Northern 7

iTrader: (3)

I'm stumped on this one and could use some input:

My car is an '83 12A with 50,000 miles on it - has always run very smooth with a solid idle - recently, after I blew up my MSD, I can't seem to get the thing to idle like it used to - I now have a slight miss at idle regardless it the engine is hot or cold or how long it has been running. I've the replaced the MSD (6A), new 8.8mm Accel race wires, 3 Accel coils (1 yr old), 3rd gen plat. plugs (2 weeks old - checked them today and they look very good - no black deposits, light tan color), cap is a yr old and contacts look good. I can't find any vac leaks but then again, If there is a leak, it must be small (can't hear it anyway). The carb has never given me any trouble and I run a can of carb cleaner through it every spring. K&N was recently cleaned and oiled. Only thing I have noticed is a get a little twitch on my tach every once in a while, almost like a blip and it's not consistant - comes and goes.

I know I'm being fussy about a little stumble in the idle, but it was never there before and came on all of a sudden. Can anyone out there comment on anything I've missed? Thanks all!!

MIKE-P-28

iTrader: (1)

MSD went bad, what are you running now, stock? Im not understanding the question? If stock then you probally got a bad ignitor or wiring?

MIKE-P-28

iTrader: (1)

Never mind, I re read it.. Sorry


I have no clue never had a MSD Sorry

Northern 7

iTrader: (3)

I don't think the MSD has anything to do with it - If anything, it helps smooth out the idle. I was just including as much info in the post as possible in order to head off some of the questions about my current set up and what I've done to try and correct the problem. I'm guessing, but I think it may be a vac leak but I don't know how to go about checking for leaks (other than listening). Anyone else??

diabolical1

iTrader: (3)

i'd start with a new cap and rotor first, then if it still doesn't sort out the idling problem, look toward vacuum and re-adjusting the mixtures on the carb. what is the heat range on the platinum plugs you're using? they might be a bit much since the car is not using any forced induction (at least you didn't mention that it did) ... but they might actually not be the best thing for a carbureted car. who suggested using them?
anyhow ... that's my 2 cents!

MarkPerez

The MSD is HOT,,good stuff,,if you replaced a part on
the car,,look at the part you just installed,,if the car
runs different then it did..and you say the plugs look
good,,so theres spark,,maybe not as hot as MSD,,
maybe something about the accell stuff isn't right...
a rough idle all of a sudden is 9 times out of 10 a vacum
leak,or coaster valve failure...i totaly understand,,the
rotory engine is so smooth, that one notices any kind
of'miss' or anything out of the normal

Northern 7

iTrader: (3)

I'm using the 3rd gen plugs as per the 3rd gen stock set up - diff heat ranges for leading and trailing (I can't remember if the hotter plug is in the lead or trail but a dealer could tell you - if I remember correctly they're 8's and 9's). This has been recommended by a few who have tried them (try a search on this site and Mazspeeds) - they are a much tougher plug and, IMO, they tend to foul much less than the 1st gen stock plug. As mentioned, the plugs look very good - I've never had plugs look and wear as good as these in my 12A. Bottom line, I don't think it's the plugs. The cap and rotor, as I mentioned earlier, are in good shape - I don't see any wear on the contacts and they are clean. I been tinkering with idle / mixture for a while now and pretty well know when I have a problem in those areas - I don't think so in this case. To be honest, vac is where I am in the dark zone - I don't know much about trouble shooting leaks. Maybe I'm off base but I think that may be where my problem is - what I could really use is some advise on how to check for leaks.

I'm thinking you may be right! But how to check?? Also, the coaster valve - how to test?? The Accel stuff is OK - I've been using their stuff for 3 yrs with the MSD - no problems (I fried a couple of these coils once but it was due to a bone head install on my part, I was using 2 power sources, the MSD and the stock sourse - not good)- a bad coil was my first thought but the problems usually associated with a poor coil are usually more dramatic than a slight miss (but I'll test them again any way - need a better ohm meter, mine's junk).

Anyway - HOW DO YOU TEST FOR VAC LEAKS - thanks all for the responses