Help - my chainsaw won't start

[Lons]

I have a Makita DCS520 petrol chainsaw which is only occasionally used and has been trouble free – ‘till now –

I needed to fell a large poplar last weekend and then chopped up most of the large branches, quite a lot of work over a couple of hours before it started spluttering and then stopped.
Dirty petrol / filters blocked I thought and put it away but spent 5 hours today trying to fix it and I’m stuck.

I’ve thoroughly cleaned every filter, had the carb dismantled several times and cleaned / blown everything through and as far as I can tell, fuel is getting through to the cylinder.
Cleaned and checked the sparkplug and tested by holding against the cylinder head whilst pulling the starter cord and get a consistent spark every time.
I have managed to get it to start a few times but runs for a few seconds before cutting out. Sounds like fuel starvation but I don’t think so as I've managed to flood it, in which case it must be electrics? :?

I feel that maybe there’s an intermittent loss of electrics but everything including the on / off switch seems ok.
Have ordered a new spark plug just in case it’s that but have run out of ideas and would appreciate any suggestions offered before I’m forced to take it to a repairer at exorbitant cost.

It's driving me bonkers - the bu**ers always pack in when you most need them

Bob

 

[MickCheese]

I assume it is a two stroke?

If so then I would do as you and start with the spark plug, on my old two stroke motorcycles I often found that getting the spark plug hot over the gas ring would assist in making the engine start, cannot think why this would help but it often did.

Then I would look at the coil, the timing and so on.

The fact it starts for a short while suggests it's not lack of compression or broken rings.

Are you happy the exhaust is not blocked?

Mick

 

[Lons]

I assume it is a two stroke?

If so then I would do as you and start with the spark plug, on my old two stroke motorcycles I often found that getting the spark plug hot over the gas ring would assist in making the engine start, cannot think why this would help but it often did.

Then I would look at the coil, the timing and so on.

The fact it starts for a short while suggests it's not lack of compression or broken rings.

Are you happy the exhaust is not blocked?

Mick

Thanks Mick

Yes it's 2 stroke.

Had the exhaust off and cleaned it.
Tried heating the sparkplug with a small blowtorch ( my dads trick as well on old cars )
Compression seems pretty tight
I emptied the fuel and replaced with fresh as well just in case
I didn't remove the on off switch but it seems ok as does all the wiring and I can get a spark so :?

Dunno how to test the coil apart from what I've done by holding the plug against the cylinder head whilst tuning the engine over and watching the spark :?

I've scratched my head so much I've got no hair left

Bob

 

[Richard T]

Could it be running too rich? Must be possible if you have been flooding it?

Don't know anything about Makitas but stihls have two screws next to the choke (usually) that are factory set controls. If your saw has similar, could they have become altered?

I know you've cleaned everything but sawdust gets everywhere - especially Poplar; how bad was the air filter, and could anything have got through? (Just wildly speculating ... )

 

[Blister]

It sounds like a fuel problem to me

is it a new fuel mix ?

I would empty all the fuel including the carb

Take the plug out and pull the starter cord about 10 -15 times to clear the cylinder

Then tip in about a teaspoon of fuel , put the plug back in and try starting it

If it started and runs for 3 or 4 seconds its a fuel problem as it has run on the small amount of fuel in the cylinder then run out and stopped

Carbs have very small drilling s / jets etc , all I can then advise it to have the carb ultrasonically cleaned

 

[Gerry]

It's probably the diapragm in the carb. It uses crankcase pressure to pump the fuel to the carburetor from the tank.

Gerry

 

[OLD]

I am with Gerry i have had this fault with a welder once.

 

[Digit]

The Helf and Safety boys will now have fits Lons, but try again with the fuel filler cap off, if the vent is blocked you will have what you are getting, and no, I'm not telling you how I know that one! :lol:

Roy.

 

[Lons]

Thanks for all the suggestions guys,
I've got some time today so will have another go. I gave up in frustration yesterday remembering that it's better sometimes to walk away and try again later.

If I'd carried on much longer I'd have hit it with a very large hammer. :lol: (hammer) (hammer)

Bob

 

[Lons]

Well................

Spent the whole morning and stripped everything down and started again from scratch. Found absolutely nothing wrong. Everything clean and spotless including tank breather and all filters as well as exhaust. Fuel getting through, diaphram and needle valve etc. seem ok. On/off switch working, plug test sparking consistantly against cylinder head, (also swapped plugs with hedgetrimmer so tests ok). New fuel again, carb settings checked, choke and throttle working. Teaspoon of fuel in cylinder test worked once then not (electrics maybe).

First time I assembled it started immediately and I ran it for around 5 mins, switched off and started again several times. Cracked it I thought =D> - Went back 10 mins later - nothing #-o - so 2 hours more trying and I've admitted defeat as I can't spend any more time on it so dumped it at a dealer for inspection. I HATE being beaten and am so annoyed with the bl**dy thing but the equivilant is at least £400 or I'd chuck it away. :!: :!:
Will have to wait now for the results and the cost.

If my workshop walls could talk they would admit to learning a number of new swear words today.

Bob

 

[misterfish]

Sounds a bit like the problem I had years ago with an old Sachs Dolmar chainsaw. Eventually it was diagnosed as the magneto failing/failed. No spares available at the time so it had to be scrapped.

Misterfish

 

[jaymar]

The only time I had a similsr problem was with an Army truck. It turned out to be a tiny scrap of paint in the petrol line. I had blown through from the carb with an air line but it seems the little flake was laying flat sometimes and then lifting at other times to block the pipe. I only found it when I blew through from the tank.

 

[Lons]

Sounds a bit like the problem I had years ago with an old Sachs Dolmar chainsaw. Eventually it was diagnosed as the magneto failing/failed. No spares available at the time so it had to be scrapped. Misterfish

**** I hope not as it's a cracking chainsaw otherwise. Bit worried though as I think Makita is a rebadged Dolmar, part of the same group, made in Germany.

The only time I had a similsr problem was with an Army truck. It turned out to be a tiny scrap of paint in the petrol line. I had blown through from the carb with an air line but it seems the little flake was laying flat sometimes and then lifting at other times to block the pipe. I only found it when I blew through from the tank. Jaymar

:lol: :lol: Good job the chainsaw line is only150mm long. I took the filter off and blasted through from both ends

Bob

 

[kostello]

it does sound like it might bea problem with the coil....................

or condensor..

i'm not sure how old this machine is but if it has points and a condensor when the condensor starts to fail not restarting when hot is a sign.......

from what i remember (hopefully)

 

[Eric The Viking]

I hate little two-strokes. I've got a petrol strimmer with (I think) a 15CC engine, and it's a right pig to start. It will sometimes go with a heated spark plug, then conk out.

Gerry mentioned crankcase compression: does it have a reed valve? they can fail with poor starting as a symptom. If it's a carb diaphragm issue, the mixture goes lean rather than rich. What colour was the plug when you removed it after it had been running, and how blue was the smoke (it always is, to some extent)?

It may just be a coked-up exhaust baffle. There needs to be a reasonably low resistance in the exhaust otherwise it doesn't scavenge properly, and there doesn't need to be much back pressure for the 2-stroke cycle to just stop, especially if it's supposed to have a low fuelil ratio.

 

[Lons]

I hate little two-strokes. I've got a petrol strimmer with (I think) a 15CC engine, and it's a right pig to start. It will sometimes go with a heated spark plug, then conk out.

Gerry mentioned crankcase compression: does it have a reed valve? they can fail with poor starting as a symptom. If it's a carb diaphragm issue, the mixture goes lean rather than rich. What colour was the plug when you removed it after it had been running, and how blue was the smoke (it always is, to some extent)?

It may just be a coked-up exhaust baffle. There needs to be a reasonably low resistance in the exhaust otherwise it doesn't scavenge properly, and there doesn't need to be much back pressure for the 2-stroke cycle to just stop, especially if it's supposed to have a low fuelil ratio.

Well it's with the repairers now........... so will see.

It's about 50cc I think and fuel is 40/1 ratio. Plug was pretty clean really and axhaust smoke only slightly blue as it always has been.
Compression seemed fine to me and exhaust ok - I tried starting it without the exhaust as well.
Thing is that it's always been a very good starter, cold or hot and it started spluttering and cut out after a couple of hours use which is why I initially thought dust in fuel / carb / whatever.
Bob

 

[Digit]

Possible breakdown in plug cap I wonder? Infuriating none the less.

Roy.

 

[Richard T]

Hmm.. After all that, sounds like it might be electrical. Something not connecting occasionally somewhere. ???

You have my every sympathy. Sometimes it's just best to call upon the services of a qualified doctor and relax, having done your best; no hammer raised, no window put through with it. :roll:

 

[Dangermouse]

My guess would be a faulty plug, had a few in my time that worked fine tested out of the cylinder, as soon they were in the head started playing up.

 

[MickCheese]

Do let us know what it was once it is sorted.

Mick