spudulike

Yup, it appears to be talked about more on motorcycle and scooter sites so very possibly...MZ, that takes me back.

The backfiring is almost definitely down to incorrect ignition timing. This would usually be down to a sheared flywheel key and the flywheel moving on the crankshaft so the ignition timing happens at the wrong time. You say you checked the key, was this a real good check as it would be the most likely cause. If it isn't this, it is more than likely that you either have the wrong coil or flywheel on the machine. Seeing as the coil has been replaced, it is most probable that the coil isn't the right one. There have been five types of flywheel for this machine and probably a fair few coils. The reverse running of a two stroke is something of legend - not seen one myself, ever.

Unless you have play in the main bearings, a shot big end or damaged crankcases, you should avoid stripping the bottom end as it is a relatively complex procedure, needs splitters to do the job properly and isn't for the inexperienced.

There should be a silicone sealing sleeve that pushes in to the cylinder and that bit you have marked pushes in to this. This part can split and it is usually best to replace. I have used nitryle fuel pipe rather than the silicone part as it works, is far cheaper and is stronger although silicone does have a higher temperature ceiling - choice is yours. You can seal with a smear of liquid gasket just don't use too much and block the impulse. The rubber intake manifold can sometimes leak as well and may benefit from a smear of liquid gasket or replacement. Make sure you put plenty of WD40 on your clutch if it was still in place when you "bathed" it.

To back up my earlier statement, all top handle saws that I had in had the internal cover taken off the clutch cover, the components inspected, the shyte blown out and reassembled. I then tested the brake by snapping it on at near full throttle. You can tell if a brake is clogged as the actuation note is dull if the mechanism is bunged up and it has a much crisper note if it is clean. The other test I did specifically on the MS201 was to actuate the chain brake on each end of the brake guard. I had a few that were difficult to actuate on the end nearest the recoil cover down to wear and tear. The top handle saw is THE one bit of kit that if it malfunctions, you are very unlikely to have support that can get to you easily being up a tree. A bad cut in the wrong place and a few minutes will see you bleeding out and dead. And THAT is why I always ensured the top handled saws always had a chain catcher and the side cover/brake mechanism was checked, cleaned and serviced.

Some on here have used a fella with username "Crocky". I can't personally recommend him as I don't know him but others have.

Just clean it as part of a regular maintenance regime after all, it is a safety device!

My understanding is that the 625 was an open transfer port version of the 630 with both pretty much sharing the same engine parts. I am sure ADW will confirm as he has a few years on me🙂

You can wake these older machines up quite considerably. I used to find that they needed a good going over first as their crank seals, AV mounts, carb parts, pressure/vac test and many other parts need checking before thinking about tuning work. BTW, I am pretty much out of the game now and am only doing a little local work if it presents itself.

Try the same when hot as well. It may just be that the carb needs a retune, perhaps a little richer on the L screw. An air leak should affect cold and hot running. These saws can leak air between the top crankcase clamp and the engineered plastic engine cradle. This can often be resolved with stripping, cleaning and resealing with a thicker coating of liquid gasket. I have had a few like this.

You should be able to measure the resistance between the cylinder (earth) and the wire that comes off the generator mounted behind the flywheel. I don't know what to expect but you should get a reading if measured on a relatively high resistance setting...say 20kohms. You could fire it up and measure the voltage from the same earth and wire connection but disconnect the generator wire from the rest of the circuit as you may have a short back to earth. I have seen the magnet on the inside back of flywheels break up (not the coil ignition magnets) and have also seen old machines have the non heated handle flywheel fitted after failure of the original. ADW will have a more detailed angle on this as I haven't done one for a long while but what I have said will prove the generator works and you may have to remove the flywheel to check the magnet or slip a thin feeler gauge round the back of the flywheel to see if the magnet pulls the feeler towards it....but do this away from the flywheel coil magnets. Checking the switch is a straight continuity test with the switch open or closed, the switches are normally sliding contact type making them pretty reliable. The rest of it is metering out the components and wiring

Shame, they were solid workhorses, well built machines if a bit heavy now. I had one I did up and used for a while, nice machine and had the later plastic chain brake guard.

The first question is what is the "sap's" as I have not come across such a chainsaw part. I think you had better re-read your post and make it more coherent.

Black means they are running rich and they shouldn't be fouling up like that unless the carb is well out. Tan, coffee colour is about right and this will come by running a saw flat out in larger cuts for a while.

One issue with this model is that the HT lead can rub on the top AV mount ( the one by the air box) and start arcing on it so it starts cutting out. The machine shouldn't knock out sparkplugs, I once had a FS1E that had a bad helicoil and it didn't transfer heat well and it would melt the plugs but not seen it on a saw. I have seen loose electrodes in Rockwood plugs but a real Bosch or NGK should last for years.

I did wonder myself....many years since I rebuilt a pile of MS200s for him.

The not returning to idle could be an air leak or just a sticky throttle control. If you pop the top cover off, rev the saw and manually push the throttle closed with the linkage on the carb itself. If the saw still doesn't snap down to a decent idle, it looks like you have an air leak. If this isn't sorted, it could seize your saw. The issue may be carb related so worth checking the gauze strainer, diaphragms and ensuring the throttle butterfly and spring are shutting off correctly.

The cylinder looks OK. Get a new piston for it with Meteor being best followed by Hyway and then VEC or Golf. Try to avoid the others unless you really have to use them. You could try using a washer behind the cylinder exhaust flange and fabricating a plug to fill the hole as others have said. You could probably get an aftermarket muffler to replace the worn one. That will be OK.

Most of the compost we have purchased is like mashed up wood chip. Very fibrous, near black and not seen the like before they did peat free compost. If growing from seed, steer clear of the compost made from councils bin collections as we had real issues growing seeds one year and put it down to weedkiller and lawn weed and feed stopping seed germination.

A fella at work had one of the "Red Rocket" CR250s air cooled and red engine hence the name, another "Lad" thought he would give it a go...hell it is only a 250! Came back ashen...white as a sheet - apparently he hadn't experienced anything like it in his time. That was back in the early 80s - it was a bit of a weapon!

Sounds like either the needle valve is leaking or the primer has been connected up incorrectly.

He has.....he killed it

I think MattyF is my go to saw killer bless him. Don't get me wrong, he is a good decent fella and have a lot of time for him but he is HARD on saws...or at least he was during the time I know him. I still remember him working on his 346 on the floor, it sort of looked like a rabid Jack Russel had his wrist in its jaws.

Good luck with that Andy. I think time on a bike sort of gives you a good approach to apexes and cleanest ways in and out of corners....plus a bit too much competitiveness than is probably healthy. Have a great day...don't smack it!

Please forget splitting the crankcases and start using the grey matter. The bar studs have nothing to do with holding the cases together and in doing this, you are just showing your inexperience. The saw isn't running - only a saw with a massive air leak will not run, small air leaks cause other running issues but the saw will fire and run. You seem to have verified that the saw has compression. It is relatively unlikely your HT system is that bad but if you take an old plug and bend the end electrode well away from the centre electrode, you can test the spark over a big gap. If it sparks, you are most likely OK. I said most saws issues are carb issues and that is....because they are. I think you said that the carb had petrol in both sides. It is quite possible that the needle valve isn't sealing off correctly which would stop the saw running, if you have a Mityvac or pop off tester, you can test the valve. If you don't have this equipment, stick a bit of pipe on the fuel union, suck on the pipe and stick your tongue over the end. Your tongue should stick to the end of the pipe and stay there. If it doesn't do this, the issue is with the needle valve. Your compression gauge sounds like a car one which isn't suitable for small engines - many use schrader valves but the ones for small engines have a valve that opens up with very little pressure and that is the difference.