[Hpmac75]

I've been running my two stroke motor on my mountain bike at 40 to 1 fuel mixture for about 2 weeks the motor will not run now and I just realized the motor was supposed to be running on 20 to 1 fuel mix. Will that cause it not to run or do I possibly have a problem somewhere else

 

[Polaristwostroke]

That sounds like a seized engine. The fuel to oil ratio is very important and not running the right mixture doesn’t give the engine enough lubrication and can cause it to seize up. I would take the head off the engine and check for score marks on the cylinder walls. If there are any I would just get a new motor considering how cheap those kits are. Does the engine still turn over, or is it more difficult?

 

[Jaguar57]

40:1 is OK for semi-synthetic oils. Which oil did you use?
Seizures are usually more a matter of jetting though. Too lean and you seize because the piston needs a tad bit excess gas to keep it from getting too hot. see www.dragonfly75.com/moto/carbtuning.html

 

[Hpmac75]

That sounds like a seized engine. The fuel to oil ratio is very important and not running the right mixture doesn’t give the engine enough lubrication and can cause it to seize up. I would take the head off the engine and check for score marks on the cylinder walls. If there are any I would just get a new motor considering how cheap those kits are. Does the engine still turn over, or is it more difficult?

Engine turns over. I took the head off and discovered that one of the piston rings broke. I know that can cause loss of compression, but not sure if it will cause a no start.

 

[Polaristwostroke]

Engine turns over. I took the head off and discovered that one of the piston rings broke. I know that can cause loss of compression, but not sure if it will cause a no start.

that can cause a no start. Make sure the broken ring didn’t do any damage to the cylinder wall and then I’d get a new ring.

 

[Hpmac75]

that can cause a no start. Make sure the broken ring didn’t do any damage to the cylinder wall and then I’d get a new ring.

I checked the piston and cylinder wall and every thing looks ok. I will order new rings. Thank you for your time and help.

 

[marsheng]

Piston seize is oil failure. There are two options, not enough or overheated.
Read here

http://www.marshland.co.nz/ftp/2Strokes/PISTON%2520SEIZURES.pdf

and here
http://www.marshland.co.nz/ftp/2Strokes/topend_rebuild.pdf

The more I read, the more convinced I am that more oil is better. Less friction and most oils burn like fuel so just adds to the combustion. High output motors need at least 20:1. From the article, they found 16: 1 was best.

 

[Jaguar57]

What you just said only applies to non-synthetic oils which is why if you want the most power then use a non-synthetic oil (but be prepared for more spooge and having to take apart the engine and clean it more often).
Seizures are more about too little gas than too much oil but if you run a non-synthetic oil at 50:1 you will probably seize.

 

[marsheng]

What you just said only applies to non-synthetic oils

That is interesting, I wonder how my used engine burner works because it do not use synthetic oils in it.

All, oils burn. Linseed, Coconut, Mineral, synthetic, Hemp seed, peanut etc If you want to talk about deposits in the engine, look at the ash content. That is what leaves deposits. Look on the specs of the oil can if you can find them.

Seizes have nothing to do with fuel mixture. You can run a 2 stoke all day at very lean conditions, just don't open the throttle over say 25%. When you have low RPM and low power, auto lubes can be as low as 200:1. Sure mixtures are related but get the facts right before you diagnose a problem.

If it is pre mix, lean mixtures means you have LESS oil. That is coupled with less cooling from the incoming mixture which means the engine is not cooled correctly, WHICH means the little oil you have overheats and breaks down and cant do its job.

If auto lube, then its just the engine not getting the cooling effect from the fuel vaporizing which still then leads to oil breakdown and seize.

Start diagnosing seizes with oil failure and go from there.

I can press in a big end pin in a crank with 5 tons. It doesn't seize. Wash them bone dry and try that again. You have a much higher chance, I'm not talking about wiping it with you finger, there is enough oil on you finger to stop it seizing.

 

[Jaguar57]

those tests showing low fuel/oil ratios as best were done with group 1+2 oils (refined petroleum oil).
If you do the same with high viscosity synthetic oils then you have too much viscous friction.
I prefer a semi-synthetic or a mix of castor and synthetic.