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036 pro rpm issue?

made_of_stihl

made_of_stihl

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I posted this question in homeowners forum, then realized there’s this chainsaw forum. So reposting this here, hope that’s not a problem.

I have an 036 pro that runs fine. Bought a tach to check rpm and help tune. It read 15k rpm wot, is that possible? Checked same on my 038 super and read around 12.6k rpm. It has limit tabs on carb, so I cut the tab on the high adjustment, but could only get it to back down in 14k range before I couldn’t turn the screw anymore (and it didn’t sound right). Another thing I noticed. I tuned the LA and low setting at the beginning of the day. Periodically I set saw down to do something else, and the idle speed would change. Sometimes I’d hear it change and look over and the chain would be running, or I’d hear it slow down suddenly.

Couple guys in other forum recommended checking impulse line and intake.

So I was able to get this saw apart this afternoon. The impulse line did not appear to have a hole. Idk if this makes sense, but where the line attaches to the motor, it spins but does not slide off. I didn’t force it off, but curious what type of connection this is. Also checked intake boot. Didn’t seem to have any holes. Only thing I noticed wrong is gas cap doesn’t seal properly and gas leaks from it.

Anyone have any suggestions on how to move forward?
 

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albert

albert

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Replace that inpulse hose now. It pushes onto a barbed nipple on the crankcase. Get the hose from a Stihl dealer, they cut it from bulk Stihl hose. Most any other hose will not hold up. Yours is hardened. A good time to replace the fuel hose and filter if not done recently.
 
drf255

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Your intake hose is typical. If if pressure and vac tests, you don’t have to replace. As said above, it’s a good time to replace it, you’re there anyway. They tend to swivel easily but be impossible to pull off the barbed fitting on the case.

Do you know how to tune by ear? That’s the safest way to know what’s up at high rpm. Please check your piston through the ex port and make sure it’s not scored by running lean.

You probably have 2 different problems. The idle condition sounds like an air leak, and it’s typically the seals. An air leak big enough to lean you out at high rpm generally results in a saw that won’t idle at all. There are times it’s a slow leak that gets worse with running, like a torn intake boot, but it’s not typical.

As for your high rpm issue, I’d check the fuel system. The line/filter/vent/carb. The carb has issues with the needle and seat often. My saws are all ported, and the needle and seat are the typical culprits. Will it hold a lower rpm for a second or two and then wind out? That’s typical of a wet side that’s getting drained before it can refill. Get a carb kit and rebuild your carb. Check vent and grab a new oem line and filter. Vac test saw and make sure the slug isn’t already toast. Report back.
 
made_of_stihl

made_of_stihl

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Do you know how to tune by ear? That’s the safest way to know what’s up at high rpm. Please check your piston through the ex port and make sure it’s not scored by running lean.
I can do the low setting by ear. I looked into setting high, and ended up buying a cheap tach. The "4-stroking" is a term I've seen a lot, and I think I know what that is. I checked the muffler side this morning and I've attached two pics of that. The only mark I see is above the rings. Does that look like a problem?

Will it hold a lower rpm for a second or two and then wind out?
It's hard to remember now, but I think that's what was happening.

Vac test saw and make sure the slug isn’t already toast.
I don't know if I have the tools to do this. If I bring the saw in its current state (see other pic) to a shop, would they be able to test it for me?

I'm going to plan on going to dealer and getting fuel filter/line, impulse line, gas tank cap, and carb kit. I need to check the vent (not sure where that is yet). I'd like to hold off on parts if I can get the vac test done now and see if the seals need worked. Thanks for all the advice, appreciate your help.
 

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made_of_stihl

made_of_stihl

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I talked to the local dealer. They can do the vac test the way it is. So I guess I'll bring it down there, unless anyone knows an easy way for me to do it myself. Thanks again.
 
Ryan'smilling

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I talked to the local dealer. They can do the vac test the way it is. So I guess I'll bring it down there, unless anyone knows an easy way for me to do it myself. Thanks again.

You need a mity-vac type brake bleeder tool. They're not real expensive. Probably cheaper than what a trip to the dealer will cost. In my experience, bringing a saw to the dealer rarely ends up being reasonably priced or particularly effective, in terms of fixing the problem. But you could have a different caliber of dealer than I do.
 
made_of_stihl

made_of_stihl

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How about this vac gauge with a t-line added? Would that work? I was thinking I’d connect one end to crankcase and suck air through other and clamp it off. What’s the best way to seal cylinder ports? I’m thinking small plates with rubber on one side.
 

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Ryan'smilling

Ryan'smilling

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Some thin rubber sheets or something like gorilla tape. Then you can bolt the muffler back on to hold that side. Not sure if you can suck enough vacuum to do what's needed, but I've never tried.
 
Mad Professor

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How about this vac gauge with a t-line added? Would that work? I was thinking I’d connect one end to crankcase and suck air through other and clamp it off. What’s the best way to seal cylinder ports? I’m thinking small plates with rubber on one side.

That will work for vac but you should test pressure too. Will need a source of vac and pressure, don't blow out seals with 100 psi air tank....

You can take a piece of tire tube to make a seal for ex port using the muffler, same on carb side using carb, if saw was still together. A rubber stopper on the intake boot would work for where you are now.

@drf255


Has good suggestions concerning fuel starvation at high RPM. Clogged fuel filter in tank, screen in carb, or leak in fuel line. Look under carb covers, sawdust can keep diaphragms from freely moving.

If you need to do seals, get a flywheel puller and clean under that and clutch real well (clutch left hand threads). I have a dealer that will do seals ~ $15-20 labor, if you bring in a clean saw with seals exposed. Gasket/seal kit is cheap from Stihl.
 
albert

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Why can't you turn the mixture screw anymore? Trimmed it should not stop. If everything is good that H screw will not be out no more than 7/8 of a turn from lightly seated. If you set it for 13.5 k warmed up and it holds for a few seconds and then takes off you need crank seals. Usually the small flywheel side. It will hold presure ok but fail vacuum especially when warm.
 
made_of_stihl

made_of_stihl

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Why can't you turn the mixture screw anymore? Trimmed it should not stop. If everything is good that H screw will not be out no more than 7/8 of a turn from lightly seated. If you set it for 13.5 k warmed up and it holds for a few seconds and then takes off you need crank seals. Usually the small flywheel side. It will hold presure ok but fail vacuum especially when warm.
If I remember correctly, I had it turned out a couple turns and then it wouldn’t turn anymore. But I could be mistaken. It was past 7/8 of a turn. It did take off, after a sec, but the initial reading was over 13.5k. Again, this is going from memory, and at the time I didn’t know what to look for, so it’s foggy.

I’m going to try and test, and if I can’t I’ll take it to a shop to run pressure/vac test. If it’s crank seals, what tools would I need? Thanks.
 
made_of_stihl

made_of_stihl

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Had a few minutes this evening. Took carb apart. Found a lot of sawdust. May have been interfering. Also, checked vent. The red circle end of the vent inside tank fell off when I moved it with my fingernail.
 

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drf255

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Had a few minutes this evening. Took carb apart. Found a lot of sawdust. May have been interfering. Also, checked vent. The red circle end of the vent inside tank fell off when I moved it with my fingernail.
You need a carb kit. That diaphragm is supposed to be flat, so it’s likely a victim of ethanol fuel and isn’t pumping correctly. Get an OEM Zama kit, don’t buy AM.

Piston looks great, that’s good news.

That rubber red tank vent, you’ll need one. The ones for Holley accelerator pumps are cheaper and work the same way, can buy on eBay. I’d remove the carb limiters, trim the tab and then reinstall.

May as well buy a Mitivac tester if youll be working on saws. As said above, the cost will be less than any trip to the dealer.

Looks like you didn’t fry your saw at least. Where in NY are you?
 
made_of_stihl

made_of_stihl

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Get an OEM Zama kit
That rubber red tank vent, you’ll need one
Probably go to local stihl dealer today and get some parts. If they don’t have a vent, I’ll try eBay like you said.

I’d remove the carb limiters, trim the tab and then reinstall.
I now have both tabs cut off. I removed the screws for cleaning.

May as well buy a Mitivac tester if youll be working on saws.
My brother’s bringing his Thursday when he visits for Christmas. He said he never uses it, so maybe I’ll buy it off him if I’m able to do tests with it.

Where in NY are you?
I’m south of Buffalo near Fredonia/Dunkirk. Where are you in our “socialists republic”? :D
 
made_of_stihl

made_of_stihl

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Got over to the local dealer this afternoon. First thing I asked him, you sell only OEM parts right? He said yes. Then he gives me an Oregon zama rebuild kit. I honestly don’t know for sure, but I’m thinking it’s not OEM. Also got fuel line and filter, impulse line, and gas cap gasket. They didn’t have a vent, so ordered one off ebay

I asked about vac/pressure test. He sends me in the back because they have a saw being tested while I was there. They use a machine for pressure test that makes smoke. You could see the smoke coming out of the crank seals, that was neat. I asked how they do vac test, he said they don’t, only pressure.

This evening got the carb rebuilt. Second pic below is how I adjusted the needle lever. I have it so the back of the lever is even with the top of the carb housing. That’s my understanding of how to adjust ... I hope that’s right. Please speak up if I should do it differently.

I almost want to put everything back together and skip the pressure/vac tests and see if the carb rebuild, impulse line, fuel parts replaced fixes my problems. Impatient I guess.
 

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BangBang77

BangBang77

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Got over to the local dealer this afternoon. First thing I asked him, you sell only OEM parts right? He said yes. Then he gives me an Oregon zama rebuild kit. I honestly don’t know for sure, but I’m thinking it’s not OEM. Also got fuel line and filter, impulse line, and gas cap gasket. They didn’t have a vent, so ordered one off ebay

I asked about vac/pressure test. He sends me in the back because they have a saw being tested while I was there. They use a machine for pressure test that makes smoke. You could see the smoke coming out of the crank seals, that was neat. I asked how they do vac test, he said they don’t, only pressure.

This evening got the carb rebuilt. Second pic below is how I adjusted the needle lever. I have it so the back of the lever is even with the top of the carb housing. That’s my understanding of how to adjust ... I hope that’s right. Please speak up if I should do it differently.

I almost want to put everything back together and skip the pressure/vac tests and see if the carb rebuild, impulse line, fuel parts replaced fixes my problems. Impatient I guess.
A lot of saws will pass a pressure test that will fail a vacuum test, due to the design of the crank seal lips.

Any shop that doesn't perform a vacuum test is useless and doesn't understand the fundamentals of saw troubleshooting. I'd find another shop. Or just a MityVac kit and an old tire innertube and call it a day.
 
drf255

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Got over to the local dealer this afternoon. First thing I asked him, you sell only OEM parts right? He said yes. Then he gives me an Oregon zama rebuild kit. I honestly don’t know for sure, but I’m thinking it’s not OEM. Also got fuel line and filter, impulse line, and gas cap gasket. They didn’t have a vent, so ordered one off ebay

I asked about vac/pressure test. He sends me in the back because they have a saw being tested while I was there. They use a machine for pressure test that makes smoke. You could see the smoke coming out of the crank seals, that was neat. I asked how they do vac test, he said they don’t, only pressure.

This evening got the carb rebuilt. Second pic below is how I adjusted the needle lever. I have it so the back of the lever is even with the top of the carb housing. That’s my understanding of how to adjust ... I hope that’s right. Please speak up if I should do it differently.

I almost want to put everything back together and skip the pressure/vac tests and see if the carb rebuild, impulse line, fuel parts replaced fixes my problems. Impatient I guess.
The metering lever looks correct. Did you take some pics before hand? On most carbs, the lever will be level with the carb body or some type of mote edges around the lever. You can generally tell, if you put the lever in and it took a ton of bending to adjust, something is wrong.

Did the smoke pour out of your crank seals, or someone elses? You could reassemble and run, as long as you dont mind pulling it back apart. If it doesnt run right, be prepared to do a vac test next before you chase any other problems.

Start your saw with both needles turned out 1 turn from fully seated. A cheat method of knowing if you have a leak Is if you require the L needle out further than 1 turn to idle. Airleaks, unless massive, always will make you chase the idle settings.

If you dont have a Mitivac, I doubt you have the OEM tool that allows you to Easily vac test with the tank and boot attached. It bolts in where the carb goes. Dont forget youll need to plug Your decomp valve to get an accurate test, but you’ll probably be ok leaving it in. The Stihl manual is realistic and calls for less than X amount of leakdown over 60 seconds pulling 5mm of Hg vac. Most of us hobbiest’s go overkill and pull like 20 and wait an hour. Its not necessary IMHO, any saw I have had that had enough leak to have a problem will be obvious. They generally wont hold any vacuum for over 5 seconds.

I’m down on Long Island. Dave @fruecrue is in Alden, which I think is close to you.
 
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