Hi all, After buying the car i had to make a technical inspection and the controller told me that the car runs too lean (he checked the CO/CO2 rates with an exhaust gas analyser). Some months later i overhaul the carb (and other things !!!) and today i go to a friend garage to adjust the carb. No problem to have the well adjustement at idle mixture screws (around 3-4% of CO) but when the engine runs in middle or high rpm the gas analyser shows a too lean mixture (around 0.2 to 0.4 !!!) . Seems that not enough fuel. When i jump on gas pedal the CO rises, thanks to accelerating pump, and then falls to 0.3. The car drives fine, maybe a little hot. Timing is 10° BTDC at idle. Carb is an Autolite 2100 DOAF-T with 55 jets (i remember the number). The DOAF-T is a 429 Autolite carb but i don't see a lot of differences with the DOAF-AA which is the original carb as said in the manual (same jets). Do you think i must put some bigger jets (57 ? 59 ?). On the manual my Autolite 2100 is listed as a 12.20 air-fuel ratio. Seems a bit low , i always learn that the correct ratio is 14.7. On the gas analyser this afternoon i read 14.6 or 14.7.
Perfect stoichiometry for an auto air/fuel mixture is 15:1 using a special test gasoline. Anything higher will burn an engine up from heat and is considered lean. Anything lower is considered rich. However because of all the additives and oxygenators added to gasoline, 14.7 is considered baseline and only managed with computer controls and oxygen sensors. Since your car has neither, it will run rich at wide open throttle for added power during passing, climbing hills or towing loads. If it pings, it's too lean. At idle and cruising speeds you are not fully on the main jets yet. I think you have misinterpreted your readings.
When i made the tests i was around 2000-2500 rpm steady and the analyser shows a very lean mixture: 0.3 to 0.4% CO (and lambda around 1.1 or higher if i remember well). Yes, if i accelerate, the mixture went richer but when i return to a steady rpm around 2000 the mixture went again lean.
At cruising rpm, your mixture is lean for maximum fuel economy. If your car cruises down the road at 55 miles per hour and doesn't ping (spark knock) then it's fine. The range between mid and wide open throttle is controlled by the power valve and a calibrated spring. Changing your jets will not accomplish anything. You don't have a race car. Changing to a lighter spring under the power valve will allow earlier enrichment, but why would you want to? Unless you have to pass a specific emissions test, there is no point in fooling around with it. Learn to read your spark plugs and forget about the gas analyzer. They didn't even use them when your car was built.
Actually, they did, but usually you only found them in dealerships. So, for that setup, you want lambda to be, oh, say, .8-1.0. Your CO percentage doesn't mean much without the CO+CO2 reading, which indicates if you have leaks in the exhaust system; leaks throw the readings off. CO+CO2 should be 14-18%, but a good system will usually be around 16%. Now, before I'd go tackling the carburetor again, what are the other readings? Here in Washington State, when we were testing carbureted cars, cars from 1979 and before had a maximum 300 parts per million of hydrocarbons (ppm HC, the indication of partly burned or unburned gasoline) and you want that to be as low as possible, with CO <.5%, and The aforementioned CO+CO2. Go ahead and pull your plugs to look at the ceramic. A light tan dusting is about the best combustion for your wagon, indicating the combustion to be as complete as possible, and as close to 13-14 to 1 air-fuel ratio as your car can get. If the ceramic is ghostly white, then it is running lean and you need to find if it's vacuum leaking or the carb is partly plugged with gunk, impeding gas flow. Now, if you have a high CO with high HC, that can indicate a rich condition; a high HC with low CO indicates incomplete combustion; good HC with near zero CO indicates lean. So, I would recommend looking for vacuum leaks in any vacuum hoses, carb and intake gaskets and anything controlled by vacuum, including the brake booster. But I would like to see all the analyzer readings, if you can post them, or better yet, shoot video as the mechanic is running the test so I can see the readings.
I've removed one plug (i put new plugs Autolite AP45 platinum some weeks ago so they don't have more than 100 miles !) and it seems that color is ok even if the ceramic is very white. I note also that voltage at ignition coil (original coil and "pink" resistor wire) is ... 5.5 V !!! I just bought a Pertronix (+ coil) and will install it soon with a true 12V voltage that i've find at ignition switch connector , because ther's no 12V "after ignition on" in the engine bay. On the pw window relay ther's a 12V but it is also present when you're in "accessory", not good for Pertronix .
Even in only 100 miles of driving, those should be showing a light coating if your engine's combustion is correct. And yes to the Pertronix unit. That and the Blaster coil will greatly improve engine operation. BTW, with points, the voltage has to be that low or the points won't last 100 miles, let alone 12,000 miles. The Pertronix unit is designed to address that.
ok but what do you think of "my" sparkplug color ? I removed it immediatly after stoping the engine but maybe not the corect conditions which seems to be after sustained speed, i.e highway and not city as i did. About 5.5 V voltage seems that itsn't a bad issue, on the shop manual they said to measure between + Bat and + coil (dist. side grounded) and this voltage neds to be between 4.5 and 6.9, so 5.6 to 8V between + coil side and ground. Very curious theses voltages, coils are NOS 6V from the '50s ?
The older charging systems were just fine for what the ignition needed, but when the change to 12 volts was made, an inline dropping resistor was needed on the coil positive to prevent burning out the points and protect the coil from overheating. It can be temporarily jumped up; that's the reason the starter solenoid has an "I" terminal...so it hot-shots 12 volts directly to the ignition, giving the car a better chance of starting. But I guarantee you, if you jumper 12 volts to the ignition and drive away, the ignition will fail quickly. The plug does show an overall lean-run condition. Your mechanic does need to eliminate any sources of vacuum leaks before deciding to changing the jets. BTW, you said the carb came off another engine but both have the same jet size? You have to remember that for any given carb model, no matter what they go on, they can have different CFM ratings (cubic feet per minute) which can affect how an engine runs. In your case, you have an FE-series 390 and the donor engine was a 385-series 429. That's not only a difference of nearly 40 cubic inches between the engines but a big difference in the cams, intakes, heads, etc., that affect engine performance in their own ways.
I don't know when the carb was switched, i don't know also why they did that ... The 429 and 390 Autolite carbs have the same jets (# 55) , i don't see many differences except air fuel ratio 13..33 vs 12.20. Below are the specifications, i must have the "yellow" and i 've the "red" When you say "need to eliminate any sources of vacuum leaks before deciding to changing the jets" it coul be anywhere on the vacuum lines (heater, headlights, booster brake, etc..) ? Could i plumb temporaly the starting of the vacuum line. at manifold or carb spacer to make tests ?
Two things: 1) since the 429 carb runs richer, for a 429, that can mean a more bumpy camshaft to pull in more air, so the carb is jetted according to that, and 2) one of the standard practices for looking for vacuum leaks is to simply pinch off the vacuum hoses at each place they tap into the manifold or carb base to see if a change happens to idle speed. If not, then spraying carburetor cleaner around the carb base and throttle shaft, and around the EGR valve and intake manifold gaskets will make a change in engine speed if a vacuum leak sucks in the cleaner. So it may come to having to rejet, if there are no vacuum leaks, and a correct 2100 model carb is not available to you without importing one from the U.S. or Canada.
Finding the correct carb (DOAF AA) will be a challenge !!! So, if i haven't vacuum leaks, how to convert my 429 carb ? With larger jets ? My first idea was to put a modern 4 bbl (Edelbrock 500 or 600 cfm) but the car drives well with the 2100 except I have some problem to start the car when hot. This carb has a spacer with heater hoses which go through, maybe not the best think to keep a cool mixture. I live in south France so no many cool days (and even less since some years !).
That was not a very good thing; when hot, it was difficult to start. There are many things you could do; changing to a 4-barrel carb and intake is one. Another is to replace the spacer with a plastic one, IF no exhaust gas goes into the current one, and a more modern Holley or Holley/Motorcraft 2-barrel carb. However, I don't know what is in your country's inspection programs, so it could be failed simply by having put a different 2-barrel carb on it.
