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Poulan adjustable carb

Posted by ray_and_laura North Calif. (My Page) on
Tue, Apr 26, 11 at 12:22

We just received a Poulan pole saw from Northern Tool. I was very relieved to see that it has an adjustable carb, although the adjustment screws are not slotted. Instead they have very fine splines.

Searching ebay turned up a seller in Florida who has the splined screwdriver. We will wait until the screwdriver arrives before even starting the pole saw. That way it can be broken in on a nice slippery 32:1 oil mixture and a rich fuel setting for cool running and long engine life.

To get to this point on my 026 saw, bought 11 years ago, and Echo string trimmer, bought 8 years ago, I had to search out and install adjustable carbs to replace the fixed jet units.

Those 2 tools are thriving on the 32:1 oil premix and slightly rich running carbs. After a lot of very hard work the pistons still look perfect and the compression seems just like new.


Follow-Up Postings:

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RE: Poulan adjustable carb

R&L: To the contrary with todays modern oil technolgy 32:1 is a waste of money and can cause excessive carbon deposits and piston demon heat and ring blowby . I have not mixed anything richer than 40:1 in over 15 yrs. , which was a Outboard motor during breakin . After which 50:1 was routine . I believe the Stihl if mid 90's vintage spec'd 50:1 and I know that the Echo recommends 50:1 also . But each to his own I guess lol .


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RE: Poulan adjustable carb

Ewalk, I am neither a metalurgist, lubrication engineer nor chemical engineer. However, I have decades of experience in racing off road motorcycles in organized competition on the Mojave desert of California. While participating in that sport, I read everything I could get my hands on concerning the mechanical aspects of the sport. One of the articles I read was based on actual dynomometer testing of 2-stroke race bike engines with oil mixed at different pre mix ratios.

Because increasing the quantity of oil in the premix increases the viscosity of the premix, carburetor metering changes to compensate for the increased fuel viscosity was part of the test to maintain a constant air-fuel ratio. I know this is hard to believe, I also found it surprising, but a 20:1 premix ratio was most powerful in the tests. The testers theorized that increased lubricity decreased power losses to friction.

After publication of that article, I ran my own race bikes and my sons' race bikes at 20:1. Instead of the expensive "designer" oils sold for high prices in small containers, I used garden variety Castrol 2-stroke oil that I bought at case quantity discounts and actually spent less money on premix oil than my friends who were using the expensive "designer" oils are 50:1 to 60:1 ratios.

As for carbon deposits, 2-stroke design has evolved to include complex "power valves" that are restrictions placed in the exhaust ports to vary the size of the exhaust port depending on engine RPM. That exhaust port restriction is where I expected carbon depostis to form quickly. To my pleasant surprise, the Castrol is so clean burning even at 20:1 that only tiny amounts of carbon formed there as well as on piston crowns and in ring lands. There was almost nothing to clean away when I opened things up for maintenance.

The ultimate bonus of this is that when I would tear an engine down after a season of racing, I would find cylinder walls, piston skirts, rings, rod bearings and crankshaft bearings wet with oil. The hone marks were still clearly visible in the cylinder walls after a year of racing abuse! From that I was sold on the concept of abundant lubrication for increased engine longevity. Just to have something to do I would replace the piston rings.

It is my understanding that manufacturers of 2-stroke equipment are under a lot of pressure from emissions bureaucrats to recommend very lean premix oil ratios and to build in very lean carburetor mixtures. My experience with my Stihl 026 saw and Echo string trimmer is that they run vastly better (easier starting, more power, higher RPMs)with adjustable carburetors tuned slightly on the rich side of optimum than they did with the lean factory fixed jet carburetors.

I have worn out many chains and a few bars on my 026 in the past 11 years but when I pull the muffler to clean the spark screen and look in the exhaust port at the cylinder and piston those items look perfect. The exterior of the saw shows it's done a lot of hard work however.


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