Have a 20hp Briggs long tail. Has a rev kit, 35hp carb with K&n filter which was tuned by ec carburetor and a dual exhaust. I run 4600ish out of the water. First time running ot after the mods and in the water I'm only 2600rpm. Actually gain 150rpm when I run it choked but it is also sputtering a bit when I do that. Any advice?

Sounds like a fuel issue if you gain rpm by choking it. You may need to add an online fuel pump if you don't have one already.

Make sure you have fire to both cylinders. Will it run and start on each cylinder alone? Is it possible you have too aggressive a prop?

Going to check the spark/coil and compression. It alo seed the longer I ran it under loan I started to loose a little rpm and the motor seemed to be getting hot.

Going to check the spark/coil and compression. It alo seed the longer I ran it under loan I started to loose a little rpm and the motor seemed to be getting hot.

I also wonder if the cavitation plate could have anything to do as I really had to push down on the tiller as the prop wanted to keep going deeper. Prop should be right just bought a new one from the guys at backwater.

sounds like you should adjust your cav plate, but Im sure that's not your problem.

Hoping to work on it Wed night, have yet to check spark and compression going to start with that but stating to think maybe a head gasket which might also explain the running hot.

In the mean time I bent my cavitation plate as the previous owner had it bent up pretty aggressively.

Well put new plugs in, new fuel pump, 2 new coils, went back to a stock 20hp carb. still low rpm and overheating. Compression is good.

With the larger carb I was at about 4300 rpm out of the water but in water it dropped to max 2300-2400 and seemed to run hot. So I went back to a brand new 20hp carb and now I only get 3600rpm out of water and still 2300 in water and still seems to run hot/overheat. Not sure maybe the wrong size prop? Or something else going on?

What size prop do you have on it?
Did the motor run fine before mods?

The motor was a hot mess when I bought it for $600....hard to find used mud motors "up north".

It needed a starter solenoid, the exhaust was half on as someone had tried to weld the rusted can back together, the air clean box was all messed up and the carb needed to be rebuilt so it ran but ran rough when I bought. I only ran it out of the water as it was February and the compression checked out good, so I figured it didn't need anything too serious.

It had a 9x3 prop which was warn to 8.5x3
I put a 9x6 on it after talking with the buys at Backwater as I had intended to do some mods. I have sent the prop back to exchange for a 9x5 to see if that helps at all.