Missfire after drag racing, common?

Twilightoptics · 08-01-2009, 11:45 AM

So I finally took my stock 7 to the track (removed emissions and cat) and upon completing 9 passes on the way home and at idle I notice a light miss every so often.

Idle and cruise was rock solid before. Doesn't seem to hickup under acceleration.

Is this common? I've got only 4000-5000 miles on a fresh tune up with the middle NGK plugs.

I thought she was stronger too! Only mustered a 17.25 @ 79.20MPH in 80º weather.

Thanks for any input.

Rogue_Wulff · 08-01-2009, 12:25 PM

Probably just got some deposits on the the plugs. Not really uncommon, as the plug heat range is designed to work better at cruise, or under hard acceleration. The "middle" range is a compromise between the 2 extremes. Works for both, but better suited for a more even mixture of the styles.

Twilightoptics · 08-02-2009, 05:55 PM

Pulled all 4 plugs. They all looked the same. Bright orangey color on the ground straps, and the electrode's nice and clean.

Maybe the few runs w/o air filter plugged somethin in the carb then.

I think I'll be getting a set of the colder plugs for racing. Definitely too hot a heat range for consistant 7K RPM.

Twilightoptics · 08-09-2009, 04:01 PM

Well I found the mixture screw was backed out a bit. Doesn't miss at idle anymore but still does a little bit at light light cruise.

rx4ur7 · 08-11-2009, 06:19 PM

Try running some SI-1 through it. (Redline fuel injection cleaner, which is the only fuel cleaner that Mazda recommended other than their own. It will not detonate in a rotary like many other products)
Make sure all the wires, connections and cap and rotor (mazda only, non-mitsubishi will cause problems, cheap rotors have a tendency to wobble) are good. You do still have the
metal spark container in the distributor. If it is missing you will have misfire issues.
Good color on plugs for stock. Check your vacuum advance units.

Factory setting for the screws - 1.5 top 2.5 bottom. If the throttle plate hasn't been played with and everything (includes all emission equipment) is working correctly it will start, idle, drive and ~0 the emissions. If emissions are high, anything above 75/100 hc or .5 co 1/4 turn out on the mix will make it drop to near zero.

08-01-2009, 11:45 AM	#1
Twilightoptics Itchin' to Turbo Join Date: Apr 2009 Location: Vancouver, WA iTrader: (0) Posts: 33 Rep Power: 0	Missfire after drag racing, common? So I finally took my stock 7 to the track (removed emissions and cat) and upon completing 9 passes on the way home and at idle I notice a light miss every so often. Idle and cruise was rock solid before. Doesn't seem to hickup under acceleration. Is this common? I've got only 4000-5000 miles on a fresh tune up with the middle NGK plugs. I thought she was stronger too! Only mustered a 17.25 @ 79.20MPH in 80º weather. Thanks for any input.

08-01-2009, 12:25 PM	#2
Rogue_Wulff Non Member Join Date: Jun 2008 iTrader: (0) Posts: 310 Rep Power: 17	Probably just got some deposits on the the plugs. Not really uncommon, as the plug heat range is designed to work better at cruise, or under hard acceleration. The "middle" range is a compromise between the 2 extremes. Works for both, but better suited for a more even mixture of the styles.

08-02-2009, 05:55 PM	#3
Twilightoptics Itchin' to Turbo Join Date: Apr 2009 Location: Vancouver, WA iTrader: (0) Posts: 33 Rep Power: 0	Pulled all 4 plugs. They all looked the same. Bright orangey color on the ground straps, and the electrode's nice and clean. Maybe the few runs w/o air filter plugged somethin in the carb then. I think I'll be getting a set of the colder plugs for racing. Definitely too hot a heat range for consistant 7K RPM.

08-09-2009, 04:01 PM	#4
Twilightoptics Itchin' to Turbo Join Date: Apr 2009 Location: Vancouver, WA iTrader: (0) Posts: 33 Rep Power: 0	Well I found the mixture screw was backed out a bit. Doesn't miss at idle anymore but still does a little bit at light light cruise.

08-11-2009, 06:19 PM	#5
rx4ur7 Rotary since 1972 Join Date: Nov 2008 Location: Tucson iTrader: (0) Posts: 231 Rep Power: 17	Try running some SI-1 through it. (Redline fuel injection cleaner, which is the only fuel cleaner that Mazda recommended other than their own. It will not detonate in a rotary like many other products) Make sure all the wires, connections and cap and rotor (mazda only, non-mitsubishi will cause problems, cheap rotors have a tendency to wobble) are good. You do still have the metal spark container in the distributor. If it is missing you will have misfire issues. Good color on plugs for stock. Check your vacuum advance units. Factory setting for the screws - 1.5 top 2.5 bottom. If the throttle plate hasn't been played with and everything (includes all emission equipment) is working correctly it will start, idle, drive and ~0 the emissions. If emissions are high, anything above 75/100 hc or .5 co 1/4 turn out on the mix will make it drop to near zero.