Chainsaw hard to start.

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Well she's back to acting up. Shooting blue flames out the muffler on choke then flooding out with fuel coming back through the carb. I'll try brand new fuel today.

Maybe starting to sound like a timing issue?
The mystery continues. Check the key on the flywheel, and check the air gap as well. ( business card works for me.)
 
I never made a mistake, thought I did once, but...

I was going to ask you how old it was, as bad crank seals can suck air intermittently and cause contradicting evidence that comes and goes as the seals get wet and try to seal.... about like your description.
Occam"s Razor FTW!
I'm glad you got her running. Ignore the perfect people and carry on!

I've got a plastic mac that needs seals and that's how it acts. Seals are unobtainium for my little yellow saw, but I'm keeping it until I find or make something fit. It's now been waiting about 20 years. I also have an original Mini-Mac I got from a neighbor a few years back, gotta order in the parts and get her running, likely seals and all soft parts.

EDIT EDIT EDITED!

OOPS - thought it was fixed, but not.
You might try pulling the clutch 1st, if it's been slipped hard and overheated, it will dry out or burn the crank seal which is only a few millimeters away. If the clutch drum shows blue, smells burnt, or it's ever had a needle bearing fail, it's worth pulling it. Use an impact and it's "right to loosen" - left hand threads here - make sure there's some slack rope on the recoil if you don't pull the recoil cover off, which you nay as well, the flywheel id standard left to loosen the nut and a large center punch in the end of the crank with some tappy - tap - tap whilst pulling on the flywheel usually pops her right off. Don't pry if you can avoid it. If you do, get a helper to tap while you put gentle pressure on it.
Good luck!
 
I never made a mistake, thought I did once, but...

I was going to ask you how old it was, as bad crank seals can suck air intermittently and cause contradicting evidence about like your description.
Occam"s Razor FTW!
I'm glad you got her running. Ignore the perfect people and carry on!

I've got a plastic mac that needs seals and that's how it acts. Seals are unobtainium for my little yellow saw, but I'm keeping it until I find or make something fit. It's now been waiting about 20 years. I also have an original Mini-Mac I got from a neighbor a few years back, gotta order in the parts and get her running, likely seals and all soft parts.
Thanks - I'll see if crank seals are available for the saw.
 
Read the owners manual? Who does that?????????
No one I know!
Well she's back to acting up. Shooting blue flames out the muffler on choke then flooding out with fuel coming back through the carb. I'll try brand new fuel today.

Maybe starting to sound like a timing issue?
Blue flames!? As I recall, blue flames are indicative of chemicals burning or of very high temperatures (trust me, I have first hand knowledge of both). Why those would be coming out of your muffler is the real question. It sounds like raw, atomized fuel is being spat out of your muffler and ignited by the spark in the cylinder. I'd try a new plug, personally. I had a Mac with a bad plug that would load up then "explode" similar to what you previously described and a new plug fixed it. Or, check your plug wire for breaks, tears, or exposed wiring. If the plug occasionally "misses" that would cause raw fuel to be spat out and cause the flames like you are describing.
 
No one I know!

Blue flames!? As I recall, blue flames are indicative of chemicals burning or of very high temperatures (trust me, I have first hand knowledge of both). Why those would be coming out of your muffler is the real question. It sounds like raw, atomized fuel is being spat out of your muffler and ignited by the spark in the cylinder. I'd try a new plug, personally. I had a Mac with a bad plug that would load up then "explode" similar to what you previously described and a new plug fixed it. Or, check your plug wire for breaks, tears, or exposed wiring. If the plug occasionally "misses" that would cause raw fuel to be spat out and cause the flames like you are describing.
Thanks for the info. It has a brand new plug. I put in a NGK BPMR7A but the spec sheet calls for a BPM7A. Have just been reading the R might cause problems in the older chainsaws? Could be worth trying a BPM7A.
 
Thanks for the info. It has a brand new plug. I put in a NGK BPMR7A but the spec sheet calls for a BPM7A. Have just been reading the R might cause problems in the older chainsaws? Could be worth trying a BPM7A.
The "R" means it's a resistive plug, resistive plugs generally create less RF interference (like anyone cares) but also cause the coil to build up a higher voltage before arcing. This can be problematic if the insulation in the coil isn't able to handle the higher voltage & breaks down. If you go the other way & use a non-resistive plug where one is called for the coil won't achieve as high a voltage causing a less effective spark. With lower voltage comes higher current & that can cause coil issues too.
In short, it's best to use the plug the manufacturer designed the coil for, but I don't think it has any bearing on your current issues... I'd be looking at timing
 
The "R" means it's a resistive plug, resistive plugs generally create less RF interference (like anyone cares) but also cause the coil to build up a higher voltage before arcing. This can be problematic if the insulation in the coil isn't able to handle the higher voltage & breaks down. If you go the other way & use a non-resistive plug where one is called for the coil won't achieve as high a voltage causing a less effective spark. With lower voltage comes higher current & that can cause coil issues too.
In short, it's best to use the plug the manufacturer designed the coil for, but I don't think it has any bearing on your current issues... I'd be looking at timing
Thanks for the info.
I'll grab the correct plug tomorrow.

In the meantime I drained the fuel, pulled the plug (gap is to spec), pulled it over 40 times, replaced plug, filled with fresh fuel and she fired right up. I suspect it was slightly rich on the low side so I adjusted slightly.
I don't have time to get it hot for a few days but i'll test again in some wood.
I'll check out the electrical side a bit later tonight.
 
I've gapped the coil to .018" as per service manual. Had to unflood again before it started but once I did that it starts and restarts very easily.

Spark is nice and strong.

Checked piston again just in case and it's still pristine.

New fuel pipe and tank vent pipe ordered.

An observation is that the tank hisses quite loudly after shutting down even while it's still cold. Opening the tank slightly or wiggling the vent pipe relieves the pressure.
The vent pipe has a very fine and restrictive filter inside it which could be causing issues?

I can also see fuel vapour coming back through the carb when operating the throttle with the engine off. Not sure if that's an indicator of any problem.

Gonna give it a run in wood tomorrow and get things nice and hot.
 
All your problems could just be from a carb that is flooding, could be an inlet valve that is not seating, a control lever that is set too high, a faulty diaphragm that is holding the valve open, or a gasket on the wrong side of the diaphragm. A simple (not very good) test is to just hook a tube to the fuel inlet port and blow into it, you can blow about 3 or 4 psi and that should be enough to tell if the inlet valve is properly seated.
Don't be misled by tank vent issues, it is normal for pressure to build up in the tank and if the carb inlet valve will stay closed to at least 8 psi (pop off pressure) it won't cause flooding, however, if the valve open at a lower pressure than what builds up in the tank, you WILL have flooding. This is why it's important to do a proper pressure test on the carb.
 
All your problems could just be from a carb that is flooding, could be an inlet valve that is not seating, a control lever that is set too high, a faulty diaphragm that is holding the valve open, or a gasket on the wrong side of the diaphragm. A simple (not very good) test is to just hook a tube to the fuel inlet port and blow into it, you can blow about 3 or 4 psi and that should be enough to tell if the inlet valve is properly seated.
Don't be misled by tank vent issues, it is normal for pressure to build up in the tank and if the carb inlet valve will stay closed to at least 8 psi (pop off pressure) it won't cause flooding, however, if the valve open at a lower pressure than what builds up in the tank, you WILL have flooding. This is why it's important to do a proper pressure test on the carb.
I'll give it a go and report back.
Might be a good time to invest in a mityvac.
Thanks for all the assistance.
 
All your problems could just be from a carb that is flooding, could be an inlet valve that is not seating, a control lever that is set too high, a faulty diaphragm that is holding the valve open, or a gasket on the wrong side of the diaphragm. A simple (not very good) test is to just hook a tube to the fuel inlet port and blow into it, you can blow about 3 or 4 psi and that should be enough to tell if the inlet valve is properly seated.
Don't be misled by tank vent issues, it is normal for pressure to build up in the tank and if the carb inlet valve will stay closed to at least 8 psi (pop off pressure) it won't cause flooding, however, if the valve open at a lower pressure than what builds up in the tank, you WILL have flooding. This is why it's important to do a proper pressure test on the carb.
Just blew through the fuel inlet barb with everything I've got and it took it without releasing. Will look at getting a mityvac and do some proper testing.
 
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