Megatron

The MS250 uses the A074 mount not the D025. (Uses Stihl 3005 as opposed to 3003). My vote goes for the 3/8 LP PS3, with 7T rim sprocket.

What are you lining the inlet manifold tab up with, with respect to the cylinder? Is the outside of the intake on the cylinder scratched/damaged at all? Was the saw pressure tested before being torn down?

What gauge is the bar and chain? (do they match) What pitch is the saw sprocket and nose sprocket on the bar? (do they match)

Pump diaphragm; 1106 640 3100 (I wouldn't order this until you know it is at fault, as it is about £14 exc VAT!) Compression should be 140+psi. If you can, check the compression tester against a known good saw before testing the 070 to ensure the tester isn't reading low etc If you pull the oil pump cover you will almost certainly have to replace the gasket as usually half sticks to either side 1106 359 0700 for the gasket. However, you can also get this gasket in the complete gasket and seal set (worth doing if you haven't got new seals yet and includes all other gaskets), part number 1106 007 1050. The gasket and seal set looks like;

With regards to the oil pump. The short black hose behind the carb does transmitt impulses from the crankcase to the oil pump. If it has a hole in not only will the auto oiler not work properly the crankcase will suck in excess air causing it to run lean! It is also possible the pumping diaphragms in the oil pump have gone bad or like you say the oil strainer is partially blocked. Although the manual and auto pumps use the same pick up, the manual pump will create greater suction. Under the oil pump cover;

First have you got the muffler cover installed yet? The HT lead can be replaced, it is screwed into the coil. You have to remove the flywheel and stator plate to do so though. If you do, mark the stator plate and crankcase with a sharp chisel before removing the stator plate or you will have to reset/readjust the timing when you reinstall. However, usually in my experience with a HT lead problem the saw will cut right out instead of die back. Hard to tell for sure but it still does sound like a fuel starvation problem, especially if babying the throttle brings the rpm back up. If the pump or metering diaphragms are warped/wrinkled/stiff they need replacing and could well be the cause of the problems. If the inlet needle has a groove on the sealing rubber tip then that should be replaced too. A tillotson DG-5HL kit is for the gaskets and diaphragms only, RK-113HL for gaskets, diaphragms, needle, seat etc e.g. Carburetor Diaphragm Kit Fits Stihl 08 08 SEQ 70 090 AVR TF350 AVE TS08 TS350 | eBay Tillotson HL Carburetor Repair Kit Replaces RK113HL | eBay (just to check i'm assuming your carb is an HL-244 or HL-324 ?)

There are actually two styles of chain brake for the 051/075/076 which use different clutches... Early models which had a chain brake used an (overengineered) isolating clutch system as well as the traditional brake band and had a different clutch to later models with the more conventional chain brake system. Not all 051/075 saws can be retrofitted with a chain brake. Earlier models do not have the necessary crankcase mountings for the chain brake handle.

It doesn't sound like a governor problem. What settings is your carb at? To "tune by ear" you need to disable the governor. Check the fuel tank vent before anything else. Have you installed a carb kit? or cleaned out the carb. That would be the most likely explanation. Diaphragms go hard with age and can warp, meaning they no longer pump fuel efficiently. Gunk can build up in the carb orfices and also partially block the fuel strainer/filter on the carb inlet.

A Time-sert should fix it... ++ TIME-SERT Spark plug thread repair inserts ++ aluminum spark plug thread repair inserts kits spark plug problems thread stripped spark plug repair damaged threads in spark plug hole stripped out

Unfortunately I don't have a spare handle. You should be able to get hold of one easy enough though, it is the same part on the TS510, TS760 cut off saws. My 075/076 was built at the "change over" time, jury is still out on what it is. Most people say the difference between the 076 and 075 crankcase is that the 075 has a oil cap on the top and the 076 the side. There are also differences in the electronics and fuel tank/recoil starter. My saw has properties of both; 076 side oil cap, 075 fuel tank/recoil, 075 electronics etc From my research I am 99.9% sure it is actually a 075 as very late model 075 saws actually had the side oil cap.

I presume this is the saw from ebay with the busted rear handle? I like my 075/076 but it is a pita to work on! I fully rebuilt mine and painted it blue just to stand out but I think I am going to change it back to the more traditional orange before long. 090 left, 070 centre, 075/076 right

Unfortunately my database doesn't go back quite that far to be able to pinpoint the year. It is an early version, judging by the colours (red shroud, cream crankcase and white handle) I would say it is most likely in the 1968-1972 era. The missing muffler deflector is part number 1106 145 2900. You will also need two of the locking plates 1106 148 3900 (need to order twice) and four hexagon head screws M4x10 part number 9008 319 0659 (need to order four times). I would definately replace the filter with the modern flleece one (1106 120 1602). You don't want the wire mesh one. With regards to the oil pump. If the manual pump works well then it is unlikely there is a problem with the pickup as they both use the same one. FYI, the automatic oil pump is adjustable though. Exactly how much oil is coming out when compared to any other saws you have? To check for leaks you need to clamp a piece of rubber between the muffler and cylinder (to seal the exhaust) and another piece of rubber between the carb and inlet manifold (to seal the intake). For this series of saw it is easiest to apply vaccum/pressure through the spark plug hole using an old spark plug base as an adaptor. Arbtalk member Spudulike has several pictures of the process on different saws in the What's on your bench today thread. I have found when these saws leak air it tends to be the decomp button or oil pump impulse hose at fault a lot of the time rather than the oil seals. Due to the age of the saw I would recommend a new set of oil seals regardless of whether they leak or not. Edit; Looks like the lower felling spike fixing is busted off? Shouldn't be a problem when milling though as you don't use them.

You can make a bar from an MS880 fit usually by just drilling new chain adjustment and oil holes. Both use the 14mm slot size. However, I have heard that some of the big Stihl mount bars sold for the MS880 have a shorter slot which won't work on the 070/090 without lengthening. So check before you buy. If you can try to find a 36" Power Match Plus bar for an MS880 and have a look at the tail pattern. You might only have to drill new tensioner and oil holes but if the slot is a different length you would have to enlarge it. The 30" Rollomatic ES bar I use was intended for MS880 use but I just drilled new tensioner and oil holes. The slot length was the same as the Duromatic bar I have which was intended to fit it.

Take off the muffler and have a look. If it is truly seized in the bore, apply penetrating oil through the spark plug hole and leave for a while. You can try to gently dislodge it by applying torque via the flywheel nut. The best method by far is to weld a grease zerk fitting on to the base of a spark plug and then use a grease gun to pump the combustion chamber full of grease, remove the bolts securing the cylinder to the crankcase beforehand though. Obviously this only applies if the piston is above the exhaust port (which it usually is, if truly stuck).

Measure the bore if you can. If the 40 was actually cast on the cylinder it might be 40mm? in which case Efco 140??? I try to stay clear of these type of saws

You will actually be making your saws run leaner by using 20:1 as opposed to 50:1 if you don't adjust the carb...

I would have thought 8T would be alright, however, if you find it bogs a lot I would change back to the 7T. The clutch shoes can burn their linings off if the clutch slips on the drum too much. Why are you using a hard nose bar? Some pictures; 070 AV which wears a 30" Stihl Rollomatic ES bar. Soon to be 090AV, freshly rebuilt. New old stock 090 clutch and drum on left vs 070 clutch shoes which have burnt their linings off in a 070 clutch drum.

When I say all parts are interchangeable... a 090 six shoe clutch still has to go with a 090 sprocket etc. But you can put a 090 clutch and matching sprocket on a 070 etc You have to watch out for incompatibility due to age also e.g. A recoil starter with pawls can't be interchanged with the morse-fairbanks starter unless you change the fanwheel

Don't know of anywhere online. You can order a paper copy from Stihl part number; 0458 106 0121. Costs about £2, they are free in the US! I notice your earlier post in the milling forum. They were sold with two pitch sizes, .404" and 1/2". A 1/2" sprocket is pretty useless if you want to use it as the chain is very hard to find. Spur sprockets usually have what pitch they are written on them but generally the .404" has 7 teeth and the 1/2", 6 teeth. I have a rim sprocket set up on my 070, which if I wanted to would mean I can run 3/8" chain by just changing the rim. Parts are relatively easy to get, however, there are some exceptions! All parts are interchangable with the 090. If you post up the first 3 digits of the serial number I'll give you a good idea how old it is. If there is anything else you want to know just post it up!

I am assuming it is a spur sprocket that has worn out? You might get lucky via a Stihl Dealer. Virtually all sprockets have become NLA from Stihl. However, part number 1115 007 1048 is for the 3/8 8T rim drive kit. Including; drum, rim and cover washer.If you want .404, or 7T 3/8 then just by that rim on its' own also. This year is the year in which it will become NLA, so you might just be in time or not...

Of the old Stihls 070, 090, 075, 076, 056MAGII, 07 or 07S saws are worth the most. Peaking with the 090 for £200+ for a complete parts saw.

Use a Dremel to cut a groove and undo with a screwdriver. Easy if it protruding out of the case, which it looks like it is.

Although the carb boot/inlet manifold is not the more modern soft rubber etc which get holes in. They can warp over time causing an air leak, same problem with 070/090, 075,076 etc The wind vane governor can be altered/stopped altogether. You can adjust the position of the end of the spring, hence, altering the tension in the spring and thus the RPM at which the governor kicks in. If you have a problem with any of the bolts vibrating loose you can change them out for Torx ones which are serrated on the underside of the head to prevent such occurances. Does the saw have a spur or rim sprocket?

Drain the fuel and oil. Turn the saw upside down and take out the two T-27 Torx headed screws joining the black wrap handle to the orange rear handle assembly. Take out the three rubber AV buffer plugs in the black wrap handle using a blunt screwdriver and undo the screws which are under the plugs. Also take out the other screw on the side of the handle which is not concealed. Remove the handle. With the handle removed underneath the sprocket area you will see a white/opaque elbow connector held down with another torx screw. This is usually where these saws leak, the elbow connector can warp and there is an O-ring on it which can perish. Found some pictures from my archive;

What reason did Mister Solutions give for the piston not fitting, different part number? Not to put too much of a downer but you could have bolted on a new aftermarket MS660 piston and cylinder for less than the cost of the OEM MS650 piston. But I would have probably gone with new OEM piston if the cylinder is in good condition. For future reference you can also save money on flywheel side bearings. It is the clutch side which are proprietary to Stihl. You can usually get the same bearing (SKF, FAG) etc for much less if you buy direct from a bearing suppliers rather than going through Stihl. In this case you wanted a 6203 open type with C3 clearance. In the second of the two videos that is the OEM Husqvarna tool. Here, is some of what I use; http://arbtalk.co.uk/forum/544588-post38.html (On stihl saws I made a tool which looks more like the OEM tool for Stihl for the flywheel side) Some very good info here (highly recommended); http://www.arboristsite.com/chainsaw/40590-2.htm#post539218 (You will have to become a member to see the pictures, rather than red X's)