just throwing it out there - tach reading are equal compared to throttle settings ? fuel pressure readings the same thru out rpm ranges ? Motors internally are the exact built specs and parts ie: piston sizes, cams, valves and so on. Props closely matched ? again just throwing it as for thinking outside the box. Good luck.

A couple other things, check your vent to make sure it's clear, and as ez said path of least resistance, add a 45or 90 to the free flowing side if there is room, to add some restriction.

I believe HTMs are singles

Yup. All of them.

So..maybe, a good excuse for a Tunnel Ram/ 2 x 4 carbs / and a fuel pump from each tank feeding one carb.

There. Problem solved. LOL.

heck I am glad you threw that out as I really need to read a little better. And its a 24 ft at that. I fully understand now 2 fuel tanks for 1 engine. My bad. Carry on.

OK how about anti siphon valve ? one might have a restriction.

fuel pick in the fuel tank some sort of a problem and or slight restriction.

That's what I'd do. $150 would buy plenty of pretty parts from Aeroquip.

That's what I do in my Biesemeyer. Tried everything else. Now just a T going to 2 cut off valves before the big fuel filter/separator. The filter separator seemed to help some but not enough.

Thx but it's a single engine boat

All fuel lines in great shape non collapsed, vents are both clear, hose length is about the same, shut off valves are mounted directly on top of tanks actually think they screw into top of tanks. Also sometimes the engine will drain the other tank,left, first but only about 10% of the time. It's completely random. Think the easiest thing would to add two more shut off valves that are easier to reach or add an electric switchable unit like one guy suggested. Thanks guys for all the input!
I've gotta change it one way or another it sux to have stop periodically on longer rides to turn off engine raise hatch climb back and switch tanks. I like the electric switcher idea the best. No stopping and only need to open the ice chest!