Mild Misfire

[Gorpon73]

Got a mild nagging misfire. Not enough to stop running, but annoying. Reviewing the current forum posts, haven't been able to sort it out yet. Here are my symptoms:

- Mild misfire a low throttle. Does not seem to be as bad or present at idle or full throttle.

- All new electric ignition/distributor/coil. Timing set according to manual advance specs.

- New fuel filter

- Plugs seem to be dry and black, which should tell me I'm running a bit rich? Using NGK BP6ES. So I know I'm getting fuel.

- Checked strombergs, lifting the piston slightly while running speeds the engine up then it goes back to idle, which I'm reading as the mixture is correct?

I live at 3,000 feet elevation. Could that possibly be affecting the air/fuel mixture?

Any suggestions appreciated.

[3lotus]

check the flex mounts on the carbs.
I redid mine and always had a funky miss at small throttle openings, at say 35mph in forth, just putting along. Anyhow after much fussing about I just tightened the flex mounts (tighter than the specs say ) and the car is so much better. Good Luck

[sprintsoft]

Hello,

Two things I would check:

1. the state of your low tension feed to the coil, you can hotwire a temporary jumper from a 12 volt feed to coil +ve to see if it cures, don’t forget to remove when you’re done!

2. the BP6 is ok if you’re flat out everywhere, but a bit cold for normal running which can show up as black plugs and a sooty rear bumper, Try a BP5 or you can try Champion N9Y, both 1 grade warmer, again just looking to see if you get an improvement.

Regards
Iain

[Esprit2]

Which electronic ignition, and which coil?

The basic Pertronix Ignitor cannot tolerate a 'hot' coil with low internal resistance. The coil should have 3.2-3.4 ohms of resistance, plus the ballast resistor. If you delete the ballast resistor, or use a coil with lower internal resistance, the Ignitor will over-heat and periodically drop-out... mis-fire.

I recently went through a long de-bugging process. Ignitor with a Pertronix coil, but it was a 1.6 ohm coil. "It can't be the ignition, they're brand new"... so I checked everything else with no success. When I finally replaced the coil with a Pertronix Flamethrower with 3.4 ohms internal resistance, the problem went away.

*~*~*~*
Which carbs?

Good luck,
Tim Engel

[Gorpon73]

Thanks for the suggestions. In process for checking all but the last one.

Interesting though. I have a flamethrower II, which is a low ohm (0.6) coil that was preferred for the ignitor II?

It stutters when cold as well, so perhaps not a hot coil issue?

[Esprit2]

The Ignitor II and III can handle lower resistance coils. It's only the basic Ignitor that can't. It's essentially a "points replacer" system, and not a hotrod ignition system.

Regards,
Tim Engel

[Elan45]

1st thing to check on Stromburgs is the rubber diaphram. Take out the 4 screws holding the top on the carb and check the diaphragm for any rips, holes or brittle cracked spots.

Roger