surging

[Barteldes]

I have only driven My 24 Coupe a few times but last weekend i noticed it was weaker than before. the transition from first to second was slower to gain speed. Also when i start it it wont start at full retard spark only about half. Then at the end of a pretty short ride it started surging? lurching like it was running out of gas. it was at hi revs in first not too high but wasn't going to shift as i was coming to the incline of my street. this weekend I'll look at sediment bowl, air screw adjustment? what's the default setting for that? what else guys? it sounds like carb or fuel to me.

[speedytinc]

Fuel & ignition issues are commonly confused. Check your timer contacts. Is it a bouncing timer roller from out of round wear? Dirty? One plug fouled? A plug failing under compression?
Check that all 4 coils are firing with hot blue sparks shorting 1 @ a time with a screw driver to locate 1 failing cylinder.
Carb setting has an initial setting of 1 & 1/4 turn which is usually rich. Adjust it for smoothest running @ idle. Check the setting @ speed also.
If the happy spots are not the same that indicates the fuel level off. Crap in the bowl? Drain some fuel bowl into a clean glass jar looking for crud.
Could be a number of things.

Do you have the service manual T1? There is good diagnostic info contained there in.

[Scott_Conger]

Bill

I always tell folks that from a dead stop at a red light, if you're in low gear beyond 1/2 way through the intersection, you stayed in low too long. FWIW, I really suspect that you should have been in high gear for a bit before being forced back into low for that incline. It just isn't useful to stay in low at high(er) revs just because you see work ahead. Similarly, going around a corner at a safe speed is a "high gear" turn and doesn't and shouldn't be a low-gear affair.

OK...to your complaint. Surging under higher RPM may very well be a fuel starvation issue particularly with a coupe sporting an NH carb. Of all the float valves available for it, only one has the correct through-put to the bowl. Every single other one has a too-small hole which constricts fuel flow by nearly 50%. If that is indeed the case, your car can be expected to cruise gently along at 28-30MPH on the level with no trouble. Spend a lot of time in low or climbing a hill and what you are describing can most certainly happen with an improperly made float valve. I mentioned "coupe" specifically, since with the tank in the rear, there is more chance of having low head pressure of fuel at the carb than vehicles with under-seat tanks or cowl tanks.

And welcome to the hobby. Have fun. Drive safe, and if you get an opportunity for an "old hand" to show you the finer points of "T" driving, take it! You may be surprised at some of the bad habits you are developing early-on (that may be hard to break, later).

[RajoRacer]

Coupes had gas tanks in the trunk - under the seat beginning with the 1924 model according to the Encyclopedia.

[TXGOAT2]

Was the weather cold? Your timer may need cleaned and lubricated with a light oil.

[Oldav8tor]

Sounds like fuel. Scott sells a Full-Flow valve which allows more fuel to the carb. They work and are one of the cheapest performance upgrades you can add.

[Barteldes]

Coupes had gas tanks in the trunk - under the seat beginning with the 1924 model according to the Encyclopedia.

ya mines under the seat

[Barteldes]

Was the weather cold? Your timer may need cleaned and lubricated with a light oil.

im finally learning how to reply in this chat lol. yes it was chilly maybe 45 F.

[Barteldes]

Sounds like fuel. Scott sells a Full-Flow valve which allows more fuel to the carb. They work and are one of the cheapest performance upgrades you can add.

Scott the one in this chat?

[Bruce Compton]

Bill; A quick way to confirm fuel starvation problems is to pull out the choke next time it surges. Don't hold it pulled, just a quick pull should tell you if fuel really is the problem. For the record, most fuel problems are electrical....... but maybe this one isn't. Timer problems are a way more common.

[Humblej]

Bill, by "air screw" you might mean the carb fuel air mixture knob. Try starting with the mixture knob opened 1 1/2 turns, after start turn it down about 1/2 - 3/4 turn and listen to the RPM. When the RPM starts to slow open it up a little. Keep playing with more and less mixture to find the sweet spot in the middle of too lean and too rich, as too much or too little fuel will cause it to run rough and the RPM to drop off. You can use the 1 1/2 turns for starting every time cold, but the exact position for running will depend on the atmospheric conditions of the day, so don't get into the habit of setting it by memory, set the mixture by finding the sweet spot. Restarting a warm engine should not require touching the mixture knob. If you ever get a loud backfire during shutdown, and maybe even blow your muffler apart, you can avoid that by shutting the engine off by leaning the mixture knob, that's how its done on airplanes, but most of us T guys just turn the key off, that way we may get a free start later.

You should never start the engine with the spark lever advanced or play with it while cranking the engine over as you run the risk of damaging the starter. You should check the timing to verify that the timer is set correctly. There are a few things with a Model t that will hurt you, kill you, or damage it, improperly timed engine and/or starting the engine with the spark lever advanced is one of those things.

[TRDxB2]

I have only driven My 24 Coupe a few times but last weekend i noticed it was weaker than before. the transition from first to second was slower to gain speed. Also when i start it it wont start at full retard spark only about half. Then at the end of a pretty short ride it started surging? lurching like it was running out of gas. it was at hi revs in first not too high but wasn't going to shift as i was coming to the incline of my street. this weekend I'll look at sediment bowl, air screw adjustment? what's the default setting for that? what else guys? it sounds like carb or fuel to me.

Not sure what how to interpret this - "I have only driven My 24 Coupe a few times" - since you owned it? in a year? this season? this month?
The duration is important in understanding the quality of the gasoline in your tank and how much is in it. Model T's don't like old gas (over a month), while modern cars can contend with it. I wouldn't fool with carb adjustments till you drained out the old gas, tank, line and bowl. You can dump the old gas in your daily driver.
The issue with old Ethanol Gas is called phase separation where over time the ethanol will attach itself to water molecules and settle at the bottom of the tank. Now there are many arguments about this and many exaggerated false tests trying to discredit its use. BUT it will happen over time. The exaggerated false test always show pouring water into some ethanol to should stratification. That's not "moisture" which they say it attracts However ethanol is heavier than gasoline on its own so it will settle below the gasoline layer which in turn would prevent the ethanol from attracting moisture. Water itself is heavier than ethanol so if its present its at the lowest point, regardless of the cause. But even if here is no "water" mix, you could have ethanol on the bottom of the tank - try to start on it. Doubtful
.

[John kuehn]

Make sure you have a full or at least a 1/2 tank of gas. Model T’s DONT have a fuel pump and a good running engine has to have plenty of gas in the tank. The less gas in the tank means a slightly less gas flow and if you’re going up hill IT will stop the gas flow.
Is the vent hole open on your gas tank cap? If it’s not the engine could develop vapor lock and that will alter your gas flow.

And make sure your sediment bowl under the gas tank is clear. They do get stopped enough to have a flow of gas but but not a good steady flow. Good luck

[vech]

One other possibility. What size steel (or copper) fuel line is running from the tank to the carb? a 1/4 inch OD fuel line will not deliver near as much fuel and not near as fast, by gravity feed, as a 5/16 OD steel fuel line. I replaced the metal fuel lines on my coupe and touring car with larger ones, for better fuel flow.. I also insulated the fuel line, (you can buy a heat barrier sheath to slip over the lines if they are close to the exhaust) because if a copper fuel line is running very close to the exhaust system, the line can get hot enough in the summer, to boil the gasoline and cause vapor lock.

[Scott_Conger]

1/4" line
5/16" line
or a firehose connected to the carb

they're almost always invariably trying to get fuel through a .093" hole in an improperly designed replacement float valve in the carb. With only gravity pushing the fuel, the Cv (Valve Flow Coefficient) of the valve is of utmost importance. Cut the area of the hole in the valve by 1/2 as most valves have, and the Cv is dramatically reduced.

Typically when pipe size is increased, it is because of a conductance issue...larger pipes will flow more fluid so long as the pipe has no restriction at either end. This is where the error in understanding typically occurs...because each pipe, large or small, is terminated with a fixed size valve at the end, the only way to get EITHER pipe to flow more, is to increase the size of the orifice of the valve, and regardless of the size of the pipe, the restriction of the valve will cause either pipe to flow identically.

a stock fuel line, running to a correctly designed float valve would drain a tank before you know it, if there happened to be no bowl on the carb.

believe otherwise if you wish, but what I state is true

[Norman Kling]

The few times you drove the T before. Did it run better at that time than it does now? How was the weather at that time? On a hot day, the T will warm up fast and the fuel adjustment can be done soon after you start the engine, however, on a cold day it will take longer to warm up. If you happen to have a water pump without a thermostat installed in your cooling system, it might not warm up at all. so the temperature of the engine is important to your fuel adjustment. Even the altitude can affect the adjustment. As you increase in altitude you need to lean the mixture a bit because less air pressure. Anyway, first thing to do is to experiment with the fuel mixture.
The other things mentioned such as age of the gas in the tank and how full the tank is are also of importance. You might need to disconnect the fuel line at both ends and try threading a wire all the way through then blow it out with compressed air. Drain the sediment bowl under the gas tank and drain the carburetor bowl. When you get everything working in the fuel system if the problem does not go away, you can check other things.
If after you have driven the car for about half an hour especially after running uphill, step out and feel the radiator. If it is still cold, your engine is running too cold. Usually it will warm up because of thermo-syphon but if you have a water pump it will keep circulating cold water through the radiator.
It is unlikely the problem is in the ignition unless the problem happened before this last time you drove the car. It is easy to check timing. See other posts on how to set timing.
Norm

[Barteldes]

Bill; A quick way to confirm fuel starvation problems is to pull out the choke next time it surges. Don't hold it pulled, just a quick pull should tell you if fuel really is the problem. For the record, most fuel problems are electrical....... but maybe this one isn't. Timer problems are a way more common.

thanks Bruce

[Barteldes]

I have only driven My 24 Coupe a few times but last weekend i noticed it was weaker than before. the transition from first to second was slower to gain speed. Also when i start it it wont start at full retard spark only about half. Then at the end of a pretty short ride it started surging? lurching like it was running out of gas. it was at hi revs in first not too high but wasn't going to shift as i was coming to the incline of my street. this weekend I'll look at sediment bowl, air screw adjustment? what's the default setting for that? what else guys? it sounds like carb or fuel to me.

Not sure what how to interpret this - "I have only driven My 24 Coupe a few times" - since you owned it? in a year? this season? this month?
The duration is important in understanding the quality of the gasoline in your tank and how much is in it. Model T's don't like old gas (over a month), while modern cars can contend with it. I wouldn't fool with carb adjustments till you drained out the old gas, tank, line and bowl. You can dump the old gas in your daily driver.
The issue with old Ethanol Gas is called phase separation where over time the ethanol will attach itself to water molecules and settle at the bottom of the tank. Now there are many arguments about this and many exaggerated false tests trying to discredit its use. BUT it will happen over time. The exaggerated false test always show pouring water into some ethanol to should stratification. That's not "moisture" which they say it attracts However ethanol is heavier than gasoline on its own so it will settle below the gasoline layer which in turn would prevent the ethanol from attracting moisture. Water itself is heavier than ethanol so if its present its at the lowest point, regardless of the cause. But even if here is no "water" mix, you could have ethanol on the bottom of the tank - try to start on it. Doubtful
.

Thanks ! good to know about the gas. I love the science. Yes im a first time driver and this is my first Model T bought in December and with the bad weather in denver only drove it about 3 or 4 times at about a mile or two each time. This particular time i had my Fat .. er i mean lovely sister with me and there was more weight in the car.

[Barteldes]

Bill, by "air screw" you might mean the carb fuel air mixture knob. Try starting with the mixture knob opened 1 1/2 turns, after start turn it down about 1/2 - 3/4 turn and listen to the RPM. When the RPM starts to slow open it up a little. Keep playing with more and less mixture to find the sweet spot in the middle of too lean and too rich, as too much or too little fuel will cause it to run rough and the RPM to drop off. You can use the 1 1/2 turns for starting every time cold, but the exact position for running will depend on the atmospheric conditions of the day, so don't get into the habit of setting it by memory, set the mixture by finding the sweet spot. Restarting a warm engine should not require touching the mixture knob. If you ever get a loud backfire during shutdown, and maybe even blow your muffler apart, you can avoid that by shutting the engine off by leaning the mixture knob, that's how its done on airplanes, but most of us T guys just turn the key off, that way we may get a free start later.

You should never start the engine with the spark lever advanced or play with it while cranking the engine over as you run the risk of damaging the starter. You should check the timing to verify that the timer is set correctly. There are a few things with a Model t that will hurt you, kill you, or damage it, improperly timed engine and/or starting the engine with the spark lever advanced is one of those things.

Thanks Jeff i appreciate the advice. Yes i meant the air mix knob. Cant wait to use all this good info this weekend.

[Bill Robinson]

Bill- I've had the same thing happen to me 3 times over the years All problems were on cars with gas tanks under the seat.
1. About 25 years ago I picked up an engine from a re-builder. After running for a few miles it would start lurching or surging. Turned out to be a slight leak in the intake manifold gasket. I tightened the manifold and the problem was gone.
2. Next time a friend's pickup would not climb a steep hill. His tank was under the seat. I was driving a Depot Hack with tank under the seat. After trying the usual fix-it's nothing worked. We swapped the metal fuel lines- put mine on his/ his on mine. On our next run- his truck made it to the top and mine stalled. Swapped back to the way they were. His stalled again. Turns out his line was 1/4" id and mine was 5/16" id. No pump- steep hill- gravity won the war. He updated to 5/16" and no problems since.
3. Next time- it was hard to figure the problem out, but thanks to my buddies on the forum I found that there was a vapor lock in the fuel line because the line was running too close the exhaust tank. An internal bubble would form and cause the problem.

I might add- if you are driving around with a quarter of a tank- or less- your problem may possibly disappear if you add some gas. Again- gravity flow.

[TXGOAT2]

If you only drove a mile or two per trip previously, in cool weather, it's likely your engine never warmed up. If there was any moisture in the air under those conditions, you can have problems with frost forming in the carburetor and intake naifold. If your car lacks the original intake air heat pipe, as many do, you can expect to have issues with poor performance until the car has been driven at least several miles.

Driving a T short distances in cool weather, especially cool, damp weather, can cause performance issues very much like you described in your original post.

[Norman Kling]

You mentioned taking your sister for a ride. I have 3 Model T's and live in the mountains. There are hills I can climb in high gear, but with an extra passenger, I have to shift down. You will notice that the pulling power decreases with the added weight. But that should not cause the engine to surge.
Norm