Running Rich

[hawthornheavyhorses]

Hi All.

 

Since rebuilding the carb on my MS260 and tach tuning it with my new Tiny Tach, it has been running brilliantly, seems to have more power than before, starts perfectly and generally makes me smile when using it.

 

Barrie is sending me out a new limiter cap for the H screw which I removed to tune it properly because I'm a bit worried about the H screw working loose without it as it has no retaining spring like the L.

 

However before I fit it I thought I'd check the spark plug colour, and the electrode is mainly black with a little brown round the edges. Clearly the saw is running a bit rich, so probably need to have another go at tuning it. It's certainly a better situation that before when the plug was white/grey.

 

Just wondered which screw I should start with? My thoughts are:

 

Lean up the L a little, reset the idle, and then tune the H.

 

But any thoughts appreciated. Seems a shame to mess with it again as it is running so nicely but want to get it right! Guessing it only needs a tiny tweak as it is running so well. If it was running really rich I am guessing I would have starting issues etc.

 

Cheers guys.

 

Matt

[blazer]

no doubt others will have a go at this one, but for me if the saw peaks at 14k top revs for a ms 260 then it must be ok or it would be 4 stroking, it could be the L screw is a bit rich but again I tune (not saying I'm right) so at bottom end it starts ok, runs ok and picks up ok then adjust the LA to set the tickover. Sometimes the plug colour can take a while to change.

 

Without having it to check I will stop at that.

[spudulike]

If you are doing what we used to call a "plug chop" in my biking days, you need to go in to a big cut and then shut the saw down quickly without it idleing and then look at the plug colour, a white coffee colour on the end and central electrode is good - black is rich, grey is hot and white is lean.

 

To set the L screw, start the saw, let it run for a few mins, turn the L screw in and the saw will race and then strart to die, undo the screw past the peak in fast idle and around 1/4 turn past the saw will sound a little poppy, I leave it there and adjust the idle using the idle screw and then see if it picks up OK.

 

The H screw should then be set to around 13,000 on a working saw or damn near 14,000 if your saw is a "boys toy".

 

Do a few big cuts and see what the plug colour is, the only saw I really keep an eye on is the ported 346 and this is coffee colour on 14,500rpm:thumbup:

 

If you get stuck, bring it round when we meet next. The metering arm height will make a difference on the H setting.

[GardenKit]

Hi Matt,

It does not sound as if you are too far out. I prefer it a little rich rather than lean.

Remember, you only get the correct plug colour when the saw is working hard, it will be a little richer looking in light work with plenty of idling.

 

It sounds like the L is OK, The H maybe a little rich but if you have your 14000 rpm you must be about right, leaning it up will send the revs up. I will often tach them about 500 below the stated max speed.

 

In any case, fit the limiter in the middle and you can tweak it a little in the future.

 

edit. Sorry Spud, was writing this a fraction behind you.

Edited January 25, 2012 by GardenKit
posted while Spud was replying

[Maxnaggle]

if its making more power than before and isnt giving you any gyp i would just leave it, so long as it doesnt start killing spark plugs? can you take a pic of the spark plug and put it up here?

 

does it rev cleanly (no flat spots, bogging at bottom end) ?

 

im guessing L is low(revs) and H is high? if thats the case then you could try tweaking the H a bit, cause if your running your saw at max revs all the time thats whats going to be affecting the colour of your plug.

[Maxnaggle]

haha was slower than both of you!

[hawthornheavyhorses]

Hi Guys,

 

I'll try and take a pic tonight when I go up to the workshop.

 

I tached it to about 13400rpm at the top, no bogging, rev's very nicely. Plug is definately more black than the old plug (replaced it when the saw stopped working when had carb issues), the old one was light brown and looked more as I would expect.

 

It's done about 3-4 hours work since I set it up. Last thing I did with the saw was fell, sned and crosscut a 30ft hornbeam, so was working quite hard, but I certainly didn't "plug chop". Was just checking out of curiosity as I always check them on my old landy as an indicator for the mix, but guess 2 strokes aren't quite the same.

 

As you say, probably not far out and at least it's not running lean and it works! I'll give it a little tweak and perhaps you can hear it running when I see you next Spud and give me your expert opinion!

 

Cheers,

 

Matt

[spudulike]

Hi Guys,

 

I'll try and take a pic tonight when I go up to the workshop.

 

I tached it to about 13400rpm at the top, no bogging, rev's very nicely. Plug is definately more black than the old plug (replaced it when the saw stopped working when had carb issues), the old one was light brown and looked more as I would expect.

 

It's done about 3-4 hours work since I set it up. Last thing I did with the saw was fell, sned and crosscut a 30ft hornbeam, so was working quite hard, but I certainly didn't "plug chop". Was just checking out of curiosity as I always check them on my old landy as an indicator for the mix, but guess 2 strokes aren't quite the same.

 

As you say, probably not far out and at least it's not running lean and it works! I'll give it a little tweak and perhaps you can hear it running when I see you next Spud and give me your expert opinion!

 

Cheers,

 

Matt

 

No Worries - at 13,500 you are fine and reckon that if you look at the plug directly after a long hard cut, it will be right.

 

You have a nice clean airfilter on the saw I hope? If it isn't, clean it and re-tach. Worth checking the plug type as well, may be the wrong temp type.