Inconsistent Idle - Fouled Plugs?
 

Car: 1980 SA RX-7

Engine: Large-streetported 4-port 13B (12A irons and GSL-SE housings) with a Holley 600 (not RB), OMP lever is fully open 24/7 due to linkage to carb not being set up. Has RA Super Seals, is dowel-pinned on the hot side and the rotors are toleranced for high-RPM use.

Carb: Run-of-the-mill Holly 600 4-bbl with mechanical secondaries. Sight plug removed and OMP line run through it. Accelerator pump delayed until about 1/4 throttle.

Ignition: Consists of twin MSD boxes (unknown model), MSD Blaster 2 coil packs, Magnacor EFI-shielded racing wires and 4 NGK BR8EQ-14's. Timing is of unknown advancement at idle, and vacuum advancement diaphragms are not hooked up. Distributor cap and rotor are in excellent condition.

Premix: 2 oz. of Havoline TCW-3 2-stroke oil per tank of gas. (Overkill with OMP?)


The Problem: :scratch:

Had the carb rebuilt and tuned with 4 new NGK BR8EQ-14's. The car drove fine out of the shop for about a month. Recently I've been having inconsistent idling problems where the car will sit happily with a brap...brap...brap...brap... sound that slowly gets rougher and drops to 1000 RPM (when it idles well it stays a tad above that around 1100). The car doesn't cut out, just idles nasty. Sometimes pops back into it's brap-ing rhythm and increases to normal idle RPM.

When not in idle the car drives normally. Good power, nice steady exhaust tone when cruising, and doesn't hesitate on acceleration.

Took the spark plugs out to check the tune a week ago and noticed the trailing plugs are both white, and the leading plugs are both black and dry at the electrode, however, they are wet on the threads and gasket. Checked my oil level, and it's decreasing at the normal rate with no evidence of dripping leaks around the plug holes. Coolant is steady as well. I don't have excessive smoking on start-up or when punching the throttle.

After checking the plugs, I swapped the leading and trailing plugs on both rotors just for shits-and-giggles to see what happened. Car idled well again, but started to have the same problem described above today.


My guess:

*Leading plugs are fouling out from too much oil. :ponder:

Note - I also read on the forum that the leading and trailing plugs should have different heat ranges?



Thanks for the help guys and gals,
HunkyDory :D

Do not try to BUMP your thread...("any ideas"..)See RULE up top.You posted less than 24 hours ago.

Have you tried to change plugs to something other than the BR type Plugs.Like something that is actually meant for an engine such as this.
BUR9EQ's?
Your Engine is not really anything "special" to warrant running plugs of that type.(no offense intended on your build..It sounds decent.)
The plugs you are using have a tendency to foul,unless you are running the engine with some boost application Colder plugs will not work correctly.
I'd start by just trying a set of regular BUR7 and BUR9EQ plugs and then post up what you find.

Note: Remember this is the NEW section and is a mixed bag of cars and questions,is IF you really want specific answers you can make your way to the 1st gen Specific section where your Generation of car is the main topic.
This section is a starting point,so it is often overlooked and off the beaten path of being viewed by other Die hard enthusiasts.

Looks like I'll be re-reading the section rules then.

I'll pick up some BUR7's and 9's today, swap 'em tomorrow and see how it goes.

Thanks.

Got new plugs in this morning. The idles slightly better, but still slips into a rough idle now and again so I'll try tinkering with the carb tune and see if things improve.