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2 Stroke engines


Steve
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Anyone know much about 2 stroke engines?

 

Bought a mini moto for a bit of fun. Has been working great but went to use it tonight and it wouldnt rev past half way. Instead just chucked out loads and i mean loads of white smoke!!

This is a air cooled engine so no water is there. Could a piston ring or something be knackered??

 

If it is will just buy a new engine, they are only about £40

 

Thanks

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All I can say is that they are very temperamental with their carb settings. Running lean will burn a hot spot on the piston crown, but sounds to me like yours is running rich [too much oil]. 2 strokes normaly smoke a lot until they are warmed up. Did you get it nice and hot? If you did and it still smoked a lot then maybe it is rich.

 

Is it pre-mix? ie; Do you have to add 2stroke oil to the fuel, or is there a seperate tank to put the 2stroke oil into. If you have to add it to the fuel, you have to be sure you get the correct ratio.

 

Spose there could be ring damage. But this is easy to check on 2 strokes. I was always having the head and barrels of my bikes, and never replaced the gaskets. Not like a 4 stroke where you have large comp ratios, and have to stop oil and water mixing.

 

We all know that with cars you have to warm them up gently before you give them any stick, but 2 strokes if you let them idle from cold they smoke like hell when you start to give them some. If you go to a race meeting and watch the 250's starting up in the pits, they rev the nuts of their bikes until they stop smoking. I think they are then considered "warm"

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Checked the mix (have to add oil to the petrol). The last time i used it it started off as the quickest bike, but as the night went on it was the slowest and smoked the most. The plug is normal, not wet (rich). Is it easy to change the ring?

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Get some kerosene...no kidding... bbq lighter fluid the clear stuff *grin*

 

Yes, it does choke the carb up if you over rich it, but it doesn't half make them shift... or some nitro fuel, the kinda stuff you run in the RC cars....

 

Failing that, speak to SlowDog and he can gas it (yes, yes, he's done it before)

 

Gav

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Checked the mix (have to add oil to the petrol). The last time i used it it started off as the quickest bike, but as the night went on it was the slowest and smoked the most. The plug is normal, not wet (rich). Is it easy to change the ring?

 

Yeah it's easy to change the rings. Sometimes they have a beveled[?] edge. Just prize it/them off gently and have a close look. IF the top or bottom edge is beveled, just make sure you put the new rings on the same way. obviously if you get the barrell off and the rings are knackered, have a close look and see if the barrell is scored.

 

If the piston has two rings and one has broken up and is unaccounted for, you may be lucky and its been spat out of the exhaust port.

 

Thats the good thing with strokers. There's not much to 'em.

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Racing in the British kart championhips (using 100cc 2-strokes revving to 21000 rpm) i have all the bits needed to seal up the bores again. Usually a quick scuff hone and IAME Piston will sort out anysealing issues. Are you using a castor or synthetic oil?? We have always used something like Shell advanced racing M (even in the bikes) or Atol. Some of the cheaper quality stuff gums up rings and oils up the plugs quite badly. Plugs usually a NGK R5883 (flat head plug) is good for the air cooled motors. Is it a Reed valve or Rotary valve engine? again v differrent. Simple engines but very temperamental too....

 

PM and ill talk you through how to check it and set up the carb etc

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I am using synthetic oil (Valvoline), It has a reed valve. I think the fuelling is spot on. I removed the plug after a long use before this problem occured and it wasnt wet or running lean but just right. Just now will not rev past half way.

What fuel mix would you use. Was told and it says in the book to use 25:1 ( 5 litres petrol to 125ml oil).

 

Thanks

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Pulled the head off earlier on, it was caked in oil. gave it a bit of a clean, there was no scoring the rings were fine. Put it back together. It now revs higher but takes a little time to get there. But smokes like a bastard.

 

Took a picture so you can get the idea of how much it smokes

 

By the way made up a new fuel mix incase the old one was wrong. Followed the book 25:1

Photo-0011.jpg

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It just has a single jet which i changed to .68 was a .64 when upgrading the plug and filter. It ran perfect. Till now. Also has a circlip which you move on the needle of the throttle cable.

What does that last bit mean?

 

can you take a pic of that?

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Well its on the end of the throttle cable where it screws into the carb. Have tried different positions but no different. i am thinking that the piston rings are fried. As i was advised that running using 25:1 mix was for running it in only so went to 50:1. It seems to be since changing it has died.

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