Timing and Temperature - 1973 85 HP Johnson

[RDJuhl]

I purchased a boat with this 1973 Johnson 85 HP motor. I have had a problem with cold starts with this engine. I have completed the following steps:
1 - Checked compression - ok - consistent at about 106
2 - Conducted spark test - ok - has a strong 7/16 inch spark
3 - Fuel - plugs are wet and black...so I believe we are getting plenty of fuel...but have not yet rebuilt the carbs.
4 - Cleaned all electrical connects - both positive and negative
5 - Replaced all spark plug wires
6 - Replaced one coil - it was cracked
7 - Checked spark plug gap - confirmed at .030 per spec
8 - Checked engine temperature with my finger...it usually ran less than hot, as I could leave my finger on the engine block for almost indefinitely.
9 - While performing some of these tests, and to check for improvements, I often ran the engine at 1000 rpm on the muffs in my driveway. I always confirmed that the water was circulating and exiting the two ports on the back of the engine.

The engine appeared to be running much better after steps 4 and 5, however, the cold starts are still an occasional problem.

10. Next, I checked the timing, and intentionally increased the low idle timing to get it within the spec of 5 degrees. It was at about 2 1/2 degrees.

Now two questions...after changing the timing, the hot horn went off after a few minutes on the muffs. In addition, I no longer see any water/mist coming out of the ports on the back of the engine. Would increasing the advance on the timing cause the engine to get much hotter? If so, would it be correct to assume I advanced the timing too much?

Or...would your guess be that I burned up the water pump while conducting many of these tests? (I do have a new water pump kit from iBoats, and will be pulling it off later today).

Regards

 

[ezeke]

Re: Timing and Temperature - 1973 85 HP Johnson

What are you using as your base full throttle spark advance? What spark plugs?

The overheat is most likely a cooling system problem, possibly vernatherm, but more likely waterpump.

 

[RDJuhl]

Re: Timing and Temperature - 1973 85 HP Johnson

The manual indicates 28 degrees is the maximum advance for WOT, and 5 degrees for throttle pickup.

 

[ezeke]

Re: Timing and Temperature - 1973 85 HP Johnson

The manual indicates 28 degrees is the maximum advance for WOT, and 5 degrees for throttle pickup.

Good.

 

[RDJuhl]

Re: Timing and Temperature - 1973 85 HP Johnson

It appears the water pump was fine...all fins intact on the impellor.

Now I am wondering if I have messed up the thermostat/vernatherm...
In an attempt to improve the performance of the engine after starting, I had disabled the automatic choke per instructions posted elsewhere in this forum. I suspect I did this incorrectly, and have in fact disabled the vernatherm. Is this possible?

Can anyone explain...is the vernatherm basically the same thing as a thermostat?

If so, where is this located? Under the cylinder head?

 

[ezeke]

Re: Timing and Temperature - 1973 85 HP Johnson

The temperature switch that controlled the "automatic" choke was located at the top of the engine, next to the lifting eye. It has no connection to the temperature switch in the warning system or cylinder head, and absolutely no relationship to the thermostat (vernatherm).

 

[F_R]

Re: Timing and Temperature - 1973 85 HP Johnson

Highly unlikely the vernatherm is at fault. By any chance, was the hub spun in the impeller? They were notorious for that. Fried many a powerhead, they did.

 

[RDJuhl]

Re: Timing and Temperature - 1973 85 HP Johnson

FR - can you explain a bit more about your question: Was the hub spun in the impellor? The key was intact...does this answer your question?

Now, I must admit I took a shortcut when I examined the impellor. I dropped the lower unit far enough to remove the impellor cover, and inspect the impellor. The impellor fins were all intact. Rather than replace the impellor, I simply put the unit back together.

Is it possible that the fins of the impellor would feel intact, but actually be worn to the point they do not push the water up to the motor?

I guess I need to drop the lower unit and replace the water pump unit...and do it correctly this time.

 

[Haffiman]

Re: Timing and Temperature - 1973 85 HP Johnson

If you want to check temperatures and water pump functions, throw the muffs!
Get a barrel and fill with water and let the garden hose run into the barrel.
Muffs are just for flushing out engines, nothing more!
You said you adjusted IDLE TIMING?
It is nothing like adjusting 'idle timing'.
You adjust 'pick up timing' which is the timing when the carbs starts to open.
What timing will be at idle, all depends on other factors like prop, water level on leg etc when boat is floating.
Engine idle may only be adjusted PROPERLY when boat is in water.

 

[mrcj001]

Re: Timing and Temperature - 1973 85 HP Johnson

The choke plates must be FULLY closed when trying to start these crossflows.

Remove the air silencer and MAKE SURE the choke plates are closing really tight.

If not sure, put pressure on the plates while trying to start it. If it kicks over, they are not adjusted right.

BTW, to much or too little water pressure from the hose could cause your problems while on the muffs.

 

[RDJuhl]

Re: Timing and Temperature - 1973 85 HP Johnson

Well, I dropped the lower unit and prepared to replace the impellor. Turns out the key had dropped out...found it in the cavities below the water pump...grrrr...pretty dumb mistake on my side. I replaced the impellor with a new one.

At any rate, the engine is now cooling as it should. Thanks everyone for the input...I learn something from everyone's comments.