strimmer motor won't start...

[The Natural Philosopher]

Its an oldy, but apperas to have bags of compression. Simply was in use, left up for a winter a couple of years ago, never started since.

Its a ltllet 2-0stroke japanese engine - probably about 25cc or so and I can;t see any spark - the pllug smells of petrol and we even dribbled some mix into teh p[lug hole, to no avail.

I whipped off the pull handle and discovered something I hadn't seen since me dads moped curca 1960. A magneto and some contacts. I adjusted the gap so it was at least closed some of the time and open some of the time, but still no visible sparks. I removed the wire off the switch that stops the thing in case this was faulty, and still no sparks.

First of all, is there some way I can identify that there really are no sparks? I stuck a car strobe light in series with the plug, but I think this runs off the LT side of the car not the HT...so probably proves nothing.

Its been years since I fiddled with a magneto, but ISTR that if there is fuel and a spark these things generally kick a bit and fire if not run. This ones doing neither.

Is it down to thimgs like stripping out the points and claening them up?

Is there anyway I can use an analogue multimeter to diagnose the problem?

[Mungo "two sheds" Toadfoot]

You *can* hold the end of the HT lead while someone gives it a tug. It's not particularly nice but it won't kill you unless you have a pacemaker or a weak heart.

The contacts should be clean and as you say they should open and close. They should open about 25 thou-ish. Is there a small cylinder anywhere with a lead coming out of it? If so you might need to replace it.

Si

[mrcheerful]

Make sure that the points actually electrically close.

mrcheerful

[Grunff]

A wire-end neon across the HT will tell you a lot. If it doesn't even flicker, then you've got nothing there.

[Pete C]

Try putting the meter on resistance range and attaching it across the points, it should read some low ish resistance when the points are open, and a short circuit when the points are closed.

Also measure the resistance between the plug lead/coil HT output and the cylinder head of the strimmer, it should read a higher resistance but not an open circuit.

Then measure the resistance between the electrode of the spark plug and the cylinder head of the strimmer, this should be an open circuit.

Next set the meter to DC volts and connect it across the points, turn the engine over slowly and you should see the needle kick slightly as the engine turns over.

Now take a neon screwdriver and put it on the HT output from the coil while turning the engine over and holding the end of the screwdriver, it should flash as the engine is turned. Repeat this with the end of the HT lead.

Now take the plug out and use a straw or thin stick in the plug hole to identify when the piston is at 'top dead centre', by rotating the engine slowly and feeling when the stick is pushed out the most. Or there may be some alignment marks somewhere on the shaft and body of the strimmer that indicate this.

Then adjust the points until they are only just open, using the meter to check for this.

Now adjust the gap on the spark plug so it's not too wide. Put the spark plug on the lead, hold the body of the plug onto the cylinder head and turn the engine over. With a bit of luck it should spark.

The only other thing on the electical side would be to check the gap on the spark plug is the right width, or the spark may not be strong enough. This might be printed or stamped on the body of the strimmer or maybe a suitable value can be got off the web.

Hope this helps, Pete.

[Ian Stirling]

It'd be a really shitty way to discover you do have a bad heart though.

[The Natural Philosopher]

Enormously Pete, thats a good suite of sensible things to try.

Thanks very much indeed.

[T i m]

LOL .. thanks Ian ;-)

T i m

(memories of my Dad doing that to me on an outboard motor .. I jumped!)

[Nick Brooks]

I've got an old petrol strimmer that refuses to start every year despite having no obvious faults. A quick spray of "Easy Start" onto the air filter usually sorts it out and once it's going it's fine.

Nick Brooks

[Jim White]

One thing that seems to be more important now than it used to is the freshness of the petrol. I drain all my garden tools every year and refill with fresh petrol /

2stroke. Once you get your electrical probs sorted out, the strimmer still might not start with 2 year old fuel.

Jim

[Eric Dockum]

I still have a cheap timing light that plugged in series between the distributor and the spark plug, basically a neon as others have discussed. Only the fancier ones have a sensor on the LT side.

Also a cheap tool that is essentially a neon bulb. You hold one end, and, I assume, make a leakage path for one side of the neon. Have the plug in the engine and the lead hooked up. As someone tries to start you approach the lead with the other end of the tool. As you do so the neon flickers if there is a spark power in the lead. Don't have to touch the spark lead for it to detect. These used to be dirt cheap in auto shops, I have one in the tool box. You can find which cylinder is missing on a car engine while it is running without having to interfere with the system. This tells you if there is a spark getting to the lead. However the plug itself may not be good.

Take the plug out and attach to the HT lead. Then lay the plug so the metal body of the plug is in contact with the metal of the engine. then try it, and the spark should jump. the return for the spark is through the body of the plug, and the body of the enginge. I have also used an old wooden pair of tongs my mum used with a top loader wasking machine to hold the plug firm against the engine.

If you get nice ble zaps you are fine on that side. The fuel quality is a good idea, also check nothing has dropped off/come loose that is giving you and air leak on the inlet side, resulting in too weak a mixture.

Finally check you have no dead lemmings etc up the exhaust. I bought a 2 stroke bike years ago that someone sold because there was something wrong with it. Performed terribly, kept stalling, was impossible to start etc. There was a perforated pipe up the middle of the exhaust that was completely plugged with coked oil. I had to get a blowtorch and chisels to get the stuff off and make it pass gas again. Put it back on the bike and the performance was transformed.

2 strokes are very sensitive to the exhaust.

eric

[Mungo "two sheds" Toadfoot]

[Ian Stirling]

Is there any reason to use starting fluid/cans, rather than a blowtorch pointed into the air intake? (An unlit blowtorch, for the avoidance of doubt)

[sylva]

EEzi start type fluids have a fuel in them that will ignite at low temperature, like ether, so that even if the spark is a bit lacking in energy the compression can set it away. However because of this very low spontaneous ignition temperature they "explode" in the cylinder, this can result in damage to the ring lands. Repeated use, typically on a diesel engine, "addicts" the engine to starting with them as the damage to the compression rings means they will never start from cold unassisted. With SI engines it is similar to forcing the engine to pink.

Blow torch would typically be propane or butane, these fuels have high spontaneous ignition temperatures couples with a fairly limited range of air:fuel ratio under which they will burn. At least with a liquid fuel there is normally some point in the phase between gas and liquid where the ratio is OK to start burning.

AJH

[The Natural Philosopher]

Yes, its made of plastic :-)

Oh. Best way to start old diesel tractors is to pur fresh diesl in on the glo plug and let it burn....

>

[Grimly Curmudgeon]

It was somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember The Natural Philosopher saying something like:

An old diesel Landy I had the unfortunate privilege of using occasionally would only start with a burning diesel-soaked rag held next to the air intake. Crude but effective.