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Junk collector
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Discussion Starter · #1 ·
Hey friends. I tried to use my repaired Poulan Pro 3816 chainsaw today and it won't idle properly, instead the engine takes off like the throttle is sticking partially open (its not, I checked). This is the saw I got at a yard sale for $15.00 practically new. The owner said it wouldn't start, I found he had put way too much oil in the gas. Fresh 40:1 and a little carb adjustment and its been cutting fantastic until today.

This saw is a current model, you can see it on the Poulan website. It has a funky Zama carb with two venturis. The upper venturi is dry and has the throttle plate. The lower is wet and has the choke plate. I'm thinking it has developed a vacuum leak somewhere, maybe between the carb and baseplate, or between the baseplate and engine. Any ideas out there?
 

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Maybe check the exhaust. If it was ran with too much oil the spark arrestor screen may be caked up resulting in restricted flow.
 

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...and change the FUEL FILTER (should be done regularly anyhow). If it's the fuel filter it will run lean an want to run-up. It probably won't cut well either as it heats up starving for fuel.
 

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Junk collector
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Discussion Starter · #5 ·
Thanks alot guys. I changed the fuel filter when I first got it and I know the air filter is clean. I'll try to check the muffler tonight.
 

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Junk collector
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Discussion Starter · #6 ·
I worked on the saw a little before work today. I found there is a hairline crack in the plastic carb mounting plate. It is very fine and does not go all the way around. Looking inside the mounting plate I cannot see that the crack goes all the way through. I'm thinking I may be able to put some epoxy on the crack, apply Permatex gasket snot (not silicone) to the mounting surfaces, and then properly torque the carb mounting nuts. Any ideas for what torque I should apply? I have a very accurate inch-pound torque wrench.
 

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Lawnboy Green
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633 Posts
Air leak is your problem. Maybe you can fix it with epoxy and a couple good gaskets? You can also buy a new insulator online through the Poulan Parts Store.

On these saws pulse is piped up from beneath the piston in the crankcase through a channel cast into the cylinder. When the channel reaches the intake port, they use the adapter to bring the pulse from the bottom of the port to the top, and this is why it has the S looking groove cast into it. Check your gaskets here. Impulse runs the fuel pump portion of the carb.

Check your fuel line closely too because the ethanol fuel will rot the older vinyl line. Look closely where the fuel line is stretched over the primer bulb connect and carb attaches. If there is a crack in the line it will allow the carb to run lean causing a scuff or piston score. You can use the larger 3/16 x 3/32 Tygon fuel line if you dont mind opening up the tank port where the fuel line comes through with a 1/8 drill bit.

Best wishes,
Bob
 

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Junk collector
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Discussion Starter · #8 ·
Bob,

Thanks for the detailed response and helping me to understand how this engine works. I worked on the saw last night and found that the crack is insignificant. It does not go all the way through and may just be a casting imperfection. What I did find is that the fuel line in the tank split and dropped the filter, I suppose it was just sucking air into the carb.

So I thought I would put a new fuel line on it and be done. Well, that wasn't to be the case. I keep rolls of 1/8 fuel line and as it turns out this saw uses line thats a size or two smaller than that, maybe 3/32? 1/8 will not fit on the carb ports, it is too small. What size do I need?
 

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my dad's poulan was doing as you describe, and I disassembled the carb and it had a small screen that was round and about the size of an aspiran tablet inside the carb itself that was clogged with fine sawdust, the saw would sometimes start and run fine until that screen got soaking wet and would swell up and cut off fuel, then the saw would die. a few days later, after it would dry out again, the saw would start rightb up again and repeat the same thing.
 

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Junk collector
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Discussion Starter · #10 ·
Yeah, I found the screen you describe and cleaned it out. Still not wanting to run.
 

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I would guess that if the orig owner had problems with it running and you have it and still having problems running. Then do one of two things ,,, get a complete carb rebuid kit or a new carb.. If it was me , I would go for the new carb since it is so new ,,,,,but thats just me ..
 

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Junk collector
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Discussion Starter · #12 ·
Yeah, thats the direction I'm heading.
 
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