COMET CENTRAL

My 200-6 started running rough; wouldn't idle at all. Checking it out, all six plugs (pretty new; 5 months, less than 2,000 miles) were completely fouled black. Put another new set on (NGK WR5) and engine started running great again.

Another clue is I've been getting really crappy MPG, <10 MPG.

Not sure that this is related, but I've been having auto-choke trouble where the bimetallic coil never moves the choke full-stroke. If I set it open when hot, it doesn't close when cold; if I set it closed when cold, it doesn't open all the way when hot. I've been leaving it open because of that.

But the MPG and fouled plugs are my real problem.

How could the air/fuel mixture be so rich? I fine-tuned the idle mixture screw back when the plugs were new. I have timing about 12º BTDC. Just took the carburetor apart to see what main jet is in it: it's a 66. From what I understand, the stock jet for sea level is the next size bigger (67). I ran unleaded reg (87) for a while, but for the last couple months I've using 90 Octane Ethanol-free.

I've read that the harmonic balancer can get off on these and throw off your timing marks. Anyone know of this? Would WAY high BTDC cause my issue?

Does it take screw in Holley style jets?

A plug somewhere in the air bleed system is my guess. Or the float is too high.

Air cleaner clean??

Do you still have points ignition? If so are you changing the gap to .035? The WR 5 are preset at .040 which would be ok for electronic ignition but if you don't have electronic then gap would be better at .035 . Would give better spark.

Points, cap, rotor, wires all good? Weak spark would cause black plugs.

Just some things I would check.

Lou

High or flooded float?

Rootsy: Screw-in. Messing with main jets is new ground for me, but since the one in it is a size leaner than stock, I can't see it as the source for such a wildly low A/F ratio. BTW, thinking about your deeper-than-stock tank you showed me, I checked that fuel sending unit that had too much travel for my tank. It has a ~5-3/4" range. If your tank is about that deep maybe you can use it. Free, drop by and get it if so.

Lou: I had to reduce a few of them, but others the .035 would hardly go through the gap out of the box. I put on new points when I installed the first new set of WR5's. Wires, cap, and rotor were like-new when I got the car (<2000 miles ago). I'm going to check coil, yet.

Sassy: Carburetor is newly remanufactured and seems very well done, but I'll check float level before I put her back together.