Why do some 2 strokes do this?

[350RRC]

Hi chaps,

I'd like you all to put on your hard hats to focus concentration, your goggles to see the problem clearly and your earmuffs and gloves because this a chainsaw question, but does apply to some other 2 stroke toys I have.

Said (cheapy) chainsaw has done a lot of work, gets used on small stuff so I don't wear out the much larger Stihl cutting stuff smaller than 12".

Starts from cold in 3 pulls, won't stall, will do whatever until the tank runs dry.

If it is refilled and pull started immediately it might start. If I leave it for 5 mins it will not restart until stone cold........ 1.5 hrs plus.

Have had other 2 stroke stuff do this in the past.

TIA, DL

[Slunnie]

Sounds like a flooding issue.

[Saitch]

Don't run it dry?

[350RRC]

Sounds like a flooding issue.

Not flooded, can sometimes get it going after 30 mins using the choke.

Was told 45 years ago that the wrong heat range plug was the reason for the same prob.

(had a Pope lawn mower engined chopper mini bike back then that did the same thing).

cheers, DL

[Slunnie]

Not flooded, can sometimes get it going after 30 mins using the choke.

Was told 45 years ago that the wrong heat range plug was the reason for the same prob.

(had a Pope lawn mower engined chopper mini bike back then that did the same thing).

cheers, DL
Ahhh,

Have you done a strip on the carby. The other thing that may be happening, depending on the type of carby is:
Check the diaphram for stretching which may prevent pumping if it goes dry
If it has a needle and lever, also check these for wear to make sure that you've got flow and its not leaking.

Likewise its probably worth clearing the mixture jets out too and checking any flap valves for deformation

For the plugs, my experiences are that once they have fouled they will always be problematic even after cleaning. Its worth running a slightly hotter plug if you get fouling. Incorrect fuel mixtures will also do this, particularly on the low speed jet.

[350RRC]

Thanks Slunnie.

My sister bought the exact same saw on my recommendation and has the same problem, which is exactly the same as what the Pope lawnmower motor had all those years ago............ before diaphragm carbs were really in wide use.

DL

[Slunnie]

Thanks Slunnie.

My sister bought the exact same saw on my recommendation and has the same problem, which is exactly the same as what the Pope lawnmower motor had all those years ago............ before diaphragm carbs were really in wide use.

DL
Oh, is your a diaphram carby?

[350RRC]

Well I assume so, same sort of carb as the Stihl has and all the various modified whipper snippers I have.

Can't be a flooding prob because it can be totally run out of fuel........ if cold fill it up, pump the bulb till fuel is obviously flowing back to the tank, choke on, it fires, choke off, will start and idle fine after no more than 2 pulls.

If warm and the above is repeated, forget it.

cheers, DL

[Slunnie]

That is weird. I normally try to start without priming after refilling firstly and then choke and then prime until it kicks. Stihl is usually pretty easy to start. Always with WOT. Mate, I'm not sure.

It might be worth checking spark too - not near the plug hole in case you ignite.

[350RRC]

I'm only asking this question after talking to a fair few people who ain't stoopid and they've had the same issue........ with outboard motors, mowers, etc, etc.

All 2 stroke and no one seems to know why.

cheers, DL

[V8Ian]

Because they're two strokes short of reliable.

[350RRC]

I do have a video of a 1974 Evinrude outboard motor, been serviced twice in its life, starting on the second pull after sitting in a shed for 12 years.

Nothing wrong with 2 strokes if one is not of the greeny vegan persuasion.

Also once bought a Seagull outboard that was seized on the main bearings........ bit of lube and mechanical persuasion to free it up and it runs fine, even pumps water.

DL

[Blknight.aus]

sticking valve in the pulse pump diaphragm and its vapor locking.

in theory you should be able to get it to restart by operating the primer before you start it you may need to give the primer bulb a push (on the engines that have them) while you pull the cord over then give it a hit to start it.

[Hay Ewe]

I think it could be something to do with the whole engine assy being hot and the fuel part of the mixture is evaporating / changing mixture, before it gets to the combustion chamber

there isn't the fuel in the mixture to get a burn and start the process

[cafe latte]

I think it could be something to do with the whole engine assy being hot and the fuel part of the mixture is evaporating / changing mixture, before it gets to the combustion chamber

there isn't the fuel in the mixture to get a burn and start the process

This is possible as air cooled engines get very hot when they stop especially 2 strokes so after 10 minutes stopped it is probably very hot indeed, too hot to run.
Chris

[incisor]

I used to work for mob called air cooled engines and if I recall correctly the old fella always told clients that it was a sign the mixture was carrying too much oil... I personally don't know enough to argue that point...

[Don 130]

I can't explain why it happens, but it's happened to me often, and most often with my small Dolmar saw. The remedy for me is to be aware of the tank level and cut the engine instantly at the first sign it's going to run out. For me, that's a slight rise in engine speed as the fuel line empties and it begins to suck air. For it to work every time you have to be very quick.
Don.

[BMKal]

My (Stihl) chainsaw will do the same thing - can be very difficult to start if I let it run out of fuel.

But the issue is not restricted to 2 stroke engines. My lawnmower will do exactly the same thing - and it's a 4 stroke Kubota. :o

Not very often that I have let the mower run out of juice, but when I do - it's always a good excuse to have a beer ................... https://www.aulro.com/afvb/images/imported/2016/04/272.jpg

[jx2mad]

I have a 5 hp 4stroke mulcher that does the same. Starts first or second pull when cold. If you have to shut it down it won't start till it is cold. Otherwise will run all day if needed. Jim

[carlschmid2002]

My Husqvarna 300 dirt bike does the same thing. I turn the fuel off, lay it down so excess fuel runs out. Stand it up, turn fuel on and it starts straight away. I pushed it for miles on my first ride. Not much fun in Townsville in February with all the gear on. I do run it at 40 to 1 and recommended is 50 to 1. All the new ones have electric start. I got mine for a bargain though.

[350RRC]

So this is a reasonably common problem.

The old Pope engined mini bike I had a loooooong time ago would often restart if I just changed the plug.

It had a slide / needle carb.

DL

[Hay Ewe]

I have thought about this some more.

When the item is running either two things are occuring to keep it running.

1) the airflow of the incoming mixture keeps it cool, and due to the revs the item is running at, despite being a small engine, there is enough mass airflow.
As the mixture is 'wet', that is why it is cool - lick your finger, stick it in the wind flow - it feels cool.

2) If the mixture is getting too warm, then it may be detonating a little earlier than intended, but at the high RPM the item is running, probably not noticable.
Then when the item stops running, the user cannot get it to turn over fast enough for the mixture to detonate at the same time as the spark.

As for the post with the Husqvaran motorbike, maybe laying it on it side, cools something enough to make the change - or something else

[Hall]

I have the ultimate cheapy chainsaw of Evilbay. No brand name other than chain saw on the box it came in. Was starting well enough, then the issues started. Was the plug. It was a Chinese brand. The local lawn mower bloke said they where garbage. As the cheap plugs age, they when hot stop sparking as the metal tongue opens enough to stop sparking. Poor quality metal being used. Put a brand name plug in ( think it was champion ) no problems since. So if you have not replaced the plug since you have brought it have a look at replacing it with a decent plug.
Cheers Hall

[scarry]

Have an eight HP 4 stroke mulcher,same thing,damm hard to start if it runs out of fuel,and is hot.
I have tried all kinds of sequencing,choke on or off,throttle half on,full on,prime different amounts,etc,etc.
It is bloody hard work trying to get it to go,as it is a big engine.

When stone cold will usually go second try,sometimes even the first,no worries at all.

My Echo two stroke leaf blower is the same,takes for ever to start if hot,and a PITA.Cold,goes first go.

The Honda 4 stroke mower is great,starts first go hot or cold:)

Maybe these engines are tuned to start when cold but not hot,or as Dave says,get a vapour lock.

[TasD90]

Same thing with my lawnmower. Cut the back lawn no problems, stop the mower , go to the front lawn, wont start.
Looked it up on Google some time ago and its caused by a vacuum or airlock generated somewhere(carby, cylinder ?) and wont let the engine fire.
Wait until both the mower and my frustration have cooled down then away we go.
Not sure what the solution is.
Peter.

[V8Ian]

Many moon ago, a mate of mine renowned for his lack of patience and short temper, bought a new Victor mower. He brought it home and immediately mowed the front yard. It was turned off to push under the house to mow the back yard, where it failed to proceed. :o
After many failed attempts to restart it, he phoned the mower shop, from where he had purchased said devil. :twisted:
The shop owner asked him if he had turned it on its side, to which my mate replied "I threw the jolly thing (or words to that effect) against the fence, would that make a difference?"
The mechanic was there within the hour to tune it.
The only reason he threw it against the fence was because the fence was 6' high, the intention was for it to go over. :D

[350RRC]

........... Put a brand name plug in ( think it was champion ) no problems since. .....................
Cheers Hall

Haven't been champs for quite a while. NGK or Bosch and you're on the money.

DL

[superquag]

... because all two-stroke engines share a common ancestor...






Satan.:twisted:

[Hall]

Haven't been champs for quite a while. NGK or Bosch and you're on the money.
Ah just showing my age I guess. New it was a name brand and it did the business.
Cheers Hall

[carlschmid2002]

... because all two-stroke engines share a common ancestor...






Satan.:twisted:

But when you are in the power band on a two stroke dirt bike. Life is sweet.

[350RRC]

But when you are in the power band on a two stroke dirt bike. Life is sweet.

And when you hit the power band on the old Mach III life got very interesting, very fast.

DL

[strangy]

I've got nothing of any value to ad, but my sthil chainsaw, brush cutter and the victa mower all have no probs starting hot and always run dry before refueling.
I must be lucky?

[Blknight.aus]

... because all two-stroke engines share a common ancestor...






Satan.:twisted:

not so...

when youve got a detroit screamer between the rails with the charger cam conversion and a pair of turbos hanging off the exhausts feeding the root and its just hanging onto 1200rpm sounding like its doing 2400 and that needles just not falling back the stacks not smoking and youve still got pedal to go.

you would swear you could hear the angels singing.

(in reality its early onset of industrial tinnitus)

[ramblingboy42]

what are you driving here Dave? an autocar?

[Aaron IIA]

not so...

when youve got a detroit screamer between the rails with the charger cam conversion and a pair of turbos hanging off the exhausts feeding the root and its just hanging onto 1200rpm sounding like its doing 2400 and that needles just not falling back the stacks not smoking and youve still got pedal to go.

you would swear you could hear the angels singing.

(in reality its early onset of industrial tinnitus)

A Screaming Jimmy. Music for the ears.

Aaron

[Tote]

If you wear headphones you can almost feel the industrial deafness coming on.....

https://youtu.be/890H6pzBbC8

Regards,
Tote

[Blknight.aus]

I forgot how good they sounded on the jake...

[V8Ian]

Green leaders, bird scarers, call them what you like, they sound a heap better than they go.