Re: jets on 1989 70hp
My book shows no adjustable jets for the 1989 70hp, however possible you have the carburetors that have a adjustable jet on the top starboard side of the carburetor, approximately 3/4 of the way back towards the intake manifold.
If so, back them out four turns, then start the engine... and yes the engine will run lousy. Now, one jet at a time, start turning the jet in 1/8 turn at a time and wait for a response. If all is well, you should hit a point whereas the engine (carburetor) will spit back sounding like a mild backfire. ASt this point back the jet out 1/4 turn and go to the next one. When finished, re-do and re-check.
If on the other hand, you're speaking of the fixed brass jets, those must be tight in order to function properly.
I can only assume that if those jets are adjustable and are indeed turned in all the way, that the carburetors possible are somewhat clogged, fouled, gummed, and if so should be removed, cleaned thoroughly, and rebuilt.
Note that having an engine die out when throttle is applied is usually caused by either a sticking timer base under the flywheel.... or fouled carburetors. Be sure to check the fixed high speed jet that's located in the bottom center of the float chamber.... clean it manually and carefully with a piece of solid wire.
