10 mph top speed

[briangcc]

Did some googling so that might be dangerous.....

Prop - pretty much a given that dropping 1" pitch will increase your RPM by about 150-200RPM.

Motor - generally found your recommended rpm range to be in the 4400 neighborhood.

Basic math.....to get from your current 2000 rpm to around recommended 4400rpm would mean a change in 2400 rpm. Doing the math, you would need to DROP 12" worth of pitch to get your missing 2400 rpm. Assuming standard prop which seems to be 19" that would mean you'd need a 7 pitch prop. I'm sorry but I seriously doubt you're finding a 7 pitched prop to fit your outdrive to get you back into your max rpm range.

So....going off math alone, provided your outdrive isn't sounding like a blender, we just ruled OUT the outrdive (boat side) being the issue.


I'm no mental genius but given your motor can't swing the original prop, you have something going on with that engine. Heed these guys advice and start digging into it.

 

[CaptnKingfisher]

Definitely sounds like engine trouble, I'd start with the easy stuff first. Check your carb linkage.. with the engine off have someone move the throttle while you look down at the throttle plate. When the throttle is full foward, is the throttle plate fully open? I think I read in here that you have ~120 compression.. little low but not low enough to explain the poor performance. Next I'd check spark with an adjustable spark tester. Very important you have an adjustable one so you can measure the strength of the spark at each cylinder. Should be jumping 7/16" or at least 1/2". While you've got your plug leads off, pull your plugs, read their condition. You're a mechanic so you should be able to tell straight away if you've got a dead cylinder or multiple dead cylinders (which I suspect is your problem). Verify plug gaps before reinstalling and put some dielectric grease on the plug wires. If everything is good so far and you've got strong spark on all cylinders and your confident that dwell and timing are correct then I guess you got a fuel issue. But I don't know what fuel issue would cause these symptoms, I got a lot to learn I guess. let us know what you find.