Two stroke engine starting (yet again!)

My chainsaw always used to be very easy to start... turn it over with a couple of pulls, then ignition on, choke out, throttle in starting position and off it would go first or second pull.
Now I had it serviced last year, and it was "ok" after that, but not quite as easy to start. Went to use it this year, and could not get a peep out of it. Gave up, and tried a few days later with some starter spray. That eventually got it going. The next time, could not start it even with that.
Its got a good string spark. The plug seems to be getting wet and is not fouled. Fuel line is clear as is the air filter. Tried a fresher petrol mix (super unleaded - from my large can - so probably 8 months old, but everything else seems to run fine on it)
So what else am I missing?
Parts diagram:
http://www.ereplacementparts.com/makita-dcs430-43cc-chainsaw-parts-c-97_98_245_10188.html
--
Cheers,

John.

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http://www.ereplacementparts.com/makita-dcs430-43cc-chainsaw-parts-c-97_98_245_10188.html
Two strokes are just like that. ;-). Alternatively, is it possible that the flywheel/magneto has slipped on the crankshaft throwing the ignition timing out?
Tim
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On 15/03/2012 22:56, Tim wrote:

Don't know - I suppose it should be possible to see easily enough... when is the spark supposed to be, just after the piston passes TDC?
Once started the other day it did run ok, although I am not sure it had quite the power it should have had.
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Cheers,

John.

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On Thu, 15 Mar 2012 23:19:53 +0000, John Rumm wrote:

4 strokes just before, it takes a finite amount of time for the mixture to ignite and you want the peak of the bang to be just fract after TDC. This why the spark is advanced as the revs go up on larger 4 stroke engines. Donno if small two strokes have advance, I should imagine they do.

Mixture not quite right? two strokes are quite fussy about mixture.
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Cheers
Dave.




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Only two stroke I had was a Vespa years ago and it had rather high advance in four stroke terms - IIRC, about 30 degrees. No auto advance mechanism.
If the plug is wet, it's either not firing properly or the mixture is too rich.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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John Rumm wrote:

http://www.ereplacementparts.com/makita-dcs430-43cc-chainsaw-parts-c-97_98_245_10188.html
Look at carburetor, diaphragms (holes in),blockages,and such.
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http://www.ereplacementparts.com/makita-dcs430-43cc-chainsaw-parts-c-97_98_245_10188.html
Rip the carb off. Clean thoroughly with a good fuel system cleaner (Redex etc) by soaking the inside overnight or use a good carb cleaner spray Blow all orifices clear with airline. Don't prod around with a piece of wire. Replace *all* carb interior components that are in a kit for the purpose. Page H 192 021-151-540 Gasket Set and any others if not included in the set
Check spindles on throttle shaft are not as slack as a sausage up an allwy, (Air will leak in more so mixture goes to cock) Renew plug Renew gaskets
Change ring and head gasket if compression is low and last of all ensure the casings are not leaking air into the mix
I've rebuilt dozens of thses units when in Hire trade and they are robust
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On 16/03/2012 06:30, Nthkentman wrote:

Seems like a good bet. I had the top off the carb the other day, but did not fully dismantle to see all the gaskets. I will have another go.
Anyone know a good supplier of parts in the UK? Bit annoying that the gasket set is $7 at the US spars places, and 16 - 20 here!

Plug is pretty new I think...

Compression still seems very good. Bore looks smooth and unmarked.

Reassuring to hear.
This one does not get particularly heavy use. It used to belong to a mate of mine who is (now) a retired builder - so he only used intermittently for the occasional bit of demolition / roof alterations etc. I only use it probably half a dozen times a year...
--
Cheers,

John.

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On 16/03/2012 06:30, Nthkentman wrote:

An update for any that are following...

Had it all apart the other day, and to be fair it looked absolutely spotless inside - the carb was clean with no deposits, the membranes looked fine. The cylinder bore and piston rings again perfect condition. However I carefully blew out all the nooks and crannies just in case there was debris in there that was not obvious.

Not done that yet, since they looked ok. Thought I would see what difference that made.

Yup, they looked fine.

New as of last service and its only done a couple of hours run time since then. However I gave the plug a good brush clean anyway.

Did not seem to be...

Anyway, I found that I can start it now, but its easier if one lays it on its right hand side when first trying (so the fuel pipe and feed to the carb are at the "bottom"). Which makes me wonder if may be suffering slight fuel starvation. Perhaps the resistance through the clunk and the fuel filter are higher than they ought to be? Might get a new filter set and see if that helps.
Now trying to remember if it was stored over the winter with petrol in it or not... Would letting the fuel system dry out be more likely to leave residue in the fuel filter? (I am using the red Stihl two stroke oil in case its relevant)
--
Cheers,

John.

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Could it be the in tank filter? Is there a non-return valve. My McCulloch has a foam filter which responds to removal and manual squeezing.

Certainly get gummy deposits on the carb. jets but you have cleaned those.
regards

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Tim Lamb

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On 23/03/2012 11:04, Tim Lamb wrote:

Yup, that is the one I was thinking off... I shall fish it out and see what gives ;-)

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Cheers,

John.

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writes

I think you should ask our Rodders, he's bound to know. Or maybe the loo tennant. *ahem*
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On 24/03/2012 00:55, brass monkey wrote:

I have another sort of filter for him... seems to be working nicely ;-)

Get a parrot to masticate on it a bit perhaps...
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Cheers,

John.

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John Rumm wrote:

Happened to me - hedgecutter WOULD NOT start till I washed the clunk in new fuel and blew backwards through it..
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On 23/03/2012 11:44, The Natural Philosopher wrote:

It may have been that I made a specific effort to drain fluids from it last year before putting it away for the winter! Seems like just leaving it on the shelf is a better solution.
(although I need to drain the chain oil otherwise that just oozes out and makes everything ikky in the vicinity!)
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Cheers,

John.

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http://www.ereplacementparts.com/makita-dcs430-43cc-chainsaw-parts-c-97_98_245_10188.html
It probably needs a new diaphragm http://www.ereplacementparts.com/pump-diaphragm-9589-p-73138.html
Mike
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On Fri, 16 Mar 2012 07:58:20 -0000, MuddyMike wrote:

Or the existing one wasn't put back in just the right place so one or more the flap valves aren't working properly. Had that on my mower, started to run very rich, took the card of an one of flaps was jamed into the hole it was supposed to cover. Corrected that and it's been fine since, several seasons...
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Dave.




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Of course they do, what you've just described is a diaphram carburetor (works any way up), rather than a float carburetor.
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