MTFCA Forum

With hot weather here now (temps in the upper 90s this week), I'm reminded that I need to do all I can to drive our '21 Touring more efficiently. I realize that I have developed the habit of not adjusting the carb, but just leaving it where it cranks best and driving. I know that the "proper, by the book" way is to lean the mixture a quarter turn or so after running a short distance. That is supposed to conserve fuel and help the engine to run a little cooler. Do all you guys & gals do it? Am I the only one that has gotten out of the habit? Who can say for sure that it makes a noticeable differance?

Tommy, i think the books are great about giving you a general guideline about where your carb should be set at, but in the end, its all about what your T likes best. I fiddled with mine for years, and have now found the sweet spot that my T responds to every time. If it works for you and your T, no need to worry about what the book says.

I just leave it where it runs best, as lean as possible. It might mean it is a little harder to start, and I will have to crank it a couple more times, but then I do not have to richen and lean the mixture. Might just have to choke it a bit more to get it to start.

A quarter turn in works best for me on each car but yes, I forget quite often. The adjusting rods hidden by the instrument panel can't be checked by sight. Reaching them is a stretch and sometimes a surprise to new passengers. My aging memory allows running rich.
Rich

I always like tweaking the spark and carburetor needle for best performance as I’m driving. When I had a straight through NH in the car I used an accessory rod with a universal joint that allowed adjusting the carb needle from the dash board.

I’m currently running a Stromberg OF carburetor which has a gas adjuster by cable to the steering column.

This comment started with the advent of summer heat effecting the "driveability" of the T. I have experienced issues with summer heat and tried an approach suggested to me. Open the jet and the engine will run cooler. It worked when we were on tour in South Carolina with the heat as recorded on the bank thermometer at 103. I richened the fuel when I noticed the motor meter getting red. It didn't continue toward the top of the red area and we were able to continue. Others overheated and had to stop and let it cool. Just another side to the story!

In aircraft we often monitor both cylinder head temperature and exhaust gas temperature - using the latter to manually lean our carbs. Leaning is usually done only at cruise unless departing from a high altitude where you must lean slightly to get the engine to run smoothly. Going along with what dickc said, when cylinder head temps start to get high, one of the things we are taught to do is enrich the mixture a bit. Doing so and watching the gauges you can see the CHT drop along with the EGT. I would suspect the same would be true for a Model T. Your mileage will drop slightly but your engine should run cooler.

In addition to what Tim just said...
I was explained by a H-D master builder.
The timing (especially on air cooled engines) will effect temperature. Too much either way and the cylinder is more exposed to the explosion, which generates heat where you don't want it.
The cylinder head dissipates heat better than the cylinder and proper timing helps keep the heat near the head...
Fuel mixture is as important. Too much fuel and you foul plugs, lose power and carbon will build up.

I leave mine where it runs the best, and don't mess with it. If I get up into the mountains, then I lean it out some.

Unlike a modern car which automatically makes those adjustments, the T has an adjustment that works best for cold starts, and another for running when it is warmed up. It also runs a bit better uphill if you run just a bit rich and saves gas going downhill if you lean it out a bit.

Drive where the engine runs best for the conditions. Also if you run too rich you can foul the spark plugs and if lean burn the valves. This information is not intended to scare you, but to show that the adjustment is important. Easiest way to make the adjustment is when the engine has warmed up pull the throttle a few notches while idling and rotate clockwise till the engine starts to slow down the rotate counter clockwise till it starts to run rough and then finally set it about half way between those two positions. On the later cars with the adjustment on the same rod with the choke, you can see which way the rod is turned and then adjust to that position each time you drive it. On the earlier cars you can still do that adjustment by reaching down to turn it.
Norm

to lean the mixture a quarter turn or so after running a short distance. That is supposed to conserve fuel and help the engine to run a little cooler.

As I recall, leaning the mixture will cause the engine to run hotter. Richening it provides a bit more cooling action by putting more fuel into the cylinders. Correct me if I'm wrong.

Mixture needs to be adjusted correctly. It is confusing to just say richening cools or leaning runs hotter. A cold engine starts and runs better when the mixture is a little richer than where it would be for normal driving. That would be the correct mixture for a cold engine. Once it is up to temperature, what was correct for the cool engine is now too rich for the warm engine. It now needs to be leaned out. If it is leaned too much, then it will run hotter. But leaning it the the proper spot is a good thing, not a bad thing.

Proper mixture and spark timing both vary with driving conditions. Modern vehicles are constantly varying these settings automatically. Even older "modern" vehicles varied these settings automatically (centrifugal advance, vacuum advance, power valves, automatic chokes, etc). While yes, a model t is pretty forgiving and one might find a compromise position for spark and mixture that will give acceptable (to them) performance, best performance will be achieved when the operator understands what these adjustments do, what the car is telling them and how to react to that. A mother usually knows whether that's a "I'm hungry" cry or an "in wet" cry. A model t owner should get to know when their car needs more fuel or more air or more advance or less advance.

Hal wrote: ↑

Mon May 27, 2019 6:52 am

...best performance will be achieved when the operator understands what these adjustments do, what the car is telling them and how to react to that... A model t owner should get to know when their car needs more fuel or more air or more advance or less advance.

OK Hal, I understand what lean and rich mean. I just don't know the signs my T is giving for one or the other. I'm a new 'owner', but have been around these machines most of my life. Mine starts and runs fine on the same setting all year around (Florida). But how can I be a better care-taker of this automobile?

My car had been stored. I rebuilt the carb when I took possession. When I got it running I leaned the mixture until it started running rough and then backed it off about a third of a turn. That's where it sits today. As for the timing, I adjust it down to about 2/3 the way. Anywhere in that zone seems to be the same. I can't tell the difference between 50% and 100%. Almost as if there were only two settings, start & run.

Is there anywhere a newbie instructional on fuel mixture and spark timing? Can you teach us?

Jeff

It is quite simple to find the proper setting. With the spark, you find the point where you get the most power with least throttle. This will vary according to the speed of the engine. So if the initial timing is set correctly at the timer with the lever all the way up, that would be used for starting so the engine will start in the correct direction of rotation. Then give it a few more notches of throttle and you will notice that when you advance the spark the engine will speed up. If you advance too far the engine will begin to run a little rough. Set the spark at the position where the engine runs fastest and smoothest. When you are driving, you will have the spark lever at about 8 oclock position. When you go very fast 34 to 45 MPH you can pull the spark lever all the way down. You will notice it has a bit more power, but if you approach a hill and the car begins to slow down, put it back about 8 oclock position. Likewise if you are going very slow such as down a gravel road and you are going about 5 to 10 MPH hou might find it runs a bit smoother at around 10 oclock position.

With the fuel mixture you need to enrich it a bit for starting a cold engine. If it is too lean, your engine might sputter but if you are crank starting will die before you can run around to advance the spark! If you make it a bit richer, it will start and run until you can advance the spark. Then as stated above, as the engine warms up you find the "sweet" spot and leave it there. For most driving this spot will be fine if you just leave it there. lIkewise if you make a short stop, such as filling the gas tank and the engine is off for just a few minutes, when you start, don't even choke it or turn the mixture, just remember to retard the spark. You might even be lucky and get a "free" start!

Best way to learn these things is by experience. Reading up on it will give you a basic understanding, but experience will teach you when you have acheved your goal. Have fun with your T.

Norm