Zama C1U – K27A gasket question

[andytw]

Hi,

I am servicing a Zama C1U – K27A. I have a gasket and diaphragm kit GND-12.

The question I have is with regard to the fuel pump diaphragm. There are 2 supplied in the kit. One is rubber and one is a thin mylar type material.
Both are the same shape with the same cutouts. I am going to use the rubber one as that is what I am replacing but wonder what the other mylar one is for.

Thanks

andytw

[Luffydog]

Not too much into two cycles but thinking one is for non enthol fuel which is the rubber one and the other is for ethanol. These days don't have much luck on rebuilds time u buy the kit and the time to rebuild almost cheaper to replace the carb with no issues rather than rebuilding. Maybe someone else will chime in that knows more about.

[bgsengine]

Mylar one is more durable and should be used in most cases where ethanol blended fuel may be used. The rubber one is not as durable , however it is more flexible and may be used in situations where an engine is more "worn out" (lower compression) as it will be easier for diaphragm to pump fuel - but in most cases, I'd go with the mylar one for long term durability

[KE4AVB]

Not too much into two cycles but thinking one is for non enthol fuel which is the rubber one and the other is for ethanol. These days don't have much luck on rebuilds time u buy the kit and the time to rebuild almost cheaper to replace the carb with no issues rather than rebuilding. Maybe someone else will chime in that knows more about.

Sometimes it is just as cost effective but not in this case; unless, there is main nozzle problems. The Zama is at least $50 and even Chinese clone on Ebay is over $35. The K27A is an easily cleaned and rebuilt carburetor too. There are carburetors that due the lack of rebuild parts that get replace. On some Zama there is a richer plunger operated by the throttle shaft (also those choke-less designs) that o-rings and the plunger itself wear out and is non-replaceable. I have only replaced two cube carburetors this year out about 50 that were rebuilt. Both were for the same customer with him bringing back the next day one of the Stihl FS85 toasted. It was straight gassed, a waste of a $65.00 carburetor.

As for if Mylar or rubber pump diaphragm as BGS suggest go with the Mylar if identical. Rubber tend to harden and curl up those pump flaps especially with the chemical additives there are in today's fuels. It the same with metering diaphragms which I now stock the most common ones along there matching gaskets; although, most GND kits are just as cost effective. The only time I use rubber version now is when there was heavy corrosion and the Mylar doesn't seal good. I do get a few in with water damage.

Also a good ultrasonic cleaning is suggested if not already done.

[andytw]

Hi,

Many thanks for your informative replies. I will go with the Mylar, then, and see how I get on.
Regards new carb, it is not really worth it, as this is an old Mantis cultivator that seldom gets used. It does get left year in year out with a tank full of fuel so when I do think I might use it I find it is all gummed up with oil. Really must drain it before storing it

And WRT ultrasound, I don't have the facility. I am not in the business, just a D-I-Y'er. I do strip out as many parts as can be removed and clean through with an aerosol brake and clutch cleaner, which is pretty vigorous, and then blast all holes with an aerosol air brush.

Thanks again,

andytw

[Mek-a-nik]

Andytw, you might want to consider one of these:
http://www.harborfreight.com/ultrasonic ... -3305.html
It's a cheap Chinese gizmo, but it works good. Amazing how well they work (ultrasonics in general). I use a mix of vinegar and Simple Green or Purple Power.

[KE4AVB]

And WRT ultrasound, I don't have the facility. I am not in the business, just a D-I-Y'er. I do strip out as many parts as can be removed and clean through with an aerosol brake and clutch cleaner, which is pretty vigorous, and then blast all holes with an aerosol air brush.

The problem using cleaners like these is that cube carburetors do have small check valves that easily damage by these and by forced air. It doesn't take much to destroy a 2.5 mm rubber check valve which why most us uses an ultrasonic cleaner. All it take one large enough to fit your carburetor in; usually a 2.5 liter unit will work fine as long as you can completely cover the carburetor with the liquid cleaning solution. You don't need to complete disassemble the carbs either; although, I do remove the mixture screws to allow more access to cleaning solution. I have and still do leave some the gaskets in place as it don't usually hurt them. Example are struck on manifold gaskets.

[wristpin]

You don't need to complete disassemble the carbs either

I'm never one for doing more work than is necessary but it is necessary to dismantle far enough to "let the dirt out"! U/S doesn't miraculously make the dirt disappear, it bombards it with tiny imploding bubbles that shake it loose and it needs to go somewhere! It's good practice to alter the orientation of the carb in the tank a couple of times during say, a half hour session so that it can "fall" out.

[KE4AVB]

I must have an oddball cleaner as most of the dirt flows upwards then disperses when it working or maybe it is because I use Dawn Ultra. Today it was Cherry Blossom scented that I used.

As far disassembly I usually disassemble enough the install a new carburetor kit or a GND kit

[Skywatcher]

Hi Andy

According to the Zama manual, if the flat surface of the pump side of the carburetor had been machined, use the mylar diaphragm. If the surface has been left as cast, use the soft flexible diaphragm. All the best,

Sky