small 2 stroke engines

[cnelsonplumber]

Hi

I am having major grief with my 2 stroke chain saw which won't start and wondered if there were any motorcycle enthusiasts or peeps with a greater knowledge than me.

It broke down a few weeks ago so i changed the spark plug after having the thing into lots of bits as the magneto was shorting out which was probably why I had no spark.

Worked fine for a couple of weeks but it's on the blink again and the spark is good.

I have removed air and fuel filters as i'm guessing a fuel problem now - no result. The spark plug isn't wet when I try and start with choke but the priming pump is circulating throug carb. ok.

Have blown the jet through which is clear and now i have run out of ideas.

Any suggestions gratefully received

Chris

 

[unclepumble]

How long have you had the petrol in it?

Unleaded jellyfies after a bit and blocks everything up.

Failing that the crankseals could be shot.

UP

 

[cnelsonplumber]

ok thanks will try new mix as the old one could be last years

 

[Steve k]

You say plug doesn't get wet?

Try taking the plug out and putting your little finger in the hole (not to far), then crank it over a few times. Is there any petrol on it? Does it try to pull your finger in? Is there a sound of air escaping/leaking?

If all is ok. (petrol on your finger, piston tries to suck your whole hand in & no WHOOOOOOOSHing noises) what colour is the spark. You don't want a big white one, if that is what you have re-gap the plug to about the thickness of a *** packet and aim for a tight little blue spark.

Is it trying to start or totally dead?

Steve

 

[battwave]

Thirty years of playing with 2-strokes, but I've just learnt a new trick from Steve K there! Thanks Steve.

 

[Steve k]

What stink wheels have you been playing with Battwave?

At the moment I have a 350LC project on the go, an RG500 Gamma and an NS400R.......and hoping to secure a KH400 Triple soon, he just needs a bit more persuading to part with it. :pray:

:

Steve

 

[battwave]

....and I've not heard the term "stinkwheel" for a lot of years.

Haven't had a 2-stroke bike for 25 years. My last was a GT185, and I've always regretted its passing.

Been on 4-strokes since. A 550-4-K until a couple of years ago and a Pegaso now.

Current problem is trying to post photos on a posting here. Posted them on "Image Hosting", but can't get to grips with the Img button above; just posts a question-mark, rather than an image!

 

[Thornyhill]

test the spark first. Two ways to do this. Ideally take the plug out, earth it and crank the engine. If you get any spark, the problem is more than likely fuel supply. If you get no spark...... it isn't fuel. A white spark will make it run lumpy, but shouldn't stop it from firing


It can be tricky to see a spark on sunny days. If you aren't sure, stick you finger inside the end of the lead and crank the engine. You will know if it is working....

 

[unclepumble]

test the spark first. Two ways to do this. Ideally take the plug out, earth it and crank the engine. If you get any spark, the problem is more than likely fuel supply. If you get no spark...... it isn't fuel. A white spark will make it run lumpy, but shouldn't stop it from firing


It can be tricky to see a spark on sunny days. If you aren't sure, stick you finger inside the end of the lead and crank the engine. You will know if it is working....

This made me chuckle I ran a breakers for a mate for a couple of years and the mechanic used to test for spark using One of the young lads, he used to pull the plug cap out and make the young lad shove his finger up the plug gap then turn the engine over, if he yelped there was juice to the plug. :shock:

Up

 

[snail59]

It can be tricky to see a spark on sunny days. If you aren't sure, stick you finger inside the end of the lead and crank the engine. You will know if it is working....

ROFPMSL. Pure Class.

 

[BarnsleyBrewer]

This made me chuckle I ran a breakers for a mate for a couple of years and the mechanic used to test for spark using One of the young lads, he used to pull the plug cap out and make the young lad shove his finger up the plug gap then turn the engine over, if he yelped there was juice to the plug. :shock:

Up

My mates brother did that to me when I was about 10, He said "Do us a favour young'n an hold this for mi while I turn her over".. *******!!! :twisted: :twisted:

 

[cnelsonplumber]

I found the problem I think. The magneto was touching the flywheel as the 2 allen screws had come loose. I thave guessed the gap as two paper thicknesses and it fires now but is difficult to start and lumpy. Would any one like to have an estimated guess at the correct gap? It's a Mac 338.

 

[TheMumbler]

....Current problem is trying to post photos on a posting here. Posted them on "Image Hosting", but can't get to grips with the Img button above; just posts a question-mark, rather than an image!

I posted a how to for flickr here

there is a link to the stickied forum how to in that post

afraid I'm of absolutely no use to the OP though

 

[Thornyhill]

I found the problem I think. The magneto was touching the flywheel as the 2 allen screws had come loose. I thave guessed the gap as two paper thicknesses and it fires now but is difficult to start and lumpy. Would any one like to have an estimated guess at the correct gap? It's a Mac 338.

I have a MAC chainsaw. Not sure of the model, but the plug is a Champion RCJ7Y. According to the specs, the gap should be 0.51mm

 

[cnelsonplumber]

I have reset the plug gap and cleaned it. It now runs, well at least starts but doesn't idle very well. I have adjusted the idle to fast lumpy instead of slow lumpy then cut out but it still doesn't seem right.

There are two other adjustment screws next to the idle but I have never touched these as i'm not sure what they do.

The spark plug is new but i'm not sure if I would say the spark is blue maybe light purple.

Think the solution may be close

 

[Steve k]

There are two other adjustment screws next to the idle but I have never touched these as i'm not sure what they do.

One of them should be the mixture screw for the pilot jet circuit.

You need to identify which one and adjust it a 1/4 turn at a time until the tick over smooths out, then turn the speed down again.
Usually, but not always, clockwise lets more air in to the circuit and the running should smooth out. Expriment and see what happens.
Don't forget to make a note of what screw you have turned and by how much, so that you can reset it and try the other one.

Are you sure that the air filter is clean and dry?

Cheers

Steve

 

[cnelsonplumber]

The air filter seems ok as it doesn't seem to make any difference if it is removed.

I have a day off next weekend so will dabble about with the settings

Thanks

Chris

 

[Steve k]

it doesn't seem to make any difference if it is removed.

Here could be your problem, it should run lean(er) and worse with no air filter. Have a good check around the air box for possible air leaks, especially where it connects to the carburettor.

Steve

 

[cnelsonplumber]

I can't see anything obvious the only gasket seems good. The air filter is only a flimsy piece of sponge so i'm not over surprised that it doesn't make much if any difference.

This little engine is taking over my life as I don't deal with being beaten too well! It now starts ok but not as well as it used to and runs well at full throttle even under load. The problem is getting the revs to climb without it cutting out. If I was still tinkering about with bikes and cars I would say it was a problem with the timing but i'm pretty sure it is fixed by virtue of the position of the magneto relative to the flywheel............. unless the gap between the two is critical.

Thanks for your continued interest

 

[Thornyhill]

The problem is getting the revs to climb without it cutting out.

Maybe you have a couple of problems. This suggests it it running too rich, but running with no air filter should negate that.. If running with no air filter makes no difference, it does sound like you have a major intake leak somewhere after the filter, but even if that were the case, it wouldn't cut out when you hit the throttle.

(The minuscule piece of sponge slows down air intake enough to allow more petrol to flow, balancing the mixture, so it should make a difference.)

Is your fuel fresh and freshly mixed, and did you use two stroke oil?