Pioneer 620 - Won't rev up clean to full throttle

[cdahl383]

Ok I was able to work on the saw a little more today after work. Replaced the points and condenser since I had both brand new parts. Still runs the same.

Started right up, idled nicely, revved up good, not perfect at full throttle but decent. Ran for about 3 minutes or so and then started to sputter, ran rough, bogged when applying throttle, idled roughly some more and then just died out. Let it sit for a few minutes, pulled it over and it fired up. Ran decent and idled again for a minute or two and then crapped out again. Basically, it runs the same as before.

So it wasn't the condenser or points (didn't think it would be the points, just replaced since I had them and the saw was apart).

Next items to check:

1.) Coil? Is it possible it has some cracks somewhere causing it to short out when it gets warm?
2.) Plug wire? Maybe the plug lead wire has some cracks in the insulation and it's shorting out?
3.) Carb? Crud under the welch plugs?
4.) Air leak? Doesn't seem possible as the pressure/vacuum test was good when I did one the other day, but maybe it only leaks when warm?

I found a new coil and I picked up a new plug wire. But the new coil has an extra wire that I'm not sure what it's for. The coil on the saw currently just has one wire going to the post connected to the points. I attached a few pics.

I can try replacing the coil next, but I have to determine what to do with that other wire first. Can't just leave it hanging out there. It's the same part number as what's shown in the Pioneer 620 parts diagram, they must have updated it at some point along the line as I'm sure it's used for other engines as well.

Let me know your thoughts or suggestions. I still have hope for this saw, just getting a little frustrating never really getting anywhere with it.

 

[buzz sawyer]

Have you tried another new plug or the original plug?

 

[cdahl383]

Have you tried another new plug or the original plug?

Still using the first new plug I bought. I have another new one. I can try that this weekend.

Do you think it could be an air leak still coming from somewhere?

 

[buzz sawyer]

Still using the first new plug I bought. I have another new one. I can try that this weekend.

Do you think it could be an air leak still coming from somewhere?

No, I don't think it is an air leak. I put a new engine on my log splitter a couple years ago. All was good for a year, then it suddenly had trouble starting and running - missing and backfiring. I first thought it was a sticking exhaust valve but turned out to be the spark plug. I still think your problem is in the carb, but the plug is easy to try. I would try the original plug as well or even one from another saw the runs well. Just make sure the threaded portion and side electrode are the same length as the orig. As for the carb, I would also recheck the fuel pump diaphragm and gasket positions and that the flat surfaces are flat - excluding the side with the raised ridges that seal against the gasket. I use a piece of 320 grit sandpaper stuck to a 1/4"thk piece of glass to flatten the surfaces. I used a flat file on the inlet needle body with the raised alignment pegs. Here are some before-and-after pics from an RA carb I did some years ago.

 

[Old2stroke]

If the extra wire is electrically the same as the one to the points (check with ohm meter) it is meant to go to the ignition switch. If there is the resistance of the coil primary (less than 100 ohms) between the two wires, then it is just a ground wire to ensure that the coil is properly grounded, not just through the mount screws. If the coil is wound on a bobbin, it might not be grounded to the steel core legs.
Still haven't removed welch plugs to see what's under them? Should have been done the first time the carb was apart. Good trouble shooting means when an engine quits, you have to check for spark AS SOON AS IT STOPS with the plug still in it. A timing light works better for this as you can see it in bright light.

 

[cdahl383]

If the extra wire is electrically the same as the one to the points (check with ohm meter) it is meant to go to the ignition switch. If there is the resistance of the coil primary (less than 100 ohms) between the two wires, then it is just a ground wire to ensure that the coil is properly grounded, not just through the mount screws. If the coil is wound on a bobbin, it might not be grounded to the steel core legs.
Still haven't removed welch plugs to see what's under them? Should have been done the first time the carb was apart. Good trouble shooting means when an engine quits, you have to check for spark AS SOON AS IT STOPS with the plug still in it. A timing light works better for this as you can see it in bright light.

I suck with electrical stuff. How do I measure ohms? Use a multi meter?

Can I run the engine with the inline tester hooked up? I could just watch it as it dies out then.

I can pull the Welch plugs this weekend. The big one I don’t think will be a problem. There’s a little tiny one though over the high speed channel. What’s the best way to remove that little guy?

 

[Old2stroke]

I suck with electrical stuff. How do I measure ohms? Use a multi meter?

Can I run the engine with the inline tester hooked up? I could just watch it as it dies out then.

I can pull the Welch plugs this weekend. The big one I don’t think will be a problem. There’s a little tiny one though over the high speed channel. What’s the best way to remove that little guy?

Yes, you need a multi meter
Yes, you can run with tester connected
Do NOT remove the small one, it’s just a plug in a drilled passage

 

[Old2stroke]

Yes, you need a multi meter
Yes, you can run with tester connected
Do NOT remove the small one, it’s just a plug in a drilled passage

I suck with electrical stuff. How do I measure ohms? Use a multi meter?

Can I run the engine with the inline tester hooked up? I could just watch it as it dies out then.

I can pull the Welch plugs this weekend. The big one I don’t think will be a problem. There’s a little tiny one though over the high speed channel. What’s the best way to remove that little guy?

Just ground the spare wire, if you still get spark, you’re good. If no spark, insulate the end and leave it tucked away

 

[Old2stroke]

I suck with electrical stuff. How do I measure ohms? Use a multi meter?

Can I run the engine with the inline tester hooked up? I could just watch it as it dies out then.

I can pull the Welch plugs this weekend. The big one I don’t think will be a problem. There’s a little tiny one though over the high speed channel. What’s the best way to remove that little guy?

After closer look at the photos, the spare wire looks bare, obviously meant to be grounded

 

[cbfarmall]

After closer look at the photos, the spare wire looks bare, obviously meant to be grounded

That spare wire is your coil ground. Meant to install behind the plastic points terminal against the metal points box.

 

[cdahl383]

Yes, you need a multi meter
Yes, you can run with tester connected
Do NOT remove the small one, it’s just a plug in a drilled passage

Ok cool. I’ll check into that stuff.

Ok I’ll leave that little plug alone then. I’ll just look at the bigger Welch plug. Thanks for the heads up on that.

 

[cdahl383]

After closer look at the photos, the spare wire looks bare, obviously meant to be grounded

Yeah I was thinking maybe it was a ground since it was bare. That makes sense.

 

[cdahl383]

That spare wire is your coil ground. Meant to install behind the plastic points terminal against the metal points box.

View attachment 1248463

Ok cool! Thanks that’s very helpful. That placement makes sense.

I’ll try out the new coil tomorrow. If it still runs goofy I’ll hook up the inline tester and see if it still has spark after cutting out.

Really appreciate everyone’s help! I’m really learning a lot with this saw.

 

[buzz sawyer]

Ok cool! Thanks that’s very helpful. That placement makes sense.

I’ll try out the new coil tomorrow. If it still runs goofy I’ll hook up the inline tester and see if it still has spark after cutting out.

Really appreciate everyone’s help! I’m really learning a lot with this saw.

Once again, I applaud your patience and sticktoitivity. I think I heard that word on the Mickey Mouse Club in the 50s.