IN DESPERATE NEED OF HELP!! 1988 70hp Mercury

skeeter11

Recruit
Joined
Apr 1, 2014
Messages
1
hi guys i just joined iboats what a great site learned a bunch of stuff on here. but i couldnt find my exact awnser to my question. heres my situation. any feedback is greatly appreciated.

I have a 1988 mercury 70 hp serial number 0B378655.

First symptoms were bogging even at WOT would only go like 10 mph.

Now the bogging has somewhat stopped but is more like a pulsing action. Takes a very long time to get on plane and wot only goes about 30 mph compared to 42 when i first got it. Also sometimes wants to die in gear.

Ive done alot of research and this is what i have done so far...
-sent carbs off to be rebuilt and put on the motor, new needle and seats
-new fuel pump diaphram.
-all fuel lines are clear of debri.
-new plugs.
-coils and electrical seem to be working because i did a spark test with a gap tester from autozone
-Did a compression all is within 10%.

Anything else im missing? i thought it would be powerpack or switchbox or coils whatever they call it. (my first bass boat). But i checked for spark and the tester showed that i had spark but idk.. im stuck.

I really need your guys help. My local boat shop charges 130 bones an hour and im a full time college student and there is no way i can afford that. I just wanna go catch some biggins. any feedback is appreciated thanks. if you need anymore info let me know
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,043
Re: IN DESPERATE NEED OF HELP!! 1988 70hp Mercury

Have you checked oil injection output ??-----Did shop find anything wrong in the carburetors ?----Run with a timing light and see if there is an ignition problem.-Might be able to pinpoint which cylinder it is.---Will the spark jump a measured gap of 7/16" of an inch ?---That is not the same as saying " tester showed I had spark " ---Report the results of that test.
 
Last edited:

emckelvy

Commander
Joined
Jan 16, 2004
Messages
2,506
Re: IN DESPERATE NEED OF HELP!! 1988 70hp Mercury

Your symptoms indicate a possible problem with the hi-speed stator windings. This is a well-known issue with Merc stators of that era.

A simple resistance check of the high and low speed stator windings will usually pinpoint the problem. Unless the resistance values are spot-on, the stator is probably bad. One sure way to cause the problem to stand out is to take readings "cold", then run the boat until the engine is thoroughly warm and take resistance checks immediately after shutdown. If the "hot" and/or "cold" readings are drastically different, that's your problem.

If you can't confirm by resistance readings, you can purchase an inexpensive "DVA" adapter harness that will plug into a digital meter and allow you to read the voltage output of all the ignition components. This is the most accurate way to diagnose the problem.

An inexpensive digital meter and the adapter will allow you to do all the expensive troubleshooting that shops charge $90/hr & up to do!

That, and a bit of technical information!

To that effect, here's a few links, to CDI Electronics troubleshooting info and also info regarding the "DVA" harness:

Technical Support | CDI Electronics

640 ESI DVA Adapter

Piercing Probe 511-9773-NL without Leads, DVA, Peak Voltage, Adapter - CDI Electronics 511-9773NL

http://forums.iboats.com/attachment.php?attachmentid=43784&d=1264473219

http://forums.iboats.com/johnson-evinrude-outboards/need-dva-meter-make-adapter-5-a-434738.html

http://forums.iboats.com/mercury-mariner-outboards/dva-adapter-multimeter-427303.html

http://forums.iboats.com/johnson-evinrude-outboards/how-make-dva-adapter-multimeter-371144.html

HTH & let us know what you find..........ed

p.s. CDI electronics makes very good replacement parts and I've had excellent luck with their aftermarket stators & other ignition components.
 
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