The Stovebolt Site Forums The Shop Area Engine Shop how to test for too lean condition

How does one test for a too lean condition under load.
i have heard of the importance of this determination when setting up multiple carbs.

Install a A/F ratio gauge.

Under a hard load it should have a steady pull through the whole rpm range, and the engine temp shouldn't climb.

You'll need to be aware that some carburetors simply can't be made to run rich enough to work in a multi-carb situation. Fuel/air mixture is mostly controlled by the volume of air passing through the venturis, and if they're too large the velocity will be too slow to create enough vacuum to draw fuel into the airstream, no matter how big you make the jets. Putting two (or more) of the same carbs that work right in a single application is a recipe for disaster. You MUST use carbs designed for an engine about half the size of the one you're running for a dual carb setup, and even smaller for triples.
Jerry

52Carl, have you pulled the spark plugs and looked at the color? Are they black, tan, white?

Depending on which carburetors you have, you may not be able to adjust high speed mixture. My twin Carter W-1s use mechanical metering rods, the more you step down, the richer the mixture. If yours use power valves, then I don't know what you would do.

I can tell mine is lean when the transmission shifts to the next higher gear, if the throttle is only partial open, it will lay over just after shifting, then pick back up when I shightly let off the throttle or step down more. If I richen the mixture by way of metering rod hight, I can get rid of that lay over, but then it runs richer then I like it to. When they are adjusted a touch rich, under full throttle you can hear it pulling hard and feel it. When lean, you can hear lots of air being pulled in but the seat of the pants feel is just not quite there, its not a smooth steady pull.

My A/F gauge shows just what I can feel, it goes way lean after it shifts, then settles back to normal.

Cruise speed ( 65 mph ) it runs about 15.5 to 16.0 Air to fuel
Idle 750 with a/c on 14.5 to 14.9 depending on the weather or fuel quality
Full throttle 4500 max rpm 12.7 - 13.5 A/F ratio

Ideal ratio is 14.7. My fuel mileage went up drastically when I started leaning it out after installing the A/F gauge and O2s. It ran pretty good but smelled like fuel all the time before.

Full disclosure, I have a Frankenstein Carter YF. The top half is a 964 and the bottom half is for a 235, likely a YF2100.
The '53 full pressure 235 runs extremely well with it. I also have a Genuine YF 2100 which I use when the ethanol eats a hole in the accelerator pump diaphragm.
I have swapped them out several times as the diaphragms go bad over the 14 years I have had this truck, and the Frankenstein carb results in better overall performance which you can feel in the seat of the pants compared to the YF 2100.
Neither of the carbs cause sooty plugs. As far as any sign of a lean condition, I am not seeing that either.

When you melt a piston, it’s too lean.

I’d say you’re probably golden. You dohave me curious about the Frankencarb. Wonder if you are getting a little better velocity through it.

I recall Pre-68 Dave commenting a notable seat-of-the pants acceleration improvement when using a 216-sized carb (and maybe manifold?) on a 235.

The siamesed ports might make this a little less than ideal, but if you wanted some sort of quantifiable thing (without investing in AF gauage) perhaps you could shoot one of those laser temp guns at the exhaust ports after a hard run. Do it with each carb and compare the results?

The laser temp gun at the exhaust ports is a great idea. I have been wanting one of them for quite a while anyway.

Just remove the hood and hire the reckless teenage kid next door to ride the fender on a long uphill pull- - - - -calling out laser temps along the way!
LOL!
Jerry

I bought a cheapy on Amazon many years ago. It just keeps working.

Let us know how this goes and if you get any interesting results.

You can buy a cheap Laser Thermometer at Harbor Freight for under $25.00. I use mine all the time.

https://www.harborfreight.com/121-infrared-laser-thermometer-63985.html