Stubborn 1982 Mercruiser 3.7 485 blows air-fuel mix back out of carb. will not start.

[82 Glasply]

Hello! First off, thanks for all the great advice, info., and tutorials here. So, just got this 1982 Glasply in very clean shape. Only problem is the Mercruiser refuses to fire / start / run. The carb it came with was dry, so I took apart the fuel pump, cleaned the diaphragm and filter looked good, so - re-assembled, reinstalled. Carb replaced with a pro-rebuilt. Now I have fuel streaming into the barrels.

Spark appears strong at all 4 new spark plugs. I sanded points and cap contacts anyway. The coil seemed to check out except for the voltage drop to 4-9V Across positive terminal to ground with key in on position. Coil replaced, new coil tests perfectly. Install of Ignitor 2 electronic ignition and Flame thrower 2 coil pending.

Oil looks fresh, no sign of water or fuel contamination. Oil change pending.

Compression is 140, 130, 130, 135 on 1-4 in that order Firing order, rotor position, and wire placement confirmed with #1 at TDC and tried at 180'. Pistons look clean from what I could see. Valve rockers look clean with same fresh, uncontaminated looking oil coating.

So, my question is: Why does the carb regurgitate air-fuel mixture when cranking with occasional back firing when primed with either fuel or starter fluid?
I suspect a vacuum issue. How do I test for vacuum?

Thanks in advance!

 

[achris]

A vacuum leak shouldn't spit fuel back out of the carb. It does sound like the spark may be firing at the wrong time. Have you had a timing light on and seen when the spark is firing? That's what I would be looking at. Identify the timing marks on the pulley and the engine front cover and see what you see.

Chris.....

 

[82 Glasply]

Hi Chris, thanks for the quick reply! Will check timing. But can only crank it. Will that tell me anything? Would going ahead and installing the Ignitor 2 help the situation?

 

[Bondo]

Hi Chris, thanks for the quick reply! Will check timing. But can only crank it. Will that tell me anything? Would going ahead and installing the Ignitor 2 help the situation?

Ayuh,.... #1 will still fire, 'n show at the timin' mark, runnin', or crankin',...

Puttin' in the new ignition may well fix it, because what's installed now, Ain't Right,....

Either the Timin', or Firin' Order is Off,.....

 

[achris]

Hi Chris, thanks for the quick reply! Will check timing. But can only crank it. Will that tell me anything? Would going ahead and installing the Ignitor 2 help the situation?

Checking timing is the same running or just cranking. My personal preference would be to get it running right with the points in. That way if it isn't right when you install the Ignitor 2 you know everything else is good and you have already narrowed the field. Put them in now and you are introducing another unknown....

Chris....

 

[82 Glasply]

Well, I have tried everything I can think of and referring back to:

http://forums.iboats.com/forum/engi...roubleshoot-a-points-ignition-system?t=335407

I am carefully going through the steps once again. With the ignition switch on I am getting 12-13v at the + coil terminal. It appears it should be only 4-9v? Does this mean that I do not have a resistor wire? It looks like original wiring with the described purple and purple/yellow wires to the +coil. Do I need one?

I have tried with cleaned points/contacts and the igniter II. New coil, rotor, cap, wires, and plugs. And tried with jumper from + battery to + coil. Testing with the grey tach. wire removed from - coil. Timing at about 8-4 BTDC turning the distributor while cranking. I have seen several times where both the spark tester and timing light fire randomly on #1 as cranking slows after holding the key in the starting position for a few seconds. Does that spark any ideas? Still just regurgitating and occ. backfire through carb.

Thanks again in advance.

 

[achris]

If the points were open when you did the voltage reading, then you will get full battery voltage at the coil +...
This 'fire randomly' would concern me. Check your cap and rotor for tracking, and the leads for cross-firing. (BTW, resistor plugs do NOT reduce cross-firing, they are only for radio noise suppression)....

I would (for sh1ts and giggles), swap the plug leads on the cap 180 degrees. So swap 1 and 4, 2 and 3.... Weirder things have been known...

Have you put a dwell meter on the points? I'd be doing that too, just to check one more thing.

Chris.....

 

[82 Glasply]

Hmmmm, guess it's time to take her in to see a pro. Almost had her catching today when I suddenly heard a horrible sound - metal on metal. She's not frozen, so I guess that's a good sign. Hope I didn't throw a rod. Could it be valves or something else? Any thoughts on if this '82 Mercruiser 485 is worth having diagnosed / fixed? What would a comparable rebuilt or crate engine installed set me back? BTW, she did sound like she was going to run with the wires installed at 180'.

Thanks Again for all the help. Any advise on what direction to take with the engine is most welcome.

Paul

 

[achris]

Since the Mercury Marine 224 engine (which is what your '485' is) is unique to Mercury, and the last was built in 1989 there are no 'crate motors' for this. You have 3 options. 1, repair the current engine. 2, find a good working 224 and build it up to a 485 with your current engine as the parts donor. 3, Find a good working V6 and do a complete new install.

BTW, spitting back though the carb after messing with plug wires and distributors is usually a sure sign that the wires are 180 out.

Chris.....

 

[82 Glasply]

Any idea what the costs might look like on the three options? Any other motors that work with my MC-1 outdrive?

 

[achris]

As 1982 was a crossover year, knowing what you have (exactly) will require serial numbers (Engine, drive and transom).

If you have the later model (easiest way to tell is measure the rear engine mount spacing, 14" is old, 10" is new), then you can find any Mercruiser V6 and it will drop straight in. If you have the older (14" spacing) then you are going to need to replace the transom housings as well... The drive should have 1.84:1 gearing, so any V6 will be fine. And that drive will bolt up to either later or earlier transom housing, but not Gen II (1991 and later).....

The flywheel housing from the 485 will only go onto the 224 family of engines, no GMs....

Costs???? No idea. You are in the land of cheap engines and things. For me (Australia) it is half the price to import a complete new package (engine, drive transom housing) than to buy it here. As for finding a V6 kicking around.... Nope! Not one single vehicle here uses that engine (which BTW is no longer. GM pulled the last one off the line, at the Romulus plant, March 7 this year....)

If it were me, and you have room to insert a V6, then find a complete Mercruier engine at the beginning of summer (just after the owner finds out that his winterising method was no good) that has a cracked block. Get a V6 engine block from a wrecked truck (Blazer S-10s seem to be popular) and spend a few eeks setting it all up in your boat of choice... (Gee, I really wish I could do that sort of thing here.)

Another option. Fly me there, put me up for a few weeks and I' do it for you...

Chris.........

 

[82 Glasply]

Good News! After doing a bit more searching I discovered that a bad starter can cause the clunk and hard to turn engine. Hoping it wasn't anything worse, I removed the starter and low and behold, I had torn up the starter gear. Once I got it out I can again easily turn the engine and compression still feels good! Found a mobile marine mechanic to help me figure out this 485 puzzle too! Hoping for all good from here.

Paul

 

[achris]

So, what torn up the starter and the ring gear? Most likely the firing order 180 out will have been trying to push the crank against the direction of rotation.... Sort the starter, sort the firing order, go boating...