84 Mercruiser 140, Turns over but won't start

[powerx3d2000]

I have an 84 Merc I/O 140 that I just bought and it had been siting for a couple of years. I just replaced the coil, wires, plugs, points, condenser, and starter. I am getting both spark and fuel but the motor won't start. Fumes seem to get shot back through the carb after cranking for 3 or 4 seconds and also through the valve cover. I thought maybe that the starter might be cranking the wrong way, but the motor is going around counter clockwise while looking at the front of the motor. I'm stumped on why this is happening.

I downloaded the manual from the thread but it was no help other than telling me that the firing order is 1-3-4-2, so I know that the wires are on the right cylinders.

 

[Lone Duck]

Re: 84 Mercruiser 140, Turns over but won't start

1st check your compression. Rings may be bad. Or valves may be stuck open, or timing chain may be broke. Or the timing may be way off. If fuel is blowing out of the valve cover , I would suspect valves.

 

[vxtech]

Re: 84 Mercruiser 140, Turns over but won't start

check timing, remove # 1 sparkplug then bring piston up to top dead center compression stroke-this is usually easiest with trigger switch attached to starter -place finger on sparkplug hole an as you crank you will feel pressure pushing against finger then just bump starter a little more to get tdc, pointer on motor should line up with mark on pulley then remove distributor cap and confirm rotor is pointing at # 1 plug terminal on cap ,if this checks out good then continue on to compression test of all cylinders
if timing is wrong compression test is useless

 

[frank246]

Re: 84 Mercruiser 140, Turns over but won't start

Did you also clean out the carb?
Does the Choke work i.e is the choke valve fully closed?

 

[Don S]

Re: 84 Mercruiser 140, Turns over but won't start

Did you have the distributor out? Did you have the wires all off at the same time? Sounds like you have it way out of time. Could have put the plug wires on one notch off ???????

 

[havasuboatman]

Re: 84 Mercruiser 140, Turns over but won't start

If you are just blowing fuel vapor and not flames out the carb, I kinda doubt your have an ignition timing problem, or even crossed wires.
More likely your problem is in the valve train. You said the boat sat for a couple years. Have you pulled off valve covers to check the adjustment of the valves? Or for that matter to see if they are moving at all.
First do the compression check. Lone duck has you looking in the right direction.

 

[powerx3d2000]

Re: 84 Mercruiser 140, Turns over but won't start

Thanks for all the input guys.

I will check the compression tomorrow. I did take off the valve covers and it seemed like they are all moving but I can't remember if all of them were. Nor did I check the adjustment of them.

 

[Don S]

Re: 84 Mercruiser 140, Turns over but won't start

Before you worry about timing with a light, you need to verify you have number 1 spark plug wire on the proper terminal of the cap. This can change if the distributor was out and installed 180 out or something.
Like Vhtech said, get it to #1 TDC of the compression stroke, then verify the rotor is point to #1 spark plug wire on the cap.

 

[powerx3d2000]

Re: 84 Mercruiser 140, Turns over but won't start

Ok, so I checked the compression and it is roughly 120, 120, 110, 90

I also throttled it up while cranking over and I got a flame to shoot back through the carb. It seems like the power stroke of the #4 cylinder is the problem or the cylinder itself.

While cranking I watched the valves and it seems like the #4 slows its down and it seems to light the gas in the carb when the same valve is down (one of the #4 valves).

There is an 85 Merc (same motor just a year newer) at the boat yard by me and they want to sell it for about $850. It seems to me that with that compression test I did, I have a bad ring and I'm not afraid of doing it myself but I'm just wondering if it would be worth the money.

Any advice would be much appreciated

 

[Lone Duck]

Re: 84 Mercruiser 140, Turns over but won't start

Ok, so I checked the compression and it is roughly 120, 120, 110, 90

I also throttled it up while cranking over and I got a flame to shoot back through the carb. It seems like the power stroke of the #4 cylinder is the problem or the cylinder itself.

While cranking I watched the valves and it seems like the #4 slows its down and it seems to light the gas in the carb when the same valve is down (one of the #4 valves).

There is an 85 Merc (same motor just a year newer) at the boat yard by me and they want to sell it for about $850. It seems to me that with that compression test I did, I have a bad ring and I'm not afraid of doing it myself but I'm just wondering if it would be worth the money.

Any advice would be much appreciated

Hmmm! #4 intake valve is not closing at time of detonation. So is it the valve or the timing? I am starting to think timing , although tonight I have had a couple of beers and a whiskey. low comp on#4 . valve or rings ? 120 120 110 90 Are there separate gaskets between 1 , 2 , and 3 & 4 ? if so maybe bad head gasket on 3 and 4. and the timing is out. multiple problems here. One more beer and goodnite all.

 

[cr2k]

Re: 84 Mercruiser 140, Turns over but won't start

Maybe you are 180 out of timing.

Make sure no 1 valves are both closed and the timing mark is on TDC.
Then check to see where the rotor is pointing. Factory is at no 1 plug.

Because it is firing thru the carb and No 4 open it seems to me like timing is off by a few cylinders.

Make sure you wired the wires in the right sequence 1-3-4-2 with the rotor turning the proper way.

Lastly while cranking shoot a little carb spray in the carb and see if it fires, if so you have a carb issue.