Hey guys this is my first mud motor and I made the mistake of buying it without the shaft put in and the u-joint. Motor runs great its a 7hp, starts on first pull every time and runs great for as long as I want. BUT, I put in the shaft and u-joint and its crazy hard to pull and I cant even get the motor to run. I take off the u-joint and the motor fires right up. Its a 6' long tail frame. Im stumped and dont know what to do. Any help or ideas to try are appreciated! Thanks!

Sounds like its not aligned properly.

The tail with the motor? So maybe cut the welds and decrease the degree of angle till it runs right and re-weld?

No, your problem sounds like the motor is mounted crooked either left or right of being straight with the shaft... not up/down.

Make double sure everything is square, just a little bit off will put a bind on the U-Joint like you are saying.

what kind of frame? friend made an adapter for his 16hp mud buddy frame and put a 6.5hp on it and it wouldnt turn over. If its a home build then it def could be an alighnment issue as stated above,too much metal, or too much angle on the ujoint .

U joint too deep on motor shaft OR
Shaft too deep on U joint OR
BOTH.

Dry fit u joint and shaft and manually turn the prop to see how hard it is to turn until you can turn it pretty easily. When you think you have it right, TIGHTEN IT UP, then run it but check for heat in case it's still binding.

You have to find the "sweet spot". Don't ever remove the U joint or shaft without marking where they are currently set.

If none of this works, fella sold you a bill of goods.

Take the spark plug out of the motor and move everything around until you can turn it freely from the prop and then lock it down.