Someone help Im stumped.. Evinrude 70 hp 1974

Skifferskipper

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Okay I Bought this engine because it started good and Idled took it to the lake and put it in the water and the engine wont perform at WOT pull the boat out and took it to the lab.. Compression is good solid 115 120 acrossed the board. So I Checked spark next It looked like the #3 cyl was a little weak (But I didnt test it with a DVM) So I replaced it. Still missing so Im looking for the miss and I Start pluging fuel lines to carbs to isolate the miss and it seems like all three carbs are running so I Figure to A Carb Highspeed jet problem.. Got it with some carb cleaner revved it up at the house still sounded a little miss'y but still reved to WOT So I Figured I might have gotted somewhere.. No Dice put it back in the lake still wont go full out.. So I pull the plugs one at the time to figure out what carb is bad and all three of the plugs look exact except One of the resisters is a little lighter then the other two Figured that wouldnt make a diffrence but no fuel and it looked to be burning the same makeing me think the carbs are performing how they should be..


Kinda stumped at this point anyone know what I should try next?
 

Skifferskipper

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Re: Someone help Im stumped.. Evinrude 70 hp 1974

Oh I Forgot to mention I Adjusted the linkage and the timeing to 17 deg at top and just past TDC At bottom the engine sounds pretty good other then not getting to WOT Does anyone know how to test the stator Because I think thats probably what I Need to try next.. Or any ideas?
 

oldrudedude

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Re: Someone help Im stumped.. Evinrude 70 hp 1974

Are you sure that 17 degrees is proper spec for that engine. Sounds a little low to me. My '71 50hp and '72 100hp call for 19 degrees and 28 degrees advance respectively. Call for 3 degrees and 5 degrees advance respectively at idle. If full advance is not high enough it could certainly explain poor performance at WOT. Sorry I don't have the spec for your engine.
 

Skifferskipper

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Re: Someone help Im stumped.. Evinrude 70 hp 1974

Im not sure what My spec is for idle but It was just past probably just about 3 or 4.. it says 17Degree on the engine So I Was assuming that was the fast stroke But it was out at about 19 20 before I Set it back.. It had the same problem both times.. I think ill mess with it a little more and see what happens.. Probably set it back to a bit faster and see if I get any clicks..
 

oldrudedude

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Re: Someone help Im stumped.. Evinrude 70 hp 1974

If it were me I would pull the carbs and make sure they are clean, properly adjusted, and properly synched. You don't want to be running lean on one cylinder at WOT or anyt other speed. You should not be revving your engine to WOT unless it is in the water pulling a load. AT the top of this topic page there is a sticky marked "top secret". There is a post in there regarding timing Evi and Jonny engines at cranking speed. You should check it out.
 

jtexas

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Re: Someone help Im stumped.. Evinrude 70 hp 1974

I've never really thought it worth the time to narrow it down to a specific carb -- rebuilding 3 just doesn't take that much more time & money than doing one, and then you don't worry that another is on the verge of needing it.

Not to mention which, if spraying the high speed jet with carb cleaner makes it run, dontcha have to worry about a partial restriction, leading to lean burn, leading to elevated temp and catastrophic piston failure?

If you got compression and spark, fuel line holding pressure, vented gas tank with fresh gas and no water/debris, and the timer base reaches its stop without sticking, rebuild 'em, with new carb kits. No point going to all that trouble then reinstalling old gaskets, orings and float valves.

idle timing is 0? and WOT is 19? but heed oldrudedude's words, don't do it unless you have a test tank and test wheel, or else follow the previously mentioned joe reeves procedure in the top secret file.
 

wilde1j

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Re: Someone help Im stumped.. Evinrude 70 hp 1974

"Got it with some carb cleaner revved it up at the house still sounded a little miss'y but still reved to WOT"

Hang on for metal parts exiting the crankcase next time you do this and make sure to wear a flak jacket, helmet and full face shield. Never over 2K RPM w/o a load.
 

Skifferskipper

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Re: Someone help Im stumped.. Evinrude 70 hp 1974

Comon guys Im stumped im not dumb I Had it in an old Pool.. And Past that I Dont really care if it blows it blows I traded a FMF pipe and an axle for a quad for it.. But it would still be cool to get it running.. Ill go ahead an pull the carbs off and rebuild them and I Still want to know if anyone knows a test to figure out if the diods on the stator are working correctly as I have heard that they kinda keep the engine at power under load. Correct me if im wrong but without the stator working properly the engine would be firing on battery power and would make sence that it would overload under heavy load right?
 

jtexas

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Re: Someone help Im stumped.. Evinrude 70 hp 1974

The stator doesn't have diodes. That would be the rectifier.

It takes least 150 volts to energize the primary windings in the ignition coils; the battery only has 12 volts, so the engine can never be firing on battery power.

The only thing the engine needs a battery for is to spin the starter motor, and you can do that with a rope so you could do without the battery entirely. But note that if you do run without a battery, it will blow out the rectifier diodes. Which won't have any effect until you hook the battery up again. Except that without a working rectifier, your tach won't get a signal.

If the rectifier fails, the battery won't be recharging, the accessories will be running on battery power even while the motor's running, and as noted, the tach stops working.

The rectifier diode test procedure is here:
http://forums.iboats.com/showthread.php?t=190638
 

Skifferskipper

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Re: Someone help Im stumped.. Evinrude 70 hp 1974

Yeah, It says 17 on the engine so im gonna go with that.. so I Ordered the carb kits im gonna get that done .. Does anyone have the procedures for Sync'ing carbs I Heard it takes some kind of Air flow reader or some kind of special tool A .. By the way Thank you all for the information its all good stuff keep it coming if you have any more ideas.
 

jtexas

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Re: Someone help Im stumped.. Evinrude 70 hp 1974

yup, 17, sorry bout that.....
 
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