Johnson 1977 70 HP, 70EL77S - Bogs down when put in gear & throttle pushed forward.

[airbus320]

Johnson 1977 70 HP, 70EL77S - Bogs down when put in gear & throttle pushed forward.

After running my engine for a period of time, at full throttle...approx 10-15 minutes, I shut down. After approx 15 minutes or more, I restart, place it into gear and advance the throttle through approx 25% of the travel (sounds like it bogs down) then it quits. It starts right back up..NP. If I advance the warm up lever for about 30-60 seconds or just advance the throttle very very slowly and wait it out, it eventually recovers and starts to operate normally again.

Conversely, If I stop after running at full power for the same amount of time and re-start the engine shortly after, or within a few minutes, throttle advance is smooth, normal and the engine operates normally.

The problem only seems to occur after it sits for more than ten minutes in-between stops.

The saga continues...Any suggestions welcomed!

Thanks, JD



Note: The only above the waterline abnormality(?) noticed recently was quite a bit of exhaust coming from the two 1/2" holes just below the cowling. I havent noticed this before.

Just done:
Head gasket for intermittent missing/dead cylinder(s) #3 seemed to be the worst - Result is like night and day. No more missing or completely dead cylinder(s). Sounds and performs much better, except for aforementioned.
Carbs removed, completely disassembled, cleaned and rebuilt
New water pump installed
Plugs and (1) coil pack replaced

Done late last season:
Water jacket gasket, thermostat, power pack, (2) coils, plugs, prop and hub.

 

[flyingscott]

Do a link and sync on the motor. When you do the link and sync you want about an 1/8" gap between the cam and roller? Those motors like a little timing advance before the carbs move.

 

[jbuote]

Hmm.. I'm going to follow along on this one..
​I'm relatively new to outboards. I have a 71 50hp.

​I would have thought based on what I've read and learned here so far, that even after a WOT run, sitting for 15-30 minutes cools the engine enough that it's like a cold start again.., Not quite like the first start of the day, but cold, so start lever and warmup for a few would be normal..

Going to watch and learn here.. LOL

 

[F_R]

Look for a sticky timer base / spark advance. Pretty common. As you advance the throttle, most of the initial movement should be the timer base, with very little carburetors shafts movement. Only after the spark has reached the full advance stop, should the carbs open wide. If the timer base does not move freely, the carbs will open before spark advance has happened and it will stumble and usually stall.

Old sticky, dried grease in the timer base mount is the culprit.

 

[airbus320]

Do a link and sync on the motor. When you do the link and sync you want about an 1/8" gap between the cam and roller? Those motors like a little timing advance before the carbs move.

If you have a link or otherwise for link and sync instructions that you could forward, it would be appreciated. I get the basic concept, just not so much the "link" part of the equation...is this checking for free play or gaps?

I will check for the 1/8" gap. Borrowing a test set from my friend this week and will do the synchronization. I've had some more time to study the problem and refine the symptoms. The motor is running so well otherwise, I've had time to run it quite a bit and focus on the aforementioned defect, now that I've peeled back all the layers. It seems to specifically related to advancing the throttle too quickly. Once I bump it a little past idle, I have to wait...then bump it a little more. The RPM will start to increase after about another 30 seconds, then I'm good to go.

>>The problem ONLY occurs when I shut the motor off for period of time more than 1-2 minutes, then try to fully advance to Full or WOT normally, without hesitation. I don't think exact amount of time between shutdown, restart and throttle movements are a factor, or only loosely correlated. My thought is that time is being consumed just finding that sweet spot and has nothing to do with the problem...maybe related to spark advance as mentioned. Temperature does not seem to be a factor or only loosely correlated. I can advance past low speed ONLY If I nurse it up to higher throttle settings OR run it in gear at slow speed, for around thirty seconds, then slowly advance. It seems to hit a point where it "comes alive"...and not like before, where there was one dead cylinder that suddenly comes alive. It is more of a slow recovery from a bog down.<<

IMPORTANT SIDE NOTE: This problem DOES NOT occur if I leave it out of gear, then advance the "warm-up lever" to high RPM...ONLY happens in gear.

So, I've kind of gotten to know the motor's deficiency and learned to get around it, as it performs so well at all higher speeds. But, I still want to get this fixed, so I don't have to fiddle around with it every time...just turn the key and "go".

Thanks for the tip...I will update with comprehensive video soon. Hopefully, this will serve to help others as well.

 

[airbus320]

Hmm.. I'm going to follow along on this one..
​I'm relatively new to outboards. I have a 71 50hp.

​I would have thought based on what I've read and learned here so far, that even after a WOT run, sitting for 15-30 minutes cools the engine enough that it's like a cold start again.., Not quite like the first start of the day, but cold, so start lever and warmup for a few would be normal..

Going to watch and learn here.. LOL

Please do follow. I've come a long way and learned a lot. On the flip side, if you have any success with your problem, let me know. I will update with comprehensive video soon. Hopefully, this will serve to help others as well.

 

[airbus320]

Look for a sticky timer base / spark advance. Pretty common. As you advance the throttle, most of the initial movement should be the timer base, with very little carburetors shafts movement. Only after the spark has reached the full advance stop, should the carbs open wide. If the timer base does not move freely, the carbs will open before spark advance has happened and it will stumble and usually stall.

Old sticky, dried grease in the timer base mount is the culprit.

Where do I look to clean this grease out? I will check this today. Thanks!