MTFCA Forum

Hi All,
Since rebuilding my gearbox a couple of months ago I have had a strange thing happening with my 1915 Speedster. When the throttle is fully opened, or even 3/4 fully opened, in high gear, generally on a hill, the car starts miss firing and sometimes coughing and spluttering. If I drop into low the problem stops, irrespective of the throttle setting; it does not cough in bottom gear even if the throttle is opened wide.

I have checked and cleaned out the fuel tank, fuel lines and carburettor, replaced the Timer (Ford Roller type), checked the timing, and checked the coils are all firing, all of which seem ok. Has anyone any ideas of what this could be? To me it sounds something fuel related but not entirely sure! It is running a Holley G carb. if that makes any difference. Also the misfire occurs irrespective of how much fuel is in the tank, I have been running with it absolutely full most of the time.

Thank you
George

Sounds like your mixture is too lean to take up the load at full throttle. Back the needle off a quarter turn and see if it will behave.

You covered most fuel related stuff.
Did you check the gas cap vent ?

It could be an ignition problem. Maybe a bad spark plug. It takes more electricity to jump the spark at high compression than at lower compression. When the throttle is fully open at low speed, the compression is highest.
Norm

I had the same problem once on a fresh rebuild. The problem turned out to be a leaky intake manifold gasket. I finally realized that the coughing was back through the carburetor.

Thank you all for your suggestions, they are much appreciated. I will check each of them and let you know how I get on!

Thanks again.
George

To check for a manifold/vacuum leak, start the car, then spray something flammable around the manifold connections. If the engine surges, you've found a leak.

(if you use carb cleaner, don't use the chlorinated version)

I would check the coils on a hand cranked coil tester. One of your coils might be bad even though you say it is "firing."

Bill and Don's suggestion are the highest probability responses.

I would have to agree with Norman. I had the same issue a few years ago. I tried all the fuel related issues and none of them solved the problem. At a friends suggestion I swapped out my spark plugs. Problem solved. One plug was misfiring under load. Very frustrating problem with a simple solution.

I just went through the same thing and new spark plugs did the trick. (I now have a rebuilt carb, and a new timer but that didn't fix it). KISS start with the simple things first. Unless you are using X plugs, spark plugs are the cheapest and easiest thing to check. Coils have to be good too.

Thank you to everyone for their suggestions, they are much appreciated.

The problem turned out to be a loose connection on the power in feed in the coil box! In the end the wire came off completely, so of course the engine just died. Having re-soldered the connection all is well again, no coughing or missing at all; I must have disturbed it when I took the engine out.

Thanks to everyone for their help.
Best Wishes
George Hounslow

George, I see you are located in England. Please be sure to not use any vintage “Lucas” wires in the Model T!

Well! I just happened to develop the same problem yesterday. It ran fine going downhill and on level at a speed about 35, but when starting from a stop, it misfired and coughed and spit out the carburetor. I had to use low and Ruckstell and keep the engine reved up going uphill.

While I was at the museum yesterday some people asked me to crank start the engine. I couldn't get it to start with the crank, but got a few "free" kickbacks. The timing rod was all the way up and I tried the starter. I could feel it kick, but got it started. Again ran OK when going fast.

I am using an Anderson timer, and I suspect the problem to be with the timer. I think one or more cylinders are running advanced and at low speeds the spark comes too soon but just on one or two plugs. Maybe even a grounded wire to the low voltage side of the coil. When I get the engine running fast the spark advance seems to work as usual. Anyway, today I will start to check on things and report back when and if I find anything.
Norm

Well! I thought I had figured out what was wrong and had it running fine this afternoon. This is what I found. The lid on the coil box was loose on one end, so was not pushing down on the coils. In fact the latch was very likely touching number 4 coil. I properly installed it and then looked at the timer. I noticed that at least two wires were touching the spring which holds the timer in place, so I moved them out of the way and it started up and ran perfectly. I went about 3/4 miles uphill in Ford high and then in Ruckstell with Ford High. Then I came down the hill in Ruckstell. It ran just like it always ran before yesterday.
Then I decided to adjust the Ruckstell shift. This one has the late shifter with the spring accessible from the outside. I loosened the spring a bit and got back in and started it up with the rear wheels on stands. It shifts better and just as I was through working I heard a pitter pitter and it smelled like gas. The float was stuck on the carburetor! I am tired of working today, so turned off the gas shut off and tapped on the carburetor.
Anyway, maybe I fixed the problem or maybe not?
Norm

To George who started this thread, I think you should check your coils, timer and coil box to be sure all the coils are vibrating and sending a good spark. I just remembered that last week a neighbor had come to see my cars and I had removed the cover from the coil box to show him the coils. Apparently I had not properly locked down the cover. Saturday was the first time I drove the car since the neighbor came to see it.
I think it was just co-incidence that the float valve leaked after I drove it. I usually turn off the gas when I park the car so would not have noticed such a leak. I was working on the Ruckstell shifter and so kept the valve open so I could run the car on stands to check the shifting.
A leaky float valve would affect the idle and low speed when not pulling, but not the high end, because it needs more gas when pulling hard.
Anyway I have ordered a new float needle and seat.
Norm