2 Stroke engine trouble

Hi guys,

Just found these forums, and am stoked with the range of topics - its going to take me weeks just to look at them all!

Since there is so much experience here, someone may be able to point me in the right direction with my new wipper snipper.

Basically, I just think there is a global conspiracy on the part of 2 stoke engines everywhere that are all just out to get me... I've never met one yet that wanted to play nice. (My 4 stroke mower is a peach - it just goes!)

I always figured it was because all the 2 strokes I'd had anything to do with were well worn and on the way out, so I was looking forward to better performance from a brand new one... I bought a Pope combination snipper / brushcutter (the best they had at Bunnings). I've had it a bit over 12 months, during which time you could count its runing hours on the fingers of one hand.

If it's stone cold, and I persist long enough to get it started, it will run OK for a short while - 10 to 15 minutes perhaps. Then after I've shut it off to pull the line head apart and get the line out because its snapped off again, it wont restart unless I put the choke back on full. Once started with the choke, it dies as soon as I take the choke off - revs really hard like it should then stops. If, rather than pulling the choke all the way off, I just move it away from full on by a little bit, it revs up and sounds promising, but has no power - as soon as the line hits the grass it dies again. Then after 3 or 4 of these cycles, it just wont start at all any more.

I'm electrical and electronic by trade, with a bit of woodworking for a hobby, but motor mechanics is just deep black magic. If anyone can easy my frustration with this machine, it may even save it from being tested as a boat anchor. It got me nearly half way through the edging today before I had to finish everything off with a spade...

...thanks in anticipation

Glen

Glen, something up the shyte with carburettion by the sounds, but maybe check a few other things.

Basics. Check/clean the air filter. Are you using fresh fuel at the correct mix with proper 2 stroke oil (not outboard mix). If in doubt, emply fuel out of unit & replace with fresh mix. Check/clean/gap the spark plug.

Pull the exhaust off & check the state of the exhaust port in the barrel. Doesn't sound like the unit has done much work but worth a look anyway. The port "cokes" up (buildup of carbon that chokes the port) after a while, exacerbated by rich mixes & not being run at 3/4 - full throttle most of the time. Common with domestic units. If port is choked up badly it can cause the engine to run poorly with drop in power. If bad, scrape it out with something sharp being careful not to scratch the side of the piston. If minimal leave it alone.

If all this is OK there sounds to be something wrong with the carburettion - either a blockage or crap floating around in the carby, or the mixture settings are up the shyte.

At this point you're best advised to take it in to a dealer for a look, shouldn't charge you much to tune it up.

If you're a born fiddler and are determined to fix it yourself, read on :p

Crap or a blockage in the carby could be the problem, can be resolved by very carefully dismantling it & cleaning out thoroughly then reassembling, having noted how it was all set up & where all the bits went :D

Otherwise, you may have to have a play around with the fuel mixture settings.

Note: incorrect carburettion can cause the unit to run too lean, ie. too little fuel in the fuel/air mix. This can cause the engine to run too hot & seize - you have been warned. :cool: When making mixture adjustments have the engine warmed up to operating temp & the choke off.

2 stroke carbys have 3 basic adjustments - idle speed, low speed fuel mixture, & high speed fuel mixture. The first one (idle speed) is usually set with a screw that limits how far the throttle returns when released. The latter two are usually adjacent & can usually be IDed by "L" & "H" next to the screws, or sometimes the high speed mixture screw is bigger or more prominent. Screwing a mixture screw clockwise (=in) leans the mixture, out/anticlockwise enrichens it. Little at a time.

The low speed (L) mixture is set first, to allow the unit to idle smoothly, with the idle speed set to let it idle reasonably slowly. Shouldn't need much adjusting here, but if you need to do it from scratch you can gently screw the L mixture screw all the way in, then back it out 1-1.5 turns. Start it up & adjust the L screw in or out, 1/4 turn at a time until you have it running smoothly at low speed. Idle speed shouldn't need adjusting, but do it now if needed. Basically want the engine to be idling OK as slow as reasonably possible.

Now the H high speed mix. When you crack the throttle open the engine then runs on the high speed mixture, and this is most critical as if this is too lean (too little fuel) you can damage the engine. You want the engine when running flat out to be just starting to "4 stroke", ie. you notice a different sound as it is only firing every second cycle. Easier to mimic than explain in writing ! Sort of running "rough".

Once again, fine tuning the existing setting is preferable to starting from scratch, so adjust the H screw in or out 1/4 turn at a time & very briefly rev engine hard to test setting, once again you want it to be just starting to 4 stroke when flat out with no load, ie. not cutting grass. If you have to start from scratch, once again gently screw the H screw right in, then out 1-1.5 turns & start from there.

If the engine runs OK at high speed but hesitates briefly when the throttle is cracked open, back out (richen) the L screw slightly (1/4 turn or so).

When you have it set right, it will start OK, run on choke til it warms up, settle down to a reasonably slow idle, then accelerate to full speed without hesitation, and "4 stroke" slightly at full speed when not under load.

Good luck, & once again, if in doubt take it to a service agent. :)


Cheers................Sean

Quote:

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Originally Posted by scooter

Glen, something up the shyte with carburettion by the sounds, but maybe check a few other things.

Basics. Check/clean the air filter. Are you using fresh fuel at the correct mix with proper 2 stroke oil (not outboard mix). If in doubt, emply fuel out of unit & replace with fresh mix. Check/clean/gap the spark plug.

Pull the exhaust off & check the state of the exhaust port in the barrel. Doesn't sound like the unit has done much work but worth a look anyway. The port "cokes" up (buildup of carbon that chokes the port) after a while, exacerbated by rich mixes & not being run at 3/4 - full throttle most of the time. Common with domestic units. If port is choked up badly it can cause the engine to run poorly with drop in power. If bad, scrape it out with something sharp being careful not to scratch the side of the piston. If minimal leave it alone.

If all this is OK there sounds to be something wrong with the carburettion - either a blockage or crap floating around in the carby, or the mixture settings are up the shyte.

At this point you're best advised to take it in to a dealer for a look, shouldn't charge you much to tune it up.

If you're a born fiddler and are determined to fix it yourself, read on :p

Crap or a blockage in the carby could be the problem, can be resolved by very carefully dismantling it & cleaning out thoroughly then reassembling, having noted how it was all set up & where all the bits went :D

Otherwise, you may have to have a play around with the fuel mixture settings.

Note: incorrect carburettion can cause the unit to run too lean, ie. too little fuel in the fuel/air mix. This can cause the engine to run too hot & seize - you have been warned. :cool: When making mixture adjustments have the engine warmed up to operating temp & the choke off.

2 stroke carbys have 3 basic adjustments - idle speed, low speed fuel mixture, & high speed fuel mixture. The first one (idle speed) is usually set with a screw that limits how far the throttle returns when released. The latter two are usually adjacent & can usually be IDed by "L" & "H" next to the screws, or sometimes the high speed mixture screw is bigger or more prominent. Screwing a mixture screw clockwise (=in) leans the mixture, out/anticlockwise enrichens it. Little at a time.

The low speed (L) mixture is set first, to allow the unit to idle smoothly, with the idle speed set to let it idle reasonably slowly. Shouldn't need much adjusting here, but if you need to do it from scratch you can gently screw the L mixture screw all the way in, then back it out 1-1.5 turns. Start it up & adjust the L screw in or out, 1/4 turn at a time until you have it running smoothly at low speed. Idle speed shouldn't need adjusting, but do it now if needed. Basically want the engine to be idling OK as slow as reasonably possible.

Now the H high speed mix. When you crack the throttle open the engine then runs on the high speed mixture, and this is most critical as if this is too lean (too little fuel) you can damage the engine. You want the engine when running flat out to be just starting to "4 stroke", ie. you notice a different sound as it is only firing every second cycle. Easier to mimic than explain in writing ! Sort of running "rough".

Once again, fine tuning the existing setting is preferable to starting from scratch, so adjust the H screw in or out 1/4 turn at a time & very briefly rev engine hard to test setting, once again you want it to be just starting to 4 stroke when flat out with no load, ie. not cutting grass. If you have to start from scratch, once again gently screw the H screw right in, then out 1-1.5 turns & start from there.

If the engine runs OK at high speed but hesitates briefly when the throttle is cracked open, back out (richen) the L screw slightly (1/4 turn or so).

When you have it set right, it will start OK, run on choke til it warms up, settle down to a reasonably slow idle, then accelerate to full speed without hesitation, and "4 stroke" slightly at full speed when not under load.

Good luck, & once again, if in doubt take it to a service agent. :)


Cheers................Sean

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what he said! :D

Quote:

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Originally Posted by scooter

Glen, something up the shyte with carburettion by the sounds, but maybe check a few other things.
...

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Wow, thanks for the detailed info....

Might take a while till I can sift through all the options, but I'll get back and let you know what happened when I get a chance to have another go at it

Thanks,

Glen

in the past I have poured petrol down the cylendar and pulled the zip start very slowly a few times. this cleans it. replace air filter and sparkplug.

G'day Glen,
Possibly you have blocked jets and / or the emulsion tube ( if it has one ) is blocked. The blockage is probably caused by the fuel / oil mixture evaporating over a period of time when the machine is not in use. the petrol vaporises, leaving the addatives and oil behind. This then dries out, leaving a gell or varnish residue in the orifices of the jets & emulsion tube which blocks or severely restricts the fuel flow. When you get the engine to run, it initially runs on the small amount of fuel that has seeped through the jet drilling. Once this fuel is burned, the ongine starves & strangles itself. You need to dismantle the carby and thoroughly clean all jets, drillings and fuel metering orifices etc in clean petrol and blow out with compressed air.
Check for blocked jets etc by holding them up to a light, you should be able to see through the bores very clearly. If not they must be cleaned out as per above. DON'T try cleaning the jets with fine drills or wire etc, you can destroy the flow characteristics of the jets & bugger up the mixture settings.
Hope that this sheds a bit of light on your dilemma Glen.
Regards,
Barry.

Yep what Scooter said. I also hate 2 strokes they always gum up.
Once you get it going again....when you go to stop the motor turn off the fuel switch and let it run till it dies. That way the jets dont have fuel left in them and will prolong your usage between dummy spits.