more on this carb problem

Zane

Rocky in MO

Rocky, Thanks for the reply, I have been fighting this thing for about 3 months now and one of the thing suggested was drilling that hole or cutting the gasket a tad between the carb halves. It was more of a diagnostic thing than a fix. When I first rebuilt the carb it looked pretty rough at the mating surfaces so I put a sheet of medium grit sandpaper on a sheet of glass and used that to get the surfaces flat and as true as I could. The choke does not help in either case, not with the hole open nor closed. This hole is very small, about the diameter of a small paperclip. This is just one of those things that I have decided "I am going to fix it, come he11 or high water". I can use it like it is, but that is not the point, something just ain't right and I want it to be RIGHT. It is not just some old junker, I have a lot of time and energy in it, as most of us do.

Have you ever had a timing light on it, to verify the mech. advance is working? (Yeah, I know, front-mount, no timing marks. Easy enough to make your own on the front pulley.)

Have you ever looked at it on an ignition scope?

And, I'd be LOST without an ignition 'scope.

You write..... ."While the final main needle adjustment is about 2 1/2 turns, and the engine runs good at WOT without a big load..... .it still cuts out and bogs too much under full load"..... .you say you've replaced the sparkie wires with good solid copper-core wires....BUT....are you certain you have yer firing order correct? thats 1,2,4,3 CCW. These N-Engines are SOOOooo goooood, they'll run on just 2-cylinders, even to WOT (specially iff'n mainjet is opened-up RICH) but they will cut-out & bog under load. Usually sparkies 4 & 3 gitt swapped. Check'em out..... ..Dell

If it is the carb, it is time to give up on that one, get a different new or rebuilt carb, and get some quality seat-time.

You might have a bad casting or one that was mis-drilled. There is a point where you have spent more time on a part than it is worth. I have a shelf out in the shop for parts like that. They sit, wrapped in plastic, until I decide to try to fix them or maybe steal parts for another project.

hope this helps, BTDT
kl

The reason I suspect this leakage is because you are using a large opening on the main jet to get proper running. So either your jets/main nozzle is too small or you have an air leak downstream of the metering system. The more I think about it, the problem is probably the latter because of what you experience when you close the vent hole that you drilled. When you do that you restrict the fuel flow rate because you've reduced the venting capability. You are at WOT and assuming an unrestricted air filter, the pressure in the carb inlet is at it's lowest value and the vent, at atmospheric pressue, is helping pressurize the fuel bowl. When you cover the vent, the pressure over the fuel is at a lower level (it's vented to the carb inlet instead of to the atmosphere) so the fuel supply is resricted. It's also adding air to the metered airflow which requires a slightly larger power jet opening than would occur it the hole wasn't there. Tape the hole over and readjust the main jet and see if that helps a little. Then check for manifold leaks.

Hope this helps.