OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Chainsaws and Concrete Cutters Petrol Chainsaws and Concrete Cutters Stihl 045 Starting Problem

Hi guys. I have an old 045 that I bought second hand in 1983. It was always a great saw that started and ran great and has done heaps of work for me. That is until I accidentally put 50:1 brushcutter fuel in it instead of 25:1. It grabbed and broke a ring which ripped up the piston but strangely did not mark the bore at all. I'm thinking maybe the broken ring might have snagged in one of the ports and chewed up the piston but didn't travel up and down in the bore. Anyway, got a new piston and rings and fitted them but now it won't start without a bit of aero. It has fantastic compression and once it starts on the aero will idle perfectly and rev freely and cut like a new saw. Once it has started and warmed up it can be switched off and restarts first pull. Any ideas on where to look for the problem?

Does it have a primer system? Given its age, I suspect not. This means getting the fuel system to prime after it has been standing idle, is relatively difficult. The following points stem from that:

- When did you last clean the carburetor and fit a new kit (both diaphragms, needle, etc.)?
- Have you replaced the fuel pickup filter and either replaced or very carefully inspected the full length of the fuel pickup hose?

These things should be addressed whenever you pick up an old saw even for a tune-up. After that, you have to consider the particular situation you are investigating.

Since you had to remove the piston barrel from the crankcase, you may now have a crankcase leak where the bottom of the barrel mates to the crankcase. This is a very common source of hard starting with those very small two strokes. If you split the crankcase for some reason, this multiplies the problem because of probable gasket leaks there as well. These problems could be made worse by a bit of minor crankshaft seal leakage just due to time and wear. After opening the engine any competent repair shop does a leakage test on the whole system before they fit the carburetor and muffler. That test, and putting the various leaks right, is often the biggest part of the overhaul job.

On another point, you should not use ether to start any engine, but especially not one with a brand new piston and rings, and above all if that saw has a chromed bore. You may have already ruined your overhaul. Inspection of your new rings and piston through the ports with a magnifier may tell a sad story.

Thanks Grumpy. No chromed bore on this old girl, she's about a 1979 manufacture date. I put a new gasket on when I replaced the piston and rings. I had a look at the piston and rings and they seem fine. Like I said, once it is started once it can be started every time first pull and it was never hard to start before. The carby doesn't have a prime system and was actually replaced not long ago so that shouldn't be a problem. I might lift the cylinder and check for any damage to the gasket and retension the allen screws. I'll also check the fuel line in case I may have nicked it during the rebuild. As to aero, I use the one specifically for 2 strokes, I'm guessing it has some lube built into it.

Unless you've put a new fuel filter on and put a new kit in the carburetor, I'll keep suspecting that the problem is in the fuel system, especially one or other carburetor diaphragm or wear on the metering needle. A diaphragm has had time to get rather stiff since 1979.

The carby was replaced less than 6 months ago with a genuine Walbro from a NOS supplier in Germany so diaphragm and wear on metering needle shouldn't be a problem as it hadn't done many hours before I misfueled it. I also got a NOS rebuild kit with the piston, rings, gudgeon and little end bearing for less than Stihl Australia wanted for one ring. Haven't had a chance yet to go through the fuel system but will do and will let you know what I find. Thanks for the support.