165 l6 voltage regulator and ignition woes?

[Steven D]

I'm having fits with a 1979 Mercruiser 165 i6 with a skip/backfire thru the carb issue. Backfires under load and has low power, idle is a bit on the rough side. It will hold 600 rpm but its a bit rough and uneven, sometimes better than others. Boat ran fine for the first 30 minutes of first lake test then developed this issue which has gotten steady worse even as bits have been replaced/rebuilt. It is a transplant motor into a 69 Sea Ray 185, plug from 79 boat was spliced into the Sea Ray as they were different. Plug configurations were matched from the manuals provided here. Again, boat ran fine at first and developed this problem on the water...

So far I've replaced points, plugs, wires, cap and rotor button, coil, condenser and rebuilt the carb. Set timing and dwell to factory spec. New intake gasket and riser gasket. Intake is presently pulled to check for leaks or cracks. No visual issues, is there a further test I should perform?

Compression is 135,142,138,140,140,143. I don't have a proper leak down meter but pressurizing cylinders to 60 lbs shows a very small amount of air moving thru all exhaust valves.

I'm wondering if there might be issues with the resistor wire or the workings of the voltage regulator where this draws power? As this is a transplant motor is there anything that I may have missed in the plug transfer that could cause something to burn out in this area? Do they go bad and cause symptoms like this? Is it an acceptable idea to disconnect the resistor wire and run a wire directly from the battery to the coil to test and see if this is the issue?

As a side (I think) note the tach works from 0-1200 rpm but stops at that point. I've tried disconnecting it with no difference in the issue.

Thanks to all for your support on this continuing (and hopefully finished soon) project.

Steven

 

[dirtyoldman]

Re: 165 l6 voltage regulator and ignition woes?

I'd start by pulling off the distributor cap and wiggling the shaft back and forth to check for wear. I would also try disconnecting the tach and seeing if your problems go away.

When you set the timing was it way off? It is possible you may have jumped a tooth on the timing chain or maybe setting timing to the wrong cylinder.

Check the fuel filter on the pump and the stone filter on the carb inlet. Lack of fuel could explain several of your complaints.

You can run 12v to the coil but doing much of this will burn out the points.

 

[kilowatts]

Re: 165 l6 voltage regulator and ignition woes?

Hi Guys:

I too have a 165 L6 and love it. I also had the same problem and after researching on this site I found that backfiring under load was usually caused by the carb running too lean. In my case I re-calibrated the carb, changed all the filters and it's been fine ever since. I'm also an advocate of Pertronix electronic ignition modules which seem to be foolproof in this application. You would need model # 1163A for the inline 6. I hope this helps.

kilowatts