spudulike

The Gunson gauge is OK and fit to measure the compression of small engines unless they have changed the type of valve they use lately. You are measuring the compression with 5-7 fast pulls on the recoil handle aren't you? The results on another decent machine will be interesting. Fine dirt in the gauze filter is a common issue, probably worth flushing your fuel tank to ensure it doesn't have any chip in it and check your fuel can as well.

Crazy dude......you smooth talker! I just like to test the theory of statements I don't believe and in this case, it was a load of bowlocks - should have used a glass full of something alcoholic I wasn't proving a point, more proving that what I thought sounded a bit iffy was in fact very IFFY! 120 is well low and even when damn hot it should pull late 130s or early 140s! Cold it should be 150-170 IMO! The issue is either with the saw or the method of measurement - just need to find out which and move on!

I usually test the squish with the carbon removed and then produce a custom gasket to give optimal compression and squish clearance.

This saw has only been out for a few months, how come they have come in for work if they are still under warranty and ultra reliable???

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.

Had it a few years back, the temperature went that high I wanted to take my eyes out and put them in iced water! The only time I felt ok was in bed with the heated blanket on full. Aches all over, over a week of feeling weak....see what I did?. I then finished it with a terrible cough and knocked the back out for two weeks before I sorted my core out?

Pretty agnostic on oil but am currently using HP Super. I don't do much cutting, mostly used for the last run up and tach before dispatch. Look at me as being the F1 Mercedes engine guru and the customer being Lewis! I rely on the end user for feedback, always have and have always got positive responses. The only saws I have detailed measurements on are the 372 and 357 as this was where I started.

Yes, the wonders of a muffler mod getting rid of excess heat!

Just put a genuine Stihl fuel filter on a pipe, dunked it in a glass of water and sucked, can't say it tasted great but it let more than a drop or two through.....well, a half glass before I had to stop! I really don't like these "internet facts" that aren't based on fact and go against the water and water damage I have found in carbs. Don't believe me - go try it yourself!

Old conventional non strato Autotune saws are OK on Stihl red although it isn't the best but they will work and not cause issues. All Strato Autotune type engines should be run on Semi or full synthetic oil. It is pretty simple, the new saws are designed to use the very smallest amount of fuel, two strokes lubricate all he internal bearings with the oil in the fuel used. Less fuel used means less oil getting to the bearings so the best oil will give better protection. As I said, pretty simple! But I don't know a lot about these sort of things

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!

Good luck with that. I can imagine their staff meetings discussing what they see as an insurmountable problem for something you may have done a hundred times before. I guess if the time gets close, they will have to weigh up the perhaps increased costs of getting the tree felled by another, the risks if it falls over or drops a bough and hurts a pupil if left in situ (not knowing the health of the tree), the risk of you doing the job etc If you can't get clearance then perhaps getting another on site with the magic qualification will do it and just stick the extra cost on the quote......customer always pays!

If you have been using a poor oil, it could be the muffler hole is blocked - easy one to check if it is a later model with a removable outlet cowl.

It is in the carb and is where the high speed fuel enters the carb throat before entering the manifold - usually brass!

Erm....the last MS260, MS460 and MS660 I did had new seals fitted and .....well I thought they had the seal pushed in to the bearing!

I don't know much about two strokes but thought that the scavenging bit happened on the downward stroke and is the releasing of the exhaust gases caused by combustion just after the piston clears the top of the exhaust port and completed by the lowering piston releasing combustion chamber pressure and producing positive pressure in the lower crankcase pushing fuel and air through the transfers and scavenging the exhaust out of the exhaust port! The heat in the crankcase is surely transferred heat from the piston and cylinder and not the exhaust gases - the only reason you would have exhaust gasses in the crankcase would be blow-by from the rings and piston leaking at combustion.

The 560 and 550 are "skinny" due to the fact the transfers being situated at the front of the saw making the cylinder thinner - like the MS461!

The seals can be changed on the 560 without splitting the crankcases and these seals in bearings are commonly used on the 560XP, 576XP, 590XP, MS660, MS260, MS650, MS460, MS440, 346XP, 550XP etc etc! They are all removable and can be replaced without removing bearings or splitting cases!

The 150 and 201 are a bit weird like that. They don't tend to react like a typical carb! It may be a dirty air filter or dirt in the check valve holding it open!

References from past jobs, do you have a portfolio of past work?

Right - 120PSI is well below the 150+ I would expect. Check the gauge out on a working saw and see what it pulls. Hones - Damn, been doing it wrong for years, I need to recall hundreds of machines.....bollocks!!! The stones are better in closed transfer cylinders but do the job in my limited experience I have recently had a failure in a similar way, my diagnosis was that the bottom ring had seized and the top ring had stayed loose and continuing to run the saw had put a very slight cavity up the bore where the stuck ring had taken microns off the bore in one specific area. My fix was a new P&C kit and it worked. I could see from the new piston that the rings were not worn in one small area, inspection of this area showed the hone had missed this part of the bore due to this vertical channel of wear.

It's in the name isn't it Rich

When you say it splutters and stops are we talking about when it is left idling the revs slow and die or during heavy cutting, it dies? If you leave it idling on its side and loosen the fuel cap, will it continue to run OK. Have you reset the autotune by cutting hard and continuously for 5 minutes? If you go from snedding to heavy cross cutting, the autotune will have set itself to lighter high rev use and then need time to reset to heavy cutting. May be worth looking at the piston through the exhaust port or put a gauge on it to measure the compression.

Damn, thought it may have been some sort of attrition normalizer, Brexit needs you!

What's an "Atronought" Stubby....new one on me