the Homelite and it ran the best it ever has.. till it locked up ! I know some machines are sticklers on mix ( Husquvarna being one ! ) and thats all the knowledge I have to pass on .. Randy Hart Ohio

 

[J.B. Castagnos]

In high compression high performance outboards, piston damage is common. These engines run at the max most of the time. Compression and timing are are as high as they can be for high performance. People use regular gas because premium is too expensive. They burn a piston. Engine is rebuilt, they fill the tank with regular gas, double the oil, lower the octane even more, because oil is like deisel. The more oil you add, the lower the octane. If a piston is scuffed on the wall or a bearing is burnt, probably lack of oil. If the piston is burnt from the ring land down, it's probably detonation. High timing can agravate this. See if the timing is adjustable on your bike and check it, lower it a couple of degrees. Use premium gas. Hope this helps. J.B.

 

[Marty]

J.B. My understanding of octane is that the higher it is, the slower it burns. Again going by logic, ( maybe that's my whole problem) I would think that high octane gasoline in a two stroke wouldn't be so good because if indeed it does burn slower, the exhaust has much less time to exit the cylinder than in a four stroke and I would think therefor that the fuel mixture would still be burning as it exits the exhaust port and ignite the incoming fuel. ????? BTW, the timing is not adjustable on this engine and yes they have pushed the performance to the max. It is an extremely radical little motor.

 

[J.B. Castagnos]

Premium fuel burns slower, but not nearly slow enough to still be burning when the ports are open. High timing ignites the fuel way before top center, it should burn past center to push the piston down. Low octane explodes and tries to push the piston backwards before top center, causing damage. A lean mixture burns real slow, causing backfiring and sneezing in a two cycle because the fuel is still burning when the ports are open.

 

[Josh]

Marty, was just trying to figure out what your problem could be. Out of all the bikes quads and sleds I have raced, never if an oil lined was plugged or pump was out did it ever turn over again. My only thought on the matter is your sleeve and piston I don't know as far as these old motors but my bikes and stuff all have different kinds of cylinders like chrome bore nickle bore ect. ect. and piston types the only thought that comes to mind is to make sure that one or the other piston and sleeve are not swelling when it's hot. The only other thing is in my personal opinion is that amsoil clogs stuff it's really thick I have VES on my sleds (Variable Exhaust System) and I got hung out on the trail cause it clogged it up!! just a thought!! good Luck

 

[John Iverson]

Too little info given to be absolutely sure .... (yr, gear ratio, etc) but I can tell you this. The older (~60,70's) single cylinder 2 cycle motorcycle engines simply do not hold up under a constant high rpm like "on road" use. They were great "off road" when the rpm varied constantly, or in town short trips, but those longer on road treks just seem fry them. I have seen dozens of these single cyl 2 cycles do just exactly what you described while using correct fuel/oil mix. I really doubt your adding that small amount was the main factor, likely only a contributor factor, it was the open highway constant high rpm that killed another one.

 

[Mark]

Re: I can't for the life of me ... The answer

Two stroke engines are picky eaters. Change the oil / fuel mixture, fuel to air mixture, heat range of plug, type of gasoline, type or size of carb., exhaust system, geographical elevation, outside temperature, etc. you need to rejet the carb.

Your engine has a main jet that the fuel mixture must pass through to be mixed at the right ratio with the air. Too much oil in the fuel causes the mixture to be thicker, which causes the air to fuel mixture to get way too lean. You thought you were adding more oil by using a thicker mixture. What really happened was that the mixture could not get through the main jet at a sufficient volume to lube the engine. You actually gave it less oil. It is like putting ten weight versus sixty weight oil in a drip oiler and still expecting six drops a minute from the same setting. You also starve the engine for fuel which also causes the engine to overheat. Kind of a double whammy.

You will need to adjust the jetting to allow the correct amount of air and fuel to pass.

Too big of hole in the main jet = too much fuel = too rich of mixture = cussing, because the engine has no power and keeps fouling plugs.

Too small of hole in main jet = too little fuel= too lean of mixture = Seize up and cause skid marks in shorts.

The solution is to always have the correct main, needle and pilot jet in your go-go bike. The first being the most important.

The wrong size pilot jet causes terrible idling and no low end response, again either too rich or too lean.

The incorrect setting of the needle valve in the slide causes the engine to not perform well once off idle, up to when it requires the fuel from the main jet.

The main jet is most important as the power required from the engine at mid to upper RPM's will need this to be very accurate.

Any two stroke will run on most fuel to oil ratios, as long as the jetting of the carb is correct. Granted the leaner the oil ratio the less likely the engine will foul a plug but there will be more engine wear.

Anyway, settle on what type of oil you want to use.

Second try to use the mfg.'s recommended ratio. If lucky, use their oil also.

If all else fails. Find a bunch of jets in a size series close to what is originally in your carb. and get to work.

Go buy a box of brand new spark plugs of the correct heat range (also keep that consistent).

Start by putting in a brand bew plug and increase or decrease the size of pilot jet until you have a smooth idling engine. Light smoke and little or no oil discharge. Increase or decrease the size of the jet until you get it right. Change the plug each time after changing the pilot jet.

Next, to set the main jet, put the needle in its middle position and put in a new plug.

Start the engine and go out and run it down the road wide open for a couple hundred yards or all the way through the gears. Once wide open at top speed, pull in the clutch and shut the engine off. Come to a stop without power and pull out the plug.

If it is black, you are too rich. If it is white, you are too lean. We used to call the optimum color a "baby sh**" brown.

Keep trying until you get it right and change the plug after each run.

Once that is accomplished, set the needle to the correct position by adjusting it up or down until the correct mid range response is correct.

This will take most of the afternoon, a little patience and a box or two of plugs.

How do I know about this? I used to build motorcycle oval dirt track engines. None of the manufacturers settings mattered when the only stock item on the bike was the manufacturers name.

Take care and good luck.

-Mark

 

[John Iverson]

Re: I can't for the life of me ... The answer

Excellent post Mark! Good info for all initial setups of 2 cycle engines regardless of application. This method works great for anything from big chainsaws with 5 foot bars to MX bikes! What I might add to it is that sometimes two setups are needed depending on the elevations you work/play at. The elevations in the Pacific Northwest that we commonly play/work varies from sea level to well over 6000ft. Many of us have multiple mixture setups in the toolbox ready to go. Beach sand dune riding one day, Coastal range mud the next!!! Then Cascade Range mountains the third.. two possibly three mixture setups depending on need.

 

[Russ Hughes]

Re: I can't for the life of me ... The answer

I realize that the circumstances are far different, but when I was a youngster I had a number of two cycle outboard engines and neither the engines nor myself knew any of these things you speak about. The engines continued to run anyway on all sorts of oils and fuels, whatever was available at the time.

Was it the difference between a water cooled engine and the typical air cooled engine found on land vehicles? My outboard engines were not called to run under competition conditions and could that have been the difference?

If all two cycle engines suffered from the same problems, I doubt that there would be as many Maytag engines still running today as there are.

Comments?

 

[J.B. Castagnos]

High perfpomance engines have high timing, high compression, tuned for maximum performance. These engines are usually run wide open for extended periods. Older outboards and Maytags were much more forgiving. Mixture was adjustable on the older motors and people tended to run them on the rich side, that helps cool things down a bit.

 

[Chuck Parcher (KS)]

I think that the 2 cycle engine guys are all correct. I only worked on a couple of two cycle motor cycles,,I had HARLEY'S back in the 70's in my OTHER life. In 1966 I bought a new 270 HP High Performance Mustang and it was hot. One time I raced a TRIUMPH 650 Bonneyville and just blew him away, so when I came up against a 500 cc. bike I thought NO PROBLEM, It blew me away. It was a three cyclinder KAWASAKI 500 I never saw anything get it's RPM that fast. He was gone...... never raced another one. Anyway. when talking 2 cycle...Granted a MAYTAG is a 2 cycle engine, but considering that it's max RPM is only 1100 rpm, comparing it with a 2 cycle Japanese motor cycle is like comparing Greyhounds, and Mules. the MAYTAG has no where close to the precision tolerances, or the materials of a modern bike. A MAYTAG would never even come close to getting the high temps. and stresses of a modern 2 cycle. Don't forget they are hit and miss and coast about 3 or 4 times between ignition. (When running right) I think MAYTAG's should be left out of the equation when discussing high performance 2 cycles or even chain saws that reach a high RPM very fast. There is just not that much in common. On top of that the MAYTAG does not have the ignition systems (Solid State) that the modern 2 cycle has.

Just a thought...........CHUCK

 

[Chuck Parcher (KS)]

MARTY: Maybe this 100:1 ratio has been doing some damage over the summer, and it finally caught up with the engine. Something that runs that hot on that little amount of oil, just does not make since to me. I don't think I would be interested in trying it. When you use words like logic. I just don't see the logic in trying to use less oil. Logic tells me they add oil coolers to cool the oil down, not use less oil that is going to run hotter. To me oil is oil and synthetic is synthetic which is fine, but those parts have to be lubricated, or guess what ....They'll freeze up. If nothing else I have gained that from these posts that I won't try Amsoil 100:1 in anything that I've spent money and time on. To me these are cautions, or warnings not endorsements. ............CHUCK

 

[Marty]

Hey Chuck, I'm certainly not going to rule out your idea of the damages coming on while running the bike all summer. It is possible. I linked the over heating of the motor to mixing the 40:1 gas/oil (which was not synthetic) to the 100:1 gas/oil mix (which IS synthetic) because the problem occured within a very short time frame of doing so. Maybe that was/is just coincidence. I also agree with you about the 100:1 mix itself. I was VERY uncomfortable with it and started using it at 80:1 but a 2 cycle performance shop down the road a spit-n-a hop where I'd been getting the Amsoil swore on his mothers grave that Amsoil 100:1 mix would coz NO problems even running full throttle out on the hiway on a 100 degree day. I still didn't like the idea but did it anyway. I will more than likely once again rebuild the motor but NO MORE AMSOIL. This motor is in a little 250 cc street bike but is the exact same engine the Company used for racing purposes. The RPM's gain so rapid that the front wheel is in the air as much as it is on the ground. Thx also to everybody else for all the other suggestions, none of which are beyond possibility. I learned some interesting things on this thread and have decided that I will continue to hate 2 strokes !

 

[oldenginejim]

Marty, get yourself a nice kick start Briggs, throw the two stroke away! No more scored cylinders,burned pistons or skid marked undies!!

To be honest, this has been an interesting thread.I`ve learned alot on this subject!!

Thanks guys!!

oldenginejim

 

[Matt Montague]

Marty, I have used the 100-1 mix Amsoil now for six years in my Echo weedeater, my polaris 4 wheeler and My 272 Husky chain saw,{6-8 cords a year} using lots and lots of gas {maybe over a 100 gallons} I have a friend that uses it in his out board when he mooches for salmon, this intails long periods of idleing. Neither one of use has any problems at all. Amsoil has a garrentee {sp} contact the dealer who sold it to you or go to their web site, and talk to there tech help. Amsoil has a very winning snow sled team and I am certain that they also have a motorcycle race team, they may also shead some light on your problems. All That I am saying is I have had excellent luck with the product, & don't think that it should be dismissed that quick. Matt

 

[Russ Hughes]

I think you are probably correct. I don't remember ever seeing a Maytag on a hot competition vehicle.

The first single cylinder engine I ever saw was a Maytag that the neighbor that lived behind us was demonstrating out in the back alley. He was trying to sell it to someone. It smoked a lot while it was running. I must have been all of four years old back then. I wanted it so bad.