I had a late 70's 9.9 that I changed to a 15 and in addition to a different carb, there was also a spacer that allowed the reed valves to open more. It was a great running motor until I let a friend drive the boat. He made a sharp turn at high speed and the motor tore off of the transom and went to the bottom of the creek. It's still there if anybody wants it!
i have a 1998 johnson 9.9 and 15hp models. Both vary low hour motors. they both will idle down to almost nothing. the 15 screams top end but seems to stumble mid range were the 9.9 remains smooth. i think the cylinder porting are different between the two. maybe thats why i only see 9.9's on sailboats
Did you swap out the prop as well to account for the extra horsepower? I’m thinking that a 33% increase in horsepower would require more pitch at the same RPM.
Easiest way to take off the carb is to take off the fuel tank and covers. Easiest way I've found. I had the same trouble with my 2005 vinson. It wouldn't idle and mine turned out to be the o-ring on the air fuel screw. It had dried out and wasn't sealing. Be careful not to lose the washer behind it as the screw will tear the hell out of the o-ring. For my vinson the magic number for the air fuel screw is about 2.5 turns out from bottom. Pretty simple little carb, but can make you mad as hell too.
They make a ( spray can ). Of rubber renewers. It’s for RV’s. They have a rubber seal on the pull out . The big campers with the walls that slide out . Any how. Look in camper section for lubricant & you will find it. Or they say , I think 202 trans seal is good but it’s hard to find & $$
After watching a bunch of 4L80e builds, there is some disagreement as to the 'right' way to do things. There is ONE thing that EVERY builder and parts manufacturers agree on and that is that the 4L80e is sensitive to END CLEARANCE and that this is what kills many of them. Either I missed it, or on this build, NONE of the 3 critical end clearances were set or even checked. If that is the case, then this is an example of how to build for a short life.
I have a 95 4l80. Attached to valve body is a plate under the dipstick hole. I’d guess it limits how deep the dipstick goes. Any idea or input on that plate