mercruiser 3.0 turns over but wont start

[russhughes1]

i have an 83 mercruiser mcm 140 3.0 serial #a439321that wont seem to fire off even thought im getting spark i replaced the distributor cap contacts and condenser,put new plugs and new coil on it i took the plugs out and sprayed carb cleaner in the cylinders and tried to turn it over but it still doesnt seem to want to start.like i said i checked for spark on all cylinders and all 4 had spark.i got the manual and found the firing order is 1342 took number 1 plug out found top dead center then found were the totor button was pointing and put the wires on in that order starting there,so any suggestions would be great.also the carb was just rebuilt and we know its getting fuel also i noticed while you turn it over it kinds puffs what im guessing is gas and air back out of the carb every once in a while

 

[choppywaters]

Re: mercruiser 3.0 turns over but wont start

Thats weird. You said its getting fuel, spark and you found tdc. Just a note, I would stay away from spraying any type of cleaner especially down cylinder walls. Use penetrating oil like WD40 or Thrust. Both of those with still fire the motor but won't was out the oils in the cylinders. Are you sure its getting enough fuel and on the flip side is it flooded from turning it over so much. I would check the plugs to see if they are fouled, if not I would spray a dose of the WD40 or Thrust through the carb and see what it does.

 

[russhughes1]

Re: mercruiser 3.0 turns over but wont start

yeah there is nothing on the plugs they are dry.could there be a wire or something that could be loose or somethingor maybe some thing like that

 

[choppywaters]

Re: mercruiser 3.0 turns over but wont start

yeah there is nothing on the plugs they are dry.could there be a wire or something that could be loose or somethingor maybe some thing like that

Well if your getting fuel, spark and timing is on it should fire. How did you check for spark? An easy way to check is ground each plug to the block while in the spark plug boot one at a time and turn the engine over to see if that particular plug has spark. You should see it arcing. Even if theres a bad plug wire it will still fire just not run smooth. After that I would spray some WD40 into the carb and see if she'll fire. Don't be shy when you spray it but don't soak it.

 

[Old Boat Luvr]

Re: mercruiser 3.0 turns over but wont start

If it's backfiring out the carb your timing is all wrong. Did you pull the distributor and reinstall it wrong? Did you install the distributor cap 180deg. off? Double check that the rotor is turning and tight. If there are alot of hours on the motor or you have the timing gear with the nylon teeth you may have jumped a tooth on the timing chain.

Hope this helps.

 

[86 century]

Re: mercruiser 3.0 turns over but wont start

You could have the timing 180? out.

Checking the #1 is ok but remember it comes up two times.
Pull #1 up again then check the timimg mark on the balancer.

 

[scottn83]

Re: mercruiser 3.0 turns over but wont start

.i got the manual and found the firing order is 1342 took number 1 plug out found top dead center then found were the totor button was pointing and put the wires on in that order starting there,

I had the same problem after doing some work on my engine. It was backfiring like hell though. Your ideal with setting the rotor button at #1 with the piston at top dead center is a great idea. I had that same idea except i pulled the diz and made sure the button was pointing at the number one plug. I rotated the engine until I got the timing mark on 0 on the timing plate. Logic was great until right now, you have a 50/50 chance of have the piston on tdc of the compression stroke. To make sure pull #1 plug out and bump the engine until the compression pushes your finger off the plug whole. Then rotate to the top of the stroke you should be able to look at the timing plate and then then rotor button should be pointed towards the number one plug wire.

 

[Don S]

Re: mercruiser 3.0 turns over but wont start

To find #1 tdc on the compression stroke, follow this. http://forums.iboats.com/showthread.php?t=427081

 

[idnjoy05]

Re: mercruiser 3.0 turns over but wont start

We have a 1974 (we think) Winner boat with a 3.0 Mercruiser engine (s/n 3841532) that will turn over but we are getting no spark. We just replaced all the points, the distributor cap, coil, ignition switch, condensor, plugs and battery. It will turn over but no spark. We have been troubleshooting it and think it may be in the electrical but cannot find a diagram of the wire harness so we can test to make sure it has connectivity.

Any suggestions on why it may not spark or a link to the wire harness boat side and engine side?