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BN2 missing on acceleration

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bighealeysource

bighealeysource

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Hey all,
My 56 100M has been running great and all of a sudden, has started to miss on hard acceleration plus run on where it usually does not. Runs fine at speed plus noticed getting some back firing on deceleration. The only thing I have done is adjust the choke cable as was too loose but when not pulled, would not be any different. I am assuming a carb issue but thought I would get some advice before I make things worse. Have new plugs and they are gapped properly and old ones looked good when changed out. Put in Bosch plugs as recommended by a couple of guys on the BCF.
Thanks,
Mike
 
I don't have a BN2 but if you suspect a carb problem you might check that one or both carb needle seats have dropped down thus flooding the engine. I know it's strange but if you take off the air cleaners and look down you should see both needle seats about the same height. Easy fix, just loosen push back up and re-tighten.

You also might check the ignition as well. You haven't said but have you added pertronix or worked around the distributor lately?
 
Sounds like you're running lean. Could be some crud in one of the jets. Did the problem start when you changed the plugs and/or when you tightened the choke cable?
 
Hey Bob,
Seem to recall I changed the plugs as got a very intermittent miss and then adjusted the choke cable. Checked to make sure on the choke cable that it is not engaging the jet levers when completely pushed in. My Healey's usually always seem to run rich but certainly possible they are running lean. Looks like the best solution is to remove the cold air box and just get in there and start over or go back to settings as advised by the workshop manual. Anyone have some easy to follow carb adjustment recipe ??? Oh, I am running a Petronix ignitor but have had no problems with that for over two years. Only other thing ignition wise was I did replace the advance capillary tube as old one was kinked so maybe that could not be functioning properly ? Is there a way to check to make sure the advance is working okay ?
Thanks,
Mike
 
If you have them, Colortunes ('glass' sparkplugs) can give a quick reading of mixture setting. Otherwise, try the piston lifting method which, if done correctly, is surprisingly accurate (as I've verified with the Colortunes).

It has some lean-running symptoms, but could well be electrical (timing, etc.). If the old plugs were running fine, and you still have them, put them back in and see what happens. I've never used anything but the (recommended) Champions, and never a problem with plugs. It's possible you disturbed something in the ignition system when you changed the plugs.
 
If you have been reading other posts regarding similar problems lately you should suspect faulty tune up parts or a bad Pertronix unit....for some time we have been getting low quality ignition parts that fail after a short time... Check the easy things first before you start fiddling with the carbs. If you have a known good coil, Replace your current coil with it and check your timing with a advanced timing light. From what you say, you seem to have been running rich....that could be a sign of a weak spark to begin with and now it is getting worse with the misfiring. I strongly suspect it's a ignition problem and not your carbs. Personally, I would focus your attention on the ignition components starting with the coil and any loose wires. When you find and fix the problem, make sure your timing is set right and start reading your plugs and begin to fine tune your carbs with the mixture screws to achieve a nice medium grey color on your plugs.
 
Although the long held wisdom is to check the ignition first, with all the troubles of fuel degradation with ethanol fuels and some destruction of rubber fuel components, I might be inclined to check to make sure your fuel is fresh and if there aren't any bits of rubber floating about, particularly after coming off a winter's layup.
 
Thanks everyone for all the recommendations, figured I would get some good feedback. I too have always heard that many times it is the ignition and not the carbs so will check that first. Probably should have just left everything alone when I changed out the plugs. Need to remember that often by passed statement - "If it aint broke don't fix it ". Think that often applies to Healey's . As to laying up for winter storage - Rick, we can drive 'em year round down here in the Lowcountry of South Carolina as opposed to y'all up in the Northeast !!!
Thanks,
Mike
 
A better scheme than "If it ain't broke, don't fix it" is to only make one change/adjustment at a time. And don't throw away the replaced part! It may be better than the new one.
 
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