2-stroke engines

[pat]

have you checked to see if spark is at plug......done by holding plug onto head by insulated (recomended) pliers and seeing if spark is present when engine is turned over.

[Chris Bacon]

Possible condenser problem? Note, with small high-perormance engines like this, the plug is critical - have you tried a brand-new one? I've seen a few "plug is OK" jobs where there's a problem with same.

[Set Square]

2-stroke engines can often be a pain to start or re-start - even when everything is in order!

Have you checked whether the plug is actually sparking? [Take the plug out and lie it on top of the engine. Re-connect the ignition lead. Make sure that the body of the plug is making good electrical contact with the cylinder head - using a wire with large croc clips on if necessary. Pull the cord, and watch the plug's spark gap. If there is a good spark, the magneto is ok].

[mutley]

Can anyone advise on 2-stroke engines? or is there a newsgroup dedicated to them?

The Q is if the flywheel magneto may function perfectly when cold, but fail when hot. I have a Stihl tool which starts and runs fine, but if it stalls when hot refuses to start again. Fuel is OK, as is spark plug.

-- Any help TIA Please reply to Newsgroup scrambled address

[Michael Mcneil]

And you are using the correct mixture?

I know that lawn mowers go out of timing after hitting roots or stones. Is it possible your chain saw is out of timing? No idea how it might happen though. But that is what it sounds like.

[Bob Eager]

Classic symptom (IME) of a condenser problem.

[the q]

yes the magneto can fail when hot but be working when cold I had this on a seagull outboard it took me age to find it!!

The Q

[Alan]

I'm not convinced it is an electrics problem. If it were then it would most likely stop running once hot.

First the obvious - I trust you aren't putting choke on when restarting it while hot?

Next, check the tuning - should be 1 and 1.

Next, how is the compression?. It is hard to describe what to look for

- you sort of know through experience. When pulling the engine over slowly you should be able to feel the compression resisting the pull. It should be reasonably strong. Try this both hot and cold.

Try that and let us know how you get on. If this doesn't work then are there any other symptoms? Does it idle ok? What is it - a chainsaw? You mention stalling - is this through bad use or does it just stall itself?

Alan.

[Chris Selwyn-Smith]

"Alan" wrote in news:1126626730.822726.93670 @g44g2000cwa.googlegroups.com:

Not neccersarily the solution to your problem but a lot of Stihl machines have a gauze spark arrestor in the exhaust that after a time can clog this will lead to loss of power and stalling

Chris

[Sylvain VAN DER WALDE]

"Chris Selwyn-Smith" wrote in message news:Xns96D2C6AD198A5chrisselwynsmithcouk@158.152.254.254...

And people often take the _crankcase_ compression for granted.

Sylvain.

[T i m]

I had similar (exhaust mesh bunged up) on my BIL's strimmer but that wouldn't 'rev' when cold either?

All the best ..

T i m

[mutley]

Thanks for all the helpful replies from everyone. I can answer some of the suggestions:

It's an 85 hedgecutter and I am leaving choke open when trying to re-start

Compression seems OK in comparison with other 2-stroke machines which I have.

Idling is OK when cold but when hot I have to have the idle screw turned right down to keep it running, but it still stalls by itself. It will only keep running when hot if I keep the throttle almost fully open and the engine running fast.

I'm unsure what you mean by this??

Re. the plug: can someone give the correct plug type and grade for an HS-85? I don't have a user manual for this.

I'll try the other tests suggested and report back! At present I can only work it for about 10/15 minutes at a time, which is frustrating.

regards to all, mutley

[Alan]

The carburettor has 2 tuning screws. These should be tightened (not too tight!) and then slackened 1 turn (ie 360 degrees) to give the correct tuning. If this doesn't work, judging by your symptoms, you can try opening the low speed screw (the one nearest the engine block) a little (1/4 a turn or so)

I don't think it is the gauze in the exhaust (spark arrester) as that would prevent it revving as the previous poser says. A clogged fuel filter would have the same symptoms. Are you sure the fuel is OK? - stale fuel is a common problem with similar symptoms. Have you tried emptying the fuel tank and using freshly bought fuel - run it for a minute or so to clear out any old fuel?

As another poster says, crankcase pressure can cause problems but IME this prevents running completely and is a very rare occurrence.

I don't know which plug this machine takes. I would pop into your local friendly independent garden machinery repair place with the old one and they will give you a new one to match.

I'm not convinced about the plug being the problem either. I think that if the tuning or fuel doesn't sort it then I would have it professionally looked at in your local repair place. My money is on a carburettor problem. Please let me know what the problem is. I am intrigued.

Alan.

[mutley]

Thanks again for the helpful reply.

There is only one on my machine (which I think is a 2001 model) and it's marked 'HL' on a circle.

My much older Stihl 015AV chainsaw has 2 screws as you remark.

Thanks, I'll try that although I thought that I was using recently purchased fuel.

I have noticed that the black ?plastic? flange where the carb. fixes onto the cylinder body has a hairline crack in it - I'm wondering if too much air is getting in, but to me that would seem to show up at bad starting -- it starts easily enough.

regards, Mutley

[Alan]

Hi,

I've not much experience with modern machines but IIRC, you are prevented from changing the tuning by much on these modern carbs so I guess that eliminates that problem.

The hairline crack is interesting - It would be worth popping the carb off and checking it out further as this may affect fuel flow. I would definitely replace it - you will have to anyway, even if that isn't your current problem, and see how you get on with that.

Keep us updated.

Alan.