2 stroke problems

Jimmy, I run a two stoke engine and after wintering I have a similar problem, leave the carb to soak in petrol for a few days to soften the oil residue. Washing the oil off of the innards wont hurt as long as you feed it with twostoke mixed fuel to replace it immediately.

Martin P

When you try to start it, does the plug get wet?

My standard answer is "Go thou out and buy a new plug". From forty years of experience with two strokes ancient and modern, this will cure your problem much of the time. It is also cheap, easy to do and doesn't damage anything else!

Just because you get a spark outside the cylinder, it does not mean you are getting one under compression.

Regards,

Kim Siddorn,

"Jimmy Gibson wrote >

And chuck away last years petrol too steve the grease

Thanks for the hints and info.

In reply to Kim, the spark plug is bone dry and it does splutter when I pour a little petrol in the air intake.

In reply to RL driver, I stored it with a dry petrol tank and I'm using fresh mix.

Coincidenlty this is the first time I've stored it with a dry tank and had this problem. I usually just leave whatever petrol is left in the tank and it starts first time the next spring.

I'll try giving it a soak in a bath of petrol tonight and maybe treat it to a new spark plug - it is 14 year old after all!

Thanks again

Jimmy

If it has a diaphragm carb then you are probably getting problems with the pump on the carb itself. It is usually operated by crankcase pressure pulses and if it dries out you could have problems with the inlet/outlet valves leaking.

Peter

-- Peter & Rita Forbes snipped-for-privacy@easynet.co.uk Engine pages for preservation info:

It is a diaphragm carb, at least there is one in what I'm refering to as the equiv of a float chamber, this has a small metal disc in the centre with a nipple which looks as if it operates a spring loaded lever which in turn operates what looks like a float chamber needle.

There is a thin semi transparent sheet on the other side of the carb which has 2 semi circular flaps. Presumably these are what operate the inlet/outlet valves which you refer to. This didn't look as if it had dried out or warped at all, and the 'float chamber' side does fill with petrol though this could be due to me priming it and not 'normal' pumping action.

I'll strip it again tonight and check the flaps and what they operate against for signs of blockage and damage and also give it a soak in petrol.

Thanks again

Jimmy

There is a very simple possibility that has happened to me. If the machine was left dry then the wick/filter thingy that sits in the fuel tank will have dried out completely apart from the now fairly gummy oil. It can take a day or two for full flow to re-establish. Seems to be much worse in old machines where the 'filter' has collected a good load of crap over the years. ttfn Roland

Yes the diaphragm acts as the float, as it distends it pushes a forked lever that shuts the valve needle, these needles often have a soft rubber point. You need to be wary of bending the fork.

These are the flap valves, between them there should be a circular area which is a diaphragm pump, it is connected to the crankcase and uses changes in pressure to pump fuel to the bottom chamber. Somewhere before this in the sequence of passages there should be a small secondary filter, check it is not clogged. If you blow through the petrol inlet you should feel the chamber filling, with both mixture screws gently screwed home there should be no leakage (although I note some modern tillotson and wambro carbs have a main jet bypass to prevent over weakening the mixture).

AJH

I would definitely check the diaphragm for hardening as this has happened to a number of the Weed Eaters that I have owned if left for a long enough time.

If it is not very flexible then that is probably your problem, no choice then but to change it with a new one.

Best regards,

Chris Kessell

Thanks for the info. The diaphragm is still flexible and looks OK, but I'll bear that in mind for the future.

I'd left the carb soaking in petrol for almost 48 hours as I couldn't work on it on Wednesday night. I put it back together last night and got more signs of life, but not much. I took my courage in both hands and removed the mixture screws, after screwing them in and counting the turns till they stopped so I could set then back to where they started. I hate fiddling with mixture screws on somthing I know is/was perfectly OK. The ends had a slight coating of rust on them, which explains the brown patches I'd wiped from the inside of the carb at the weekend. So I cleaned them of an gave a good squirt of carb cleaner down the holes and put it all back together again.

This resulted in me getting a longer splutter of life. I richend the mixture as I could only get a splutter with the choke fully closed, I gradually got longer and longer splutters until it would run continuously with choke fully open and half throttle but cuts out when I open it up fully. I've had both mixture screws fully out and only the one marked L makes any difference the one marked H has no effect at all.

I'm presumming the L screw is for adjusting low rev/load mixture and the H is for high rev/load mixture. I think the jet controled by the H screw is still blocked so I've stripped it fully including mixture screws and dunked it in the petrol bath for another soak.

Hopefully this will do the trick. If not I'm thinking about trying to push a bristle from an old tooth brush or scrubbing brush through the jet holes to push out whatever is blocking them.

After this experience it's the last time I'm storing it dry over winter.

I've got a petrol hedge trimmer to wake from winter hibernation and I hope I haven't got the sme problems with that.

Thanks for all your help, at least I've a better understanding at how these tiny carbs work now.

Jimmy

Definately sounds like you have the HS needle / jet still blocked, as this is restricting fuel flow through the LS needle. - The HS jet acts as an air bleed for the LS at low speeds.

Tim..

Begins to sound like fuel starvation, there is simply not enough fuel getting through for the highspeed jet to have any influence. Could be caused by poor pumping but more likely the fuel filter in the tank has failed. When the choke is closed the additional depression is sucking fuel from the tank rather than the fuel being pumped. Have you blown from the fuel feed back into the tank? It should bubble away and the over pressure on release push a squirt of fuel out before the pressure compensation for the tank has an effect.

Because they use crankcase pressure fluctuations to pump bore wear can affect pumping, but this is normally characterised by inability to maintain a steady slow tickover and high power use is not changed, other than lack of power.

L is a tickover mixture adjustment, H is the high power adjustment but it is not compensated like a normal carb, in essence the device is for ON/OFF operation, at full throttle with no load the mixture should go over rich and just four stroke, this rev limits the device.

AJH

I'll give this a try tonight, but I dont think the fuel filter is blocked as it primes up OK when I use the priming nipple - but you never know it could just be on the limit.

It worked perfectly last year on both tickover and full load before being bedded down for the winter so I don't think it can be bore wear.

Thanks for this info - I'm learning more and more of how these work all the time.

Jimmy