1983 johnson tilt/trim problem. Please help!!!

I have a 1983 70hp Jonson on my pontoon. I just bought this boat, it had'nt been on the water in ten years when I bought it but is in great shape. The T&T work fine when it is parked or going at slow speeds. However, when I give it full throttle and the boat starts to really take off, the motor instantly drops to the full down position with a noticeable "clunk" causing high drag in the water, slower speed, and a strong pull to the right. While going high speed I cannot trim the motor back up at all until I slow way down or come to an idle. I checked the T&T fluid and it is full. This is my first boat with T&T so any useful information would be greatly appreciated. Thank you.

Re: 1983 johnson tilt/trim problem. Please help!!!

Sounds like seals are leaking, but I would bleed the air out of it first and see if that works. Do a search here on bleeding a T&T and give it a try. Good luck.

Re: 1983 johnson tilt/trim problem. Please help!!!

Thanks for the reply! I've tried bleeding the system or atleast I thought I did about a week ago. I raised the motor completely and opened the fill plug till it was loose and barely threaded in, then I proceeded to lower and raise the motor completely several times while checking the fluid level each time. It was shooting out fluid while I was operating it, possibly air too. Is this what you meant by bleeding? Regardless, it did not work. I still had the same problem. So, if it is the seals, where should I start? Is it something an average person could do or would I need to take it to a professional? Like most people I'm on a budget! Thanks again.

Re: 1983 johnson tilt/trim problem. Please help!!!

With the fill screw closed run the motor up and down five times; then with motor raised open the fill screw and see if you can add more fluid, raise and lower (with screw closed) the engine five more times andsee if you can add more fluid. I've had to do one at least fifteen times to clear all the air out. It supposed to be self-bleeding. If that doesn't work then seals may be leaking. if you raise the motor above the trim rings and try to go WOT then the tilt rod will not hold it up. Good luck.

Re: 1983 johnson tilt/trim problem. Please help!!!

Thanks for the reply. Can the problem be leaking seals if there is no fluid leaking out of the T&T system? Like internal seal failure? Maybe bad check valves?

Re: 1983 johnson tilt/trim problem. Please help!!!

It could be bad internal seals but I vote for a check valve/s in the unit.