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Rev LimiterMax RPM 70 HP OMC

S

sweetwater

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" Needing some info...
Late 8

" Needing some info...
Late 80's model 70 hp Johnson, that cranks and runs good. When first got the boat the previous owner stated that it began to cut-out at full throttle. I began to check it out. This engine is equiped with a rev limiter. I disconnected it for troubleshooting and it stopped cutting out. But I don't have a tach for a 3cyl, nor do I know what the max rpm setting is. So I backed the max out so the control would not go so far and it would not set off the rev limiter. First of the season it went into the shop for this and other things. The shop backed off the setting I made so it made max rpm but didn't run it long enough to set off rev limiter. My rambling ceases here!!!

What should be max rpm on 1988-89 70hp Johnson?
What other conditions could trigger rev limiter or some other feature to shut down a cylinder?
Can an automotive tach set for 6 cyl be used by dividing reading by 2 (if scale is high enough)?
If so, how do you place an automotive tach in this ignition system?

I just found this board today. Great info!!
Thanks,
Sweetwater (24ft poontoon) "
 
"The 1988/89 70hp Evinrude/JOh

"The 1988/89 70hp Evinrude/JOhnson reaches its horsepower at 5500 rpm. Full throttle is considered between 5000 and 6000 rpm, not to exceed 6000 rpm which is of course the top rated rpm.

I have no idea how you would rig a automotive tach with that engine.

If the engine is equipped with the "S.L.O.W." feature (Heat sensor in cyl head would have a tan wire, and also a white/black wire), overheating would cause the rpms to drop. I don't think that engine has that feature though.

You say the engine cuts out, then later you mention "shut down a cylinder". If a carburetor high speed jet is somewhat clogged, that would shut down a cylinder, so to speak. What, exactly, happens? Does the engine hit full throttle, then suddenly lose power?

What is the compression on the engine, and does the spark jump a 7/16" gap with a strong blue flame on all cylinders? When you remove the s/plugs, do they all look the same or do they vary in appearance?

Joe
"
 
" Hey Joe,

How do you chec

" Hey Joe,

How do you check for spark exactly.........with the spark plug in the wire holding it close to the block, or a screwdriver in the wire, screw driver close to the block? "
 
"Brian.... The spark plug will

"Brian.... The spark plug will tell you nothing as you can not set the gap to 7/16". You can use a medium size philips screwdriver that will fit inside the s/plug terminal, or rig a board with wires connected to a couple nails. Set the nails so that they're bent and the tips are 7/16" apart. Have one wire going to ground, the other wire going to the s/plug wire terminal.

Joe
"
 
" Hi Joe,
Found a manual for

" Hi Joe,
Found a manual for it & here's the s/n:J70TLESB.
I think it's a 1990 model.

Yes I think it does have the tan wire going to the top cyl head. Ok, so that's for overheat? The manual states that in overheat the horn will sound continious. So I don't think that is my cut out problem. I'm pretty sure it's the rev-limiter. In troubleshooting, I disconnected it's wire and the engine ran at max rpm and never went into this cut-out mode.

So if the engine is to not exceed 6000 rpm I should set the max throttle set screw to reach 5500-5700, depending on load.

thx "
 
"There is no maximum throttle

"There is no maximum throttle set screw to my knowledge. If you're refering to the set screw thats located on the starboard side of the engine that prevents the vertical throttle arms travel when throttle is applied, that's to set the throttle butterflies to an even level (full throttle position). The top rated rpm (not to exceed 6000 rpm) is attained by setting the timing to factory specs, then choosing a proper propeller that will not allow one to exceed that rpm under an average load.

Joe
"
 
" OK, that's the info I ne

" OK, that's the info I need. I have not adjusted the set screw on the starboard side for butterfly position since the boat returned from the shop, & I won't. I will get a proper tach & check the rpm as it reaches max setting and see what it is reaching.

Thanks a bazillion & I will report back my test results. "
 
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