Can't get up on plane

[fonce]

I recently bought a 1994 Johnson 140 HP V-4 engine. The gear case was off when I bought it. I had to bend the shift shaft in order to get it to work properly. After replacing the power pack and the 4 coils,the engine would not get on plane. I have a 20' Aquasport. The prop is a 15 1/4" x 17". I tried a "test wheel" and the engine will not rev over 2500 RPM's. The lower unit gear ratio is 2:1. The fuel system and the carbs have been checked. The engine will rev to 5500 RPM's wih no load. I removed the gear case and noticed the spline on the main shaft was all chewed up. Does any know what the gear ratio should be? Also, any ideas why the engine won't rev under load?

 

[jtexas]

Re: Can't get up on plane

welcome to the forum.

The engine won't rev under load due to poor compression, insufficient spark, inadequate or poor quality fuel, or some combination thereof.

First do a compression test.
Then a spark test. Set your tester at 7/16" and look for strong blue spark. Don't test for spark using spark plugs - that won't tell you anything.

Report your results.

If "carbs have been checked" means anything other than removed, disassembled, soaked overnight in carb cleaner, blew through passages with compressed air (or aerosol carb cleaner), and reassembled with new carb kits, then carbs are still suspect.

Go ahead and order a factory service manual from marineengine.com or kencook.com - you'll need it to tear down the gearcase in order to install your new drive shaft and shift rod. It will explain in detail how to adjust the shift rod height, so you don't have to bend it.

 

[jay_merrill]

Re: Can't get up on plane

Just a suggestion - don't run your engine at 5500 rpm with no load. Without anything to hold the motor back, it would be very easy to accidentally over-rev it.

 

[Haywood123]

Re: Can't get up on plane

I don't have a Johnson on my current boat, but I had the exact same issue, motor ran great until it was under load. Did you try reverse? Mine ran fine in reverse as well, but any load I couldn't get 2500. It ended up being my powerpacks. At 2500 RPM's, plug 1,3,&4 were all firing correctly, but 2 was firing at 8000.

 

[Benny1963]

Re: Can't get up on plane

run your motor under load with a timeing light on each cyl that will tell you if you are breaking down under load also run comp check
bennyb