1979 Johnson 70 HP RPM question

[benyshep]

I installed a tach, but am not sure on what RPMs I should be getting as I don't have a service manual yet. Can someone please provide me with idle and WOT RPMs. On the muffs, it's reading 1800 high idle, 1200 low idle. Haven't had it lake yet this year.<br /><br />Thanks in advance....

 

[fireman57]

Re: 1979 Johnson 70 HP RPM question

On the water you will probably idle around 650 somewhere. You will want to set it about 1100-1200 on muffs as the back pressure from the water will drop it. Don't know about your WFO rpms.

 

[benyshep]

Re: 1979 Johnson 70 HP RPM question

Thanks; I had been wondering why the idle seemed high with muffs. Does anyone have what the book shows for WOT RPMs for the 1979 Johnson 70HP? I was guessing about 5800 RPM. I hope to get it out this weekend, running with different props (14 1/2 x 17, 13 x 19) and finding the best combo for this 1974 Glastron V140.

 

[fireman57]

Re: 1979 Johnson 70 HP RPM question

Check out a manual at your local library. If you won't buy one then read up on this engine with theirs.

 

[Chinewalker]

Re: 1979 Johnson 70 HP RPM question

The 70s are rated at 5000 revs. I like to prop them a few hundred over that (about 5400 or so) with a light load.<br />- Scott

 

[Bradg]

Re: 1979 Johnson 70 HP RPM question

My 1982 factory shop manual has 4500-5500 for 70hp at full throttle.<br /><br />Idle rpm in forward gear is 700-750.

 

[benyshep]

Re: 1979 Johnson 70 HP RPM question

Thanks for the info. I had it out today and it ran 38 MPH (speedo) at 5700 RPM with light load using the 13 x 19 aluminum prop. I didn't get the chance to switch out props and try my 14 1/2 x 17 aluminum, but expect similar results. With the RPMs on the high side, should I consider a more aggressive prop or just throttle back when light?

 

[sprouticus]

Re: 1979 Johnson 70 HP RPM question

i can't even top 30 MPH with my 1977 70 hp evinrude, so you must be doing someting right. I run 2 props.a 13 1/4 x 17, and 13 1/4 x 19.