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Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 14304
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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1978 Johnson 70. No power under load. New power pack, new head,

Customer Question

1978 Johnson 70. No power under load. New power pack, new head, new gaskets, carbs cleaned 4 times, New proper spark plugs (look perfect - like toasted marshmallow, no oil residue etc.), new fuel pump, compression 120 on all 3 cylinders. Spark plugs clean meaning to me that fuel is burning good and all are sparking. all linkages good and loose. carb butterflies work perfectly. Fuel at load flowing from high speed jets. no leaks. starts ok, idles ok, when put under load just revs up a bit and stays there. barely 8mph. 16ft boat. Timing advances as it should to end (doesn't even hit the stop screw). Tried moving the timing advance under load and it goes no higher. Moved it lower and engine slowed down even more. Tried choke manual and with key under load and engine bogs down further. Tried pumping bulb under load and no difference (in fact seemed to slightly bog down but only slightly).Totally at a loss here. Stator looks ok as far as I can tell.
Submitted: 7 months ago.
Category: Boat
Expert:  Tan replied 7 months ago.
Hello. My name is***** does the engine rev to under a load?
Customer: replied 7 months ago.
I don't have a tach but not very much. Like I said 9mph when it should do about 30+
Expert:  Tan replied 7 months ago.
Does the engine sound like it is revving high and you get no speed.?
Customer: replied 7 months ago.
No, it even sounds low. Like it was pulling a huge raft.
Customer: replied 7 months ago.
revs fine in neutral and starts right away (that is if I don't flood it!).
Expert:  Tan replied 7 months ago.
Ok when you advance the throttle to full throttle does the timer base # ***** advance to the screw? If no can you move the timer base manually with your hand till it hits the stop screw? The engine doesn't have to be running for this test.Does the timer base move easily?http://www.marineengine.com/parts/evinrude-johnson-parts-diagrams/EVINRUDE/41051.gif
Customer: replied 7 months ago.
yes it all moves as it should as far as I can see. It did touch the screw so I tried moving the arm manually further and moved the screw out to try it also. This was all done under load in the water. No change at all in speed or power. The timing base was at the end point. Tried moving it manually backwards and it tried to stall. Yes it moves very easily. All linkages are free moving and lubricated.
Customer: replied 7 months ago.
if timing was off would it not be really hard to start as well as idle really poorly?
Expert:  Tan replied 7 months ago.
Have you checked the spark at full throttle on all 3 cylinders with a timing light?What is the timing set at idle and full throttle?
Customer: replied 7 months ago.
I don't have a timing light. What generates the spark at full throttle? Is is not the coils?
Customer: replied 7 months ago.
The engine runs smooth right across the board, just no power under load.
Customer: replied 7 months ago.
are there any tests I can do with a meter?
Expert:  Tan replied 7 months ago.
The stator generates the voltage that supplies the power pack which in turn sends voltage to the coils.If the timing isn't correct at full throttle it won't have any power. If the timing is off or to low at idle the engine won't idle correctly.We need to verify spark on all cylinders when engine acts up and timing also.
Customer: replied 7 months ago.
so timing at low speed is different than at speed?
Customer: replied 7 months ago.
The plugs look great, not fouled, all dry and the ceramic looks light tan in color. Does that give any indication to spark?
When I pull wires while idling they all have same effect as expected.
Expert:  Tan replied 7 months ago.
Yes timing is different at both ends of the rpm range. The timing at idle is near TDC and the timing at full throttle is about 17* Well there is but if you say you have spark on all cylinders then their isn't anything to test. Now we could do a voltage output from the stator but you need a peak reading volt meter.
Customer: replied 7 months ago.
just have a regular cheapy model meter.
Customer: replied 7 months ago.
I did notice on the stator that there are bubbles in the resin but no drips etc. Can't tell if it was made during the mold process or heat.
Expert:  Tan replied 7 months ago.
Yes you can have spark at idle but not at full throttle you could have a cylinder misfiring. We can only do ohm tests with that and they aren't accurate as it can read good and still be bad. You really need a timing light to check timing and spark on all cylinders at full throttle. Then if we do have a misfire we will need a peak reading volt meter or a DVA adapter for your meter.
Customer: replied 7 months ago.
I guess I have to find a timing light...
Customer: replied 7 months ago.
again, under load the engine sounds ok, just not revving up as high as it should. What I mean is that there are no misses, sputters etc. Just thought I would say...
Customer: replied 7 months ago.
ok, so how do I adjust timing if that is the cause?
Expert:  Tan replied 7 months ago.
Ok get a timing light and let me know what you find and we can go from there. Check spark on all cylinders with the light at full throttle. What you want to do is watch the flash of the timing light on each cylinder at full throttle. The flash should be steady with no dead spots. Then check the timing at full throttle and idle. The timing pointer will be at the front of the engine just above the top carb. The degree marks will be on the flywheel.Post back with findings and questions.
Customer: replied 7 months ago.
will do.
Expert:  Tan replied 7 months ago.
Here is a diagram of the screws to adjust wot and idle timing. Move the screw and check timing.
Expert:  Tan replied 7 months ago.
The specs for the idle are TDC and full throttle 17 degrees. Post back with findings.
Customer: replied 7 months ago.
Can't do it until I get a timing light
Expert:  Tan replied 7 months ago.
Ok just let me know. I will be available all week. My hours are 8am - 5pm PST every day.
Customer: replied 7 months ago.
I have been reading more and found that timing rarely gets messed up. Still will test it but it just seems that it must be something else. Do coils run differently under load? There is nothing else to change as I did everything. It doesn't sputter, just won't run harder.
Customer: replied 7 months ago.
I will run electric diagnosis with a meter also. I have a manual that I found.
Expert:  Tan replied 7 months ago.
Yes coils can fail under a heavy load. This is why we need to check spark when engine is acting up on all cylinders with the timing light.I didn't know if you had messed with the timing adjustments trying different things. If you have turned any of the screws on the linkage you have messed with syncronization and timing. This is why I like to verify these are correct. Here is your statement that made me think timing could be an issue. "Timing advances as it should to end (doesn't even hit the stop screw). Tried moving the timing advance under load and it goes no higher."
Expert:  Tan replied 7 months ago.
The only diagnostics you can do that are accurate are with a peak reading volt meter. The ohm tests aren't accurate all the time.
Customer: replied 7 months ago.
The only screw moved was the bottom one on control arm but arm under flywheel still touched the rubber stopper and that screw was not moved. This was done while moving.
Expert:  Tan replied 7 months ago.
Ok we still need to verify that the timing is actually advancing to 17 degrees. We have to be sure we can't assume anything at this point. We still need to verify that you have spark on all 3 cylinders at full throttle. If you drop just one cylinder you will have no power.
Customer: replied 7 months ago.
Ok. So the only way is to put the boat in the water and have someone drive? Can I test components any other way?
Customer: replied 7 months ago.
It's just that weather here will be bad for almost a week.
Expert:  Tan replied 7 months ago.
No the boat has to be under full load as you have checked everything with no load and they all check good. The boat has to be acting up to find the problem. Here is a pic of the timer base it has 3 coils these are what fire the cylinders if one is bad this could be your problem. http://www.cnautiquefrance.com/22822-thickbox/timer-base-sensor-65-70-75-hp-johnson-evinrude-581251.jpg I'm not going anywhere and there is no time limit on the question. So just post back when you get the chance to run the boat.
Customer: replied 7 months ago.
Explained symptoms to local mechanic where I went to inquire about parts. I mentioned that it bogged down slightly while pumping bulb under load. He immediately said to replace carb float needles. I did that and now when I pump the bulb it actually stays hard. Never did that before. Also now that I remember there was a bit of fuel dripping from air silencer after running. Might go for test drive. Could this be it?
Expert:  Tan replied 7 months ago.
That would cause flooding. You said you did the carbs. Did you not put carb kits in the carbs? When ever I take a carburetor apart and clean it I always put kits in the carbs. The spark p[lugs would be wet and black from to much fuel if the inlet needles were the problem. Bogging is usually clogged high speed jets. But you said you did the carbs.
Expert:  Tan replied 7 months ago.
Here's a Test that will tell us if it is fuel related. Run the boat till it acts up then push the choke. Does it run better?The other test is squeeze the [primer bulb when engine acts up. Does it run better?
Customer: replied 7 months ago.
No didn't change needles until now.
Expert:  Tan replied 7 months ago.
Still the engine would be flooding and as you stated the plugs looked good. I am basing my diagnosis on what you tell me.
Expert:  Tan replied 7 months ago.
This was your statement. "spark plugs (look perfect - like toasted marshmallow, no oil residue etc.)" If the inlet needles were the problem the plugs would have shown signs of to much fuel. You did the choke test which would eliminate the carbs. The primer bulb test eliminates fuel starvation and fuel pump.
Customer: replied 7 months ago.
hi,
I know you must be getting tired of me, but here goes. Yesterday I replaced the carb float needles. Apparently they did need changing because now when I pump the bulb it goes hard and stays that way. Never did that before. But power issue still present. A weird thing happened though, Started engine on lake (break in the weather) and it started right up. Idled ok. Put it in gear and it died immediately. This happened about 5 times. Idled fine. Finally after a few tries able to run in gear but low power (lower than before by half). After a while of that I just idled around a bit in forward. Then decided to try throttle again and it gained a bit but only a bit more (still very slow only, 8mph). Tried pumping bulb and no difference at all. Took out plugs at home and all looked identical. Dry, slightly tan in color no fouling at all. Decided to check fuel system once more. All good, tight, no leaks or possible air flow. Fuel pump works fine. Tried pumping fuel with bulb and fuel pump disconnected and it gushed out ok. Then, since I don't have a timing light yet (today) tried some bench tests on electrical components. 3 coils all good resistance on primary and secondary. Stator tested ok on ohms. Sensor base shows specs of 30-50 ohms but I get 8 ohms on all three triggers. Saw a video online and those showed as 12 ohms so not sure what that means. No ground issue there either. Whatever I read about and try it all shows ok. I know I didn't do timing light yet but I will. Further thoughts? Ideas? Rants?
Expert:  Tan replied 7 months ago.
I still think something is going on under a load and if we can't verify that we have spark on all at full throttle we don't know for sure. With the engine running in the water pull each plug wire off does the engine drop rpms on each cylinder? On the trigger/timer base you need to test between black/white to white/blacks. The spec is 10-20 ohms on OE and 30-40 on CDI components.
Customer: replied 7 months ago.
Will test under load and timing light. Am getting 8ohms on triggers
Expert:  Tan replied 7 months ago.
Since the engine is running some of the triggers have to be working as the engine runs. So ohm tests aren't accurate.Another test you can do with the cover off the front of the carbs. Run engine up as fast as it will go and put you hand over the front of each carb momentarily. Does the engine react?
Customer: replied 7 months ago.
When I did the hand thing the engine slowed more .
Expert:  Tan replied 7 months ago.
Ok do you have the same prop you've always had?
Customer: replied 7 months ago.
Whole unit is new to me. Prop says 13.5x17 in perfect shape.
Expert:  Tan replied 7 months ago.
Ok we need to do the timing and spark test.
Customer: replied 7 months ago.
On my way to store
Expert:  Tan replied 7 months ago.
Ok
Expert:  Tan replied 7 months ago.
When you run the boat make sure the throttle plates in the carbs are fully open. The plates should be horizontal.
Customer: replied 7 months ago.
Timing at idle tdc. At full throttle 18-19. Spark gap tested up to 3/4" + good on all 3. Even spark via timing light as far as I can tell. Now what? This is frustrating. How would I verify fuel starvation? Symptoms?
Expert:  Tan replied 7 months ago.
Squeezing the fuel primer bulb eliminates fuel starvation.Did you check the throttle plates at full throttle? Were they fully open horizontal?
Customer: replied 7 months ago.
Yes open
Expert:  Tan replied 7 months ago.
Well I am going to opt out as I don't know what else to check. Someone else will come on if they have anything to add.Soory wish I had an answer this is a stumper.
Customer: replied 7 months ago.
Thanks
Expert:  Jason replied 7 months ago.
..
Customer: replied 7 months ago.
Hi
Ideas?
Expert:  Jason replied 7 months ago.
No sorry. I am not involved with your question. I responded to another customer and my response to him accidently got posted to your question page. Sorry for any confusion.
Customer: replied 7 months ago.
Can you help? This issue is unresolved

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