Zama Carb C1U-K68

[lefty]

I have this Zama carb that came off of a PB-200 echo blower.

The machine was running fine for years, fine meaning... it would start within about 7 pulls, take about a minute to warm up and then run great. I was always chomping at the bit to dig into her but figured if it ain't broke, don't fix it.

Well recently I noticed more fuel spitting out of it than going into it and of course, as you may guess, the lines had deteriorated so I figured I put a new fuel kit in it and clean out the carb.

So after examining the carb, I figured I'd replace the diaphragms as they are pretty stiff and a full kit was only $9.

So I upon inspection of the pump cover, I noticed air will not move through the primer circuit. From my experience, if I blow a little air through the primer nipple, I should get flow through one of the holes on the top that is covered by the primer bulb. But it's all stuffed up. I lightly inserted a skinny wire into the holes and it feels like there may be some type of rubber part or o-ring in there so I don't want to force. Is this the case? Am I feeling a rubber part in those holes or is that crud blocking the holes. I've been very gentle to this point as I have heard there are several non-metal parts in some of these small circuits.

[lefty]

Here's a picture. From my limited experience, if I blow with my mouth through the nipple at the top, air will come out the top hole closest to the nipple. But it's stuffed up.

[KE4AVB]

Here's a picture. From my limited experience, if I blow with my mouth through the nipple at the top, air will come out the top hole closest to the nipple. But it's stuffed up.

If you doing this and air is coming out the check valve then the check valve is either stuck open or you have destroyed it. You should only able to pull a vacuum ie air out the fitting and not push air into it. The other hole in the primer assembly is a inlet from the carburetor body chamber and should not be able blow though it either but able pull air in from carburetor. If either these check valve are stuck open or stuck closed you will not be able to prime. Sometimes you can clean these in an UC unit but other times when they are damage it is replacement of the primer unit or the whole carburetor.

Never ever probe these check valves. They only 3mm or less in diameter flat rubber pieces that are spring loaded and are non replaceable. This advice also goes nearly every other in a two cycle cube carburetor as a lot of the ports are check valves including the main nozzle.

Here is some info the basic operations of the cube.
http://www.zamacarb.com/page/carburetor-systems-operations

[lefty]

Thank you for the explanation on the operation. My perception, armed with this new knowledge, is that it is operating properly. I put the bulb on and operated it and can clearly feel it operating properly knowing now that it should pull through the inlet. The other side appears to operate properly as well.

I was sure not to probe aggressively on this. I gently "felt' with my tool as I anticipated something like that. After reading many posts recently on the forum, I know there was likely very delicate parts in here. So I don't think I ruined anything at this point but will report back either way.

Thanks again for sharing your knowledge.

[lefty]

I got the fuel kit in and the carb back together and she runs...pretty well. But after cleaning it, I'm thinking it may be running rich. It doesn't seem to climb as high in the RPM's as before. When I feather on the choke, it gets worse so I'm guessing I'm not starving for fuel.

So I want to at least try to adjust the carburetor but it has some of those tamper proof features. See pic. I think I recall you can just pry that red cap off but I'm not sure about the other screw. Any tips on this? I'm not adverse to buying the necessary tools but this is my own machine so if there is a hack, I'm all hears.

Thanks.

[KE4AVB]

On the K68 it only has one main (H) mixture the other one is a dummy plug and is not to be removed. Remove the limiter cap, lightly seat the mixture screw (CW), and then back out 1-1/2 turns (CCW). This is your initial setting. Once the engine is warmed then you fine tune the mixture at full throttle for best speed plus a little on the rich side for safety. It always better to be a little rich then too lean.

Best tuned with an rpm meter to 7000-8000 high speed. If you're exceeding 8000 tune richer to slow down.

Your idle speed should be set at 2700-3300 after you set the high speed.

[lefty]

On the K68 it only has one main (H) mixture the other one is a dummy plug and is not to be removed. Remove the limiter cap, lightly seat the mixture screw (CW), and then back out 1-1/2 turns (CCW). This is your initial setting. Once the engine is warmed then you fine tune the mixture at full throttle for best speed plus a little on the rich side for safety. It always better to be a little rich then too lean.

Best tuned with an rpm meter to 7000-8000 high speed. If you're exceeding 8000 tune richer to slow down.

Your idle speed should be set at 2700-3300 after you set the high speed.

Excellent. Thank you. I have a tach so I will clock the RPM's.

[lefty]

Done and done. Thanks for the help. Dialed in and runs great now.