I have an older (1986) Skeeter Strada with a 70hp Johnson.

Ive used this boat very few times since it seems to go very slow.
It starts up on the first crank and it sounds like it its going full power but yet only travels at maybe 15mph or so (just guessing, never chronoed speed)
Could it need a carb cleaning or is there something I can look into?
Any advice would be appreciated.

Could be a spun prop hub. If it has the rpm's and no mph. It is a pressed in rubber inside the prop.... if that is it about a $40 fix. Takes somebody with the know how and a big press. Press old one out and new one in. That's what I would check

Thanks bud!
I�ll check into it.

Yep sounds like something with the prop, like the gentleman says if it has to have a new gear hub it has to be pressed in.

Few things I always check:
-Check if you are getting spark to each cylinder
-Check your compression on each cylinder
-Check the fuel line, as the new fuels eat away at the inner liner

This absolutely could be a carb issue among a number of other things (bad fuel pump diaphragm, dry rotted fuel hoses, dead cylinder) But the carb will have low speed jets and high speed jets. If the low speed is fine and but the high speed is clogged it could cause exactly the problem you're having. How many RPMs are you getting at WOT? If it's low then it could be the carb. If RPMs are high then its probably the prop.

I agree......prop problems

THIS. Typically with a fuel or spark issue it will sputter or shake and it will normally sound like the speed it is going. If this sounds like you are going fast and you are not, then check on the prop.

I was going to be funny and say pull up your anchor, but I hate when my boat ain't right... not a haha moment. Good luck with the fix.

Those boats didn't set the world on fire speed wise any way but should be running at least close or at 35 mph.could be over propped or like rest said slipped hub.Also hard to give advice if you cannot gps speed with your smartphone, May be nothing wrong at all.