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

[cdahl383]

I have been following along with this thread and have a suspicion about the troubles that now exist, a compression test is needed when the cylinder is warmed up. I have not so far seen a pic of the cylinder/piston on the exhaust side. Why I ask is that my family and myself ran these Pioneer saws from 1957 on up through 69-70. I myself have a 600,610,620,620Super and several 650`s. During the years running these saws I have seen many different problems pop up and repaired all of them here at home, when the cylinder warms up the engine can loose compression if the piston is worn undersized or the rings are about worn out. We had one RA the predecessor of the 600, have .022 ring end gap it would run ok at cold idle but as soon as it warmed up it became impossible to tune it and keep it running.

I’ll try to get some better pics of the piston and cylinder later. It looked good when I checked it a while ago.

I’ll try to get it fired up and warm and then run a compression test just to compare cold vs hot.

Here’s a brief video I took a while ago checking the piston and cylinder…

 

[cdahl383]

Ok I ran out the garage real quick and checked the compression.

Cold was 145psi (first photo)

Hot was 145psi (second photo)

I took a couple videos as well. Will post those up later tonight.

Took one of it running. It runs goofy once warmed up. Kind of wondering if it gets an air leak once warmed up or something.

 

[buzz sawyer]

I don't see an accelerator pump in his pictures. Didn't a Homelite 1020 or 1050 have that?

Yes, my 1050 has the pump.

 

[cdahl383]

Here’s a video of it running from earlier today…



Started right up. Ran good at first but after it warms up it starts running inconsistent. It revved up good prior to when I started the video. You can see how it sort of fluctuates while running. Almost seems like an air leak or fuel starvation. Then at the end it just craps out.

 

[cdahl383]

Here’s a video I did checking the compression once warmed up. It was about 145psi cold and 145psi warm. Didn’t seem to drop at all really.

 

[buzz sawyer]

I just saw this thread and followed it all the way through. First, I admire and applaud both of you for your patience and perseverance. I restored an RA a few years ago so I am familiar with most of the issues. Most questions or comments I thought of have been addressed. All I can add is - I had a similar high speed bogging problem with a small Husqvarna saw. It idles fine and revved up but bogged soon after. Would up being crap under one of the welch plugs. If I let it rest, the foreign matter would move away but when I revved it, the increased fuel flow would move the FM back over the passage. Found it when I pulled the welch plug.
FWIW, here is the Homelite 1050 with the accel pump - circled in blue.

 

[buzz sawyer]

Actually, I just thought of something - make sure the carb mounting flange surface is flat - where it mounts to the engine. This area is often warped a little and I believe the crankcase pulse passage goes through the flange. If leaking, it may not get a strong enough pulse to work the fuel pump efficiently. I flatten the carb mounting flange with a large flat file or with progressively finer grades of sandpaper on a thick piece of plate glass. I also flatten the carb mating surfaces, except the fuel pump side with the sealing ridges.

 

[cdahl383]

I just saw this thread and followed it all the way through. First, I admire and applaud both of you for your patience and perseverance. I restored an RA a few years ago so I am familiar with most of the issues. Most questions or comments I thought of have been addressed. All I can add is - I had a similar high speed bogging problem with a small Husqvarna saw. It idles fine and revved up but bogged soon after. Would up being crap under one of the welch plugs. If I let it rest, the foreign matter would move away but when I revved it, the increased fuel flow would move the FM back over the passage. Found it when I pulled the welch plug.
FWIW, here is the Homelite 1050 with the accel pump - circled in blue.

That’s a good point. Could be some crap under the Welch plug. Never thought of something moving back and forth like that inside that area.

What’s the best way to remove those plug? The low speed looks like it has the bigger plug. The high speed has the little gold one.

 

[cdahl383]

Actually, I just thought of something - make sure the carb mounting flange surface is flat - where it mounts to the engine. This area is often warped a little and I believe the crankcase pulse passage goes through the flange. If leaking, it may not get a strong enough pulse to work the fuel pump efficiently. I flatten the carb mounting flange with a large flat file or with progressively finer grades of sandpaper on a thick piece of plate glass. I also flatten the carb mating surfaces, except the fuel pump side with the sealing ridges.

Ok, I could pop that off and check it with a straight edge.

Do you think it could be ignition related though? That’s the route I was sort of heading towards before after messing with the carb.

 

[cdahl383]

Check this video out, near the end. It sure sounds like it has an air leak or starving for fuel. Second guessing my thoughts about it being ignition related now.

When I pressure tested the saw I had blocked off the intake right up against the engine. Maybe it’s pulling in air around the intake?

 

[cdahl383]

Was talking to another guy that has some Pioneer saws. He brought up a good point. He mentioned that it's possible the needle is sticking in the seat and not allowing fuel to pass through. At idle this isn't as vital since it needs less fuel. Once you rev it up it needs more fuel obviously. He said on his saw, he had a needle that wasn't hooked or captured, it just relied on gravity to come down off the seat. That's what I have currently.

I'm going to pull the carb apart and put one of my many newer needles in there that has a hook or button on it to hook onto the metering arm. When it's captured or hooked to the metering arm, it will be both pushed up by the metering arm and then pulled back down by the metering arm. No chance it will stick.

The problem with the other needles was I had a hard time getting them to seal properly. I'll just have to keep messing with them until it seals up properly. Maybe once some fuel is in there it will seal better.

I'm going to try that first before I do anything else as that's easy and free.

If you listen to that video above, it sounds exactly like my trimmer when it runs out of fuel when I'm trimming by the creek. It stops revving up good, it idles but kind of funny, and when it finally runs out completely it idles up and down several times until it just dies.

I find it hard to believe I have an air leak still after replacing the crank seals and sealing the crankcases. It passed the pressure/vacuum test, the carb has been cleaned and all new gaskets around the intake area, new fuel lines and filter, etc. The only potential obstruction for fuel at this point would be the needle. If it were intermittently sticking, that would explain why it runs inconsistently like that.

 

[buzz sawyer]

Sures sounds like fuel starvation to me. Of all the older saws I've restored, only one had a bad condenser. One had a bad coil but it was literally falling part. I always file the points - just to eliminate the question. Also, wider point gap advances the timing. The spark occurs when the points open. You may be able to mount almost any Tilly HL to try - just work the throttle manually. Also, those older saws had a lot of reciprocating mass so they accelerate and decel a little more slowly than modern saws.

 

[cdahl383]

I swapped needles just to see if that was the issue. The old needle was not hooked to the lever. Thought maybe it was hanging up in there restricting fuel flow. However, no change with the hooked needle and metering arm. Same as before.

I did another pressure vacuum test today while the saw was still warm. It had a really minor leak down. I read where most Stihl tech bulletins say if it holds for 20-30 seconds it’s good. Read another bulletin where it said passing was losing less than a third of test pressure in a minute. Mine passed on both criteria.

I may try popping off the Welch plugs and try cleaning in there. I’ve got nothing to lose at this point. Seems like whatever I try it doesn’t work anyway.

If that doesn’t work then I’ll try swapping ignition parts. It just really sounds like it’s running out of fuel. But I don’t have an air leak and the carb is getting fuel.

 

[rocketnorton]

how long is it running w/o shroud?

 

[pioneerguy600]

When you had the carb off did you blow some comp air down through the impulse passage? I have had carbs idle before with a bad impulse signal/ blocked passage and other times a badly fitting, loose hose on another make of saw but they would not rev up to full throttle.. Also make certain the gasket between the carb and its several gaskets and insulating block are lined up correctly so the impulse circuit is continuous and seals tightly.

 

[cdahl383]

how long is it running w/o shroud?

Just a few minutes, not too long. I know it needs the heat shield and hood on to help circulate air around the engine. I figured a few minutes wouldn't hurt it. Plus it's only 40 degrees or so outside as well.

 

[cdahl383]

When you had the carb off did you blow some comp air down through the impulse passage? I have had carbs idle before with a bad impulse signal/ blocked passage and other times a badly fitting, loose hose on another make of saw but they would not rev up to full throttle.. Also make certain the gasket between the carb and its several gaskets and insulating block are lined up correctly so the impulse circuit is continuous and seals tightly.

No, I did not do that. That's a good idea. I have to take the carb off to remove the block off plates (rubber seals) I have on there now for the pressure test. I'll blow some compressed air in there when I take the carb off later.

 

[cdahl383]

I think I found the problem or at least part of the problem. The saw has a leak around the brand new clutch side crank seal. But it's not leaking around by the crankshaft and rubber seal itself, but rather from the outer edge of the seal where it fits into the bore!

When I installed the seal a few weeks ago I just sprayed water around by the crankshaft area and when I saw no bubbles I said okay it's good. Then I pressure/vacuum tested the saw and it came back good based on what I read. It had a minor leakdown, but based on what I read it was still good. So I moved on to other things.

Today when I checked, I sprayed a bunch of soapy water all over the place and a little happened to pool in one area by the outer edge and I thought I saw a bubble. I sprayed more in there to fill it up more and sure enough, there was a steady stream of bubbles coming out of one little spot between the outer edge of the seal and the seal bore. I missed that last time, so that was my bad.

Now the question is how to fix it? Can I clean the area and smear some motoseal around that area and let it cure for a day or two, then try doing another pressure test to see if it leaks still? Or do I have to pull this seal and replace with a new one?

I figured I could try smearing some motoseal around the edge as I really have nothing to lose. If it doesn't work, I'm pulling the seal again anyway. If it does work and it holds, then I'm good.

Any thoughts on that approach? I don't mind redoing the seal, but I'd just hate to waste a seal if it's sealed good around the crankshaft and there's an easy fix for it that might work.

Here's a video to show what I'm talking about...