1967 5hp idles fine but wont rev

[cjist1]

New poster here.<br />I have a 1967 5hp Johnson model LD-12a. When I first got it, it wouldnt start. I did a carb rebuild, now it starts and idles fine, but when you increase the throttle it doesnt want to build RPM's. I ordered a new fuel pump, am I on the right track? I did a search and couldnt find anything. Thanks in advance for any help.

 

[Texasmark]

Re: 1967 5hp idles fine but wont rev

Sounds like it. Increasing rpm's requires more fuel (and air should follow along with that). So any reason for inadequate fuel delivery, fuel pump as you are after, including too lean a high speed jet setting on the carb could be your problem.<br /><br />Mark

 

[Chinewalker]

Re: 1967 5hp idles fine but wont rev

My money is on the motor only running on one cylinder. I'll be that if you pull one plug wire with the motor it'll either stall completely or continue running like nothing happened...<br />- Scott

 

[Backlash]

Re: 1967 5hp idles fine but wont rev

I'm with Chinewalker.

 

[cjist1]

Re: 1967 5hp idles fine but wont rev

Ok, if I still have a problem after the new fuel pump is installed, I will try pulling on of the wires. If it is firing on one cylinder, what would cause this? Bad points/condenser? And thanks for the input so far.

 

[Paul Moir]

Re: 1967 5hp idles fine but wont rev

I'm with Chinewalker and Backlash too.<br /><br />If you're running on one cylinder, it can be due to a couple things. Most likely candidates are dirty points, next is a cracked ignition coil which is a common issue on older 2 cylinder Johnson/Evinrudes. After that I think cracks in the spark plug wires, but those can usually be found just with a careful examination.<br /><br />A healthy ignition system will produce sparks about 3/8" long. You can get cheap ignition spark testers for a couple bucks each from automotive tool stores. If you can produce sparks like those, then you can rule it healthy and move onto compression, water leak & fuel supply problems.<br /><br />Condensor failure is extremely rare on J/E outboard motors, though they're

 

[cjist1]

Re: 1967 5hp idles fine but wont rev

Well I got my fuel pump today...that seemed to be it. I checked spark and both cylinders have good spark. The motor seems to rev real good now and run at high RPM's. I will have to get it out on the lake and see how it does. Thanks for your help everyone.