Ms150 high jet.

[lurkalot]

26 minutes ago, spudulike said:

Have you tried a new plug as these 10mm ones can give some dodgy running issues CMR6A from memory!

Think it's a CMR6H

[Gerbutt]

If the muffler has been drilled then it won't be blocked. It is worth looking at the piston through the exhaust port and seeing if it is scored - you should be able to see the horizontal turning marks still on the piston and there should be no build up of carbon encroaching on the port and closing it off.
The check valve is a one way valve that stops fuel being pulled from between the main diaphragm and carb body when the saw is on idle. The fault is that this valve either stops flow in both directions causing no high speed running or flows in both directions that can cause the saw to load up at idle and get smoky and not run well at all. The valve should only allow fuel to be dragged from it by the vacuum in the carb throat causing a venture effect on it.
This valve is the device that shuts the high speed fuel system off when the throttle valve is closed and allows the low speed system to work alone.
I recently had a MS200T with a dodgy open check valve - symptoms were very a poor/rich idle but would rev out OK.
Is your choke valve opening fully - I know it is a very simple lever. A dirty air filter would cause this issue but you have checked this. Is the plug black or tan?
It is possible that the kill wire is shorting out which will cause interesting running. Have you tried a new plug as these 10mm ones can give some dodgy running issues CMR6A from memory!

Thanks for all that bud. The saw seems to have as much compression as always, but I will check the piston when I take the exhaust off. The plug is a tan colour. It ticks over fine but when it has been for a little while it’s really groggy when you first start to rev it again and a bit smokey, and then clears up but still doesn’t rev out clean - as if it’s real rich. I will check the choke has full movement.

I’m thinking it may be the valve from what you explain. I’ll take the carb off and see if I can locate it and give it a clean. I will also try a new plug.

I’m considering taking it all apart and giving the ports a very mild tweek, have you any advice for that?

Thanks for the time you’ve taken to explain things [emoji106]

[spudulike]

It is very difficult to get to. The limiter, unless removed, makes cleaning it difficult as you can blast some carb cleaner down the H screw hole and this generally will help this issue and the last ditch attempt is the ultrasonic cleaner.

It does sound a bit like the valve although it may be worth leaning up the L screw a bit more than usual as I find these saws don't like a rich L screw setting and do exactly what yours is doing. Take the L screw in until the revs die, take it out past the area where the revs pick up and leave it just after that for a clean pickup with no smoke and bogging - seems the mods do cause this issue and need a bit of special care on the carb setting.

[Gerbutt]

Cool, I’ll have a go a that tomorrow and see how it responds. I did the exhaust mod a few years ago and it’s been fine. Then about a year ago it started playing up near when Honey’s had a Black Friday deal on the 2511t, so I got one of those and didn’t use the 150 for ages. Then I thought it was a waste of a saw so got a carb kit and that brings us to here. So, the carb settings were good up until the problem. Strange isn’t it!?

[Gerbutt]

I’ve put a new plug in it today and tried adjusting the carb but to no avail. Just took a carb off to see if I could find that valve and whilst taking it to bits I found the little gauze covered in a brown mush! I’ve cleaned that and the rest of the carb and will have a start up tomorrow afternoon to see if it’s helped!

[spudulike]

It will help but it must have been running lean rather than rich!!! Make sure you flush your fuel tank and check your fuel can as they probably have a bit of chip inside them!

Reckon it will be fine now!

[Gerbutt]

I was thinking the same but hopefully it’ll be ok. I couldn’t work out how to take the jets out so if this doesn’t help then I think I’ll get a new carb. When I googled 150 carb problems there were post saying dealers had replaced loads, they put it down to ethanol eating them away!

[spudulike]

Mmmm, only changed a handful of carbs over the last few years as I tend to fix them....strange that. I reckon you have solved it as a blocked gauze strainer will lean the saw down giving lack of power and poor idle.

[Gerbutt]

Yeah some folk were saying it was dealers just replacing as an easy fix, and on bloke said he runs aspen so that throws the ethanol reason out the window!

I’ll report back tomorrow after I’ve had go [emoji106]

[Gerbutt]

I’ve had a quick go and it’s just the same. Start it and it ticks over fine, give it a few revs and it then let it tick over for a couple of seconds and it picks up fine. Give it a few revs and then let it tick over for ten seconds and then rev it and its real fluffy and groggy, after a few seconds of reving it clears up again?