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Author Topic: Chainsaw starts funny then comes down to idle  (Read 1398 times)

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Offline Guydreads

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Chainsaw starts funny then comes down to idle
« on: October 28, 2020, 09:51:54 AM »
Hello! I recently bought a Partner 500 chainsaw that is nearly 40 years old (more or less). I almost have it running, it just needs a little carb adjustment. What I'm really here for is the fact that when I start it (when it's been running for a little bit) it revs up to around 5,000 to 6,000 rpms (that's a guess, it's quite a bit higher than the idle) for around 1 1/2 seconds then settles back down.  I dropstart my saw with the trigger completely on. Is it just the lag of the trigger? Or is it something worse, or is it just normal? Thanks

Offline Real1shepherd

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Re: Chainsaw starts funny then comes down to idle
« Reply #1 on: October 29, 2020, 12:19:33 AM »
No, it's not normal.

Conventional wisdom says when you buy a saw that old with unknown maintenance....

You replace all the fuel lines and filter.
You do a vac and pressure test on the case with the muffler and carb ports plugged(should replace both crank seals for age anyway).
You put a complete carb kit in after cleaning it and new spark plug.
Then figure out what the factory setting was for that Walbro carb and adjust to that for starters.
Get a tach, because 6,000rpm is just a little off idle....not nearly enough. Should be 13,500rpm according to Acres.

Kevin

Offline kantuckid

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Re: Chainsaw starts funny then comes down to idle
« Reply #2 on: October 29, 2020, 09:12:15 AM »
And, to continue, the so-called, average person cannot properly do the case test even though they  might be quite able to adjust, replace or repair the carb, fuel lines/filter, etc., so you (most likely) g ;Dtta p ;Dy somebody to do the above checks -before you buy parts. 
Kan=Kansas;tuck=Kentucky;kid=what I'm not

Offline Guydreads

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Re: Chainsaw starts funny then comes down to idle
« Reply #3 on: October 29, 2020, 02:29:43 PM »
Ok. Thx for the information. I'll see what I can do to do the tests. I will let you know in the future what happens. Thanks very much!

Offline Guydreads

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Re: Chainsaw starts funny then comes down to idle
« Reply #4 on: October 29, 2020, 02:32:32 PM »
I also dug into the carb, only to find specks of dirt, and my air filter is quite dirty, so yeah that could be a problem. The saw DOES rev up to the specified 13,500 rpms by the way. Also, when I dug into the carb, the diaphragm was in really bad shape, just stiff and dry, so I ordered a repair kit for the carb. Oh, and the jets were quite dirty.

Offline Al_Smith

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Re: Chainsaw starts funny then comes down to idle
« Reply #5 on: October 29, 2020, 02:53:25 PM »
Every time I buy a used saw ,which BTW I don't buy new I just figure to rebuild the carb .I think a failed carb is why most of them are sold in the first place .

Offline Real1shepherd

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Re: Chainsaw starts funny then comes down to idle
« Reply #6 on: October 29, 2020, 06:33:09 PM »
At the very least, clean and rebuild the carb, check the fuel lines and filter and replace the crank seals.

You could be into your third tank and it goes lean and dies.....crank seal and probably damage inside the jug.

Just sayin'.....if you don't have the test tool for the vac/pressure test, at least replacing the crank seals puts you out of danger.

Any saw over 30 yrs old should have new crank seals put in as a matter of course. You're gambling your saw on those seals.


Kevin

Offline Guydreads

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Re: Chainsaw starts funny then comes down to idle
« Reply #7 on: October 30, 2020, 07:16:43 AM »
Ok. The guy did say as well that the carb needed cleaning, so definitely that was the problem with the saw. It was not running when I bought it. It was bought as a project saw so if I do (which is VERY likely) replace those crank seals, it'll get me some good experience. Thanks SOOO much for the input. I will make a follow up post to let everyone know if the saw runs. 
Are there as many selections for crank seals as for carbs? Or are they pretty much compatible? I really have no experience with crank seals. I do have one more problem. After watching a Youtube video on how to vac and pressure test, I realized that it wouldn't be easy, because there is no impulse line, and no place for an impulse line! There is only one fuel line on the saw, and that is from the tank to the carb, and there are no outlets or inlets for any other fuel lines that I can see after quite a bit of inspection. Anyway, I've ordered a carb repair kit, and hopefully I'll be able to find crank seals after further info on where to get crank seals from you guys. I love this community! So helpful and really polite. Thx a lot guys.

Offline Tacotodd

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Re: Chainsaw starts funny then comes down to idle
« Reply #8 on: October 30, 2020, 08:04:48 AM »
@Guydreads , there has to be an impulse line. HAS to be. That along with that funny gasket/diaphragm inside the carb IS the fuel pump. The seals, when done correctly cannot hurt the saws feelings! This might be part of the issue you are having.
Trying harder everyday.

Offline Real1shepherd

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Re: Chainsaw starts funny then comes down to idle
« Reply #9 on: October 30, 2020, 09:35:43 AM »
Ok. The guy did say as well that the carb needed cleaning, so definitely that was the problem with the saw. It was not running when I bought it. It was bought as a project saw so if I do (which is VERY likely) replace those crank seals, it'll get me some good experience. Thanks SOOO much for the input. I will make a follow up post to let everyone know if the saw runs.
Are there as many selections for crank seals as for carbs? Or are they pretty much compatible? I really have no experience with crank seals. I do have one more problem. After watching a Youtube video on how to vac and pressure test, I realized that it wouldn't be easy, because there is no impulse line, and no place for an impulse line! There is only one fuel line on the saw, and that is from the tank to the carb, and there are no outlets or inlets for any other fuel lines that I can see after quite a bit of inspection. Anyway, I've ordered a carb repair kit, and hopefully I'll be able to find crank seals after further info on where to get crank seals from you guys. I love this community! So helpful and really polite. Thx a lot guys.
A lot of the older saws have no boot & impulse line, The have an impulse channel built into the intake manifold. All the rebuild kits I see now for Tillotson carbs for example, supply the wrong intake to carb gasket. It's a diamond shaped thing that doesn't cover the impulse channel completely causing the saw to run erratically. DON'T use that gasket. The correct gaskets are out there and you can also make one from gasket stock.  

That has been covered in here and I brought it up in a couple of threads. Crank seals are easy to find. The only caveat there is to stay away from Chinese seals if you can. You can always take the seal down to a bearing house and let them find a replacement. Husky and Jonsereds for example, share the same size crank seal on many of their saws.

Once you know the OD, the ID and the thickness of the crank seal(this will be in mm), you can start your search. Amazon even has seals. Look for the vendor to brag about where the seal is made or ask directly. Japanese seals are fine if that is your choice. It's become a new world order now for bearings and seals....just stay smart about it. Some guy saying he uses Chinese seals "all the time" is not a testimonial for quality/durability.

95% of the time a vac/pressure tests that indicates a leak is from the cranks seals. The other 5% will show a leak at the cylinder base gasket or even the case halves themselves. So if you replace the crank seals, rebuild the carb and replace the fuel/vent lines, you'll have a 95% chance of completely fixing your saw. Who wouldn't take those odds? Lol....

Kevin

Offline Hilltop366

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Re: Chainsaw starts funny then comes down to idle
« Reply #10 on: October 30, 2020, 09:45:23 AM »
To pressure or vac test with no pulse line you can make a plate to cover the intake and put a hose fitting on the plate.

Offline Tacotodd

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Re: Chainsaw starts funny then comes down to idle
« Reply #11 on: October 30, 2020, 11:15:15 AM »
Kevin, NOW Iím learning somfin new and previously unbeknownst to me. Thank you for enlightening me!

GREAT job in saying all of these things!

Todd
Trying harder everyday.

Offline Real1shepherd

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Re: Chainsaw starts funny then comes down to idle
« Reply #12 on: October 30, 2020, 03:00:47 PM »
Kevin, NOW I’m learning somfin new and previously unbeknownst to me. Thank you for enlightening me!

GREAT job in saying all of these things!

Todd
Why thank you!

I use a thick piece of rubber that's wedge shaped to cover the exhaust port and then screw the muffler back down. Of course you could fashion your own plate with a rubber gasket if you want to get real adventurous.  

On the carb port, I usually use a couple of pieces of cut bicycle tubing as a gasket and bolt back the carb. VERY first things to check for with the vac/pressure test are the plugs you just made...lol! Otherwise, you'll be chasing your own tail.

Kevin

Offline sablatnic

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Re: Chainsaw starts funny then comes down to idle
« Reply #13 on: October 30, 2020, 06:06:24 PM »
Just two things.
You can't pressure test it, only vacuum test, as it uses a rubber pipe towards the cylinder. Two actually, the puls connection uses a rubber pipe as seal too.
If you need to take off cluch or flywheel, you can lock the flywheel by pushing an insex wrench through a hole in the saw body and into a hole in the flywheel. The hole is to the left of the clutch. About 4mm wrench will do. 
You can use the crank seals, intake and pulse seals for a Husqvarna 50, 51 or 55. 
The crank seals used to be named 505 27 57-19. Can't remember the other parts, sorry.
Your saw is basically a Partner 5000 with a different cylinder.

Offline Real1shepherd

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Re: Chainsaw starts funny then comes down to idle
« Reply #14 on: October 30, 2020, 07:24:27 PM »
Sounds like you have experience with this saw.....I'd have to see some pics of this pulse arrangement to understand what you're saying. It's fine to just vac test, but pressure too is always best.

As I said before, he doesn't need to buy a dual switchable Mityvac to do this......he can just replace the crank seals, replace the fuel filter, fuel filter line, vent line if there is one and rebuild the carb. Chances are, that fixes his saw.

Kevin

Offline sablatnic

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Offline Guydreads

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Re: Chainsaw starts funny then comes down to idle
« Reply #16 on: October 31, 2020, 10:52:44 AM »
First off, I want to say thank you to all of you, but especially to sablatnic! Thanks or taking the time to find those parts diagrams! I'll put those to good use. As far as the crank seals go....... hmmm. I watched a YouTube video on a chainsaw that had bad crank seals and well it could've been my saw. So that's probably one of the major problems with the saw. The carb repair kit is coming in the next few years. Lol just kidding. I took off the clutch and the drive sprocket was broken, because I . I ordered a new drive sprocket. The muffler could probably use replacement. I probably will order a used muffler from a parts saw. I repaired the broken wire that makes the circuit to cut off the saw. That was scary when we started the saw and we couldn't cut it off. And to make matters worse, at that point the saw was revving like crazy because the chain wasn't on, and because the low was waayyyyyyyyyyy to far out. Anyway, all I need to replace: Crank seals, carb diaphragms, fuel lines, and filter. Also need to put on a new sprocket. Once again: THANKS for all the help. I will let you know if the saw runs after the new parts are put on.

Offline Real1shepherd

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Re: Chainsaw starts funny then comes down to idle
« Reply #17 on: October 31, 2020, 12:00:47 PM »
Yeah, still need to see the saw in front of me to know why you can't do a vac and pressure test both.

In any event, great sharing on the IPL's.

Kevin


Offline Hilltop366

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Re: Chainsaw starts funny then comes down to idle
« Reply #18 on: October 31, 2020, 02:20:32 PM »
That was scary when we started the saw and we couldn't cut it off.


Another great use for the choke.

Offline Guydreads

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Re: Chainsaw starts funny then comes down to idle
« Reply #19 on: November 01, 2020, 08:24:51 AM »
Yeah, except the choke wouldn't actually bog down the saw, I had to use the low idle screw to stop it


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