Stihl 031AV Rebuild Still Won't Run, Thinking Coil?

[Boog]

Well I finished the rebuild job (previously posted as "Adjusting Points - 3 lb sledge) and tried to get it running ....... spent most of yesterday trying to get her running. I can get it to cough and sputter but thats it. Been through all the fundamentals:

1. I believe the rebuilt carb is good as the saw was running decent for a short period before I started the big rebuild. Have tried every combination of L & H screw settings from the most conservative to the excessive where I had gas dripping backwards out of the air filter, still no go. (the gas comming out of the carb at excessive screw settings could be a sign of backpressure from the cylinder but I put in new rings as part of the rebuild). The best coughing and sputtering was with the Low screw about 1/4 to 1/2 open and the High screw 1 to 2 ...... sort of what I would expect.

2. I have what I would think is a decent steady spark, at least via visual observation of the plug against the side of the cylinder. Even opened a plug up way beyond .020 and had spark. Points are at .016, flywheel .010, I even took it half-appart again to check those.

3. I have a Mega-fire module in transit that I ordered to try but I wanted to see if the old points and condensor were still good. Assuming that I install the Mega-Fire module next week replacing the points and condensor, and it still won't run, that kind of leaves it to the coil, assuming that I not missing something somewhere else. I may be getting a visual spark but not enough of one to make it run under compression.

If the coil is the problem, I can not find any source of a good coil, new or used, other than a guy on ebay who rebuilds your old coil for $70.

Anyone have any suggestions where to go from here, (besides trashing the old gal)

 

[MasterMech]

You wouldn't happen to have an air gap ignition tester would you? Would allow you to verify spark under compression.

 

[raybonz]

Well I finished the rebuild job (previously posted as "Adjusting Points - 3 lb sledge) and tried to get it running ....... spent most of yesterday trying to get her running. I can get it to cough and sputter but thats it. Been through all the fundamentals:

1. I believe the rebuilt carb is good as the saw was running decent for a short period before I started the big rebuild. Have tried every combination of L & H screw settings from the most conservative to the excessive where I had gas dripping backwards out of the air filter, still no go. (the gas comming out of the carb at excessive screw settings could be a sign of backpressure from the cylinder but I put in new rings as part of the rebuild). The best coughing and sputtering was with the Low screw about 1/4 to 1/2 open and the High screw 1 to 2 ...... sort of what I would expect.

2. I have what I would think is a decent steady spark, at least via visual observation of the plug against the side of the cylinder. Even opened a plug up way beyond .020 and had spark. Points are at .016, flywheel .010, I even took it half-appart again to check those.

3. I have a Mega-fire module in transit that I ordered to try but I wanted to see if the old points and condensor were still good. Assuming that I install the Mega-Fire module next week replacing the points and condensor, and it still won't run, that kind of leaves it to the coil, assuming that I not missing something somewhere else. I may be getting a visual spark but not enough of one to make it run under compression.

If the coil is the problem, I can not find any source of a good coil, new or used, other than a guy on ebay who rebuilds your old coil for $70.

Anyone have any suggestions where to go from here, (besides trashing the old gal)

I would suspect the mixture screw adjustments are incorrect. Let a saw guy have a look and see what he has to say..

Ray

 

[Boog]

You wouldn't happen to have an air gap ignition tester would you? Would allow you to verify spark under compression.

Yeah, I wish I did, none of my neighbor gearheads do either. Best I could do was the old "open the gap way up" trick. If I can't ultimately get her going I'll take it in. The mega-fire ought to be here tomorrow, no deliveries today with the holiday.

 

[Boog]

I would suspect the mixture screw adjustments are incorrect. Let a saw guy have a look and see what he has to say..

Ray

I kept thinking that too Raybonz, I started out with a 1/4 on the low and 3/4 on the high, usually a good starting point. Got some sputtering, so I tried going up first .... no change until it wouldn't cough at all and I had gas dripping back out of the carb, flooding it. So I went back to that start point and tried going down from there, wouldn't cough at all. Seemed like it sputtered the most at that 1/4 - 1/2 low, 1.5 ish high range. If I can't get her going I'll end up taking it in. I've got enough into it now that I want to get it right.

 

[Boog]

You wouldn't happen to have an air gap ignition tester would you? Would allow you to verify spark under compression.

I would suspect the mixture screw adjustments are incorrect. Let a saw guy have a look and see what he has to say..

Ray

MEGA-FIRE to the rescue! I received the mega-fire module today and installed it. As soon as I hooked it up I could immediately see the difference in the spark from the plug against the cylinder. What I thought was a decent spark before was NOTHING compared to what the mega-fire delivered. It was several times the intensity of my previous spark. I screwed the plug in, gave it a few pulls and presto, it fired right up full tilt. The carb screws were close and needed just a slight adjustment, that baby is screaming again. In reality, that was probably all this old saw needed to make it run again, but I'm glad I did a pretty major overhall on it for the long run. The megafire success should point to the condenser as the main cause of my problems, the points looked great, they were gapped right, and I now know the coil is fine. Can't wait to put the 20" bar back on her and have at it tomorrow. I'm working on the top of a big old shagbark at the moment, it doesn't stand a chance!

Thanks again for suggesting that module MasterMech! Owe you one!

 

[MasterMech]

Classic saw meets modern technology. I like it.

 

[Dyno625]

Glad to hear you got it running, I absolutely love my 031. something about them old saws!

 

[Boog]

Glad to hear you got it running, I absolutely love my 031. something about them old saws!

Yes, I'm kind of partial to that one, it was my "first love". If you ever have trouble with your ignition, go the Maga-fire route as MasterMech suggested. I mounted it on the underside of the top with the wires going down into the saw near the spark plug wire. As small as it is, there was not enough room to mount in inside by the coil. There are two prethreaded empty holes under the rear left corner of the top, not sure what they were for, but I simply used an appropriate sheetmetal type screw to secure it there.

Wow, a Fiskers for every size Stihl, nice man! I'm still trying to unload more old ammo for stihl saws. Just got off the phone with a guy on CL to trade some old 9mm and 7.62 x 39 for his "like new" 180C with easy start. Will make a nice saw for my teenage daughters if he goes through with it.