Olddevonstihls

Thank you. Even quite big differences (and settings in between) on both H and L) don’t seem to overcome the fundamental problem. Carb stripped down again and inlet gauze/screen replaced (again) as there was some residue on it. Another new set of diaphragms and gaskets on the carb. New fuel line still ok, and tank/vent still passes vac and pressure test. But the half choke start remains and symptoms still suggesting air leak but where is it?

Thanks. Very helpful. I probably wasn’t being clear about the tests, sorry. Normal vac/pressure was with rubber seal behind carb (ie next to cylinder inlet), impulse sealed by the connection to the carb, exhaust sealed similarly behind muffler, and test hose connected to modified spark plug. Both vac and pressure holding solidly at 0.5 bar. Carb itself holding pressure separately. The other pressure test, when I sealed the air filter side with the carb attached was to establish if there were any leaks on the carb side, including at the gasket between carb and cylinder: there were not, other than at the throttle linkage. I look again at the other things you suggest, but there is new fuel line (a split in the original lead to starting difficulties and fuel starvation and so was replaced) and filter. Carb settings at the specified starting positions of L 1 turn/H 3/4 turns plus a small amount and giving the right engine characteristics but perhaps they need richening up more boldly.

Aftermarket from L&S Engineers. I did an 038 at the same time with the same kit from L&S and that’s fine. The reason I’m circling around the carb is that the symptoms of needing half choke to start were the same before the failure as now.

That is the problem. If I could be sure it was a defective carb then buying an original new one might be worthwhile if it gets the saw going. But £150 and it is still not working …. are there any sources of after market carbs that are better than others?

Hi, having a lot of trouble with MS240. Seized up with damaged piston last year. Just before it finally went bang it would only start on half choke. From what I’ve now learnt this suggests either an air leak or saw otherwise running very lean. When rebuilding, replaced seals and fuel lines etc. It now runs, but seems low on top end power, and will only start reliably on half choke still. Idle is around 2800-3000 and wto 12500 rpm. On vac and pressure tests with inlet blanked off BEHIND carb it’s tight as a drum. When I do the same tests with the front of the carb blanked off it doesn't hold pressure at all. Bubbles come from around throttle linkage. A bit of grease on the linkage improves things so that it will hold pressure which slowly subsides. I’ve tried a cheap Chinese carb replacement but that also shows leakage around the throttle and won’t tune properly. The original carb is the genuine stihl/walbro item that came with the saw (15 years old) and has had two rebuild kits. From what I’ve read on other threads here throttle linkage leaks are common and should not generally cause these sorts of problems. Can anyone suggest where else I might be looking (I’ve read the long thread about an 024 that had a mysterious air leak). thanks.

Answering my own question, it’s the oil pump drive and associated seal.

Hi, new here. I’ve got an old 051 which a pressure and vac test reveals needs new seals, at least on the clutch side. I’ve ordered a set (with difficulty) but now I’ve stripped it down what I have doesn’t match what I’ve been sent and, on closer examination, the fitting on the end of the crank doesn’t match the standard parts diagram. The diagram and the supplied seals indicates two biggish seals (30x42x7 and 25x47x7) but what I have is 25x47x7 and then, on a sleeve with a drive bar dog which engages with the sprocket, a tiny one, probably something like 15x20x5. I can see neither this tiny seal, nor the drive sleeve on the diagram. Existing seals with drive sleeve shown in attached photo. Can anybody suggest what I might be dealing with here? Many thanks.