1988 70hp ignition testing ?'s

horiconducker

Petty Officer 3rd Class
Joined
May 12, 2008
Messages
96
Ive got a 1988 70hp johnson that has always seemed to run rough at slower speeds up to about 1800rpm (especially 1000-1800rpm)then its like a switch is flipped and it runs smooth as silk all the way to 5600rpms. Ive lived with it for awhile, but its now getting to me cause i know it should run better in this range. I have a oem manual and ordered a dva adapter to test ignition components. I know its not a carb or lync and sync problem. Im not new to working on outboards, but don't have a lot of electrical experience on them. I hooked up spark testers set to 7/16 gap to all cylinders and they jump the gap. To the questions, I disconnected the wires from the stator to power pack, and checked the voltage between the brown and brown with yellow stripe wires. First time i got 550v, way out of spec, came here on iboats did some searches went back out and retested, now i get 350v. Kept testing it a few more times, sometimes i get 550v others, i get 350, what could cause this? I then tested voltage on oranges wires going to coils from power pack and i only get 2.5v, same for all three, oem manual states it should be least 230v and cdielectronics says atleast 150v. Im not sure if I'm doing something wrong or what. The timer base seems to check out ok, I get around 2.5v on each wire, which seems high but the specs state only a minimum of .5v. Thanks for any input. ducker
 

interalian

Commander
Joined
Jul 23, 2009
Messages
2,105
Not sure about chasing ignition if it's working fine at higher speeds. Have you elimated any problem in the low/mid carb circuits?
 

sutor623

Rear Admiral
Joined
May 23, 2011
Messages
4,087
You sure your meter isnt set to the wrong decimal point when you get 2.5v from the power pack?

Did you check resistance of your stator? I have seen issues where the stator doesn't supply enough voltage down low (causing misfire) and then once that flywheel really gets spinning the stator starts to supply the proper voltage.

Siednote: Do you have the DVA adapter yet? If not you will NOT get accurate voltage readings because these tests require a peak voltage reader.
 

WernerF

Petty Officer 1st Class
Joined
Sep 5, 2011
Messages
320
A four-stroking area between idle and say 2000rpm is somewhat normal. Especially at light loads.
 

horiconducker

Petty Officer 3rd Class
Joined
May 12, 2008
Messages
96
Yes I've eliminated carb problems. Couple years ago I put a set of carbs that have adjustable low speed jets.
 

horiconducker

Petty Officer 3rd Class
Joined
May 12, 2008
Messages
96
Yes I do have the DVA adapter.I believe the meter was set correct it was on the same settings that I get 350 to 550v directly from the stator wires while cranking. I ohms tested the stator got .54 ohms. That reading is super low supposed to be 560 ohms, No matter how I set the meter I could not get it to read 560 was always .5. I ohmed out the timer base and that checked out good all wires were at 10 ohms.when I did the stator to ground test I also got some voltage which there should be none. I'm confident the stater has some issues but I'm not sure if the power pack does too? Thanks again Ducker
 
Last edited:

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,030
If it kicks in suddenly it is likely a spark problem.---Do the simple , no cost as follows.---Run with a timing light to see which cylinder is the one.----Start with # 1 in your test run.
 

horiconducker

Petty Officer 3rd Class
Joined
May 12, 2008
Messages
96
Did some more testing. I disconnected the 3 pin connector going to the power pack and checked the kill wire(black/yellow) for voltage. I connected my meter to the harness side (not the pack side) of the black/yellow wire and i was getting around 8v. My understanding is there should be no voltage on this wire with engine off and the key either in the off or on position or am i wrong? I disconnected the main harness and still have the voltage on the kill wire so its not the ignition switch. thanks ducker
 

Tim Frank

Vice Admiral
Joined
Jul 29, 2008
Messages
5,333
Yes I've eliminated carb problems. Couple years ago I put a set of carbs that have adjustable low speed jets.

And why could you not have a carb problem now?
Just because you have adjustable low speed jets doesn't eliminate problems, especially if you have retro-fitted non-standard carbs.
 

flyingscott

Fleet Admiral
Joined
Apr 8, 2014
Messages
7,985
These motors do not have the smoothest idle chasing that issue is not fun and you may or may not get it fixed. When evinrude went to the 56 cube block they lost some idle quality over the old 49 cube block. What did you get the carbs off of those came on different block styles they are not all the same.
 

horiconducker

Petty Officer 3rd Class
Joined
May 12, 2008
Messages
96
I have had this issue for three or four years ever since I've had the motor.OEM and aftermarket carb rebuild kits and finally a set of carbs off 91 70 hp this issue has not changed one bit. You can spray pre mix into the carbs one by one it will not fix this issue.I had just gotten frustrated and gave up and used it the way it was.A couple weeks ago when I was using it I was in some small swells (on a 16 foot StarCraft)going up the small swells it would run rough I would crest the swell and go down The other side smooth as silk that's how small the RPM difference I'm talking about
 

horiconducker

Petty Officer 3rd Class
Joined
May 12, 2008
Messages
96
Well I think I'm getting somewhere, My black and yellow Killwire to the powerpack was getting 8 to 10 V all the time.disconnected control wire harness from motor wire harness still had 8 to 10 V. Found the problem to be in the big red plug on the engine harness I could wiggle the pin for the black and yellow kill wire and watch the voltage go all over anywhere from 1 to 10 volts
 

jakedaawg

Rear Admiral
Joined
Jun 26, 2012
Messages
4,275
I would expect that you now have powerpack damage due to voltage on the blk/yel. I can't begin to count the number of times someone has used the blk/yel under the dash for a ground for some piece of fishing electrics and ruined their power pack. Power packs can be funny and give erratic operation at times while running perfectly at other times. Fix the blk/yel and harness issue before installing the new pack.
 

flyingscott

Fleet Admiral
Joined
Apr 8, 2014
Messages
7,985
Hello again when you went over the swells the motor had to work getting the boat over them the idle gets rougher motor working harder. When you went over the swells basically you are going down hill the motor is running unloaded not doing any work. Its normal for that to happen in that situation if you want to smooth your idle in gear out try a 4 blade prop. What is your idle speed in gear should be 700-750 rpm in gear
 
Last edited:

horiconducker

Petty Officer 3rd Class
Joined
May 12, 2008
Messages
96
At idle (700rpm) it runs pretty good(not as smooth as my V4 cross flows did) but I understand that's the nature of the beast with these three cylinders. As I stated in my first post 1000 -1800 RPMs is where it really runs rough. I know how it runs in this RPM range is not right, if I bought this motor new and it ran this way I would be one po,d customer and be back at the dealer for sure
 

flyingscott

Fleet Admiral
Joined
Apr 8, 2014
Messages
7,985
Do a linc and sync is it timed right there is a low speed timing for that motor. What is the high speed jet number in the carbs you have. It sounds like your motor runs rich at an idle and clears up as you accelerate.
 
Last edited:

Fed

Commander
Joined
Apr 1, 2010
Messages
2,457
Well I think I'm getting somewhere, My black and yellow Killwire to the powerpack was getting 8 to 10 V all the time.disconnected control wire harness from motor wire harness still had 8 to 10 V. Found the problem to be in the big red plug on the engine harness I could wiggle the pin for the black and yellow kill wire and watch the voltage go all over anywhere from 1 to 10 volts
I'd think there should be power on the black/yellow and grounding it stops the motor.
It all depends on how, where & when it was measured which wasn't mentioned in your post.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,030
There should be no 12 volt battery voltage on the black / yellow wire.----None at all.
 

Fed

Commander
Joined
Apr 1, 2010
Messages
2,457
I think there has to be some voltage on the black/yellow when the motor is running racerone, notice I never said how much and made no mention of battery voltage.
 
Top