Quote:
Originally Posted by caper
I think you still have a carb problem - rpms where you are having problems are transition from low speed to high speed circuits . . .
|
I agree. I think you have a lean misfire problem. Outboard carbs are very simple devices, especially the idle and main jet circuits, but the transition between the two systems is pretty sensitive and a little bit of dirt in the idle circuit is all it takes to create your problem. I've been able to create exactly your problem on my old 'Cuda 340 4 barrel Carter AVS carb by adjusting the idle mixture screws too lean, which causes the carb to get VERY lean during the transition stage. Or a slight air leak at a gasket might cause the same problem, where both the idle and main circuits are rich enough to mask a slight air leak, but not during the transition stage.
If your motor is like my old V-4 Evinrude, it will have two 2-barrel carbs, one barrel to feed each cylinder. If you can do a cylinder drop test at 1000-1200 rpm(short out the ignition on individual cylinders; if no rpm drop on one cylinder, that's the one with the problem!) you can narrow it down to which carb needs attention. A quick fix, IF your motor has idle mixture adjustment screws (many just have fixed jets) would be to just richen up the idle mixture on the problem cylinder. But the problem carb really needs a good cleaning.
Personally, I think the old carb motors are so simple and easy to work on that it's hard to justify paying someone $100/hr to do anything on them that doesn't require special tools or the acetylene wrench, so you can save yourself big $ by getting a factory service manual and learning to do your own work! And the ability to diagnose and fix your own motor when you get out in the boonies with no experts around is priceless!