bilge runs then motor runs ruff

Roostertail · 08-06-2009, 11:28 PM

I have a 1970 4 cyl. 120 horse marine chevy engine. Runs Great It's in my Fiberform. At idle and higher rpm's when I turn on the bilge pump then the motor runs real ruff. What could be the cause?
Thanks for you help!

Okie · 08-07-2009, 06:33 AM

My guess is that the bilge pump is drawing excessive current from the battery and lowering the voltage, there fore effecting the ignition of the engine and making it run bad.
Fixing the problem may be larger sieze wire to the bilge pump to carry more current.

Good Luck

Orca · 08-09-2009, 05:41 PM

Yes, likely current (voltage) problem to the ignition coil. You will find a real crusty corroded up connection either on the battery or elsewhere. Wiring diagram would be handy to see where the voltage for the coil comes from.

Roostertail · 08-10-2009, 02:42 PM

Here is photos of some of the electrical Any tips or comments about why the motor runs ruff when the bilge turns on.

Orca · 08-10-2009, 06:54 PM

You'll need a volt meter, also get a couple of jumper wires with aligator clips at both ends.

Clip onto the coil + and a ground (but not the - on the coil). With the ign switch on, you should see something like 8 volts, with engine running, maybe 9.5 or so. With engine running, turn on the bilge pump. If you see a significant voltage drop at the coil, then I suspect a corroded terminal somewhere.

That solenoid between your starter and battery is a likely candidate, as is the starter + terminal. The coil voltage likely comes from the solenoid. You can see the battery goes to the starter, then the coily red wire on the left comes from the starter up to the solenoid. You can check for the same voltage drop at the starter, and at the red wire side of the solenoid. I would just take both these apart and clean them up, along with the far right side of the solenoid. The solenoid looks pretty clean, so the problem may just be at the starter.

This is a guess on how this is wired, but:
In this order, if you see voltage drop at the battery to starter connection - there is battery terminal corrosion + or -.
At red wire on solenoid - bad connection at starter.
On far right side of solenoid - bad solenoid likely.
Only on coil - bad coil connection.

If you have no significant voltage drop, then you will want a spark checker. They make ones you can put on a plug, then put the plug wire on top, and wacth the plugs spark. Ask at the auto parts store, maybe Bi-Mart. You may get good spark in the driveway, but it can then fail to spark under load, so you may have to test on the water. No spark could be a voltage issue as above, weak coil, bad points, cap, rotor, or condensor.

Okie · 08-10-2009, 10:54 PM

Quote:

Originally Posted by Orca

You'll need a volt meter, also get a couple of jumper wires with aligator clips at both ends.

Clip onto the coil + and a ground (but not the - on the coil). With the ign switch on, you should see something like 8 volts, with engine running, maybe 9.5 or so. With engine running, turn on the bilge pump. If you see a significant voltage drop at the coil, then I suspect a corroded terminal somewhere.

That solenoid between your starter and battery is a likely candidate, as is the starter + terminal. The coil voltage likely comes from the solenoid. You can see the battery goes to the starter, then the coily red wire on the left comes from the starter up to the solenoid. You can check for the same voltage drop at the starter, and at the red wire side of the solenoid. I would just take both these apart and clean them up, along with the far right side of the solenoid. The solenoid looks pretty clean, so the problem may just be at the starter.

This is a guess on how this is wired, but:
In this order, if you see voltage drop at the battery to starter connection - there is battery terminal corrosion + or -.
At red wire on solenoid - bad connection at starter.
On far right side of solenoid - bad solenoid likely.
Only on coil - bad coil connection.

If you have no significant voltage drop, then you will want a spark checker. They make ones you can put on a plug, then put the plug wire on top, and wacth the plugs spark. Ask at the auto parts store, maybe Bi-Mart. You may get good spark in the driveway, but it can then fail to spark under load, so you may have to test on the water. No spark could be a voltage issue as above, weak coil, bad points, cap, rotor, or condensor.

This is good advice and should help fix the problem. If after cleaning everything there is still a voltage drop when your sump pump comes on it is obvious that your sump pump is drawing to much current and lowering your voltage. The generator on the engine should off set this so it's possible it is effecting the generator and it's charging the battery. Bad connections can cause all kinds of trouble.

Good Luck

Swampdog · 08-11-2009, 10:34 PM

It might be a long shot but I had the same situation and was able to buy a used boat for a great price...might be worth a check.

A boat I recently bought had the same symptons and the previous owner had just done a bunch of work and could not get this bug worked out and just gave up. One of the things he worked on was installing an electric choke. The electric choke takes 12v and slowly heats up a metal strip, as the metal strip expands from the heat it opens the choke. When he went to find a 12v source he used the feed off the nav lights; meaning the choke would only work as intended with the nav lights ON. When the nav lights where in the off position the choke would never open and when warmed up would run rich and flood. The poor guy pulled his hair out over this because it was somewhat an intermittant problem. I suppose if he launched in the early morning or in fog and had his nav's on it would run great, next time out with the family in the afternoon with nav's off and he's got problems again.

Luckily for me he replaced literally everything before giving up and buying a new boat.

Anyway- check the basics first. That 120hp is a very solid and reliable engine and only has a few circuits to troubleshoot. Trace out your bilge pump wiring and untape any splices and junctions and find every inch of that circuit and you will likely find your problem. Maybe send a dedicated (and fused) power and ground to your bilge, unhook and bypass whats there (temporarily) and see what happens. Also as in my case make sure that your bilge switch only powers your bilge pump.

Good luck!!!

Roostertail · 08-12-2009, 01:10 PM

I haven't had time to handle this ordeal yet. I cleaned off the regulator connections and the coils. I also cleaned off the connection on that round rubber looking unit with one orange wire next to the starter and below and left of the coil. What is that and what is that for? Attached to the coil is what looks like a condenser, but under where you can't see, has a hole in it with no wire. It was like that when I bought it and should it have one and where would you connect the wire? If there is someone in the Molalla area that knows this kind of motor and would be willing to come help me learn more about this engine I could sure use the help.