I have a 1983 12A engine. The engine runs fine during acceleration and is strong. It will not run without missing at a cruise rpm or any rpm that is in a steady state. It has 90k miles on it. We have drained the fuel tank and removed over a pint of rusted water.

Changed the fuel filter, replaced the trailing igniter with a used one that checked out to be good, using the test illustrated in the Haines manual. I also noted a test of resistance across two poles of the igniter and found all the igniters I have to be of greater resistance than specified. 1k ohms is the spec called out and mine are measuring 1.2 & 1.3 k ohms.

I have changed the plugs and all ignition wires using a 1984 salvage car that has many usable parts. We checked the resistance across all the ingition wires and they appear to be OK. I cannot find data covering the resistance for ignition wires. They read 4.9 k ohms.

I intend to disassemble the carb. and install all new gaskets etc.

The engine idles fine, oil pressure is fine, there is lots of power upon opening the throttle. It will just not run smoothly at any steady rpm and sounds like a two cycle engine, then intermittantly sounds as it should, that is the traditional buzzing sound. Also I should mention the exhaust terminates about 24" down stream of the catalitic converter.

Can someone offer some thoughts on how to pinpoint the miss fire problem?

 

Go with MMO first. Sounds like a stuck apex seal. As a reference, good MSD wires will show 2.0 K ohm resistance for the 12A set. Salvage yard wires may look good and be cheap, but they're burned up for sure. Could even be they're the reason the car's in the junkyard! Well, maybe not...

 

check the distributor. That could be the problem. Maybe the pickups or something.

 

I don't have any specific ideas, but I wouldn't worry about anything being internally wrong with your motor. It doesn't sound anything like that. If it idles properly and makes good power, I would suspect you have ignition or carburator problems. Sorry I don't have any better ideas, but what I'm saying is it sounds like you're on the right track, and you're looking at the right stuff to solve your problem. Good luck!

 

i got lucky today...after trashing my distributor cap and plug wires.....during a umm..battery relocation incident..i was in the scrapyard..got a cap and rotor and all wires for 2 bux

put it on...ran beautifully...im soo happy now......
i just figured id try this route before buying new ones......

just my 2 cents

Paul

 

paul - did your battery go for a trip during hard braking?

Jeff

 

cmon jeff...get your physics right......hard braking would of put it into a headlight...


hard accelration.....into distributor....
and that is how, folks, to successfully ruin a distributor cap and spark plug wires....


Paul

 

nice... that's why they invented the bungee cord

 

i would check you filter again. the gas tank will probably come back to haunt you. chances are the **** in the tank is in your lines and carb. rebuild the carb and make sure you can blow through the hard lines. then attack the electrics.

 

If you really removed a pint of rusty water, and the thing sat for a long time, then I got five bucks on water ****** up the fuel pump.
The pump is an oscillating piston design. If you got crap in there, or it has rusted, you might need a new pump. Since it does'nt spin on the inside, crud could be limiting the travel of the pump piston, allowing it to work, but not at full capacity.
Check the output of the pump by putting the carby fuel line into a can. (The larger diameter line. Haynes has the amount per minute +/- guidline specs.)

mar3 suggests a good ole' fashioned Carter pump.

 

 

Thanks for all your suggestions. I will post the results as soon as I am able to implement the ideas.

Best regards, THC

 

if you disconnect the large line, 1.1 litres of fuel should come out in a minute... so it should almost fill a pop bottle (600ml) in 30 seconds... If any less than that, check your fuel filter, pump, and lines for blockages. Start cheap, and get more expensive with the parts (eg. filter, lines, pump)

Jeff

 

I suspect that is the true problem...he has a factory hand-assembled and clearanced Carter fuel pump....

 

For what it is worth, I removed the fuel pump and re plumbed it so I could apply 12 vdc and test it. That is a suction line to a milk bottle of fuel with a return line back to the jug. Fuel flowed fine, however it took very little finger pressure to close off the flow at the return line which did not stall the pump.

I would think it would take a lot of force on the finger to stop flow. I have an 84 parts car and intend to run the same test on it. Wish I had a pressure gauge?? Can't seem to find one with the required metric fittings.

Let me know what you all think??

THC