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Can't figure out why engine is missing on BN2

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bighealeysource

bighealeysource

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Hey all,
Got a mystery here. My engine runs great for maybe 30 to 45 minutes, usually going somewhere and then stop for whatever reason and then start out again. Like yesterday, ran like a champ going to a club meeting, maybe 30 minutes in. Sat a few hours and on trip back started to miss. I have changed the plugs and even a new coil. Using a Petronix module and it is working fine - understand it either works or it does not as no adjustment there. I just can't figure out why it will run great to start and then later on start missing. I considered a carb issue but runs great at first so unless their is a gremlin out there messing with my SU's doesn't make sense to be fuel/carbs. So, guess it would be electrical. That's the reason I put in new plugs and changed the coil. Using a 3 ohm to go with the Petronix. Anyway, any thoughts or advice would sure me welcomed.
Thanks,
Mike
 
This sounds like a ignition issue and that's where I would focus my attention. I would check the basic things and not start fiddling with the carbs. Any loose wires or connections? If you have a spare Pertronix try switching it out. Dirty fuel filter maybe.
 
You don't say what sort of miss. Does it occur: under power, when accelerating, at cruise, at idle, at high revs? Is it rhythmic or random?
 
Hey guys,
It's not as noticeable at lower speeds like 35 to 45 but at 55+ get a definite pretty regular miss. I have side exhaust so really can notice it better than standard and you can feel it from the engine. It's pretty rhythmic versus random. Just really perplexes me that it only does it after I have been driving for a while, like to the 30 + minutes I mentioned above. Did check all wires as well as battery terminals and everything is tight and non corroded.
Thanks,
Mike
 
Check the compression when it is hot... Could be a tight tappet maybe? Do you have an original cast iron head?
 
Hey 57_BN4,
It's Andy isn't it ? Anyway, you bring up an interesting point. I do have a noisy tappet and going to adjust the valves on Monday. I will let you know if that might solve the problem as know the Healey workshop manual does mention 'valve adjustment' as a possible reason for missing. And I do have the original head on the 100M engine.

Just took it back out for about 20 minute run and as usual runs like a champ. But not long enough to possibly bring on the missing issue.

Regards,
Mike
 
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