Chinese chajinsaw carbys

[geobee]

Hi all, new here. Have plenty of electrical experience so may be able to help others if need be in future. My issue today is with several brand new Chinese carbys I have on hand. With all of them there seems to be an issue where the fuel primer bulb cannot pull the fuel through the carb. I have the top connection on the carb going directly to the tank, and the side connection going to the suction barb on the fuel primer bulb, with the outlet from the bulb returning to the tank. All the components are new, the bulb, tried three new ones, fuel lines, tank strainer is clean, and as I stated, I have several of these carbs, all the same result. Even tried reversing the carb connections, just in case they were wrong, still the same result. Uploaded a carb pic which may help. Any ideas would be great. Many thanks.

 

[lecbr600]

Side connection shall be connected to the tank. Top connection is the impulse line, from engine/carter pressure/vacuum line. Impulse line lets carb to act as a fuel primer, to suct fuel from tank


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[geobee]

Hi, thanks for the quick reply. I tried it that way also, no go. When you say impulse line, not sure what you mean there. The carb has a small hole at the top of the engine flange which I believe once the engine starts, creates the suction to operate the fuel suction pump at the carby top. I can only assume that the primer bulb would then go on that top connection to act as a fuel pump to prime the engine until it starts and it's own pulses will draw the fuel? I tried to draw fuel through the carb by mouth, using the connections you say, but cannot get anywhere, so the primer bulb wont either. Beats me.

 

[Thommo]

The fitting on the side is the inlet from the tank. It should be connected to the fuel hose with the filter on it in the fuel tank. If your carby has the impulse hole drilled into the front to get the impulse from the carby insulator on manifold , then the top fitting will go to the suction side of the primer. If the primer is not pumping fuel through the carby the first thing to check would be a kinked or pinched fuel hose or a blocked fuel filter in the tank.

 

[geobee]

The fitting on the side is the inlet from the tank. It should be connected to the fuel hose with the filter on it in the fuel tank. If your carby has the impulse hole drilled into the front to get the impulse from the carby insulator on manifold , then the top fitting will go to the suction side of the primer. If the primer is not pumping fuel through the carby the first thing to check would be a kinked or pinched fuel hose or a blocked fuel filter in the tank.

Hi, thanks for that, yes, I hooked it up that way and got the saw to start and run, after using aerostart spray, but once stopped, it would not start by itself. The primer bulb doesn't fill with fuel when pressed several times. No kinks, strainer is good. Just cannot pull fuel into the carb, and primer stays empty.

 

[nenicu]

Ok ,i presume that your saw is a 52cc or 62cc Zenoah Komatsu clone. The top black fitting is for the impulse line that comes thru the partition that the carb is mounted to. A small black line. The side black fitting is for the fuel line that comes from under the carb. The small copper tube on the left of the carb[if it's there] is for the primer. If you have connected the lines this way and you can not prime the carb, the next step is to switch the lines at the primer bulb. Good luck.

 

[nenicu]

Usually the primer lines are clear lines. You got them wrong. For visual aid you can go on Ebay and look at pictures with saws like yours.

 

[Thommo]

The hose from the primer bulb to fuel tank is the return line. The primer should suck fuel through the carby to primer bulb then return to fuel tank. If the primer bulb won't fill with fuel when used then you either have the hoses on the wrong way around or have a blockage somewhere. If the bulb pops back out after you press it but only has air in it, then you have the hoses on the wrong way around so it is only sucking air from the return hose. If the bulb stays pressed in after you push it, then you have a kinked hose or blockage somewhere.

 

[geobee]

Many thanks, took the primer out of the saw and it pumps fuel as normal. On the carb it will not pull the fuel through. I have tested the suction direct from the tank and it is good, no blockages. All 4 carbs are new but none will allow fuel to be pulled through them by the bulb or by mouth test. When pressing the primer bulb as it should be setup, it comes back out slowly, but no fuel in it. I believe it is struggling to because of the carb fault. Remove the line for the carb and it works as it should. May have to order a different brand of carb. Beats me.

 

[Thommo]

Its quite likely that you have the wrong carby for your saw. The primer nipple is usually on the side just in front of the mixture screws. The carby you show looks like the top nipple is the impulse which is a vacuum hose that runs to the crankcase to operate the fuel pump in the carby. You really need to undo that screw that holds the top cover on and see what is under there. It is the fuel pump diaphram under there and you need to check if that top nipple leads to the fuel side of the diaphram or the vacuum side.

 

[geobee]

Yes, maybe correct about the wrong carb, I was given the saw, an Ozito sold by Bunnings, as a ''too hard'' project and it has been. I cannot locate a service manual for it to check the carb system, just a user manual that kind of shows the carb and primer, but not very well explained. A repair manual would be great if I could have a look at one, but these Ozitos are a Bunnings brand and very little support. I have other saws, Husk's etc, but this thing is testing me. https://www.manualslib.com/manual/895003/Ozito-Pcs-406.html?page=8#manual

 

[Thommo]

Looks like the 38cc version which will be the same as a Baumr ag SX 38. There are heaps of other brad names that are the same saw. It has the primer fitting on the carby just in front of the mixture screws pointing downward.

 

[nenicu]

Your carb is for the 52 cc clone. For the Ozito you need another carb with impulse from the intake spacer and built in fast idle. You can make this carb work by drilling the impulse passage in front of the carb[ has a little sign allready] and mounting the top part from the original. You loose fast idle and gain a little bigger venturi on the carb you have. The primer lines can be blocked . And you may have to adapt the choke rod.

 

[geobee]

Your carb is for the 52 cc clone. For the Ozito you need another carb with impulse from the intake spacer and built in fast idle. You can make this carb work by drilling the impulse passage in front of the carb[ has a little sign allready] and mounting the top part from the original. You loose fast idle and gain a little bigger venturi on the carb you have. The primer lines can be blocked . And you may have to adapt the choke rod.

Hi, many thanks. I did look at that section a while back, then took different directions with it. Will drill that impulse hole and put the original top cover on, which I have , luckily. The choke rod seems to be going to hook up ok. So I guess with this idea, there will be no need for a primer, as when cranked, the engine will draw it's own fuel by the impulses via the carby impulse hole. Will let you know how it goes.