86 OMC Still Backfires

[Sdecker78]

I recently started having a backfire issue and have done the following : new coil,new points ,condenser, rotor, cap, wires, alternator, trim solenoids (both),carb base gasket, battery, cleaned ground cable, added additional ground cable, cleaned cables on starter, changes fuel/water filter. the backfire usually starts when using the engine trim or the trim tabs. I noticed tonight real small water droplets on the carb plates after running it in the driveway so I pulled the filter and emptied it in to a container to check for water but found none. It will run perfect in the driveway, but in the water at 1/2 to full throttle it will start to backfire sometimes without trimming as well as when using the motor trim. At trolling speed to 1/2 throttle no issues at all.Today I used the trim tabs while on the lake running about 2500-3000 RPM, and it started to backfire as well. Man I am out of IDEAS

 

[jerryjerry05]

Either a fuel restriction or the new coil could be bad.
The coil: is it an internal resister?
Measure the voltage to the coil.12v+
Then measure the voltage from the coil should be 9v
Test when the motor starts acting up. Touch the coil and see how hot.
If it too hot to keep your fingers on it?? Then it's bad.
This test ok?

Then go through the fuel system.

If it backfires when you hit the trim: more than likely there is a bad ground or connection someplace.

 

[Sdecker78]

thanks jerry. The new coil is an internal resistor, but the one I took off was an external resistor. I have looked at the wiring to try to find the resistor with no luck. I put the old coil back on and it made no difference. I checked voltage before I switched them and had 10.6 volts on the + side and 6.4 volts on the - side? the coil did not get hot. I ordered an electronic conversion to eliminate the points and condenser. That's my next step. Also we pumped the fuel out to check for water and found none. I also took the top of the carburetor and checked the float and needle. They look fine, no water in the fuel bowl. I haven't checked the fuel pump pressure yet, but I don't think it's starving for fuel? any other ideas would be greatly appreciated. This thing is driving me crazy.