Problems with Mercury 650 1970

[PeO]

We have bought an 4 cyl Mercury 65 hp.
The guy we bougt it from said he couldnt get it to run well... ha had connected the power backward and burned the ignition module but had replaced it with parts from a Volvo 240.

To start with the gearchangeaxle had rusted and I have to pick it out and welld it together again.. then the tiltlock started work too...

Then we put it in water and tried... it work as it should but in fulll power tha boat run in 10-20 seconds and then lower the revolutions... its just to wait with less gas and then it does the same again over and over...

I took the fuel pump apart and found no diafragm... Ok I bought a servicekit and mounted it... and thouth now should it work... but not its still the same fault..!!

I have tested fuletanks, hoses, handpumps... but I dont know if it get to much or to less fuel.... somebody who can help me..???

[SmithCraft64]

Take a look at the 2 strokes functionality. They work differently than a 4 stroke in the way that they draw fuel as far as the number of strokes. There are many other ways that they are different also but with your particuliar problem and being given some background information on the engines history. Let me explain what might help. A four stroke works:
a. Intake b.Compression c.Power d. Exhaust
a. Inlet valve opens;piston draws fuel and air mixture into cylinder. b. both valves close. Rising piston compress the mixture. c.At the upper limit of piston movement;both valves closed, mixture is ignited. Explosion then forces the piston down on the power stroke. d. exhaust valve opens,rising piston pushes spent gas from the cyl.
Where a 2 stroke provides power impulse for each two stokes of the piston;each revolution of the cranshaft.
a. Mixture o fuel and air from carb enters engine crankcase through a checkvalve. When piston is at the bottom of the cylinder,port is uncovered. As proceeding movement of the piston has compressed gas in crankcase,mixture flows into cylinder. Further compression in cylinder starts as soon as the piston reverses and covers the ports.
b.At the same time compression is occuring in cylinder, movement of piston has created vacumn in the crankcase which draws a fresh charge of mixture from the carb into the crankcase. Charge is fired at limit of piston movement.
c. As expansion of burning charge forces piston downward, check valve in crankcase closes and mixture in crankcase is compressed.
d. As piston uncovers ports at bottom of stroke, compressed mixture from crank case enters cylinder and is deflected by baffle on piston head into outer end of cylinder. Incoming fresh mixture assits in pushing spent gas out of cylinder. I will return for the rest of my analysis of your problem and refresher on carburetor troubleshooting. I have been called away. sorry Take alook at what I have written so far and see if can see where im headed. Smitty

[PeO]

Thanks for the answere... waiting for more..

but there are no checkvalves in this engine... I cant find any anyway..
Well I think it works anyway with ports in cylinders...

I've got the feeling that it loose the ignition at high revs.. and get wet until I dry it a tlow revs !?!
We try yesterday in water and jumped over our own waves... with a real bump.... then it work for full in 5 minuts... and then went back to the bad mode...

We find out that it dont load up the batterie... Somebody who know how much current it should load? and only at high rpms? Can it be a broken rectifier?