I have been trying to figure out why my MCM140 is running rough at idle.
So far this is what I have done.
Set point gap to .022 with feeler gauge.
new spark plugs set to .035"
new condenser
changed oil
set timing to 6* BTDC
took carb apart and cleaned it out 100%.
set float drop to 27mm (1 3/32")
set float level to 14mm
running fresh fuel.
new fuel filter in fuel pump.
I did not replace the points, rotor or cap yet since the spark is a thick blue spark when place near a ground.
When the engine is cold, I pump 2 squirts of gas from the throttle and turn the key. The boat fires up almost right away. It idles around 1400 rpm when cold. the choke is 100% closed. The engine has a slight shake to it. As I take the idle down to around 900 the engine starts to shake more, and I can see the Tach needle jumps about 1/4" at times. I have pulled each plug when the engine is running and the engine gets worse when I remove each plug so I know they are all firing. I have adjusted the idle mixture screw to rich until it gets rough, and then change it to lean where it gets rough, I then found a middle spot in between. However it did not smooth out the idle. the engine revs up and sounds great and there is no shake when it revs up.
I am now looking at the electrical / ignition now and I am getting confused. I am reading about a resistance wire that should be connected to the coil. My coil only has a purple/yellow that goes down to the starter, and a brown (or dull red) that goes into the loom where I cannot find where it comes out on the + side. On the Neg side it has a black wire from the dist, and a gray wire that goes into the loom where I have not located the other end. I do not see a purple resistance wire on the coil. I do however see a purple wire that comes from what looks like the from of the boat, and connects to the "breaker reset button" panel.
I tested the purple wire, and when the key is in the "on" position, it is getting about 5.5 Volts. I am wondering if that purple wire needs to be run to the Coil instead.
When I put a multimeter on the + coil and ground the other prob to engine block with the key in the "on" position, it reads 10.5 volts, I thought it would be closer to 12 volts. After I start the engine, I am still getting 10.5 volts. i thought I read somewhere that the votes should go down after the engine is started. On a side note, my coil that was in the boat had a crack in the top and was dripping oil. I had a coil laying around but i think it is a ford style coil. I installed it and it seems to work good and produced a nice spark so I left it. I tested the OHM with the multimeter set at 20 value. put the red probe on the lead battery terminal, and the black probe on the start of the battery cable and got 0.8 ohms. I then put the probe on the battery terminal and the other probe on the starter where the red cable connects and it read 5.5 ohms. is this too much resistance?
Could a battery that might be on its last leg cause bad idle at lower rpms?
Anyways, here is a picture of my coil area. does this look normal wiring, or am I missing something on the coil connection?
in this picture the arrows are labeled.
#1- where the purple wire currently connects to on the reset button
#2- the purple wire coming out of the loom that appears to be coming from the front of the boat.
#3- Purple/yellow wire that goes to the starter area.
#4- Brown or dull red wire I have not traced where it goes yet.
#5- gray wire going into the loom
#6- black wire coming from dist.
Any help would be appreciated.
So far this is what I have done.
Set point gap to .022 with feeler gauge.
new spark plugs set to .035"
new condenser
changed oil
set timing to 6* BTDC
took carb apart and cleaned it out 100%.
set float drop to 27mm (1 3/32")
set float level to 14mm
running fresh fuel.
new fuel filter in fuel pump.
I did not replace the points, rotor or cap yet since the spark is a thick blue spark when place near a ground.
When the engine is cold, I pump 2 squirts of gas from the throttle and turn the key. The boat fires up almost right away. It idles around 1400 rpm when cold. the choke is 100% closed. The engine has a slight shake to it. As I take the idle down to around 900 the engine starts to shake more, and I can see the Tach needle jumps about 1/4" at times. I have pulled each plug when the engine is running and the engine gets worse when I remove each plug so I know they are all firing. I have adjusted the idle mixture screw to rich until it gets rough, and then change it to lean where it gets rough, I then found a middle spot in between. However it did not smooth out the idle. the engine revs up and sounds great and there is no shake when it revs up.
I am now looking at the electrical / ignition now and I am getting confused. I am reading about a resistance wire that should be connected to the coil. My coil only has a purple/yellow that goes down to the starter, and a brown (or dull red) that goes into the loom where I cannot find where it comes out on the + side. On the Neg side it has a black wire from the dist, and a gray wire that goes into the loom where I have not located the other end. I do not see a purple resistance wire on the coil. I do however see a purple wire that comes from what looks like the from of the boat, and connects to the "breaker reset button" panel.
I tested the purple wire, and when the key is in the "on" position, it is getting about 5.5 Volts. I am wondering if that purple wire needs to be run to the Coil instead.
When I put a multimeter on the + coil and ground the other prob to engine block with the key in the "on" position, it reads 10.5 volts, I thought it would be closer to 12 volts. After I start the engine, I am still getting 10.5 volts. i thought I read somewhere that the votes should go down after the engine is started. On a side note, my coil that was in the boat had a crack in the top and was dripping oil. I had a coil laying around but i think it is a ford style coil. I installed it and it seems to work good and produced a nice spark so I left it. I tested the OHM with the multimeter set at 20 value. put the red probe on the lead battery terminal, and the black probe on the start of the battery cable and got 0.8 ohms. I then put the probe on the battery terminal and the other probe on the starter where the red cable connects and it read 5.5 ohms. is this too much resistance?
Could a battery that might be on its last leg cause bad idle at lower rpms?
Anyways, here is a picture of my coil area. does this look normal wiring, or am I missing something on the coil connection?
in this picture the arrows are labeled.
#1- where the purple wire currently connects to on the reset button
#2- the purple wire coming out of the loom that appears to be coming from the front of the boat.
#3- Purple/yellow wire that goes to the starter area.
#4- Brown or dull red wire I have not traced where it goes yet.
#5- gray wire going into the loom
#6- black wire coming from dist.
Any help would be appreciated.
