Low speed missfire.

Another problem surfaced today during my wind up of a 1000 mile trip. At low speed, the engine had a regular miss untill about 2500-3000rpm, then it would clear up. the proeblem was intermittant while the engine was hot.

The car has new plugs and has the norwood conversion, (8 cyl chevy cap, chrysler magnetic pick up and modified ford rotor, msd 6al and Blaster coil).

Just before the trip, i replaced the plugs with NGK 6 range plugs and noticed that the plug extenders, (6 out of 8), were cracked, but saw no signs of arcing, so, I am wondering if the extenders are arcing or ????

I am also thinking about pulling the carbs to check the foat levels and the cleanliness of the idle passages. I just recently reverted to the stock 55 idles from 60's and noticed a marked reduction in "stinky engine".

Any thoughts, even wild speculations, welcomeed
Mired in ignorance, again,
chris

 

The problem started many months after the conversion. I just re installed the stock idle and main jets and everything looked clean. The fuel filter was also recently replaced. I checked it to see if i had taken on a load of contaminated gas and it looks ok.
I'll try new extenders and rubber boots, (they look really ratty, probably the originals).

I will post my findings. Any other ideas also welcome.

thanks,
chris

 

Hi John And Erich,

Just after i replaced the thermal reactor with the flowmaster, i went up on the jets to help with the backfiring, popping and flames. Subsequently, i did a little better job balancing the carbs and the idle mixtures. I went back to stock jetting after reading all of SNJ's posts and running an LM-1 AF Ratio meter.

So while doing the change, i checked for plugged jets and everything looked ok. Driveability is a little better but the mileage is still 16.5 on the road.

The plugs were changed just before the trip, but i had a few little missing eppisodes, most noticeably at low rpm and possibly at high rpm as well. some times it is hard to tell at high rpm.

My next step is to pull the carbs, clean all of the passages, install new needles and seats, carefully set the float heights, then use two 4 tube manometers to really set the carbs to pull evenly, just off idle, then use a friends infrared to set the idle mixtures, hopefully, this wil allow me to get it down to "lean and mean" with crisp throttle response and the best possible, (or probable) fuel economy.

I have a theory that when running many carbs, that getting the mixture "right" for all of them, equally balanced, especially at low throttle openings, (where we usually are at highway cruise) is difficult and that the "easy fix" for this is to richen up all of the carbs, at idle, midrange or top end, to get the darn thing to run smooth, and so we are often left with a car that runs rich, stinks, gets poor fuel economy and has stumbles or poor throttle response.

I hope to get this balanced out with the help of the two 4 tube manometers and the lm-1 a/f ratio meter.

I just spent $500+ on new plug extenders, rubber boots, (all of them really ratty) and a pair of cam cover gaskets, choke, gasp - but ah well, it is for the green car .

best,
chris