90 HP Runs fine in my driveway, but not when I put it in the lake

Hello,

I desperately need some advice.

I can run the engine in my driveway ( hose attached to the ear muffs) no problem. I can rev the engine and it runs beautifully. Just after doing the above in my driveway I drive down to my boat ramp (1/2 mile away). I start the engine again on the trailer with the boat in the water. It runs great. I launch the boat and back away from the trailer and then the trouble starts. In both forward and reverse the enging runs rough. I try to increase the rpms with the throttle and it sputter and dies. I can do this numerous times and the same result.

I went through this process three times this past weekend. The engine runs in the driveway, but not when I drop the boat in the water.

Here are some things I have checked:

-Fuel Filter appears clean
-I squeezed the bulb while the engine was running and it was not
completely soft, but one squeeze made the bulb hard again
-The choke solenoid is not getting stuck
-The fuel lines from the tank to the bulb do not have any visible damage

Please advise. The engine is a 90 hp 4 stroke with 500 hours.

Thanks in advance,

Justin

You probably have a main jet blockage in one or more of your carburators. This is just a guess.

The correct trouble shooting methodology would be to take compression and check spark.
I assume you probably do not have the tools for this. So, we will try the cheap and dirty way.

Next time out (actually, you can do this while it is still on the trailer), put it in forward and when it starts to fall on its face, activate the choke momentarily and see if the engine picks up in speed. If you have a side mount box with a fast idle lever, you will not be able to activate the choke from the helm. You will have to have someone by the engine manually pulling the choke out (partially and momentarily).

If it picks up, you have a dirty carb or more.

If it does not pick up, you may have some other issues. If only one of your carbs is having a problem, this quick choke method may not cause the engine to pick up since it will be giving more fuel to the bad carb and too much fuel to the ones that are working ok.

You should also check your spark plugs and see if they differ. If you have not changed them for a while, change them now. Use NGK DR7EA. Do not use Densos, Autolite or some other equivelant.

Check your oil level. Make sure it is not too high.

You can try to run a heavy dose of Sea Foam through the engine, then let it sit overnight. If it is a main jet that is plugged, this may help. If it is a problem in your midrange jet and or transition ports, you will have to completely disassemble all carbs and clean each one.

Mike

Dude,

Thanks for the reply. Ran Seafoam through the engine. I also drained each carb into a jar to see what I could see. The top two carbs drained no problem. The bottom two not a drop came out. Does this mean fuel is not reaching these two carbs? Does it mean that the drain is blocked? So right now I am repeating the Seafoam treatment and will let it sit overnight again.

Spark Plugs look good (they are new).
I have not had the time to go to the boat ramp again. I will wait until Monday when I can occupy the ramp without causing ramp rage in other boaters.

You can completely remove the drain screws. If you still have no fuel coming out, take a wire and poke it in the drain screw hole to assure there is no blockage.

If nothing comes out, then no fuel is getting into the bowls. The float valves could be stuck closed or you could have a blockage in the bottom fuel pump or fuel lines from that pump to the carbs. Most likely scenario is the stuck float valves.

You can try putting your Sea Foam solution into the bottom carbs by putting the drain screws back in but not tight. Then try to fill up the bowls through the drains using the clear plastic drain hose. You will have to move the hose as you go.

If you are getting no fuel to those carbs, the test of operating the choke will not work.

Once you fill the bottom carbs, after a while you may want to tap lightly on the two bottom carbs where the bowl joins the rest of the carb. Hopefully, you will jar the valves loose.

I am not very optimistic that this will work, but it is work a try.

Otherwise, it sounds like a carb job is in your future.

Mike