70 hp runs strong then loss of power

[Joe Serpico]

I ran my 70 hp evinrude (mid 1980's) at about 3/4 throttle for about 15 0r 20 minutes give or take. ran fine whole way then bog down. it never stalled but I could not get it throttled up. it would run at high rpm in neutral but nothing in gear. I limped back to the ramp (about two hours). changed the coil packs, wires, and byp***ed the fuel/water separator (went from the tank direct to the primer bulb). put the boat back in the water and problem solved! NOT!!! ran lovely for 3 minutes and then same problem. am I looking at a power pack, or do I go after my fuel? please help, cant sleep
I did the pump the primer thing, nothing.
I have the primer type choke. tried bumping that, got a little response but nothing substantial.

[boats.net]

Probably need to remove and clean carbs.

[Joe Serpico]

did that last night. actually found them to be very clean except for the bottom one. i did find a small blockage in the high speed jet in the bowl. I ran it on the muffs and it did not sound promising. i did put a cheap spark plug tester on it and it showed an orange light on all three. also pulled the plugs and found top and bottom wet, middle one dry. is it possible the plugs are fouled from running it with a bad coil or clogged carb? my plan is to change the plugs and i ordered a power pack. should be on and tested by this weekend. i havent had the chance to run it in the water under a load yet. but i was not happy with the way it idled.

[Joe Serpico]

OK, so I changed the plugs. NGK gapped at .030. big difference at first. I thought i may solved the problem. boat ran strong on the muffs for about 15-20 minutes. Ran some sea foam through the primer ports. even better! Then after a few minutes it started to break down again. Erratic or rough idle. had to give a little throttle to keep it runninig. but wont smooth out. eventually stalled. became hard to start, (which is never the case especially when it is at operating temp).
so far i have

Fuel System
**elliminated any obvious fuel issues by running from a separate tank with different fuel lines. currently back on the original tank with new water separater(original was clean).
**Fuel pump inspected and pumping strong.
**Fuel filter mounted near fuel pump is clean and good volume visible.
**rebuilt all three carbs (which did not appear to be dirty or clogged, except for a small piece of dirt in the lower carb. not sure if it contributed to my problem or not).

Spark/Electrical
**New plugs NGK gapped at .030
**New wires
**New coil packs

I'm waitnig for the Power Pack to come. Found a new, old stock on EBAY 50 bucks. Now i'm thinking, does it sound right or reasonable that when the power pack heats up... it starts to react?? could it be that there is a connection or diode, or something like that, that when it is cold works ok but eventually breaks down after it heats up???? Is it possible??? not sure where to go with this.

i have looked at my temp sensor, looks ok to me. gauge works, boat operates at 140ish. boats reacts the same wether it is hooked or not. not sure that that senario even applies to my motor.

If I cant go fishing... my whole family suffers!!
On behalf of my wife and children please help!!

Always appreciate advice from you guys. Thank ya'll

[dkonrai]

use a heat gun or hair dryer to heat up the pp and see if you have the same problem.

[Joe Serpico]

New power pack installed and trialed the boat. Ran strong, out of the hole no problem. Ran about 20 minutes at 3/4 throttle whenever possible. While motoring in to the ramp at low RPM's it started to occasionaly miss. At the ramp I had rough idle and the occasional "sneeze". I'm starting to consider a "too lean" condition. Should I eliminate the VRO?

[boats.net]

Thats usually plugged p***ages or jets in carbs, air leak at manifold. Recheck carbs and mounting gaskets.

[phillnjack]

first thing to do is go buy the right plugs for the engine.
NGK are no good in a omc engine full stop.


now the first thing to do that most people never do is check out the 5 pipe plastic fuel manifold for any dirt or fuel pipe debris!!!
the little plastic fuel thing where full goes from the pump to this then split into 4 different pipes.
i small pipe goes to electric choke thing and three separate pipes for each carburettor.
this can often be the problem of clogging up and causing carb like symptoms.

this is if your engine has this fitting, a mid 80's onward normally has this.

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