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Reply to "Weird Carb Issue and Solution: Jet Doctors(Long and Technical)"

Now I'm really scatching my head! So I get out my trusty Innovate MTX-L(wideband A/F gauge), but it goes into error mode and has random LEDs on or off. Basically, junk. DO NOT BUY ONE! A quick search shows lots of failures. I tried reflowing all the solder joints but no joy. Ordered a new APSX gauge with a harness and new O2 sensor on Wednesday. It arrived on Friday with cheap shipping about $5. Way to go US Postal!

https://www.wide-band.com/

My new car has a new exhaust, so no O2 bung. Get out the drill and welder and get to it. After a conversation with Stan I ended up putting the bung after the final center merge at the tailpipe. I was considering putting two so I could alternatively monitor the 2 cylinders on the same head, but he convinced me otherwise. Thanks, Stan!

So now I go for a drive without making any changes at all(60 idles and F7 emulsion). It is PIG rich all over the bottom(under 9 to 10.5), settling down to 12.5(perfect) under full load above about 3500. But especially bad in the transition from 2 to 3K. 

So I start really thinking, because even with the richness, it is still running better with less hesitation than the other day. The other day it was 85F and low humidity and sunny. Today it is cool and cloudy so the air is denser, which translated into leaner(denser air=more air/less fuel). So now I'm wondering exactly how incredibly rich it was the other day.

Then I get an idea. The CB Jet Doctors put the idle air entrance right near the lip of my velocity stacks, which are 1 1/4" high short ones. So I remove my Turbo Hats and quiet 2" cone air filters and swap the velocity stacks for the original 2 1/4" tall stacks. throw the original air filters on and it is driveable again! Pig rich, but driveable. My cam has a very high overlap and there is major intake reversion/pulsation going on above the carbs. You can actually see the fog of fuel hovering above the carbs at higher rpm. Making the velocity stack a good inch above the Jet Doctors isolates the tube from the reversion: EUREKA!

Put the 57.5 idles and F11 Emulsions and now it runs like it used to in the old car: QUICK and SMOOTH! I still think I can lean it a little more with smaller 55 idles and possibly larger air correctors(leans top end of transtion and upper end). Tweaked the pump adjustment a little and darn, she runs SWEET! The A/F gauge reads 13.8 to 14.7 at idle fully warmed up. 12.5 under full load but dipping into the 11s and high 10s in the low range, which is why I think I can use smaller idle jets.

So does this prove that a wideband A/F gauge is a very good(indispensable?) tool expense?

To be continued

Last edited by DannyP
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