OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Kirby H4-4A engine rebuild

The carby on this engine is a simple governed, fixed jet unit with a float bowl and pressure primer. The only adjustments are for the mixture and idle and these are usually factory set. The other style of carby fitted to these engines is a diaphragm type. Diaphragm carbies will work better than fuel bowl types at higher angles of tilt, though unless you are mowing at angles greater than 45 degrees, there is no real difference. Fuel bowl carbies are a bit more robust (no diaphragm to rot) and all types of carburettor are sensitive to dirty fuel and fuel residue build up (varnishes) over time.

All I did with this one was to strip it then clean it in carby cleaner. I blew it dry then reassembled it with new gaskets and needle valve. I also cleaned the fuel tank and screen filter as well as the metal fuel line. I replaced all the flexible fuel lines and checked the fuel tap and primer.

The cable tensioning spring and governor spring were both OK. A new air filter (oil soaked foam type) was fitted.

I reset the two carby screws to about where they were and refitted it all to the engine.

When I started the engine and let it warm up to operating temperature, I opened the throttle fully and adjusted the mixture screw to the midpoint between too rich and too lean (the engine runs roughly at both extremes). I adjusted the idle screw so the engine idled at a reasonable speed. That's it.

The governor can be checked by moving the lever and making sure that the butterfly opens and closes (engine revs will rise and fall).

Finally, the two limiting screws can be set. These seem superfluous - maybe someone else can tell me what they actually do.



Cable and spring set up. Speed limiting screws can also be seen.



Throttle cable tensioning spring attachment.



Governor spring.



Wire link between governor and butterfly. Mixture screw on left and idle adjustment on the right.
The small pinhole above the float bowl on the body of the carby is used to check the carby.
If fuel is coming out of here, then the float is either not set correctly or isn't working properly.



Primer. This one was OK and only needed cleaning.


Chris