Chinese 45cc chainsaw was running fine till recently, now won't start. Trouble shooting so far, I know it has good spark (removed plug and turned over engine while holding it against engine), good compression (tests at about 100psi) and I have removed and cleaned the carby. When I pour a little petrol/oil mix down the carb, it makes no difference, still won't start. So what am I missing?
bill1451,
Jul 1, 10:47pm
I have had a lot of experience with small engines (lifestyle block) even tho the spark plug looks good, for the few bucks involved I would get a new one, as it could be intermittent. I would then try squirting a little bit of fuel in the spark plug hole replace plug and see if it fires, basically with 2 strokes its carby, fuel or spark. How old is the fuel, maybe mix up some fresh and try that. After a FEW PULLS on the cord remove plug and see if there is any sign of fuel on it, also check spark gap, rule of thumb(rough) I use a hacksaw blade.
bill1451,
Jul 1, 10:51pm
when you say you have removed and cleaned carby, does that include disasembly because if you have pulled carb aPART that usually means you need to put a new kit in it as the rubber diaphragm is very delicate and most likely need replacing.Empty fuel out of tank and blow out with air compressor also check fuel filter (in tank on end of plastic fuel line)
macman26,
Jul 2, 1:26am
Had a Sthil (in fact still have it.) would run great then stop. Ages to start. Would check the plug and all good. few carby kits later still issues. Then one day no spark across the plug. Replaced the plug and hasn't missed a beat in almost 15 years. So yes they can be intermittent. Could also be the timing has moved. I've heard of keys shearing. But as mentioned post 2 . Start with replacing the plug.
aprilguy,
Jul 2, 8:28am
Thanks all. It has a new sparkplug with the correct gap and the fuel is fresh mix. I did not put a kit in the carb. Strange that it does not try to start even with a bit of fuel poured straight in the carby. Air leak? I will take the muffler off today and look for clues.
gettinggrey,
Jul 2, 9:15am
My old cobber had a cheap chainsaw. It was new, but stopped working one day. I had a quick look and found that the fuel line pickup head had a felt filter in it. Very tiny strings of felt fibre had gone into the fuel pump and stopped those tiny wee 'flapper' valves from seating properly. Cleaned out the fibres, and chainsaw ran properly again. It did the same trick a few weeks later and I cleaned out the fibres again and this time I insisted that my cobber go to the chainsaw shop and buy a decent little filter head that didn't have felt fibre as the filter medium. No more trouble after that. So. do make sure that it's not the fuel pump. If you just blow out the carb jets then you aren't sorting out the real problem.
hulloitsme,
Jul 2, 12:04pm
Is the spark arrestor in the muffler fouled?
macman26,
Jul 2, 1:02pm
Also. Some have a reed valve. If that packs up that can cause issues. Pouring fuel down the carb. I usually just pour a bit on the filter as too much can cause flooding symptoms and will cause issues with it firing. But see if you can get the timing checked.
pettal,
Jul 2, 5:26pm
Blocked spark arrester ,, also try drop starting it as opposed to on the ground starting it .
aprilguy,
Jul 2, 9:19pm
Today I removed the muffler and inspected the piston and rings which look shiny and the rings can move so not the culprit. Looked for a spark arrestor but could not find one. Then I decided to check the primer/purge bulb and lines. This saw requires a lot of disassembly to get to the back of the bulb, almost everything apart from the engine has to come off! I did it and one of the lines from the bulb was cracked but I think it was the one leading back to the fuel tank and would not be preventing a startup. In the fuel tank there was a filter of the fibrous kind mentioned by Gettinggrey above so I swapped it for a better one. I said above the saw has spark but my buddy says a bad coil can give a weak but still visible spark so tomorrow I will be testing the coil with a multimeter.
aprilguy,
Jul 2, 9:20pm
Pettal drop starting? Sounds like a ticket to hospital!
muppet_slayer,
Jul 2, 10:06pm
Did you make sure the muffler was not clogged and blocked? Start a small wood fire and chuck the muffler into it to burn the insides out for an hour or so.
aprilguy,
Jul 2, 10:15pm
I will blow through the muffler tomorrow. It did not look clogged but I did not test it. I hesitate to throw it on the fire because I do not want to replace it and it is already slightly corroded.
pettal,
Jul 2, 10:24pm
you'll be fine - just keep the saw away from your body
blocked spark arrestor = there is probably a fine mesh / gauze in there , rip it out with a small screwdriver or something
muppet_slayer,
Jul 2, 10:29pm
Opps that's right it's chinese. It will probably fall apart or warp it. Main point being to make sure it is not blocked.
muppet_slayer,
Jul 2, 10:36pm
I am sure they mean holding the saw up in the air and dropping the saw while still holding it and pulling the pull start at the same time. Basically trying to start it in the air. You don't actually let go of the saw as such. Is that right pettal?
aprilguy,
Jul 2, 10:52pm
You can start your saw in the air if you want, I will start mine on the ground with a foot holding them down.
pettal,
Jul 3, 9:45am
Correct .
gunna-1,
Jul 3, 3:13pm
I have never herd of a chainsaw doing this but maby a shorn off allen key on the flywheel?.
gunna-1,
Jul 3, 3:15pm
Even with a busted diaphram and a massive manifold leak it should still fire with spark and gas poured down the carb, the only thing i can think of is the timeing being way of, like a shorn off flywheel key, unless the crank seals are so far gone it isnt funny, did it run bad before, like lean and running out of gas at idle.
aprilguy,
Jul 3, 4:15pm
Mystery solved! It must have been the fuel lines or bad fuel filter because I reassembled it today and it's running fine. Took a good few pulls to start, then I put my thumb in the muffler hole to check the flow was OK and it backfired, then started next pull. A bit of H/L adjustment and it's running fine with power, though I have not cut with it yet. I pulled the saw apart to get at the Primer/purge bulb and replaced one line from the bulb to the fuel tank. I replaced the fuel filter in the tank for a non fibrous one (actually an oil pickup filter but does the job) and also the on/off switch because it had perished and no longer fit properly in the case. I also pulled the fuel pump off, blew on it and replaced it, retightened the screws on the carb and was very careful about refitting the carb to the body, there is a lot crammed in around there and easy to pinch something or misalign something.
bryshaw,
Jul 4, 10:42am
Had two McCullough cheapies and both lasted two years the gave up the ghost. Had enough of wasted time so bought a Huskie, and goes first pull. In some cases you pay for reliabilty.
budgel,
Jul 4, 2:53pm
Good on you, well done for working your way through it!
kryptonite21,
Jul 13, 10:15am
You're right, and the thing is that there's not a huge amount of difference in price if you buy at the right time. The shops don't want a bar of the cheap saws when it comes repair time and the peace of mind in owning a reliable saw more than offsets the price difference?
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