Hey guys I just bought a used 20 horse long tail. I think it's a beaver tail. I just tested it out and I'm having some issues. First of all my boat is a 1448 Lowe riveted. With me and another person my size, around 450 total weight plus some gear I was only able to get 11 mph. This is way too slow right? Also when at idle and I take the prop out of the water I hear a loud rattle and then a few seconds later a pop noise. After I pulled it out of the water I noticed that the prop is loose. By loose I mean I can rotate it with out moving the drive shaft about 90 degrees in one direction or the other. This isn't right I'm assuming? Finally I measured the prop and it is 8 1/2 inches. It should be 9 right? Thanks for the help in advance I clearly don't know a whole lot about these things but duck season is in 5 days and I'm running out of time

What RPMs are you at WTFO? Most longtail props will have a little "slip". Not a big deal, helps with impacts. Can you post a pic of it? That prop is worn, but you should still be seeing a little more speed, I'd guess around 14-17 with that load.

That rattle and pop you describe sounds like shaft whip, then the u joint binding as it spins. Do you have any play in the shaft against the bearing? Full of grease?

I checked the u joint for play, didn't find any, also there isn't any play in the shaft bearing. I will grease everything tomorrow. What do you mean by shaft whip? Also, I'm not too concerned about the lack of speed I am just making sure something isn't messed up or getting worse. No clue on rpm, however the motor is clearly not under heavy load. Very little difference between WOT out of water vs WOT in the water

Shaft whip is the driveshaft wobbling inside the tube. If the unit is older, and only has a lower and upper bearing the shaft will 'whip' in the middle. Some of the newer LTs have a center bushing or bearing to help support the shaft. If your not consuming a lot of grease, and everything seems tight I wouldn't worry about it.

Tacs are cheap, and really easy to install. One wire just wraps around the spark plug wire. I've used hardline tacs as replacements for tiny tacs ~$20 or so on Amazon.

Next thing to check is where your prop is running at full throttle. It should be just under the surface. Also try moving your gas tank or battery up front to even out your load.

Exactly what BigBend said: What RPMs are you at WTFO? Most longtail props will have a little "slip". Not a big deal, helps with impacts, you should be able to rotate the prop slightly by hand, this can also cause a noise when starting the motors as the prop treads it self tight. That prop is worn, but you should still be seeing a little more speed stock it should be 9 inches. If you are looking for a new prop I suggest Backwater Inc. They have every size you could need, are priced better then most I have seen and will even let you test the prop in clean water and return if necessary.

20hp Briggs? or Honda?

If you bought it used I would change the oil/filter, air filter and check valve lash right away along with making sure everything is greased.

20 horse Honda, guy at beaver tail said it's probably a late 90s setup. I haven't done the valve lash but I did service everything else. Think I'm going to buy a new prop. It came with a 9 x 5. Anyone consider switching to a 9 x 6 since my rig is fairly light? Or just stay with the factory?

You would probably be fine with a 9x6 prop on there. I just put a 9x6 prop on my 20hp briggs longtail and I am pushing a 1546 mod v all welded alumcraft with pods (much heavier then your rig). I haven't GPSd it yet but, motor was a wreck when I bought it(got a good deal on it) and had an undersized prop of 9x4 which was worn to 8.5, hence why I changed props.

Also on a motor that old I would def check valve lash, no clue when someone adjusted it last, and guessing it has a decent amount of hours on it.