Adjusting carb using exhaust temp

Geo-TH,In

Well-known Member
There have been a lot of posts about adjusting carbs and engine dieseling, so I decided to look up how the old single engine airplanes adjust their carbs in flight using exhaust temp. So, If you can find a better source, I would like to read it.

It basically goes with what I've been saying that going lean will cool engine. My defination for lean is going past 14.7:1. However what I've learned is that getting the max exhaust temp, 14.7:1 fuel/air, will also create the max internal engine temps which could result in burnt exhaust valves and holes in pistons. Going too rich produces cooler engine temps, carbon build up on piston and spark plug, wet looking plugs, gas getting in to oil, and excessive engine wear.

Excessive internal engine temps will show up on spark plug. The electrode and tip will be rounded off. Cermanic will appear to have bubbles. NO carbon build up, gray or white power on plug. Perhaps that's why many years ago at Indy, cars would run a few test laps, then they pulled the plugs and checked them over.

The article I'm posting states that leaning past the max exhaust temp will cool things down inside the engine, loss of a little hp, and it saves gas.

I have seen pistons with a nice round hole in the top. What caused the hole? Too hot plug? Carb adjustment set at 14.7:1 (ideal)? Carb adjustment set at 12:1(rich)? Carb adjustment set at 16:1(lean)? I know that Chrysler in the 70's experimented a short time with lean burn to produce cleaner air, 16:1-17:1, before fuel injuection, oxygen sensors in exhaust and better computers came along. Don't think Chryslers had holes in pisons by going lean.

George
leaning carb during cruse
 
(quoted from post at 16:56:59 07/26/14) There have been a lot of posts about adjusting carbs and engine dieseling, so I decided to look up how the old single engine airplanes adjust their carbs in flight using exhaust temp. So, If you can find a better source, I would like to read it.

It basically goes with what I've been saying that going lean will cool engine. My defination for lean is going past 14.7:1. However what I've learned is that getting the max exhaust temp, 14.7:1 fuel/air, will also create the max internal engine temps which could result in burnt exhaust valves and holes in pistons. Going too rich produces cooler engine temps, carbon build up on piston and spark plug, wet looking plugs, gas getting in to oil, and excessive engine wear.

Excessive internal engine temps will show up on spark plug. The electrode and tip will be rounded off. Cermanic will appear to have bubbles. NO carbon build up, gray or white power on plug. Perhaps that's why many years ago at Indy, cars would run a few test laps, then they pulled the plugs and checked them over.

The article I'm posting states that leaning past the max exhaust temp will cool things down inside the engine, loss of a little hp, and it saves gas.

I have seen pistons with a nice round hole in the top. What caused the hole? Too hot plug? Carb adjustment set at 14.7:1 (ideal)? Carb adjustment set at 12:1(rich)? Carb adjustment set at 16:1(lean)? I know that Chrysler in the 70's experimented a short time with lean burn to produce cleaner air, 16:1-17:1, before fuel injuection, oxygen sensors in exhaust and better computers came along. Don't think Chryslers had holes in pisons by going lean.

George
leaning carb during cruse

Hole in center of piston is caused from detonation/knock. A too hot plug can act like a model airplane engine's glow plug and light the mixture too soon.
Two strokes in particular with broken rings, cracked pistons and holed pistons. All too often a lack of lube oil is considered the prime suspect. When the problem was detonation from too much lube oil, a sooted up combustion chamber, too lean of a mixture or too low of fuel octane.
 
Before you get too wraped up in leaning out your mixture like is done on airplanes stop to consider;
At higher altitude the air is not as dense so when a pilot mentions leaning out his fuel what he really is doing is compensating for an over rich condition brought on by the change in air density at whatever altitude he is flying at.
He is watching his EGT as conditions are continously changing and he does not want to melt his engine and die.
 
Running lean-of-peak is nothing new. Lindbergh used LOP mixture settings so he didn't run out of gas crossing the Atlantic, and he taught his technique to P-38 pilots in the Pacific.

So, if LOP has been around for at least eighty years, why isn't it more commonly used? Pilots are generally taught to use full rich mixture on takeoff and only lean after reducing power. This is usually done seat-of-the pants by leaning the engine until it gets a bit rough, then enrichening the mixture. In other words, there are probably a lot more pilots running rich-of-peak than run lean-of-peak, even though avgas is ridiculously expensive. There are several reasons why: To do it right, you need an exhaust gas temperature gauge with probes for each cylinder. Also, carbureted engines have poor fuel distribution, and even most fuel injected engines have quite a bit of variation in the amount of fuel that gets to each cylinder. So the conventional wisdom is it is safer to run rich-of-peak EGT than lean. Never mind that a lot of pilots (including Lindbergh) have proven it works.

FWIW, you probably drive a vehicle every day that is running a fuel mixture that is at peak EGT. Most cars with catalytic converters and oxygen sensors run very close to a stoichiometric air-fuel mixture, because that's where the catalytic converter works best.
 
"When the problem was detonation from too much
lube oil, a sooted up combustion chamber, too lean
of a mixture or too low of fuel octane."

Yep, that's right! People think more oil is
better, in reality it does everything you
described.

The main jet doesn't know the difference between
gas or oil. The more oil, the less gas that gets
through. Result is a too lean mixture.

Then the hot burning, oil rich mixture starts
attaching itself to the cylinder wall around the
exhaust ports, reduces the already too hot piston
clearance, and... Well "now it won't idle good"!

Something to think about when pouring another can
of oil in the "almost empty" gas can from last
season!
 
Just a few points of information about Chrysler's "Lean Burn" engines of the '70s....
First off, the "Lean Burn" was only a trade name, and in reality had no direct relationship with the mixture. Lean Burn technology was limited to a few sensors and synthesized ignition timing. Under some conditions, timing could advance 50 degrees or more. There was no mixture control. Mixture became effectively leaner based on highly advanced ignition timing.

I got this straight from a Chrysler factory rep in 1974.
 
Steve, you are correct.

Detonation occurs on the boundaries of rich pockets. This will not occur if the fuel is COMPLETELY incorporated, or is to lean to form these pockets. It does need to be rich enough to ignite.
 
Where I live we have epa formulated fuel to help
emmisions, E10. Will adding a little more ethanol
increase or decrease the octane? Will more ethanol
make a leaner fuel/air mix? Will ethanol increase
or decrease combustion temp?

In the winter we have winter blend. I think I read
that butane is added. I get about 10-15% less
milage using winter blend. My Jubilee needs more
fuel(richer) to make horsepower to push show. From
trial and error I've learned it needs 2 1/2 more
turns on main jet. So is there more oxygen in the
winter blend? Or does my jubilee need more fuel
because of the cold air?

Without an exhaust gas analizer, which I don't
have, how lean is too lean? How far past lean of
peak can a person go without damaging pistons? Or
should I run at peak? Or should I run rich of
peak?

I have a 10 year old 20 hp kohler command. No way
to adjust carb, no adjustable jets. Plugs are
clean. Doesn't use oil. Runs and starts great.
Uses about a gallon of fuel an hour. Has 1500
hours on it. When engine is hot, I turn it off, it
sometimes may want to run backwards. Would that be
a clue of carbon build up? Pre detonation? Perhaps
too hot of a plug?


By the way, my old tractors are in good health.
Both have been rebuilt, they don't use oil. Don't
have black carbon deposits on plugs.


Thanks,
George
 
Mark,
So running an engine at peat EGT won't hurt engine? And running a little LOP I can fly the alantic without melting pistons?

Has anyone put wings on a Ford Jubilee and made it fly?

Thanks for your reply, it confirms what I've been saying, exhaust temps cool after a certain point.
George
 
Now, if you really understand how an internal-combustion gasoline engine works, you'll know you're not burning gasoline in the combustion chamber in a liquid state; it's the fuel that vaporizes and mixes with air that ignites. [And before someone tosses the term "vapor lock" into this discussion, let's also understand that "vapor lock" occurs when the fuel turns to a vapor at a point in the fuel system PRIOR to the point at which the fuel system is designed to handle vapor. The fuel lines, pump, and carburetor are designed to handle liquid fuel, not vapor. And "vapor lock" is a sign that your fuel system needs to be running at a cooler temperature.]

Benzene in your winter fuel mix vaporizes easier than gasoline, which makes it easier to combust in the cylinders than cold gasoline that stays in droplets rather than turning to a vapor. And why does a choke work on a cold engine? With a smaller percentage of gasoline turning to a vapor, the choke reduces the amount of air available to mix with that gasoline vapor...and with less air, the vaporized fuel is actually in a more stoichometrically correct mix and more prone to burn properly. The unvaporized fuel is what burns poorly and creates carbon deposits from incomplete combustion. [Google "Reid vapor pressure" for more information than you probably want to know on the subject.]

And as that engine warms up, the fuel system also absorbs some heat from the engine, the cold gasoline enters the combustion chamber a little warmer that it would on initial start-up, meaning the gasoline vaporizes a bit easier. When the engine reaches normal operating temperature, the gasoline should be vaporizing normally and the choke should be completely open.

SO...to answer your Jubilee question...it needs more gasoline in the winter, not only because of the cold air--which IS denser and contains more oxygen--but because less of the gasoline vaporizes properly in a cold engine. "Oxygenated" fuels are used more often in smog-prone areas in warmer weather, when the gasoline blends vaporize much more easily."

To completely kill engine run-on, first do what you can to remove carbon from the cylinder(s). Then when the engine is shut off, make sure the throttle is closing completely so that no additional fuel is entering the combustion chamber. With NO fuel entering to interact with the hot carbon, there should be ZERO "run-on" after the switch is turned off [which either kills current to the coil, or grounds the magneto...depending on your ignition system].

This isn't rocket science. It IS science, but not rocket science. No hoodoo/voodoo/magic is involved...honest.
 
George, I'd guess your need to open up the main jet in winter has less to do with the fuel you're burning and more to do with air temperature. Old tractors seldom have heated air intakes (relying instead on one-piece intake/exhaust manifolds), so in the winter the air is going to be more dense. Pilots call this effect "density altitude", and most pilots know to lean the mixture on takeoff if it's a hot day.

The other effect of cold weather is incomplete fuel vaporization. The main difference between summer and winter fuels is, as Buzzman said, higher allowable vapor pressure in winter. In the old days before fuel injection this was done to improve cold-weather starting and to prevent vapor lock in summer. Now it's mainly to reduce summer evaporative emissions while allowing the use cheaper distillates (such as butane) in winter. But chances are you're still running summer fuel in winter, and in many areas there's not a big difference between summer and winter fuels. Anyway, assuming you use fuel with the same vapor pressure year-round, vaporization is going to be better in summer than winter, meaning you need a richer winter mixture.
 
Buzzman and Mark,
Totally agree with what both of you said on all issues.

I've seen carbs frost up at an idle, heat of vaporaztion. Just like freon changing from a liquid to a gas, it requires heat energy.

Is there is a simple way to make an air pre heater for winter. I had a 71 duster that had an air pre heater, part of breather.

Still like to know a simple way to decarbon, is there a snake additive? Hate the idea of manually removing it.

An old VW mechanic said get engine hot, running real fast and sprinkle bon-ami in carb. It's like sand blasts the carbon loose. No thank you, I'm not stupid enough to do that. Years ago when I worked on oil furnaces there was Chimney sweep. An oil like spray you would apply to the soot inside the furnace. When furnace was on, the heat would make the chimney sweep burn off the soot. Glowed like a cigarette. Not brave enough to spray chimney sweep in cylinder. Has anyone tried it?

What about ethanol? If I make E15 or E15 by blending E85 with E10 would that make the octane go up? Or would a higher E20 produce more oxygen when it burns putting me more in the LOP zone? From what I've been reading the holes in piston is caused by low octane and lean fuel mix. For today's cars to use 87 octane, they use EGR to prevent pinning, pre detionation. We don't have that on our old tractors.

Thanks, It's nice to chat and learn from people on YT.
George
 
Steve,
So what's the least expensive way to boost octane?

Is there a simple way to remove carbon short of taking engine apart?
George
 
GM used to sell combustion chamber cleaner. Not sure what it was. I have heard that introducing water to a hot engine will loosen combustion chamber deposits. If you have ever seen a cylinder that has lost a head gasket, you would see this theory in action. I am not nearly brave enough to try it. Anyone know more about this?

Oh BTW, this is one of the most interesting threads I have read in a while and the bit about the 2 stroke going lean was news to me. I learned something.

Aaron
 
A carbon removal method I have not tried, but was told many years ago involved plain water. This was on a car. Remove air cleaner and holding engine at a fast idle,pour water down the carb throat. Not so fast as to stall it but as much as it will handle. Supposedly he could see chunks of carbon coming out the exhaust.
 
DO NOT USE BON AMI or any other abrasive! The Bon Ami "solution" was what GM mechanics were told to use when the small block Chevy engines came out with chrome rings that were difficult to break in. Introducing the Bon Ami, in a controlled amount, was the alternative to tearing the engine down and re-honing the cylinders to a finish that would cause the rings to "wear" in and seal better.

Ever see an engine that's had a head gasket leak? You can tell which cylinder that the coolant was leaking into by looking for the one with NO CARBON. Old-time mechanics used to take a 6-1/2 ounce Coke bottle of water and trickle it down the carb at a fast idle to remove carbon. The water in the cylinder turns into steam, and effectively steam-cleans the combustion chamber. But the key word is TRICKLE, not DUMP...you don't want to hydro-lock the engine and break things.

With a small engine like the Kohler, you might use a spray bottle, like the ones most folks keep on hand for their barbecue grills to keep the flames down.

Ever use an acetylene torch? That's an example of what happens with too lean a mixture. If you want to heat something with a rosebud tip, you use more acetylene [fuel] with the oxygen than you do when you're using it as a cutting torch. Ever hear of N20, or nitrous oxide injection? It works because N20 is 36% oxygen, rather than 20% oxygen like outside air. BUT...to keep from torching engine parts with N20, you also have to inject more fuel. The early adopters of nitrous learned these lessons the hard way.

I haven't looked into what the alky burners did back in the '60's...but I'm sure some research into their experiences might educate us as to some benefits/drawbacks of increasing the alky content of our gasoline-based fuels. With most gas tractor engines having a static compression ratio of 7.5:1 or less, in most cases increasing the octane of the fuel isn't necessary, providing the rest of the engine is in a good state of tune. Now, there are exceptions...if the dynamic compression is higher due to valve timing [a function of the camshaft grind], then a higher octane fuel might be required. But in most low-compression tractor engines, if a higher octane fuel is needed to prevent run-on, that's usually a sign that you have other things going on that should be attended to, either in the fuel system or in the ignition system.
 
Today is the first I used IH C to mow with after turning the main jet out another 1/4 turn. It takes about 40 minutes to mow yard. Tractor was up to normal operating temp, 135 degrees. The boss was using it today. When she turned the tractor off, the throttle was in the middle position, more than a fast idle. I was expecting a little dieseling. Nothing, engine stopped like it should.

I think this is proof that a LITTLE lean of peak temps in THE COMBUSTION CHAMBER are cooler. Going way past lean of peak, from what I've read, will cause detionation, pinning, and do damage to pistons and valves.

I'm happy with my experiment, well worth the $22 for an exhaust temp meter. Bet the gas savings will pay for it really fast.

Now I need a way to lean out the 20 hp kohler, which and no carb adjustments.

Thanks to all for your positive comments.

George
 
Couple questions George,What was the engines doing when you were checking exhaust temps.and what were you getting for temps?No load and 3/4-full load makes a lot of different ones.I know from the past setting gas tractors up,you would have a black-dirty exhaust not doing much work,but 5-10minutes working you had a pure white exhaust outlet.
 
massey,
The proof will be if tractor diesels after working her hard. The plugs are telling a good story. Not the case with my 20 hp kohler, which I can't adjust the carb, no adjustments. So I'm going to make my own E15 in an attempt to lean it out. I'll post pics of the old spark plugs vs the new ones. It diesels, actually runs backwards when spark is removed, has some carbon on plugs.

It would be better to have an O2 sensor instead of an EGT, but they are too expensive.

I'm happy with results.
george
 

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