Car Running Terribly After New Plug + 8mm Wires??

[Moto-Mucci]

I just installed a new set of 8mm Magnecor wires and Denso Copper plugs. Plugs were gaped to .027"

It ran well before, but since the install, it now runs very rich. It's very blippy / stutters a lot while coasting at low RPMs. Idle and WOT are smooth, yet rich.

The tech at Magnecor just left for vacation, so I was hoping to get some answers here before I drive 1000 miles back home on Friday.

The previous set up was stock 7mm wires with Bosch OEM plugs.

So far I've tried:
Checking for vac leaks via carb cleaner
Disconnecting/reconnecting the battery

Any ideas? I'm planning on returning to stock wires to see what happens. Then Bosch Copper plugs if nothing changes. Are the copper plugs not capable of handling the 8mm wires?

[nando]

why gapped so small? the factory gap is .032". A wider gap is better, if you can get away with it (spark blowout is a concern).

I doubt it's the wires - larger wires have less resistance, your plugs aren't going to care about that.

never tried a Denso plug in the M20, though. what style are they? what heat range? resistor plugs?

[Moto-Mucci]

It's an M30B35 actually.

I got the plug gap off an e28 forum. I didn't have the Bentley with me at the time. The Denso's also state a .027" gap.

After reading through a few more threads, it looks like many people gap to around .032 - .035." I assume the smaller gap produces less spark and therefore makes the car run rich?

About the Denso plugs:
B; O.E. Recommended Resistor Plug With Patented U-Groove Design
Denso Spark Plug Denso's standard plugs have always offered a patented U-groove ground electrode producing for a larger, hotter spark. Copper core for better thermal conductivity. Machine rolled threads to reduce cross-threading and seizing . The plug insulator is constructed of purified alumina powder for extreme stress with 5 ribs to prevent flashover. Technical Specifications - 14mm Thread, 19mm (3/4") Reach, 13/16" (20.6mm) Hex Size, Gasket Seat, Resistor, Removable Terminal, Fully Projected Tip, U-Groove Ground Electrode, .027" (0.7mm) Gap

I ordered some Bosch OE plugs. I'll try those tonight at a .032" gap to see if that helps.

[Hey_You]

I had a similar issue with my little m10, when I gapped the plug per the "suggested" gap. They suggested .027" as well, but everyone is running about .035" I pulled out my plugs (which showed a rich condition) and regapped. So far no issues and low rpm pull is better with very little stuttering.

[Moto-Mucci]

That's the kind of news I like hearing. A zero cost, minimal time solution :)

[KenC]

Yeah, gap them to 35

[Moto-Mucci]

I swapped in some NGK V-Power copper core plugs (don't have the PN on me) last night, gaped to .034" and she runs smooth as butter now.

What's interesting is the Bentley specs a .027" gap, as did the Denso plugs - yet the car ran terribly. Which brings me to the conclusion.... Denso is shit.

[Hey_You]

No, that's not the problem, hell, even my Bosch's did the same. Just means the manufacturers don't know as much as the enthusiasts (Well, not true, but sounds right :P)