Surging after about 15 minutes of run time

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Corvette Guy
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Surging after about 15 minutes of run time

Post by Corvette Guy » Sat Sep 05, 2020 4:39 pm

My TT has a True Fire ignition and after running for 15 minutes it starts surging and bucking. I tried adjusting the carb and timing and that didn't help anything. I think it might be running hot as it gurgled for a few minutes after I shut it down.

Not knowing if the radiator was the problem, I fired it back up and checked temps with a non contact thermometer. At idle the top of the radiator was 178 and the bottom was 110, which I think is pretty decent. At a higher engine speed the top was 182 and 174 at the bottom, which I don't think is good. Then again it could be due to a lack of airflow as I was parked.

Thoughts?

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CudaMan
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Re: Surging after about 15 minutes of run time

Post by CudaMan » Sat Sep 05, 2020 4:58 pm

What kind of shape is your coil box in? I haven't experienced it, but others have mentioned that the Truefire is sensitive to low or intermittent input voltage. I installed the Regan kit and all new contacts and insulators in my coil box as extra insurance.
Mark Strange
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1924 Cut-off Touring (now a pickup)

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Re: Surging after about 15 minutes of run time

Post by GrandpaFord » Sat Sep 05, 2020 7:56 pm

Check that the hole in the gas cap is clear.

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Re: Surging after about 15 minutes of run time

Post by CudaMan » Sat Sep 05, 2020 8:37 pm

I think Neil is on to something. 15 minutes is a long time for a rough running problem to show up. I actually drilled the vent hole in my gas cap a drill size bigger than stock to make sure that the gas tank was adequately vented.
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Norman Kling
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Re: Surging after about 15 minutes of run time

Post by Norman Kling » Sat Sep 05, 2020 9:23 pm

When you adjust the carburetor, sometimes it is very sensitive and just a few degrees will make a difference. Usually when it is rich it will surge, but when it is lean it just slows down and acts like it might run out of gas. The sweet spot is just a few degrees. It is only about a quarter turn between too rich and too lean. Another thing which could cause it to surge, would be too high float level. So I would think first about the carburetor. Others, who are more familiar with your non stock ignition system might be able to steer you through how to adjust or fix the problem if it turns out to be an ignition problem.
Norm

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Re: Surging after about 15 minutes of run time

Post by Hap_Tucker » Sat Sep 05, 2020 9:29 pm

We missed the Christmas parade one year because we added more gas than Blackie's gas tank was used to having. The crud & rust from the tank stopped up the gas line. It varied in how long it took for the car to start starving for Gas. And back in those days, I just opened the carburetor drain valve and saw that it was dripping really slowly - not enough to keep the engine running. EPA might not think that was a good idea today. Sorry, I don't recall what year TT you have. So I posted a link to the 1925 Ford Service manual with the repair tips for running poorly located on page 237 see the link at: http://www.cimorelli.com/mtdl/servicemanual/default.htm ..

From that 1925 Ford repair book the following pages may be helpful:

Note I sometime have problems getting the pages to post in the order that I would like. So there will a couple of posting with one attachment to each.

And see also the index for other things like rebuilding a carb etc. No it doesn't cover True fire.

Respectfully submitted,

Hap l9l5 cut off
pg 237 - trouble shooting misfire.JPG
By the way -- did it used to run good and then you installed the true fire and you had the problem? Or it ran good and you changed something else and then it ran poorly?

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Re: Surging after about 15 minutes of run time

Post by Hap_Tucker » Sat Sep 05, 2020 9:30 pm

pg 238 - trouble shooting misfire.JPG

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Re: Surging after about 15 minutes of run time

Post by Hap_Tucker » Sat Sep 05, 2020 9:30 pm

pg 239 - trouble shooting misfire - coils.JPG

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Re: Surging after about 15 minutes of run time

Post by Hap_Tucker » Sat Sep 05, 2020 9:31 pm

pg 240- trouble shooting misfire - valves or Fuel Sytem.JPG

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Re: Surging after about 15 minutes of run time

Post by Hap_Tucker » Sat Sep 05, 2020 9:31 pm

pg 241- trouble shooting misfire - Fuel Sytem.JPG

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Re: Surging after about 15 minutes of run time

Post by Hap_Tucker » Sat Sep 05, 2020 9:32 pm

pg 242- trouble shooting Back Firing.JPG

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Re: Surging after about 15 minutes of run time

Post by Hap_Tucker » Sat Sep 05, 2020 9:33 pm

pg 243- trouble shooting Back Firing.JPG


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Re: Surging after about 15 minutes of run time

Post by Corvette Guy » Sat Sep 05, 2020 9:39 pm

The coil box is ok, I think. I've got 2 six volt dry cell lantern batteries running it and I've got 10 volts. The True Fire will run between 6 and 12 volts so I think I'm good there.

The hole in the gas cap is clear.

I talked with a local guy and he thought it was my gas line getting hot. I moved it away from the exhaust and zip tied it to the the torque tube. I took it for a spin and didn't experience any problems, but I'm not calling it a win yet.

Another guy emailed me and said that I might have the wrong sized float valve in the carb which could starve the engine. In addition he said that my fuel filter could be causing problems too.

I've got to go for a longer drive tomorrow and go from there.

It ran when I got it and it already had the True Fire installed. I didn't change anything and only took it for short drives up and down the road (incase it broke down). Now that I've got a cab and bed, I'm taking longer trips to town and additional problems are popping up.
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Re: Surging after about 15 minutes of run time

Post by CudaMan » Sun Sep 06, 2020 8:12 am

If you determine that the fuel system is OK and you focus attention again on the Truefire, double check the timing using Truefire's recommended procedure, shown in this thread:

http://www.mtfca.com/discus/messages/59 ... 1473784166

I found that I had to substantially lengthen the stock timing rod to get correct timing with the Truefire, to the point where it can touch the timer terminals as you move the timing.

I ended up fabricating a longer-than-stock timing rod out of music wire to get the required length and clearance.
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custom_timer_rod.jpg
Mark Strange
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