running rich with carbs?

[37yrold911]

My motor seems to be running a little rich - there is a lot of soot in the exhast tips -- not a buildup really, but a definite layer there.

I have PMO carbs and I set the pressure regulator down to just below 3 psi, and the fuel levels in the float bowls is at or below the dot for each one.

Any ideas?

Or is the soot normal?

[Eric911S]

Hello; I think you may have the wrong jets in those carbs. You may also have someone check the mixture with an O2 gauge to see if it is too rich or your burning some oil. Hope this helps. Thanks Eric

[JohnT]

Remember that today's unleaded gasoline leaves exhausts (and spark plugs) black. You need to be running leaded (gasp!) gasoline to see the traditional gray tailpipe of a proper running engine.

johnt

[GreenT]

Here's some ballpark figures from PMO. But they are just that, ballpark. You need 1) an Experienced Mechanic or 2) time on a dyno or 3) to buy an LM-1 unit to begin to sort it out, there are just too many variables for most people to sort it all out without some hard data

But - if you think you're running too fat, you spend most of the time on the idle circuit. If you find you are currently running .060 idle jets, it's cheap and brain dead easy to swap those for say, .55's and see what kind of improvement you get. Other things aren't quite so easy to sort out.

If you really want to figure it all out yourself, the LM-1 units are a great way to go. I drove around for a week or so with one wired up to a laptop in the passenger seat showing realtime values under all driving conditions to get mine sorted out once and for all. No way a DIY'er could do that a few years ago...

Have edited this, the data from PMO's spreadsheet doesn't want to format very well here, hope it's readable -

Recommended Settings for Weber Carbs


Engine Size & Cam Main Venturi Main Air Idle Emulsion Tubes
2.0E 30 125 180 55 F26
2.0S 32 30 180 55 F3
2.2E 30 125 180 55 F26
2.2T 30 125 180 55 F26
2.2S 32 130 180 55 F3
2.4T 30 130 180 60 F26
2.4E 32 135 180 55 F26
2.4S 32 135 180 60 F3
2.4 CIS T
30 130 180 55 "F26,F3"
2.7 CIS 32 135 180 55 F26
2.7 CIS w/Tall AV's
34 140 180 60 F3
"2.7 E, S"
34 145 180 60 F3
"2.7 E, S w/ Tall AV's"
36 155 175 60 F3

Note: Tall AV's = Auxilliary Venturi's
CIS : Indicates CIS Cams



You should go through your Carbs and make a note of all the sizes of the different components.
This will help in the trouble shooting if you have any problems. Often the sizes of jets are only
"finalized by trial & error. Many variables can affect your Webers performance such as fuel available,"
"elevation of driving area, engine options and the environment. All must be taken into account when"
trying to determine the proper jets.

The settings were provided by PMO.

[Steve@Rennsport]

John T speaks volumes of wisdom here.

One cannot judge fuel mixtures by looking at exhaust pipes due to the chemical makeup of unleaded gasolines. They will always appear to be too rich.

Non-EPA approved unleaded and leaded fuels still provide a "Kentucky Windage" glance for roughly determining A/F ratios, but reading spark plug insulators is far more accurate if you know how to do that. Its an art form and an aquired skill.

One can read plugs, install & use something like the Innovate LM-1, or go to a chassis dyno with a wide-band setup that will give you WOT HP, torque, and air-fuel ratios.

My experience is that if the fuel pressures are perfect (3.5 psi), the float levels are spot-on, and the jetting/adjustments are close, you'll be in good shape.

[Bobby Smith]

37yrold911

You didn't mention if the car runs well. I had a 70S with carbs that had blackened tailpipes. The fumes of "richness" would nearly choke you if you stood behind the car while running, but it ran like a bat outta hxll. It was rich at idle and perfect at 4500rpm when the cams came on. I could have leaned it out to "cure" the richness, but it would have lost performance.
Bobby

[Eric911S]

Hello: Those jet settings above are for Weber carbs. If you have PMO carbs the jetting is totally different than the Webers. The LM-1 unit is great and tells you real time mixtures. It works so well when you use different types of fuels it shows up. You may want to give Richard a call at PMO to give you some suggestions. Hope this helps. Thanks Eric