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

[cdahl383]

Worked on the carb some more this evening. No luck. Found a needle/seat/spring combo that held 7psi with a minor leak down of 0.5psi after a minute. Other needles I used leaked down immediately. Cleaned the carb again too. Nothing. Not even a pop off like it was trying to start. It’s like the more I work on it the worse it gets. It actually ran before I took it apart. Feels like I’m just wasting my time now.

Any ideas on where to look next?

Could it possibly be an ignition issue? Weak spark? Coil failing? Timing issue? Points?

 

[cbfarmall]

Start by drying the cylinder again, pinch off the fuel line and give it a small prime. That will get it to pop with some cranking. If that fails, the ignition is your problem. Did you clean the points and carefully set them? Besides the points being dirty, a failed condenser is the next common ignition failure I encounter. Was everything put together properly? No wires grounding or rubbing the flywheel? Fortunately, points and condenser should be easy to find for that saw. I rarely replace points anyway. Just clean them with a file and ultra fine sandpaper.

 

[cdahl383]

Start by drying the cylinder again, pinch off the fuel line and give it a small prime. That will get it to pop with some cranking. If that fails, the ignition is your problem. Did you clean the points and carefully set them? Besides the points being dirty, a failed condenser is the next common ignition failure I encounter. Was everything put together properly? No wires grounding or rubbing the flywheel? Fortunately, points and condenser should be easy to find for that saw. I rarely replace points anyway. Just clean them with a file and ultra fine sandpaper.

I could just pull the fuel line right out of the tank I guess. The fuel line on this carb is almost non existent between the sediment bowl and carb. There's nowhere to pinch it. It's only 1" long or so and it's almost all fittings inside the line, no open space.

I'm leaning towards it being an ignition problem now. It may be as simple as the spark plugs I'm using are fouled out now from being drenched in fuel while I was working out the carb issues.

I did another spark test today and found the newer plug I bought recently wasn't even sparking when I pulled it over! Another time I got it to spark just a little bit a couple times. The old plug that came in the saw doesn't spark that well either.

I put a new NGK plug in the boot that's for my dirtbikes (never ran it yet) and it sparked just fine. It wasn't a huge spark, but it was consistently sparking. I think I need to get a new plug now to use going forward as those other ones are probably done after all the fuel soaking and flooding.

I didn't touch the points when I had it apart as spark was not an issue. I figured I'd just leave well enough alone. Maybe that was a bad idea. I'm going to try a new plug first since that's simple, cheap, and easy. If that doesn't work, then I'll take the starter/flywheel off again and check/clean the points. I just had the flywheel off so I doubt it will be difficult to remove now. It came off just fine with the puller I had anyway.

I don't believe any ground wires are rubbing anywhere. I put everything back how it was originally. The plug wire is pinched a bit from the previous owner smashing the heat shield over it. I looked at it when I first got the saw and it didn't go through the insulation on the wire. I wrapped it with electrical tape in that spot just to be sure.

Maybe while I have the fuel line out of the gas tank, I can remove the filter and hook my pressure tester up to it and check the carb again that way now that it has fuel in it?

I did notice some fuel was coming out of the exhaust while I was doing the spark test. But I was also pulling it a zillion times too. I would expect it to draw in fuel when pulling it over that many times. If it were dry then it would likely have a fuel problem.

I'll try the new plug first, then go from there. Would be nice if that's all it was haha!

Here's a video I did earlier this morning with three different plugs. First the new J8C plug I bought a couple months ago. Then a brand new NGK plug for my dirtbike. Then the original old J8J plug that came in it when I bought it.



I did a spark test when I first got the saw with the original J8J plug and you can see it was sparking just fine. I think the two plugs I'm using now are fouled out and shot.

 

[cdahl383]

Ran up to the hardware store on my lunch break and picked up a couple J8C plugs. Just for kicks, I gapped them at .025" and put one in the spark plug boot and pulled the saw over. It sparked like crazy! I think those old plugs are just fouled out now from all the flooding.

I'll try messing with the saw later today if I have some time and see if it'll fire with the new plugs. Sure would be cool if that's all it was!

 

[cbfarmall]

I definitely think you should go back and clean the points. Did you reset the gap even?

 

[cdahl383]

I definitely think you should go back and clean the points. Did you reset the gap even?

Ok I'll keep that in mind. Maybe I'll double check them. No, did not reset the gap.

You said you clean them with sandpaper? Like 400-600 grit maybe?

 

[cbfarmall]

I flatten the points and remove pits with a flat file. Try to keep the surfaces parallel. Polish with real fine sandpaper, I have 1500 wet-dry. Degrease with contact cleaner and wipe clean. An old trick was to clean with a dollar bill. Some points come apart so you can clean the contacts separately. Reinstall and set to .020. You should be able to spin the flywheel by hand and get a fat spark.

 

[Old2stroke]

When a plug gets fouled, you can't just let it sit and think it will be fine once it's dry. The fuel will evaporate quickly but it will leave a film of oil behind that is a good conductor and will effectively short out the plug. When you pull a plug out of a flooded engine, just dip the end in straight gas, brush it with a toothbrush, dry it with a heat gun or compressed air and it's as good as new. YOU DON'T HAVE TO KEEP BUYING NEW PLUGS.

 

[cdahl383]

When a plug gets fouled, you can't just let it sit and think it will be fine once it's dry. The fuel will evaporate quickly but it will leave a film of oil behind that is a good conductor and will effectively short out the plug. When you pull a plug out of a flooded engine, just dip the end in straight gas, brush it with a toothbrush, dry it with a heat gun or compressed air and it's as good as new. YOU DON'T HAVE TO KEEP BUYING NEW PLUGS.

Cool, I’ll keep that in mind! Thanks!

 

[cdahl383]

Tried starting the saw again today with the new spark plug. No luck. Doing the same thing as before. It'll pop and light off for a second and then that's it. Never takes off and fires. Then it's back to nothing again.

The inline spark plug tester finally showed up the other day. I hooked that up. Turns out it's not sparking inside the cylinder! Only lit up a couple times. One time when it lit up the saw actually popped on the bench which sort of made me jump haha! I pulled the plug back out and pulled it over outside the cylinder and it was sparking. It wasn't a big fat kernel though, it was like two or three little lines.

The plug was a little wet afterwards but I had pulled it numerous times. It was not drenched and there wasn't tons of fuel spewing out of the muffler like before. I think I have the carb sorted out now. I believe I have some sort of weak ignition issue going on.

I'm thinking of checking the kill switch first (just unhook and see if that's causing any problems). Then maybe pull the flywheel off and look at the condenser, points, point gap, coil, wiring, spark plug lead wire, etc.

Any advice on how to proceed or what to tackle first? I've never been the best at diagnosing ignition issues, but I'd like to learn with this saw here now and hopefully figure this out soon.

 

[cbfarmall]

Points. That is my advice. You took the ignition off and reinstalled without cleaning and checking points. Almost guaranteed to be the source of your no start condition. If it ran before you tore and down not after, it only makes sense. Try unhooking the kill wire but I doubt that will do it.

 

[cdahl383]

Points. That is my advice. You took the ignition off and reinstalled without cleaning and checking points. Almost guaranteed to be the source of your no start condition. If it ran before you tore and down not after, it only makes sense. Try unhooking the kill wire but I doubt that will do it.

Ok. Will check kill switch first. Then check points.

Probably a bonehead move on my part not to check the points earlier. Figured they worked fine before why mess with them? Lesson learned haha!

 

[cbfarmall]

Doesn't take much dirt to make points inoperable. Put another way, cleaning and resetting the gap was normal maintenance for these old saws and yours is 60 some years old. You could still have other ignition problems but the smart money is on the points. File and clean them and set the gap carefully.

 

[cbfarmall]

You did reinstall the points cam? Doesn't this saw have a removable, keyed cam?

 

[cdahl383]

Doesn't take much dirt to make points inoperable. Put another way, cleaning and resetting the gap was normal maintenance for these old saws and yours is 60 some years old. You could still have other ignition problems but the smart money is on the points. File and clean them and set the gap carefully.

Yep, good points…haha get it! I’ll clean them and see what happens.

 

[cdahl383]

You did reinstall the points cam? Doesn't this saw have a removable, keyed cam?

Yes, that I know I did. It only fits one way as well. Hard to screw that up.

 

[cbfarmall]

Yes, that I know I did. It only fits one way as well. Hard to screw that up.

Also, the cam should have an arrow to indicate direction of rotation. Should go without saying, points gap is set with the piston at TDC.

 

[WoodmanSr]

Yes, that I know I did. It only fits one way as well. Hard to screw that up.

Ideal fix is OE points & Condenser, clean / gap / etc.

Fyi, the small engine universal ignition chips will usually spark a good coil.... or serve as diagnostic check to eliminate Points & Condenser. But, like other Chinese electronics can be a gamble. Either no issues or occasional premature chip failures.

Never could get Nova-II to survive on a Homelite XL-923 although #9334 (Kawasaki) style has been fine. This saw is my only experience.. required as previous owner gutted SXL-925 electronic ignition & converted to XL-923 coil (where 925 had no points cam on crankshaft, required chip) I've read that some Stihl may want negative polarity chip installation.

Ignition Timing, if crucial performance situation, might warrant manual timing without a Flywheel key.

Also, these chips can behave as a bugger. Trigger at very low speed. More apt to rip rope handle out of your fingers.
-- pull twice, Ignition OFF (intentionally no spark), full choke
-- then; choke off & Ignition ON. Pull normal but grasp rope hard. It's likely to rip out of your fingers.
-- repeat with Choke if doesn't fire.

Search: "Ignition Chip Replaces Points & Condenser"
▪︎Nova-II chips (2 wire, support "+" or "-" installation polarity)
▪︎Single wire (positive polarity) as Oregon or Rotary # 9334,
Electronic Ignition Module for Kawasaki Engines
# 31-9334

Ref., Lil Red Barn -- Compatible with Stihl 028, 020AV, 015 & Others Ignition Chip Replaces Points & Condenser [NOTE: THIS CHIP WILL NOT WORK ON STIHL 030, 031, 032, 041 CHAINSAWS].