hi I have been having a problem were my A12 engine misfires only under load never at idle it more noticeable when yo get to 4000rpm it will misfire a few time.

I had this problem a few weeks ago so I reset the point dwell to around 50 degrees before this it would misfire really bad problem seemed to had gone but has reappeared.

i rechecked the plugs and points and all seems good I also tried a different (original) coil and does same thing.

Any ideas?

Thanks!

Try replacing your condensor on the side of the dizzy. This can do the same thing and gets to the point where the car bunny hops and misses and has no power what soever.
This happened to me yesterday on the way home from work, put a new condensor on it and she's good as new, no missing or nothing.

hmm this was changed along with the points 5000km ago could it go bad so quick?

Yes, they can go bad that fast. Try fitting the old one that you replaced as a test.

I would suspect the spark plug gap. Re-gap the plugs to 0.035 inch, any wider than that can misfire slightly.

hi so i this problem is getting worse but im not sure if i can say ts a misfire.

i changed the condensor with new one no help i happens while im driving feels like its cutting out and it seems to backfire from the exhaust and carb every know and then.

i thought it could be blocked jets i checked them all even idle jets and its all clear fuel bowl is clean so is the filter.

it more if im accelerating or driving constant speed will be smooth then from no where car will jerk like a misfire?

any ideas?

Thanks!

Sounds like a misfire. Which can have many causes, spark or fuel related.

So setting the dwell to specification fixed it before, then after two weeks it came back. Now it is time to check the dwell again. If it is out of spec after two weeks, most likely the cause would be lack of grease on the distributor cam lobes.

If the well is still 49-52 degrees, I would put the old set of points on and see if it makes a difference. The points (although fairly new) could be bad. Or maybe not. You won't know until you either test or otherwise solve the problem.

Checked fuel filter?
Sounds like fuel bowl is draining under load.

I had a similar issue when running e10 [10% ethanol] fuel. The filter was full of horrible crap from the tank. E10 is known to dislodge the crap in tanks of older cars. Car would idle just fine, but anything under load, simply not enough fuel could be supplied. I always keep a spare filter in the glove-box.

hi thanks

the only fuel i use is 98 octane from shell or bp

but i was testing the resistance on my HT leads and i get around 6000-8000 ohms of resistance

i then checked the lead from the coil to the dizzy cap the multimeter was on 20k but would read nothing i set it to 200k then came with a value of 34 so i guess thats 34000 ohms?

i had a few HT leads lying around (new) so i made one up and so far around the block it has not misfired. Will see tomorrow when i take it for longer drive.

1000 ohms per inch is typical for spark leads (spark wires)

34 ohms sounds wrong. 34000 ohms sounds wrong. Is the center terminal of the cap or the coil slightly corroded? That usually indicates a bad coil lead.