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Want experts opinion on metering diaphragm

Started by GlenM, January 29, 2010, 10:52:00 AM

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GlenM

After years of cleaning, re-kitting 2 cycle carbs, I've almost come to the conclusion that the main problem with these carbs is most always the stiffening of the metering diaphragm, the pump diaphragm most always seems to be pristine and the metering needle is good.

Anyone have an opinion on this?
I'm talking about a thorough cleaning and just installing a new metering diaphragm.
Thanks,

joe_indi

GlenM,
You are right, partially. It would be more appropriate to say that the metering chamber is the area where most of the problems crop up.
A leaking metering needle, blocked fuel passages, stuck jet valve, you take your pick, and yes the metering diaphragm.
It is quite easy to check the pump diaphragm for proper functioning.
But the metering diaphragm is not that easy.
You can only compare the diaphragm with a new one to check for stiffness.
Even a slight stiffness is enough to change (lower) the fuel level in the metering chamber.
The other check you have to  do is for air leaks.
The pump chamber is easy to check with a compression tester.
That is not the case with the metering chamber.Its easier to just replace the gasket.

Joe

GlenM

Joe,

Appreciate the info in your reply.
Most, if not, all the Walbros I've re-kitted use the same 95-526 metering diaphragm, and the shop where I buy the kits stocks these separately, so, I bot several. I have a couple to clean/rekit on workbench, everything else being tested good, I'm gonna try to get by with just new metering diaphragm.

Thanks again,
Glen

Ed

My experience also, I think did 3 of my saws last winter, the newest was 12 years old, they were due.

Ed

GlenM

Quote from: Ed on January 29, 2010, 02:20:06 PM
My experience also, I think did 3 of my saws last winter, the newest was 12 years old, they were due.

Ed


Thanks,
Forgot to mention I would only do this to my stuff, someone else's I would insall entire kit.  All get a thorough cleaning.

g

Al_Smith

Most of the newer carb kits use a material for the fuel pump/check valves  which is more resiliant to ethanol fuels .Unfortunately they have not yet developed a much better metering diaphragm than the old stand by buna-n impregnated cloth which has been around since shep was a pup .Buna -n does not hold up to alcohol very good .

GlenM

I believe you're right.  Took a carb apart this afternoon that had the buna type pump/valve gasket, it was stiff and one check valve curled up.
I guess that's why they came out with the blue mylar type pump and the little brown teflon one.

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