40hp 4 stroke

have the motor on a pontoon and the motor runs smooth, only problem it's only running at about half speed, checked everything I Know, anyone else ever have this problem?

2000 Mercury 40hp 4 stroke

Starts good, idles good and runs smooth

it feels like the throttle needs to go futher but it's not that.

Steve, not exactly sure what you mean when you say running at half speed.

It's only going half as fast as it used to on the same boat?

It's only making 3000 rpms and it used to hit 6000?

OR it just "feels" like it's not running at top end, even though you really have nothing else to compare it to when it comes to this boat/motor combination.

A pontoon is an awfully big, hydrodynamically lacking "boat" and on that type of rig a 40 is a very "tiny", severely underpowered engine, depending on the size of the boat. I wouldn't expect it to give you much more than double the hull speed on a 'toon (the hull speed on a 23' pontoon would be about 8 mph, so if you got 16 mph with a 40, that would be "exceptional", even if it was a bigfoot model)

It's only going half as fast as it used to on the same boat, I did remember I added a foil to help with pulling the grandkids on a tube could the foil possibly be a cause?

Hydrofoils can make it more difficult to turn (wants to run straight) and would maybe make a pontoon a little slower - that's not really something I have looked at/seen myself.

Foils are normally used on a planing craft to keep the bow down, which helps it plane at a lower speed or correct porpoising (nose bounce).

A pontoon is a whole different "creature". Until very recently (some new designs) they were not a planing craft - more like a big dock with a motor on the back.

I would remove the fins and run her again - see if maybe they are the cause (might be causing the front of the tubes to "plough" too much water) which could severely restrict your speed.

Best to try that first. No sense troubleshooting the motor when it's possibly a rigging issue.