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

[cdahl383]

You can use a large punch and work your way around the seal to drive it. As big as it is, you can probably tap directly on it with a ball peen hammer. If you are feeling brave, you look to have enough room to add a small chamfer to that seal bore to ease installation. I know for Poulan 3400 saws this is a must.

Whatever you, if it seems like the seal is starting crooked, stop and try again. Once you distort the seal, it's trash.

Ok cool, maybe I can try that. Just makes me a little nervous striking one side without something supporting the other side. I used a socket to drive in the flywheel seal, but that was a lot easier to do without the shaft in the way.

I started chamfering the outer edge a little bit. I used a little bit of sandpaper to round off the sharp edges. I did that when the old seal was in place as that caught most of the crap. I could put some towel/rags in there at the bottom to catch any junk/shavings if I worked on it more, then just flip the saw upside down and remove the towels.

What would work best for chamfering that edge? Sandpaper is just good for sort of taking the sharp edges off, but not sure that's the best thing to use for doing more than that. I have a small dremel tool with attachments like sanding stones, that could work I guess.

I have a Poulan 3400 too, but luckily it didn't need seals. Just fuel lines, filter, and a few other minor things and I was able to get it up and running. I'll keep that in mind if I ever do the seals on that saw.

I'll take my time with driving the seal in place. Hopefully with some patience I can get it in straight the first time.

 

[cbfarmall]

Just don't strike it, work around the edge and tap it. It will probably try to rock one side up when you tap on the other. Idea is to start it and drive as evenly and square as possible. Nothing wrong waiting till you gather the right tools, though.

Dremel would work well-don't nick the crank. I believe my buddy used his pen knife and scraped a chamfer in the aluminum.

Judging from the picture, that case already has a decent chamfer. I'd leave it alone.

 

[altatim]

If you have a 3D printer they are invaluable in making random punches and seal drivers.... Simple cylinders that cost less than a dollar once you have a printer. I've used it to make oddball drivers and weird tools and even the odd part.

 

[cdahl383]

If you have a 3D printer they are invaluable in making random punches and seal drivers.... Simple cylinders that cost less than a dollar once you have a printer. I've used it to make oddball drivers and weird tools and even the odd part.

I've heard a lot about these 3D printers but I have no clue what they are or what they can do haha! Sounds cool. Do you have any photos to share?

 

[cdahl383]

Well I attempted to install the seal over the weekend. It was a fail. I picked up a larger socket to drive the seal in. I brought some old film negatives out to the garage and got everything set up. I couldn't get the seal started. I took everything off, greased things up more, then set it back on and started to drive it in. It went in nice and straight, but I forgot to put the film negative back over the crankshaft before I started driving it in. At that point I figured well I can't remove it now, might as well just keep driving it down and hope it goes over the step on the crankshaft. Nope. Part of the oil seal got snagged and lifted up. The seal was trash. At that point I said some choice words and went inside.

I ordered another seal that should be here mid-week. I'll drive that one in using the film negative this time haha! It was really a shame too because I drove the seal in nice and straight, it would have been perfect. Oh well, live and learn. Hope to have the new seal in later this week and then reassemble the saw over this upcoming weekend. Getting tired of seeing all these parts all over my work bench haha!

 

[cbfarmall]

I generally roll the shim up in the seal and then push it down over the crank. Easier that way.

 

[cbfarmall]

Also, you just learned why I buy 2 of each seal for these jobs.

 

[cdahl383]

I generally roll the shim up in the seal and then push it down over the crank. Easier that way.

Yeah that's what I had set up originally. I rolled it and fit it inside the crank seal, then slipped it over the crank. Of course it only works if you leave it there and don't remove it and forget to put it back haha!

The seals showed up early at O'Reilly's today so I picked them up. Should be able to give it another try sometime this week. I'm going to check out another saw later today after work.

I was working on my snowblower last night. We have a big storm headed our way and I don't have the tractor/plow set up yet, so I thought I'd get my snowblower going again. It quit running a few years ago and I just put it away and didn't want to deal with it. Dug it out last night, took the carb off, cleaned it really good (it was all gunked up), put it back together, changed the oil and spark plug, and it fired right up!

 

[cdahl383]

SUCCESS! I got the crank seal installed correctly this time! I used a little strip of film negative and that did the trick!

I put oil all over everything, crankshaft, seal bore, outer surface of the seal, inner rubber seal, and then put some grease on the bore and film negative and stepped area of the crankshaft. Everything was super lubed and slick. I got the seal started and kept it as straight as I could as I drove it down. Once I got it over the stepped area I knew I was good. I then pulled the film negative out and it was good!

I did another pressure/vacuum test. Pumped it up to 7psi and it held for a minute without moving so I called that good. Then I switched to vacuum and pumped it to about 13"hg. It had a very miniscule leakdown, but nothing to be concerned with. At this point, I'm going to call it good. When I started with this saw, I couldn't even pump it up to 4-5psi before it all leaked out. Not to mention the audible hissing sound of the air escaping from around the flywheel/crankcase area. After replacing that side and sealing it back up, I was able to pump it up to 7-8psi, but it leaked down a little too quickly. Now that I replaced the clutch side seal, it holds 7psi firmly. The vacuum side didn't hold well at all before the seals were replaced. Now it holds well with a very minor leakdown.

The amazing part is that it actually ran before like that with terrible air leaks everywhere. I would imagine it would run much better now with new crank seals and a new crankcase gasket.

I'll work on reassembling the saw over this weekend and hopefully by Sunday I'll have it back up and running again!

 

[cdahl383]

Put the saw all back together today. Unfortunately I can’t get it to fire. It popped off a few times but never started.

Fuel is shooting out of the muffler. Clearly it’s getting flooded out. I rebuilt the carb a while back and I put a new kit in it. I pulled the carb off and did a pressure test on the carb, it leaked down a little bit. Removed the needle and seat and cleaned again. Tested again and this time it held 7psi for almost 2 minutes with no leak down. Put the carb back on the saw and still won’t fire. Plug getting wet, flooding out.

Low speed screw is 3/4-1 turn out. High speed is 1 1/4 turn out. Metering lever is even with chamber floor of carb.

Saw is getting spark. Checked that few times, nice bright blue spark. Has great compression. The saw ran before but just not that well.

I know the timing is good as I set it at 30 degrees btdc. All you have to do is line up the marks. Looks the same as the photos when I disassembled it. Pretty sure it’s not a timing issue.

It seems like it has to be something with the carb. I think at this point it’s flooded out.

I’m going to try pulling the plug and turn it over upside down to get the fuel out of the crankcase after I drain the fuel tank. Otherwise it’ll just pull more fuel as I’m pulling it over.

Not how I envisioned today going. Kind of a letdown. Hoping it’s just flooded.

Any other ideas?

 

[cbfarmall]

Check spark under compression, with an inline tester? I seen saws that acted flooded but really had poor spark. Anyway, pull the plug, crank it a bunch to clear it out and use air to blow out the cylinder and try again. Instead of the choke, try squirting fuel down the carb to start with.

 

[cdahl383]

Check spark under compression, with an inline tester? I seen saws that acted flooded but really had poor spark. Anyway, pull the plug, crank it a bunch to clear it out and use air to blow out the cylinder and try again. Instead of the choke, try squirting fuel down the carb to start with.

I don’t have an inline tester. Will have to pick one up. Never used one before.

I cleared it out. Flipped it upside down and tons of fuel came out. Put the plug back in, turned the choke on, and pulled it over. Popped on the first pull. Turned choke off and pulled it over, popped again a little more but wouldn’t fire and run. After a couple more pulls nothing. Plug wet and flooded again.

It ran before, so I’m not sure it’s weak spark, but it’s definitely a possibility.

Wondering if maybe I have my low and high speed screws out too far? Allowing too much fuel in?

 

[cdahl383]

Check spark under compression, with an inline tester? I seen saws that acted flooded but really had poor spark. Anyway, pull the plug, crank it a bunch to clear it out and use air to blow out the cylinder and try again. Instead of the choke, try squirting fuel down the carb to start with.

Just picked this up online. Will give it a try once it shows up next week.

 

[cbfarmall]

Tons of fuel sounds like carburetor. What's the pop off psi for your carb? Thinking it should be 15-20. Maybe stretch the spring a bit.

 

[cdahl383]

Tons of fuel sounds like carburetor. What's the pop off psi for your carb? Thinking it should be 15-20. Maybe stretch the spring a bit.

I’m not sure. What does that mean? Pop off pressure? The spring holds to 15-20psi and then it opens? Should I pump it up to 15-20psi and see where it opens as a test then?

So you’re saying perhaps the spring is too weak, causing the needle not to fully seat during operation?

 

[cdahl383]

Ok I pulled the carb off this morning and took another look at it. Everything is in the right place (gaskets, diaphragms, etc), and the metering arm appears to be set correctly (flush with bottom of chamber floor). I pulled out the needle/seat/metering arm/spring and replaced it with the new stuff in the carb kit. Everything looked good, put back on the chainsaw, pulled it over with choke, popped after a couple pulls. Turned the choke off and pulled, nothing. Pulled plug, it's wet with fuel, and fuel spitting out the muffler.

At this point I'm convinced there must be an internal leak in the carburetor somewhere. Fuel must be getting pulled into the cylinder that's unmetered from the carb.

I was reading up on welch plugs. It says if they are leaking, the saw will flood or run rich. The welch plug sits above the L speed screw area and at the bottom of the metering chamber. If it were leaking, fuel could seep down into the L speed screw port and get pulled into the carb that way. I never touched the welch plugs, so perhaps that is the problem.

I've never messed with one before, so I'm going to read up on them a little more to make sure I don't damage anything removing it. I believe I got a new one in the carb rebuild kit I bought, so I'll make sure I have a new one first as well. Maybe that's all it is?

Maybe I could pull the carb off, remove the L speed screw, and then put some fuel or soapy water on top of the welch plug, then blow some air in that area? If it bubbles, I know it's leaking.

I just don't see how it could be the needle as it held 7-8psi for over 2 minutes with no leakdown. The metering arm is set correctly as well. Must be some other way fuel is getting by into the cylinder.

 

[cdahl383]

Took the carb off and tried a few things. I wanted to see if there were any leaks. I poured fuel into the metering chamber and it leaked out! The needle was in the seated position and the fuel just went right down through the seat and out the carb. When I checked it earlier it was seating. Apparently the needle is not seating properly.

I would think if I dumped fuel in the metering chamber and the needle were properly seated, the fuel would just sit there forever right? If it's leaking down then it must be getting by somewhere. The weird thing is it stops at a certain point. Even with the needle removed it gets to a point and then stops.

The carb has to be upside down when working on it, so perhaps that's part of the problem. But the vacuum from the cylinder pulling through the venturi would pull fuel through just like gravity is pushing it through when it's upside down.

I poured fuel on top of the welch plug and it stayed there. Didn't leak down. The only leak appeared to be by the needle/seat area. I'm going to look at that further and see what I can do to get that to seal up properly.

 

[cdahl383]

Here’s a video. Seems like if the needle were seating it would not leak fuel past it.

 

[Old2stroke]

Is there a rubber tip on that needle and a brass seat, or rubber seat and metal tip on the needle? Either way they have to be carefully cleaned and the metal part polished with rubbing compound to ensure a perfect seal. The needle should be a loose but not sloppy fit in the tubular passage above the seat, if you have changed the needle and the new one is sloppy, it could be skewing off center and the needle point might not be concentric with the hole in the seat, causing intermittent seating.