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Bluest

Member Since: 23 Apr 2016
Location: Lancashire
Posts: 4267

2007 Defender 110 Puma 2.4 XS CSW Java Black

DIY chainsaw tuning

I screwed up the carb adjustment of my chainsaw. My fault. I was having running problems, so after giving it a service to no avail I decided to twiddle mixture screws. Both of them. This made things worse. I then discovered the issue was nothing to do with the carb, it was a blocked breather hole causing a vacuum in the fuel tank. Fixed that and it now runs more like it should but idles too fast and bogs down too easily under load. Anyone know how I can get it back to the factory settings? It's a 40cc McCulloch CS400T. Ran great before. 2007 110 TDCi Station Wagon XS

4th Apr 2025 6:43pm

Devon-Rover

Member Since: 22 Jan 2015
Location: South Devon
Posts: 925

2014 Defender 110 Puma 2.2 USW Aintree Green

It'll take a bit of fanagaling but..

Get it started and turn the idle down in increments and each time adjust the Low screw either Anticlockwise (rich) or Clockwise (lean) you will hear the note change and it'll sound happy. Keep going until the chain stops turning by itself so in effect the clutch stops engaging.

Since you state it Bogs then Either too much or too little fuel. IMO reset the High screw by all the way in and about a turn maybe a turn 1/4 out.

it's a case of check / adjust / check / adjust by slight tweeks to the mixture screw to get it sounding happy. It might need a bit of time and a few test cuts but just small 1/8th turns and see how it runs freely by revving versus underload.

Of course this description is far harder to type than just having the saw in my hands and fettling it. Also can be found on Fb, Ytube, Insta & Twitter @4WDSouthwest

4th Apr 2025 9:11pm

Dinnu

Member Since: 24 Dec 2019
Location: Lija
Posts: 3547

2012 Defender 90 Puma 2.2 CSW Santorini Black

I normally adjust the air screw 3 half turns out. So fully tighten first, and 3 half turns (or 1.5 turns). Then adjust the idle screw to get proper idle and clutch disengages.

Hope this helps. 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing
2012 90 CSW, 2.2TDCI, Santorini Black

5th Apr 2025 12:05pm

Bluest

Member Since: 23 Apr 2016
Location: Lancashire
Posts: 4267

Thanks for the tips. I've found a suitably chunky old gate post to use a dynamoeter. I'll give it a tune up at weekend. 2007 110 TDCi Station Wagon XS

7th Apr 2025 4:11pm

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