Help: Jonsered 621 very hard start & stalls

[RCR 3 EVER]

We are having a running and starting problem with our Jonsered 621 saw when used for cutting firewood. The saw dies as if you turn the saw off at the switch both at idle and when the saw is in a horizontal position as if cutting a felling notch. My dad took the saw in to a repair show when it stopped when idling and would not restart.

REPAIR # 1: The carb was replaced, a new fuel filter and spark plug was installed. After running about 10 to 15 minutes, with some time at idle, it again stopped when idling.

REPAIR #2: Next went to another shop. They installed a new fuel filter, a new spark plug, a "genuine Tillotson" carb, and new points and condenser. They said that the previous carb on the saw was an "after-market" part and the Tillotson should be better. They also said they touched the spark plug boot and the engine stopped. The wire was found to be broken and was replaced. They also recommended to only use Shell 93 octane which was used for the next try. Again the above problem appeared. Pulled the plug--wet with fuel.

It is not a case of bad gas as this problem has occurred over a period of several months and different gas can fill ups. We also use the same gas/oil mix for other saws and they have had NO problems.


REPAIR #3: Returned the saw to second repair facility. They said a weak clutch spring would require the idle speed to be too low to keep chain at rest. The spring was replaced. They also said some of the carb parts which appeared to be elastomer impregnated cloth were distorted which indicated bad fuel again. They changed those bad parts in the carb, "pressure checked" the system, and installed new fuel. They also told us to only buy the 93 octane from a Shell station 20 miles from our house that they use exclusively for fueling their equipment, I guess that is the only gas station in state of MI that sells good gas?

Again the problem of stalling described above reappeared although the fuel in the saw was the same as put in by the shop. The saw had to be run at a high speed with the chain moving rapidly to keep from stalling after cutting about 20 pieces of firewood 3" in diameter. In addition to the idle problems, the saw would quit suddenly when held horizontally. It would not restart. The repair people now say the problem must be an air leak. More money to line their pockets? Why don't they test the saw?

We need help, repair shops say bad gas, yet our other saws run fine from same gas and oil mix. We even used their own special mix! Went through 2 carbs, 2 spark plugs, plug wire, 2-fuel filters, points, condenser,clutch spring, system pressure check and still problem remains.


Now I am contacting the forum with the real experts and operators for help. We are in need of some expert suggestions or some plain old advice before we give up on it, as we have spent too much on it already. I have received quite a bit of help on prior issues and hopefully my Dad and I will still be able to use this saw. This was the "always reliable saw" and he put it to me when I showed him my new Stihl and I couldn't start it and his started with 1-2 pulls and a grin ear to ear.


In summary, the problem as of now:

Cold start requires many pulls and you have to rev it for several minutes to keep it running on its own. Dies when rotated to horizontal position.

Tried restarting at WOT (wide open throttle), still no go. After cooling for one hour, restarted but had to keep chain running constantly and revving the throttle before it stalled again.


I have a workshop manual I downloaded that covers models 625/630/670. Will this manual be compatible with the 621?

Thanks in advance

 

[WadePatton]

i accidentally discovered the problem with one of mine tonight by cranking on it in very dim light.

i spotted a stray spark. which led me to re-insulating the plug wire as it was grounding out. so i say run it in the dark and look for sparks. do this with as many covers removed as possible.

good luck with it.

 

[Cantdog]

621 Troubles

Well you sure have done a bunch of stuff to this saw!! Or at least others have. I'll start with the easy stuff first.
(1)Have you checked compression?
(2)Have you removed the muffler and visually inspected the P&C for scoring?
(3)When the carb was replaced/rebuilt are you sure that they have the correct gasket between the carb and the isolation block (intake manifold) The gaskets that come with the rebuild kits will NOT work. They are not big enough to completely cover the impulse corridor. (air/vac leak)
(4)Have you checked the cyl bolts for tightness? Loose bolts will allow the case gasket to fail (air/vac leak)
(5) Check that the bolts are tight and gasket is good between the isolation block and the cyl.
If all this checks out it's on to checking the crankshaft seals. When you say that they "pressure checked the system" does that mean they pressure checked the carb only or did a pressure/vac test on the case?
Try the above easy stuff first.
The 621 is a very dependable, tough unit. You don't need "special" gas for it. All mine get regular or sometimes mid grade and run just fine.
No the manual for the 625,630,670 will do you no good except on how to adjust the chain!!
My suggestion is to investigate the above possibilities in the order given and let us know what you find. Good luck!!

 

[flyingtim01]

I see they've put about a dozen fuel filters in it, but did anyone change the fuel line? If you can visualize it, the filter hangs off the end of the line and into the fuel tank, and when you turn the saw on its side, the filter will swing down (and stay in the fuel) so the saw doesn't run starve for fuel. On old rubber lines, the ethanol in the fuel has a way of wreaking havoc and making them soft and sticky, so that when the filter swings down, it pinches the line closed. If the saw sat for a while, the fuel line may have also become hard and cracked, and again, when the fuel filter swings down, you're opening a crack in the line. I'd recommend changing both fuel lines (the line in the tank as well as the line from the pump to the carb) Sounds like you've already spent a lot on this saw...the fuel lines should be about $10, labor included. Hope this helps.

 

[stinkbait]

I had a saw that had a pin hole in the fuel line inside the gas tank. The saw would crank run fine and cut fine, but if the gas got below the pin hole the saw would start running irratically and cut off. As long as the pin hole was submerged the saw ran fine, but turn it on the side and it would die.

 

[Cantdog]

10-4

:agree2: Both good suggestions from WadePatton and flyintim as well. Both easy and cheap enough to eliminate. Either a bad coil or wire or pinched/collapassed leaking fuel line could cause these conditions.
Can't believe that a shop would not have replaced the fuel line when replacing the filters though. But you NEVER know.

P.S. One other thing I thought of is the tank vent valve could be stuck. It is the shiny fitting located on the square plastic connection block under the carb left hand side, where the fuel line to the carb connects. Remove the fitting and there is a small ball inside that should rattle when shaken. You can check this by just starting the gas cap when running (with not so much fuel in the tank as to leak out!!) and see if it changes anything. If this is clogged/stuck it will run ok at first and then starve for fuel after a short time. Just another thought and something else to check.

 

[HiOctane]

Cold start requires many pulls and you have to rev it for several minutes to keep it running on its own. Dies when rotated to horizontal position.

Tried restarting at WOT (wide open throttle), still no go. After cooling for one hour, restarted but had to keep chain running constantly and revving the throttle before it stalled again.[/COLOR]


I have a workshop manual I downloaded that covers models 625/630/670. Will this manual be compatible with the 621?

Thanks in advance

It loks to me that your mixture is too lean caused by few things.Does opening the LO needle give you a better idle ,mainly when saw on his side ?If you dont feel no difference,and shops have cleaned carb and such,then your problem is an air leak.Have a test done,i know its still money but a two stroke has to be sealed perfectly to run correctly.And your description of the problem looks like an air leak.

 

[jra1100]

I had the same problem

It turns out that some, maybe all of these had an epoxy liner in the gas tank. I took it to my local shop, which is a great place, and they put in carb kits and all sorts of things before they found this "gunk" in the tank. They scoured it out as best they could and replaced the fuel filter and got it to working. It did the same thing after a few tank fulls. I was down to Mark's in Dike, the Mac guy, and he had found the same problem with his 621. He had put some nuts in the tank and filled about half full of mix and sloshed it around every time he was in the shop, then dumped the gas and repeated. It took a couple of weeks (he is in the shop a lot when he's not on the road), and he got it cleaned out. New filter and gas line and he was good to go. I did the same thing, and now mine is right with the world. Might not help ya with your problem, but it worked for us. JR

PS. That tank valve thing could be caused by the same thing.

 

[WadePatton]

I see they've put about a dozen fuel filters in it, but did anyone change the fuel line? .

yeah, i had this thought too after logging off for the night.

 

[SawTroll]

I believe in checking the simple things first, like the LO setting and the tank vent - but this really has "smelled" air leak from post one.........

 

[bama]

It turns out that some, maybe all of these had an epoxy liner in the gas tank. I took it to my local shop, which is a great place, and they put in carb kits and all sorts of things before they found this "gunk" in the tank. They scoured it out as best they could and replaced the fuel filter and got it to working. It did the same thing after a few tank fulls. I was down to Mark's in Dike, the Mac guy, and he had found the same problem with his 621. He had put some nuts in the tank and filled about half full of mix and sloshed it around every time he was in the shop, then dumped the gas and repeated. It took a couple of weeks (he is in the shop a lot when he's not on the road), and he got it cleaned out. New filter and gas line and he was good to go. I did the same thing, and now mine is right with the world. Might not help ya with your problem, but it worked for us. JR

PS. That tank valve thing could be caused by the same thing.

I used a few hundred bb's and ran the saw for awhile with them siting on the bottom.

 

[jra1100]

Bama, or others that want to chime in, is this just a 621 thing, or were there other saws that had this epoxy coating? I don't recall it being mentioned ever on AS, but I've only been here since 07. I thought about posting this question before but forgot about it. Any help as always appreciated. JR

 

[Cantdog]

Tank Coating

I've never seen any kind of coating on the 621s. Just red paint inside. However I have an 80 that when I got it had some kind of coating on the inside of the tank. It was all wrinkled and falling off. I had quite a job getting rid of it. I just assumed it was something that some (previous owner/s) one had done at home, like "creme" tank sealer or some such "miracle mess" instead of fixing a tank gasket leak.
Two of my three 621s did come to me with about 3/8" of black varnish and sludge that was a real trial to clean out. The 80 had this as well as the failed sealer. Usually you can't really see the glop in the bottom of the tank but by reaching in with a screw driver or paint paddle you can find it if it's there. If this has happened to the OPs saw that would certainly cause it to run poorly!!

 

[flyingtim01]

Like Cantdog, I haven't seen anything special in the tanks of either my 621, 90 or 70e, just bubbling red paint and a bunch of varnished muck in the 90 that took 2 weeks of soaking to remove.

 

[RCR 3 EVER]

Great ideas and suggestions, I wonder why the shops never thought of the fuel line, air leak or vent prior to all the costly useless repairs, I even wondered if it was getting starved of fuel.

Anyway, I will pass along all the info to my Dad and we will work on the saw. Or rather he will I will watch since he is mechanical minded. Besides I am having some surgery on back tomorrow and will be out of it for a bit.

I will keep you informed of any results of our findings.

Is there a shop manual for this saw?

 

[RCR 3 EVER]

I've never seen any kind of coating on the 621s. Just red paint inside. However I have an 80 that when I got it had some kind of coating on the inside of the tank. It was all wrinkled and falling off. I had quite a job getting rid of it. I just assumed it was something that some (previous owner/s) one had done at home, like "creme" tank sealer or some such "miracle mess" instead of fixing a tank gasket leak.
Two of my three 621s did come to me with about 3/8" of black varnish and sludge that was a real trial to clean out. The 80 had this as well as the failed sealer. Usually you can't really see the glop in the bottom of the tank but by reaching in with a screw driver or paint paddle you can find it if it's there. If this has happened to the OPs saw that would certainly cause it to run poorly!!

I know we NEVER have painted the inside of the gas tank as far as I know it is in original condition. THis is first major problem with the saw.

 

[bama]

I've never seen any kind of coating on the 621s. Just red paint inside. However I have an 80 that when I got it had some kind of coating on the inside of the tank. It was all wrinkled and falling off. I had quite a job getting rid of it. I just assumed it was something that some (previous owner/s) one had done at home, like "creme" tank sealer or some such "miracle mess" instead of fixing a tank gasket leak.
Two of my three 621s did come to me with about 3/8" of black varnish and sludge that was a real trial to clean out. The 80 had this as well as the failed sealer. Usually you can't really see the glop in the bottom of the tank but by reaching in with a screw driver or paint paddle you can find it if it's there. If this has happened to the OPs saw that would certainly cause it to run poorly!!

I suppose I have seen the grey coating on half a dozen 621's. Looks like it was pretty evenly sprayed on, but I have no idea if that was done in a factory. There was no leak on these saws so it wasn't done for fuel leaks. I used a scraper on the tanks when I had the cases split on some. Very thin, plastic/epoxy type coating that was bubbling off the case.

 

[Cantdog]

Sealer

Yes bama on my 80 it was very even but ruined, and it had no leaks either.

 

[bama]

So......Where did it come from and who put it there???? Could it have been a factory option to put a sealer in the tank? Now that I think about it, I remember having to clean out 2 451EV's that I worked on.

 

[RCR 3 EVER]

I don't use the saw as it is too heavy for my aching back. My dad usually uses the saw and he is saying it is a sign that maybe he should not be cutting anymore. Hopefully, we can figure out the problem without taking it back to idiot shops who are ripping us off. We have not been able to find any others nearby that work on older Jonsereds.
How difficult is it to remove the fuel lines, where can we get a shop manual to help out?