Hitch

I've been reading up quite a bit on Barry Grant carbs to try and figure out exactly what I need to do to finally get rid of what I think is a rich condition. The A/F meter that I have wired into the exhaust shows rich, my eyes burn and I can smell it pretty good. I would think that this would lead us all to believe that I have a rich condition.. Then I run across this little gem of a post from two people here on the forum that I have a lot of respect for and I'm confused..... Can anyone explain this to me...



"CO is odorless, so you can't smell a rich condition. HC (resulting from misfire) is what smells "rich." A/F-related misfire on a street driven vehicle is most often from a lean condition - not the rich end of the spectrum. He has worked with rich-end racecars a lot, so he's seen that situation, whereas I work mostly with mild street driven vehicles, so I see the lean end problems as the common occurrance. Either one can occur, but if you're a couple of jet sizes down form the stock setup, I can assure you that you are not rich - you're getting a lean misfire that makes it appear to be rich (because you're throwing unburned fuel right into the exhaust froim the lean condition, as bizzarre as that may sound). The other thing that a very lean jetted carb will do is cause you to crank the idle speed screw up off the idle circuit. This can cause it to then go rich due to fuel now being sucked out the transition circuit and due to the power valve potentially cracking open. So a lean condition can screw you up all over."

Plasticman

Having done a tad bit of testing, I always try alternate jets (or rods) depending on the carb to see what the net effect is. Pretty easy to tell when you are getting too lean or too rich (and know which way you are going).

I can understand the poster's logic, but it does not agree with what I have seen over the years by actually adjusting the carb both ways and seeing what happens. The key here is to go in both directions, not just stop when something says "too far" (such as lean surge or overly rich looking plugs). Same as how we adjust idle mixture to find the best mix.

The above poster's comments should really get the comments coming!

Plasticman

bweaver999

Why not take a peak at your plugs? I would expect them to be dark if rich, light if lean.

Hitch

The plugs look great... Nice and tan.. I went down 4 jet sizes in the primary and the secondary from what was in the 750 and it seems that I'm more rich now than when I started...

Frankie the Fink

IMO your last post makes no sense - plug initiate the combustion; if they are showing non-rich symptoms how do you define richness ? After fighting with my carbs for 4 months I solved my richness condition (wrong parts inside the carb)....but I still have the richness smell (much less though) and small black sooty spots under my rear exhausts if I idle my dual carbs too long. They just naturally 'load up'.

That is the nature of the beast with these cars. After attending the NCRS regional in Florida a week ago I must have been near 6 or 7 C1s and C2s that started up or were idling; they nearly all had a slightly 'rich' smell. So IIRC did most '60s muscle cars of any note. If you are just judging by your nose I think you are way off on this. If your A/F meter is indicating rich but your plugs are not - you need to figure that out first. One of these is lying to you.

Shurshot

IMO plug reading at anything other than at WOT on a warmed up motor and a brand new plug is less than ideal even though we all do it. Freeway rest stops by the re-entry point and changing two easy to get to plugs is my idea of how to do a good WOT test....... just need to keep an eye out for the HP LOL

My own rule of thumb of plugs is the outside color is controlled by the carb and the inside by heat range and timing. Auto Zone recently tripped me up for a bit when they said there had been a change in NGK V series numbering system when there had not been one

With you I assume that there have been no other changes such as plug range, timing or available air but I got frustrated with BG and gave up...... do you have that carb tuning DVD by them? That might be of some use.

Doug

tangel2

I say trust the oxygen sensor. Just make sure that you have the car warmed up and the sensor is close enough to the engine to get hot enough to provide an accurate reading. You'll probably have to drive the car to heat the sensor up enough for good readings. I remember David Vizard wrote something along the lines of "plug reading is somewhat of a black art, and can get you in the ballpark on full throttle runs on a dragstrip. The oxygen sensor is much more accurate and is the best way for tuning across the throttle range on a street car.

Hitch

I would like to believe that the A/F meter is correct however my nose is telling me something different. I know that I will get some stink by the crap fuel that we have now a days but I think that my situation is excessive.