Paxton

it sounds like you have an Autolite carb, so please disregard any statement I made about the kick-down linkage. I was thinking you had a Holley with the generic kick-down linkage attached to the carb,

If your kick-down cable or rod is properly adjusted then it should operate Independently of the presence of the supercharger.

As far as the jetting goes, I don't know the autolite system for jet numbering, but if your a/f ratio is in the 11's at cruise, then you need to lean out that circuit.

what is the af/ ratio under a load at part throttle, like accelerating up a long incline ? What is it at full throttle ?

Z.

Edited by - zrayrichter on 07/20/2010 22:28:07

<BLOCKQUOTE id=quote><font size=1 face="Verdana" id=quote>quote:<hr height=1 noshade id=quote> ".............. The carb I have is a Holley 650 DP, and I would believe that I have size 45 jets.

The AFR is 11 at cruising and around 12 when accelrating slowly and appx the same when I have WOT.

Should I try going down 2 sizes?

What size do you have? ......" <hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana" size=2 id=quote>

the jets I'm using are 67 in the primary float bowl & 78 in the secondary float bowl. When I have bought carbs from C. Conley in the past he had 69's & 84's installed. I'm a little thrown by the 45 number you have reported. Can you email or call Conley and ask him what size jets he put in your carb.

Are you using a K&N air filter ? If so, I would suggest first removing the air cleaner very briefly to see if the a/f reading changes considerably before doing any jetting changes. It's possible that the filter is just over oiled giving a too rich a/f reading.

Z.

Edited by - zrayrichter on 07/22/2010 08:44:08

the reason C. Conley sends out carbs with jetting on the rich side is entirely due to caution. Lean running carbs are risky enough, but with the added power of the Paxton a lean condition can ruin an engine in short order. For the same reason I hestitate to reccomend to others what I have done myself.

As I mentioned above I'm using 67's on the primary sidel & 78's on the secondaries. That may be right for your engine, or not right. I'd go down two sizes at a time until you find the combination that works best for you.

Another thing to consider is lowering the floats 3-5 flats below the stock setting. I had to both lower the floats & reduce the jets before I was satisfied.

Z.

But it sure runs great with a leaned out system, just before the engine goes "poof".

Jim

<BLOCKQUOTE id=quote><font size=1 face="Verdana" id=quote>quote:<hr height=1 noshade id=quote>

But it sure runs great with a leaned out system, just before the engine goes "poof".

Jim

<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana" size=2 id=quote>

I was never brave enough to do much "leaning out" until I got a wideband a/f meter. Very addictive.

Z.

glad to hear you have things sorted out to your satisfaction. I am curious to find out if you have the same phenomenon I have, which is that the a/f ratio changes considerably depending on the ambient air temperature & humidity. The a/f ratio difference between 75 degrees & 105 is amazing. I've just settled on a correct setting at 90 - 95 degrees. Texas will maintain that temperature well into October. I will have to re-jet for the winter, or gag on the rich running engine fumes.

With the Paxton disconnected, the temperature variation has a MUCH smaller impact on the a/f ratio

Z. Ray

Edited by - zrayrichter on 08/11/2010 18:05:40

first of all, let me say I don't entirely make sense of this, but here goes. At plus 95 degrees the a/f ratio reading at idle and low speed cruise is 14.0 - 15.0. At 80 degrees or less the a/f ratio reading at idle and low speed cruise is 13.0 - 14.0. a full point difference.

Seems to me when the air temperature is higher, the engine should be running richer, not leaner. But not in my case. Any theories ?

My theory is that the change in humidity, not temperature is causing the fluctuation in the a/f ratio.

The higher the humidity the less space there is for additional molecules of air and therefore oxygen. As the humidity increases there is less oxygen and therefore the engine runs richer.

In my part of Texas, and elsewhere for all I know, when the temperature is low in the mornings, the humidity is high. When the temperature is high in the afternoon, the humidity has dropped. And (here) it's the very low humidity of 5% to 15% that is allowing the increased oxygen in the air.

Z. Ray

Edited by - zrayrichter on 08/12/2010 17:53:56

p.s. there are several web sources that basically have the same information regarding humidity & a/f ratios. A google search of "humidity & carburetion yields a lot of info, most of it consistant.

Z.