Chainsaw cuts out if not revved

[MrHairy]

The saw is a Makita DCS3400TH. Link to an exploded diagram.

 

I've had this saw for about 10 years with no problems. Recently it started cutting out on tickover, and has got progressively worse until it won't tick over at all. It runs fine when revved, but when the revs drop it cuts out, if I keep blipping the throttle then I can keep it running.

Carb is made by Tilliston.

 

Thing's I've tried:

Replaced clutch drum/sprocket, guide plate, bar, chain and toolstrop eye, not that I thought these would fix it, but they needed replacing anyway and I thought the tickover would be an easy fix.

Adjusting the idle screw has no effect.

Cleaned the carb with carb cleaner.

Replaced gasket behind the carb.

Replaced carb membranes/gaskets with genuine carb kit.

Thoroughly cleaned the whole saw.

Fuel pipes are all fine, tank filter is clean.

New fuel, new stihl 2 stroke oil (50:1 mix)

H & L screws seem to have a cap on them, so I've not touched them, not sure how to, or if it's possible or even needed to adjust them.

 

I don't know what to try next.

 

Any help would be greatly appreciated.

[wisecobandit]

Possible air leak somewhere? Check the inlet manifold well for cracks and splits/deterioration

|Assume you have tried a different sparkplug? What does the colour of the plug look like?

[C.J]

Usually the idle screw stops the throttle closing all the way.

 

You need to investigate why it's not making any difference - why its not pushing the throttle open.

[mikerecike]

Getting those adjusters off and re-tuning the carb would be my no:1 port of call. Not sure how thoroughly you cleaned carb when you changed dias and gaskets???

[MrHairy]

Possible air leak somewhere? Check the inlet manifold well for cracks and splits/deterioration

|Assume you have tried a different sparkplug? What does the colour of the plug look like?

 

I did have a look for cracks, splits etc, but I'll double check extra thoroughly in the morning. I have swapped the plug with my mowers plug, and nothing changes. I'll have a look at plug colour too, but last time I looked it was a good biscuit brown colour. Probably a good idea to get a new sparkplug just to make sure.

 

 

Usually the idle screw stops the throttle closing all the way.

 

You need to investigate why it's not making any difference - why its not pushing the throttle open.

 

The idle adjuster works, it just has no effect because it won't idle at all, even with it fully in.

 

Thanks for your input.

Edited September 7, 2014 by MrHairy

[MrHairy]

Getting those adjusters off and re-tuning the carb would be my no:1 port of call. Not sure how thoroughly you cleaned carb when you changed dias and gaskets???

 

I had a look at the caps where the H & L screws usually are but couldn't see how to remove them, I suppose there must be a way.

I cleaned the carb very well, using half a can of carb cleaner, squirting into every hole, I'll give it another once over just to make sure.

[mikerecike]

I've no idea what these limiters are like...pic????...in the past I've used a piece of hacksaw blade to cut the plastic and pliers to pick them off bit by bit.(on other carbs not this one)

[geoff]

Run a compression test if all else fails, might need a new set of rings/ piston kit.

 

Most likely a carb or ancilaries issue, these things generally are, but at ten years old, depending on use, it could just be feeling tired.

[Andrew McEwan]

Even if the lines look fine, if they are old probably worth changing to rule out small cracks you may have missed. Re. carbs last one I did it was cack on the ends of the needles, so had to remove the plastic guards to get a flat head screwdriver on them, to get them out. Hope you get it sorted.

[Ty Korrigan]

The saw is a Makita DCS3400TH. Link to an exploded diagram.

 

I've had this saw for about 10 years with no problems. Recently it started cutting out on tickover, and has got progressively worse until it won't tick over at all. It runs fine when revved, but when the revs drop it cuts out, if I keep blipping the throttle then I can keep it running.

Carb is made by Tilliston.

 

Thing's I've tried:

Replaced clutch drum/sprocket, guide plate, bar, chain and toolstrop eye, not that I thought these would fix it, but they needed replacing anyway and I thought the tickover would be an easy fix.

Adjusting the idle screw has no effect.

Cleaned the carb with carb cleaner.

Replaced gasket behind the carb.

Replaced carb membranes/gaskets with genuine carb kit.

Thoroughly cleaned the whole saw.

Fuel pipes are all fine, tank filter is clean.

New fuel, new stihl 2 stroke oil (50:1 mix)

H & L screws seem to have a cap on them, so I've not touched them, not sure how to, or if it's possible or even needed to adjust them.

 

I don't know what to try next.

 

Any help would be greatly appreciated.

 

It's 10 years old man! sell it and treat yourself to a new one!

Ty:lol: