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Author Topic:   Twin 1986 Johnson 70 VROs - What RPM should I run at?
ecutlip posted 07-14-2004 03:13 AM ET (US)   Profile for ecutlip   Send Email to ecutlip  
I bought a 1986 18' Outrage a few months back. It has twin Johnson 70 VROs on it from the same year. When I am running I usually run them at about 4000 rpms because it "sounds right" to me - actually I told my wife they kind of remind me of a swarm of bees :) But I have run them up to about 5000 rpms for a few seconds at a time. What is a safe rpms to run these at? I figured it was better to be cautious with old motors that I can't afford to replace - but I also like getting where I'm going :)


brisboats posted 07-14-2004 10:16 AM ET (US)     Profile for brisboats  Send Email to brisboats     
Sounds like you found a "sweet spot" . You could safely run those up to 5500 rpms and listen to the angry swarm of bees. Running where you are now is much more efficient and should get you there plenty fast.


Bigshot posted 07-14-2004 02:46 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
They redline at 6k I believe. 4k is great and economical, 5k i sfaster, burns more gas and shorten engine life. For constant running keep it under them WOT for 30 seconds or so each trip to clear the plugs.
ecutlip posted 07-14-2004 05:25 PM ET (US)     Profile for ecutlip  Send Email to ecutlip     
Thanks - I'll keep running them at the 4000 rpms.

Does WOT mean exactly what is says - that is to give it all the throttle it has? I've never done that with them - or any of my other outboards I've had. Does the WOT mean up to 5500 rpms instead? Is there any risk that may be worse than the plug problem in doing the WOT for 30 seconds an outing on the old motors? I mean like is there a better chance of having the piston rings go toast on the cylinder walls or something? These might be stupid questions. Even though I have done all my own maintenance on all the outboards I've owned - I don't claim to be a knowledgeable mechanic type - mostly I just follow directions well :)


Joe Kriz posted 07-14-2004 05:47 PM ET (US)     Profile for Joe Kriz  Send Email to Joe Kriz     

I owned a 1985 70hp Evinrude since new.

The WOT is stated in the book as 4500 to 5500 RPM.
The motor should run at 5500 RPM at WOT with just yourself onboard.
Usually the person before you would have set this up via the Pitch of the Prop(s).

I ran a 13 3/4 by 15 Pitch Prop 90 per cent of the time because it gave me a better hole shot and the 5500 RPM at WOT (Wide Open Throttle).
You will not attain the 5500 RPM when you are loaded.
The other prop I used was the 13 1/4 x 17 pitch which gave me a mile or two and hour faster but the hole shot was a little slower.

I ran my motor at WOT for long periods of time without any problems at all although I would probably not do this on engine(s) that I did not own since new. I also never changed my water impeller in the 15 years I owned it.
I know, everyone else says to change to water impeller every year or so. Well, I never did and never had a problem. I still would suggest making sure you have new ones before taking the boat any distance.

Other then that, those engines are just about bullet proof. All I ever did was change spark plugs.

Bigshot posted 07-15-2004 04:17 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
1986 or 1987 they changed the 70hp and WOT went to 6k. If block is black I believe 6k is redline. Running it WOT for a brief time is a great way to clean her out and have some fun. I never recommend WOT for long periods being it will shorten engine life extremely quicker than running it at 7/8's throttle. Run where they are happy but the lower the rpms the less fuel you burn and the longer she will last(to an extent).

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