PM700 scored cylinder

[FixIt20]

Any idea where to look for a NOS piston?

 

[FixIt20]

An update on the PM700...

I bought gaskets and a carb rebuild kit and a few other parts and reassembled the saw. I used the old piston and cylinder, whether I'm foolish for doing that is yet to be seen. I couldn't get the saw running, and after a couple of times flooding it, I got it to pop a few times. Then, (I think because I had the spring wound too tight where the spring "bottomed out" before the cord did) the hook on the spring broke off. So, back to ebay to buy a recoil spring. I just got that today, and put it on. When I got the saw together the first time and was trying to start it, I noticed that the cork gasket for the fuel tank was leaking, so when I got the saw out this evening I checked the fuel level and the level was below the gasket. I thought that was kind of strange, but I used the moldable gasket that came in my gasket kit and sealed up the gas tank and filled it back up with fuel.
I gave the cord a pull and to my surprise, it fired right up.
I had it running for just a little bit, and then shut it off. Then I couldn't get it started again. I noticed that the muffler was wet with fuel and if I let the saw set, the muffler would stay wet with fuel and there would be a spot of fuel under the saw. I figured out that the needle in the carb was not seated and therefore allowing fuel to siphon into the cylinder.
After adjusting that and pulling the cord a dozen times with wide open throttle, it fired up. I adjusted the idle and L and H screws to where they are close to where they should be-I think. I did one cut through a maple log and it cuts good and seems to have good power.
I hope to do some further adjustment of the carb when it is daylight so I can see what I'm doing and so I don't have to worry about annoying the neighbors quiet evening. The reeds in the "muffler" are broken off and it is not much of a muffler. It is more of just a passageway for the exhaust to travel through. As those of you know that have used PM700s, it is not the world's quietest saw.

 

[heimannm]

The wrist pin bearings are a standard SN76 drawn cup needle bearing, should be able to get them for $12 each +/-.

The NOS rings are currently unavailable most places and $40 a set sounds about right.

I've used a few LRB pistons and the rings and bearings seem to be O.K., just don't try to reuse the wrist pin as they are undersize and will not be a proper press fit in the connecting rod.

Mark

 

[heimannm]

Sounds like you are on the right track now.

Mark

 

[FixIt20]

Just curious if there is a good way to get the gas cap to seal on the pm700. The oem cork gasket doesn't seem to seal very well at all, and I tried a rubber o-ring, but that doesn't do much better. I was wondering if there's something I'm missing, or what you guys have found as a solution.

Thanks

 

[heimannm]

The cork gaskets get old and compressed, try a new gasket. Sometimes, doubling up the gaskets will help.

In many cases it is the duckbill valve in the cap that has failed and leaking. There are several different styles of fuel caps but many are serviceable to allow you to replace the valve.



Depending on which fuel cap you have, either the red Homelite duckbill valve as shown above, or the green Poulan duckbill valve as shown below will work.

Mark

 

[FixIt20]

Is there a reason that the carb on my pm700 would lose tune? It seems that I have to retune the carb midway through a tank of fuel. My Mac130 seems to do the same

 

[heimannm]

It is possible that the screws are moving slightly. You could always try a bit of blue loctite on the threads to see if that makes a difference. If is it actually changing and needs readjusted start looking for an air leak. Carburetor gasket, spacer (insulator) gasket, tank/insulator gasket, cylinder/insulator gasket, crank seals, even the automatic oil pump can cause the crankcase to leak but that is generally accompanied with bar oil into the crankcase burning off leaving dense white clouds.

Mark

 

[FixIt20]

I can understand how those things can cause poor tuning, but why would it continue to change?

 

[serdie]

I can understand how those things can cause poor tuning, but why would it continue to change?

An air leak will get bigger as heat tends to expand things.

 

[FixIt20]

All the spacer gaskets are new, so I would least expect those to be leaking, but the crank seals are still original as far as I know, so those could definitely be a potential problem. Any way to test them without dismantling the entire saw, or would you just replace them? If so, would I be able to buy them from someone on here for a reasonable price? They are available NOS on ebay, but $25 for two crank seals seems a little excessive.

 

[Maintenance supervisor]

Half way through a tank? Everytime ?Could have a pin hole in the fuel line, I ve seen that smoke a saws piston before.

 

[FixIt20]

I had thought it could be something to do with the fuel level changing, but the fuel line is new. Unless I would've somehow damaged it when I put it on.

 

[Maintenance supervisor]

I had thought it could be something to do with the fuel level changing, but the fuel line is new. Unless I would've somehow damaged it when I put it on.

Where did you find the fuel line?
I know that I have pulled pretty hard on a fuel line and put a small tear in a new one , ever the hemostats I used tore one once.
Sharp edge on the tank port?
It's an easy thing to check first and eliminate before anything else.

 

[A.C.195]

Is there a reason that the carb on my pm700 would lose tune? It seems that I have to retune the carb midway through a tank of fuel. My Mac130 seems to do the same

Does it ravv up all on it's own?
Mine does that too . Can't figure out why. It will after a bit off cutting, I set it it down, and it revs up all on its own. Why?

 

[FixIt20]

Does it ravv up all on it's own?

Mine doesn't do that at all.
It works fine until it is mostly warmed up and then when it's revved up, if I release throttle (as in coming out of a cut), it almost dies, but then comes back up to a normal idle. When it gets all the way warmed up, rpm will drop far enough that it dies unless I feather the throttle a little bit and gradually let rpms finish slowing down, then it idles fine.
Also, after it is warmed up, an immediate restart is easy with one pull of the cord. But, if I let it set for a little bit, such as refill with gas and oil or just slightly longer, it is almost impossible to restart. It also starts with a couple of pulls when it is cold.

 

[Maintenance supervisor]

Did you check the pop off pressure of the carburetor?
It almost sounds like your flooding out as it goes.

 

[FixIt20]

That reminds me...after it gets warmed up and starts acting up, I was going to loosen the fuel cap to release any pressure in there and see if that made any difference. I'll try this and see what happens.

 

[FixIt20]

When I open the fuel cap and release pressure the saw runs normal again. Any ideas?

 

[heimannm]

Pressure test the carburetor, I think you will find the metering needle is leaking.

Mark