1985 50HP 4-cylinder power loss

[BWR1953]

The PT application and no water run time does make it tough to read the plugs. You said that spraying the PT in the bottom carb didn't affect the idle and the 2 bottom plugs don't have the distinct light brown around the electrode. Something isn't right with the bottom 2 cylinders.

Addressing the elephant in the room, the first thing to do anyone says is run a compression check and with your compression numbers being 70 ish, I really don't know how much time and money I would exert on the motor. Personally on my old motors I have no problem sinking money into them if the numbers are above 120, I know I can get many years of use on the cheap before they start to loose their will to live.

I know the feeling is that the motor has ran really good up until now but with low compression numbers it's on borrowed time to where no amount of new parts will make it run better short of an internals rebuild.

Regarding the bottom carb, which was less affected at first by the PT treatment, I'm wondering if a carb problem could give that kind of indication?

And yes, I'm definitely concerned about throwing money and especially time, at this engine if it's not worth saving. Both of those commodities are significant for me.

I do have an option if the 50 is Tango Uniform... I could use one of the 70HP blue band engines from the Chief project and literally bolt it right onto the KF. But that's a no-no in this state. Still worth thinking about though.

 

[jimmbo]

The 70hp of the 70s has its own unique eccentricities because of the 2 carbs for 3 cylinders design
I understand the TU encryption, but, Chief Project and KF?
As for 'no-no' legalities, both are 2 strokes so it can't be emission related

 

[BWR1953]

The 70hp of the 70s has its own unique eccentricities because of the 2 carbs for 3 cylinders design
I understand the TU encryption, but, Chief Project and KF?
As for 'no-no' legalities, both are 2 strokes so it can't be emission related

The Chief and KF are my Chieftain and Kingfisher boats. Both are aluminum 1976 Starcraft. There are links in my signature for those projects.

The KF is a 16' side console open fishing model, rated for 50HP max.
The Chief is an 18' cabin boat, rated for 150HP max.

The 50HP Merc in this thread is currently mounted on the KF, which was splashed 2 years ago and was First Runner Up in a 2 boat race for SOTY!

I have a pair of 1982-83 70HP Merc blue bands that I've been planning on installing on the Chief. I'm currently in the hull repair phase of the Chieftain project.

 

[jimmbo]

Oops, Blue was used until 84. When people say blue band I just default to 72-79, forgeting the 80 - 83 scheme

 

[BWR1953]

Oops, Blue was used until 84. When people say blue band I just default to 72-79, forgeting the 80 - 83 scheme

Yeah, I should probably start a separate thread about those engines for my Chief. Plenty of info needed.

Right now I just have too many irons in the fire to start another major thread though.

 

[BWR1953]

Sooo... as I'm sitting here sipping my first cup of coffee and waking up, I had a thought.

Is it possible to swap the powerhead from my 1983 70HP 3 cylinder onto the 1985 50HP 4 cylinder? Hmmm... could be interesting.

 

[racerone]

Not a chance that it will fit.----Do some simple trouble shooting on the 50 HP

 

[BWR1953]

Not a chance that it will fit.----Do some simple trouble shooting on the 50 HP

I have been doing simple troubleshooting. Have you read the entire thread?

 

[racerone]

No need to.----Simple trouble shooting must be done.-----Trouble shooting is very simple but difficult to teach.----If compression is at 70 / 80 PSI the motor needs to come apart for rebuilding !!

 

[BWR1953]

New compression gauge arrived this evening. Testing again tomorrow morning.

 

[Faztbullet]

Chinese junk label under different names.... below is what ya need.

 

[BWR1953]

Chinese junk label under different names.... below is what ya need.
View attachment 366014

I need a picture of an unbranded gauge with no other info?

C'mon, don't tease me! Gimme the brand, a link, a price or something!

In my first set of compression tests, I used a $15 HF special. The second set, I used a $25 HF special. The new gauge is $50, came from Amazon and has great reviews. I hope it works.

 

[Faztbullet]

here...

Amazon.com

 

[BWR1953]

here...

Amazon.com

Thanks for the link.

 

[BWR1953]

Todays update is a good news/bad news deal.

We went out this morning to do a compression check with the new gauge.

Hooked up the muffs, turned on the hose and fired up the engine. I let it idle at about 1100RPM for a minute or two, then pulled the throttle back down to normal idle. It ran well for a couple minutes, then struggled and bogged and stopped running. I fired it up and tried again a few times and it struggled and fussed, so I shut everything off at that point.

I decided to go ahead with the compression check since the engine was pretty warm already.

Results were excellent, all cylinders were ~150 psi! Looks like no engine teardown is needed!

Cylinder #1.


Cylinder #2.


Cylinder #3.



Cylinder #4.



And as a double-check, we retested with the old gauge. Still 70 psi.


What was really interesting is that when we first started testing with the new gauge, the top 3 cylinders showed 130 psi. But, when we got down to Cylinder #4, we couldn't fit the gauge in with this adapter so we removed it.


After testing Cylinder #4 (without the adapter) it showed 150 psi! So, we went back and retested the others and they were all the same. Cool stuff!

That's the good news.

I decided to see if we could figure out why the engine struggled and died prior to testing. We fired it up and tested by squeezing the fuel bulb...

And the bad news is... I forgot to turn the water back on to the muffs prior to restarting the engine!

I'm so used to testing in a water barrel that I overlooked that simple thing.

Tomorrow we'll take the leg off and see if I just need an impeller or if I need a whole kit. Sigh.

 

[BWR1953]

Yeahhh... it's burned. Heading to the repair shop to pick up a new one now.

 

[BWR1953]

The water pump housing was shot, so I bought the entire kit yesterday afternoon.




And last evening, the new spark tester arrived.



We'll install the new WP and then test it out. Following that, we'll try the spark test with the new tester. Not sure if I'll be able to see anything in the daylight though. If we can't see the spark well enough, we'll try again later this evening if it doesn't rain.

If the test shows good spark, we'll pull the carbs. Otherwise, no. I don't want to pull the carbs and rebuild them if it isn't necessary.

 

[BWR1953]

Break time's over.

We got back on the job. This morning we finished installing the new water pump and it tested out fine. We finished up about noon and it was too hot to do anything else.

This evening we completed the spark test. Looks good to me. I'm thinking that I need to move on to carbs. What say y'all?

The test gap was set at 7/16".

 

[jimmbo]

set it for 3/8"

 

[BWR1953]

set it for 3/8"

7/16" is wider than 3/8"