Mercruiser 140 Carb/Fuel?

[turand]

Having a very minor issue with my 1986 Rinker with a Mercruiser 140 Alpha One Gen One, I want to address it before it becomes a major issue. It starts and performs generally well. I've noticed two things: (1) upon initial acceleration, there is a momentary hesitation before it picks up, (2) at higher rpms (3000 or higher), I am hearing an occasional pop which I presume is coming from the carb.

I'm almost done with the first tank of gas (stabilized from winter storage), so I will be loading some fresh fuel shortly. To start the season, I've already replace the carb filter, fuel water separator, plugs, and points. So I'm guessing the carb might need a little love. Is it advised to do a fuel treatment first and/or carb cleaner first or go right for a carb kit?

Thanks!

 

[Scott Danforth]

your accelerator circuit in your carb is plugged

the pop could be a lean sneeze (go back to the carb), or improper timing

there is no mechanic in a can. however snake oil does come in a can.

so........ pull the carb apart and soak the pieces in carb cleaner and chase every passage with a fine wire. then put the carb back together and set everything properly

service your ignition system and properly set timing.

 

[kenny nunez]

When the carburetor is apart look closely at the power valve spring that it is not rusted. That can also cause a lean out problem If water ever found it’s way in the fuel system.
With the distributor cap off try to see if there is any slack on the rotor shaft where you can open the points even more. Remove the breaker plate and inspect the centrifugal advance weights and springs. The posts that hold the springs in place sometimes loosen up. That will cause the dwell to constantly change and not hold steady through the rpm range. This causes the timing to go beyond the setting.

 

[turand]

Hmmmmm. Well, the plot thickens. Before I got to the carb, I checked the timing and it was WAY off (like 12 or 14 BTDC) and specs have it at 6. So, I adjusted the timing, reset the idle and mixture. Had a heck of time finding the sweet spot, but eventually got it. Still at idle, the RPMs seem to have a wider than expected variance. Figured it was the carb, but before moving onto the carb, I decided to do a quick compression test.

Oh my.

#1 and #4 look good at 130. #2 and #3 are both around 65. I re-checked with two separate kits to be sure. I can't source the equipment to do a proper leak down test, but I have another clue.

The prior owner even told me the only time the boat left him stranded was when the thermostat went out. The very inexperienced buyer (and very eager buyer --- me), dismissed it since he had a spare thermostat onboard "just in case."

Yah.... my money is on a blown head gasket which he fried when the thermostat went out.

This whole ownership experience has been an education, but honestly I am having a lot of fun learning and I have the time over spring and summer to roll up my sleeves and jump in.

The boat is not exhibiting any other symptoms that are inhibiting it's use (no white smoke, temperature stays stable around 135-140 if the temp gauge can be trusted) and I can reach WOT rpms.

I have to consult the boss on next steps, but I figure I have 2 options:
- do the right thing and tear off the head to see what is the problem (hoping its just the gasket and the head and block surfaces are still within spec and I see no cracks)
- considering it's still quite usable, put it back together, run it and hope it makes it to the off season and deal with it then at the risk of creating more damage to the cylinder head and/or block, etc.

Thoughts?

 

[Eric 3.7LX Alpha 1]

I personally wouldn't run it with two bad cylinders. Pull the head and see what you have.

 

[kenny nunez]

If the head gasket is leaking between 2&3 and you keep running it you will cause a “flame cut” either on the head or block surface.
It would be a good time to have a valve job done while the head is off.

 

[turand]

We are back baby! Confirmed I did have a blown head gasket between #2 and #3. After a head gasket replacement & valve job, #2 and #3 are back to 110 and 120 compression. Lake test later today and fine tune idle, but summer is back! Thanks all for the feedback and advice. I'll keep an eye on that carb too!

 

[poconojoe]

We are back baby! Confirmed I did have a blown head gasket between #2 and #3. After a head gasket replacement & valve job, #2 and #3 are back to 110 and 120 compression. Lake test later today and fine tune idle, but summer is back! Thanks all for the feedback and advice. I'll keep an eye on that carb too!

That's great!
Enjoy!