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

[cdahl383]

Start with just cleaning and setting the points. If it still acts up, I'd try a new condenser as the next likely problem. This is all assuming there isn't some more obvious problem like an unintentional ground or shorted wire.

I started working on it last night but ran out of time to finish. Will work on it more this weekend.

On first glance, it appeared that the one points arm (not sure what it’s really called), was up a little higher on its pivot point. This was causing the two contact points to not meet up exactly even. I pushed it back down and got them lined up properly.

Then I took some 600 grit sandpaper and cleaned the points up. Finished with a shop towel soaked in brake clean.

Next I rotated the piston to tdc by looking through the exhaust port. I found that when I did that, the lobe on the cam was not at the center high point like I thought it would be. I guess this makes sense as the timing is set for 30 degrees before tdc. The cam is keyed so I don’t see how you could be off with this anyway.

I checked the gap and it was much too large. It was closer to .028” or so instead of .020”. I closed the gap up to .020” where the feeler gauge was just dragging a bit.

Cleaned up a little more inside there, put a few drops of oil on the felt pad and closed it up.

Will put it back together today and see what happens.

 

[cbfarmall]

I haven't really messed with these 600s much--mostly the RA models and 700s. Anyways, I pulled out 2 manuals and both point out the timing is set to 30 BTDC but neither say explicitly where you set the points gap. I ran into this once on my Solo Rex and set the gap at TDC. I didn't know the points were already closing by the time so the gap was much wider and the top of lobe. This made the timing too advanced and the saw kicked like a mule when cranking. Once I set the points correctly, the saw fired immediately and smoothly. So, set the points to .020 at their widest, at the top of the cam lobe. When you check for spark, just set the flywheel on the crank snugly, by hand and give it a quick spin, by hand, spark plug out. If everything is right, you will get spark. Unlike modern electronic ignitions which need a minimum cranking speed to produce a spark, these old mag ignitions are capable of hot spark at low RPM. I also like to use a drill with a socket adapter to check for spark at speed, with the plug out. A drill won't undo the nut like an impact will.

 

[cbfarmall]

From a wico manual.

 

[cdahl383]

I got it running. Unfortunately it’s doing the same thing as it did before. Starts on the first or second pull. Idles nicely. Revs up a little but then bogs down. It won’t die, it just bogs down. Then it recovers and idles again.

Are you saying to set the points gap at the highest point of the cam lobe? Previously you said to set them at TDC.

Any ideas? Ignition? Timing? Carb? Maybe still has an air leak?

Here’s a video of what it’s doing…

 

[cbfarmall]

I thought about it, rechecked and realized the points should be set at their widest not necessarily TDC.

Sounds like the saw spins up when you get on the trigger but then bogs. I'd check fuel. Did you go thru the fuel line. The bowl gasket can allowing air in or either of the fuel lines. Did you go thru that stuff?

 

[cdahl383]

I thought about it, rechecked and realized the points should be set at their widest not necessarily TDC.

Sounds like the saw spins up when you get on the trigger but then bogs. I'd check fuel. Did you go thru the fuel line. The bowl gasket can allowing air in or either of the fuel lines. Did you go thru that stuff?

Ok, so maybe my points are set wrong then? So you just eyeball the highest part of the cam lobe and set them there?

It has brand new fuel line, new fuel filter, etc.

You may be on to something with that bowl gasket. Still using the old one, but I noticed it’s leaking a little fuel. Might also be pulling in air there? I’ll make a new gasket for that and replace that. Easy enough to do.

Do you think the points gap being off would cause it to run like that?

 

[cbfarmall]

If it's leaking fuel at the bowl then it's also sucking air in.