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This issue has been addressed before on Jul 8, 2017 and Jan 16, 2023. I am renewing the query because the symptoms on my 1960 Triumph TR3 were not gradual, but sudden. Here is a chronology before the problem started, what I have done so far; and what I plan to do now.
I bought the car sight-unseen a few weeks ago and it drove beautifully. I drove it several times.
Just before the problem started:
I changed out both master cylinders that were leaking fluid.
I filled up with gas at a station (that later my mechanic told me has sold bad gas before).
I drove to a nearby town and it started faltering, just a little on the way.
On the way back it faltered so badly, carburetors backfired? It came to a halt.
It seemed like it was starving for gas. Frantic pumping of the pedal seemed to help but ultimately to no avail.
Upon inspection at home I found that one of the master cylinder lines I moved during installation had caught the lever under the pump (primer lever?)) and was partially opening it. I fixed that, but was driving with it in that way. I may have damaged the mechanical pump.
I saw that one of the SU carb dampers on top and was open to air. (it may have happened during a carb backfire under pressure?)
I changed a dirty transparent fuel filter between the pump and carbs.
The car starts up cold and it runs pretty good... until it warms up and then falters out.
Yesterday:
I took it to the mechanic who always "checks fire before gas." He found the points were nearly closed all the way. He gapped them at 0.15 and changed the Bosch platinum plugs to new NGK plugs gapped at .025. The car instantly started and drove. Problem seemed to be solved. It started on first click of the button and idled perfectly. But on the way home, it started to slowly falter again when I reached higher RPMs or the engine was under load (going up hills). It got progressively worse, just like before. I barely made it up the hill to my home.
When I got home I, checked the points, and they are still gapped perfectly at 0.015 fully opened.
I rechecked the new NGK plugs for soiling (under rich fuel conditions). They were still clean and properly gapped.
I refill the tubes on the carburetor with oil where the damper goes and came loose. It only needed a little.
I used 20 weight and filled to 6mm from the top.
I checked both carbs with with an airflow meter and made only minor adjustments to equalize.
I waited to drive it until morning because it was raining.
Today:
The TR3 drove great after morning start up. But after it warmed up, it floundered again. I barely made it to the mechanic shop at high RPMs so the engine would not shut off.
My mechanic and I emptied the gas tank, put in a new fuel line from tank to mechanical pump. We then installed an electric pump preceded by an inline filter.
The carbs get plenty of gas now. But it was the gas I originally bought just before this whole problem started.
The engine still falters badly.
We discovered that a gentle pull on the wire from the coil to the distributor came loose and came right out. We repaired the existing wire that as best as we could.
The engine faltered badly.
We re-set set timing to advanced 4 deg. It was only slightly off. It did not make it work any better,
Tonight I ordered a Pertronix Flame Thrower D176600 electronic distributor. A Pertronix 40,000 volt 3.0 ohm coil, and Pertronix 8mm flame thrower spark plug wires. They arrive tomorrow and I plan on installing them tomorrow when they arrive. I will also put new gas.
I hope this fixes the problem. It has been towed three times since this began.
Was it bad fire or and issue with no gas pressure? It would seem that it was both. That's weird, since it happened at the same time.
I bought the car sight-unseen a few weeks ago and it drove beautifully. I drove it several times.
Just before the problem started:
I changed out both master cylinders that were leaking fluid.
I filled up with gas at a station (that later my mechanic told me has sold bad gas before).
I drove to a nearby town and it started faltering, just a little on the way.
On the way back it faltered so badly, carburetors backfired? It came to a halt.
It seemed like it was starving for gas. Frantic pumping of the pedal seemed to help but ultimately to no avail.
Upon inspection at home I found that one of the master cylinder lines I moved during installation had caught the lever under the pump (primer lever?)) and was partially opening it. I fixed that, but was driving with it in that way. I may have damaged the mechanical pump.
I saw that one of the SU carb dampers on top and was open to air. (it may have happened during a carb backfire under pressure?)
I changed a dirty transparent fuel filter between the pump and carbs.
The car starts up cold and it runs pretty good... until it warms up and then falters out.
Yesterday:
I took it to the mechanic who always "checks fire before gas." He found the points were nearly closed all the way. He gapped them at 0.15 and changed the Bosch platinum plugs to new NGK plugs gapped at .025. The car instantly started and drove. Problem seemed to be solved. It started on first click of the button and idled perfectly. But on the way home, it started to slowly falter again when I reached higher RPMs or the engine was under load (going up hills). It got progressively worse, just like before. I barely made it up the hill to my home.
When I got home I, checked the points, and they are still gapped perfectly at 0.015 fully opened.
I rechecked the new NGK plugs for soiling (under rich fuel conditions). They were still clean and properly gapped.
I refill the tubes on the carburetor with oil where the damper goes and came loose. It only needed a little.
I used 20 weight and filled to 6mm from the top.
I checked both carbs with with an airflow meter and made only minor adjustments to equalize.
I waited to drive it until morning because it was raining.
Today:
The TR3 drove great after morning start up. But after it warmed up, it floundered again. I barely made it to the mechanic shop at high RPMs so the engine would not shut off.
My mechanic and I emptied the gas tank, put in a new fuel line from tank to mechanical pump. We then installed an electric pump preceded by an inline filter.
The carbs get plenty of gas now. But it was the gas I originally bought just before this whole problem started.
The engine still falters badly.
We discovered that a gentle pull on the wire from the coil to the distributor came loose and came right out. We repaired the existing wire that as best as we could.
The engine faltered badly.
We re-set set timing to advanced 4 deg. It was only slightly off. It did not make it work any better,
Tonight I ordered a Pertronix Flame Thrower D176600 electronic distributor. A Pertronix 40,000 volt 3.0 ohm coil, and Pertronix 8mm flame thrower spark plug wires. They arrive tomorrow and I plan on installing them tomorrow when they arrive. I will also put new gas.
I hope this fixes the problem. It has been towed three times since this began.
Was it bad fire or and issue with no gas pressure? It would seem that it was both. That's weird, since it happened at the same time.
Last edited:
I learned a lot about old British engines and SU carburetors in all this and I really enjoyed myself. 
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