Boat engine starts fine, idles fine,,but when it water and put into gear it wont gain rpms under load????????

Question

1988 johnson outboard,,been sitting a few years...just had carb rebuilt,,,new wires, plugs, good (slightly low) even compression, old gas

Answer 1

Depending on how old the gas is I would suspect that first. Gas loses octane rating as it sits. If you put 87 in the tank a few years ago the octane rating drops and drops with age. Before long you are sitting there with some low low octane in your tank that couldnt get lit with a blow torch let alone a spark from a spark plug. Swap out a good fuel supply or put new in your tank and see what happens then.

Compression check is a good start but remember that a 2 stroke may have great compression above the rings but the pistons skirts may be shot under rings. 2 strokes pull a vacumm the same time they do the compression stroke. That vacumm sucks the gas into the crankcase and in through the intake port. With little or no vacumm then fuel cant get into the cylinders to be compressed. If it idles fine in the water then I would say you have good vacumm.

There is ton of things that can be wrong with it. From the old gas to not having spark on the high speed side of your stator. Try the new gas first then get back with us.

Answer 2

i have a 1984 johnson 90 outboard. when i got it a few years ago it seemed to run fine out of the water, then we put it in an it would not build rpms past a certain point. it turned out that it was only firing on 2 cylinders. i dont know if it is the same problem but you could check it out.

Answer 3

Before you do anything......put the engine on a portable gas tank and determine that it is the engine and not your fuel system on the boat.

Answer 4

(checked by removing one by one and noticed a drop on all)

That tells me it is running too rich. Possible causes could be wrong float setting, carb not adjusted correctly, carb/ignition not synchronized, weak spark (bad coils/wires), or as simple as bad gas, or poor mix.

Drain off all the old fuel (I run it in my old truck! does fine), and mix some new carefully measuring a 50-1 mix. That might be the entire trouble.

Answer 5

After you have done all of the rest of the checks, verify that the air vent on your tank is free and fully open. If the tank has not been used in that length of time, I suspect that you are not getting full fuel flow either from lack of air or lack of pressure to the tank depending on the type of system you have. You might try replacing the fuel hose from the tank, it could be restricted or the hose could have deteriorated internally and is restricting the fuel.