Outboard Issues

[eclark53520]

Long story, but maybe someone here can shed some light...

Problem -

Engine starts and idle's fine but won't get up to speed, only reaches about 2400RPM @ WOT

Specs-
1977 Johnson 70HP 3cyl unknown hours
Compression is 120PSI on all 3 cyls
Spark jumps 1/2" gaps easily
Fresh carb rebuilds just done a week ago
All new fuel lines from the tank through the carbs, new bulb, new filter, brand new fuel ever since the carb rebuilds


History -

I bought this boat from a high school friend, he and his brother bought it from an old guy that bought it from the original owner. The old guy apparently only used it maybe 10-15 times and owned it from 1985-2000. My buddy only used it maybe 10-15 times until i bought it in late 2010. He always had problems with the outboard from day one. He is not mechanically inclined at all so he just kinda dealt with it.


Diagnosis -

I'm pretty sure i'm down a cylinder and i'm almost positive it's an electrical issue and not a fuel problem. Spraying fuel in the carb throat does not cause the engine to 'pick up' as they say which makes me think it's electrical.

Tonight i will be moving the coils around and doing some testing on the power pack and wires...if it's not raining like a mofo

Anyone got any other suggestions?

EDIT: Also, i rebuilt the carbs because it was starting on the hose, but not in the water. Rebuilding the carbs allows it to start easily in the water but still won't get up to full operating revs @ WOT.

[bobkyle2]

I dont know jack about johnrude's but ill give it a shot


I would check fiire on on plugs.. Be sure to have nice fat blue spark...
Be careful useing sprays on a 2stroke ..
120psi on all cylinders is a good thing... That tells me its not fuel related or it would have burnt a cylinder down by now...
Are you sure you just aint proped wrong?

If everything is checking out good... I would throw a new set of plugs in it and run it for a little bit... and read the plugs... If you can post up the plugs on here .. I can help you

Also i know these motors run good on 2 cylinders.. Just wont have any speed

[Izzy]

Sounds like a bad coil,but also check that all carbs are in sync,all three must be set to open at the same time. Check the throtle cable adjustment,make sure you are actualy getting to WOT.

[eclark53520]

Thanks for the advice guys, i'll try to answer all the questions individually:

BobKyle -

I have fire on all cylinders as checked with a gap tester @ 1/2" hot blue spark

I sprayed a 50:1 fuel mixture in the carb, not starting fluid, so no worries about lack of oil.

I'm sure the boat is propped correctly, as i have had the boat running well before and it runs about 30mph and about 5300RPM's which is about perfect.

Izzy -

Bad coil was my next guess too and i swapped the #1 and #2 coil's last night. Found something very interesting but i don't know if it was the problem or not. There was a ground on the #2 coil that was on top of a wire loom that used the same bolt. I put the ground behind the wire loom so it was right against the ground. It seemed to run MUCH better after doing that.

All carbs are perfectly in sync, i made sure of that. And i'm definitely getting to WOT, all three throttle blades are 100% open when I'm WOT @ the control.

Thanks for the help guys, i'm going to put the boat in the water(if it stops raining) an see if swapping that gound helped.

[bobkyle2]

If you are getting hot blue spark... I dont think it could be a firiing problem.. I hope that fixes your problem though!

[eclark53520]

Originally Posted by bobkyle2

If you are getting hot blue spark... I dont think it could be a firiing problem.. I hope that fixes your problem though!

I think the problem is the ground.

Bad grounds can make electronics act very weird. I'm assuming the ground was good enough to create spark while at low RPM's such as idle and checking spark, but not enough to keep good spark at higher RPMS which was causing me to drop a cyl when attempting to go WOT.


We will see though....i have yet to water test it. Rained all day yesterday.

[bobkyle2]

DO WORK SON....

If you are still having an Issue after that... I would do it old school... Pull a wire off... run it ... If it changes ALOT... Then that cylinder is fine..plug it back up pull the next one run it....... So on and so on...

Have you ever checked out iboats.com... Place is ran by like hitler... But they got some good info lol...

[eclark53520]

Originally Posted by bobkyle2

DO WORK SON....

If you are still having an Issue after that... I would do it old school... Pull a wire off... run it ... If it changes ALOT... Then that cylinder is fine..plug it back up pull the next one run it....... So on and so on...

Have you ever checked out iboats.com... Place is ran by like hitler... But they got some good info lol...

Yeah, I've been on there since i bought the boat....search a lot, but i don't post much.

I've done that a few times but you can burn out power packs or coils doing that if the spark power backfeeds. The middle cyl was the one having trouble firing. I quick pulled it after swapping that ground and it definitely was firing at idle as were the other two.

Before i swapped the ground, pulling the middle one did nothing, and pulling either of the other two stopped the engine immediately. Now i can pull any of them and it doesn't die.

The water test will verify.

EDIT: Another theory i have is that the bad ground was giving good spark on the tester, but not inside the combustion chamber. It's more difficult to spark inside the chamber than it is in open air. Which also may have caused my problems running.

[eclark53520]

Well, i have mixed results from the water test.

On the way to the fishing spot, it ran great. Full power, on plane, sounded great. Got to the fishing spot and it hot started perfect. On the way back to the dock, the first three times i attempted to go WOT, it bogged and on the second two it died completely. Started it and let the engine sit at high idle for about 45 seconds and all was good again...

I guess i'm going to try to find a way to check the coil's...but i'm going to have to try to figure out how to check them while i'm in the water and they are acting up...Might try to do an inductive timing light...that way i can just clip onto the wires and check as we're running.

Any other suggestions?

[bobkyle2]

Sounds like fuel problem