20-30hp Johnnie25 conversion base line test

So...took the little 12ft Valco out on Patagonia Lake...calm...made a strong pass...clocked 17 mph..full gross on the boat...showing 9600 on the tach..assume that means about 4800 since its a twin
This was the ONLY strong pass that I could make...we cruised the entire lake for hours at low or mid throttle. But every time I rolled into it...it would pick up nicely...then fall on its face...missing...maybe fuel flow? (replaced the fuel line from tank to engine with OEM line, fittings and bulb)...fresh Champion plugs. ANy suggestions? Would old fuel cause this??? (Gas/oil mix has been in this tank, indoors since Spring)

Thanks in advance

Mike

PS This test is BEFORE the conversion,,,was just looking for a baseline with the Johnson 20....

I'd get some fresh gas in there to start with. My guess is that it's not the problem sure won't hurt to try. Could be a number of things like dirty carb or maybe failing ignition parts. Let us know what you find.

Nowhere near enough information here. Your topic indicates some sort of conversion you did on an engine. How about starting with what the engine was originally and then go into what you did to "convert" it into what it is now. Helpful we try to be....mind readers we are not!

If i read right papoy. This test was before any work was done as a
Baseline

Still seema sluggish for a 20hp on a 12' boat

Valco 12ft loaded to full gross...2 mature adults and 2 kids
87 Johnson 20 hp STOCK

last time out..similar conditions 20-21 mph (GPS) fuel line/bulb leaking replaced w/ OEM parts

Note mini tach reading 9600 at WOT shall I assume that is really 4800 since its a 2 cylinder?

i beleive its reading 9600 because its picking up every stroke of the piston/plug wire you have it connected to (2-stroke divide by 2?)......i could be wrong but i think thats why. whats your max rpm range? on my 80 25hp its 5500 so im guessing your right near your top range....

that was my assumption as well..

Cant find a chart specific to the 1987 20 hp...find 15 and 25...but WOT RPM varies from 4500-5500 or 5500-6500?