This very intermittent problem is driving me bonkers!

Firstly I'll describe the problem, then the supposed cures, all tried!

The car proceeds normally, then without warning looses power, I can feel the throttle has nothing, one can press it right to the floor, the engine sounds like it's trying, but the speed drops from say 30MPH to about 10, then applying the manual choke, helps, but just a smidgen, up to say 15MPH, but the engine is labouring, never actually stops, but thts probably next!

Then all of a sudden normal again.

I changed the coil, and all the leads. It drove perfect, all evening, I thought, at last.

Next day 200 yards out and the same again!
This started last year, firstly the fuel pump, then all the plugs, keep in mind the carburetors were rebuilt about a year or so.
Glass fuel bowel full, no sigh of contaminates.
I can hear the pump. but to me I feel fuel problem?
any new thoughts are welcome.

 

At this point it sounds like it's starved for fuel.
Make sure your ignition is OK _ the usual aside from what you've done and didn't mention.
Condenser _ all the internals of the distributor are OK, nothing lose or causing intermittent shorts ??? If it's a bad condenser the points will be burned.
The coil is getting 12 volts all the time, you may want to hook it directly to the battery and bypass the ignition switch _ just to rule that out.
You said you replaced all the leads _ what about the one from the coil to the distributor ?

Once that's done, even though the carbs have been rebuilt, I would check the float needle valves to make sure they're not sticking.
Check the floats them selves to make sure they're not sticking and closing the needle valves off.
When this happens, the floats stay in the upper most position closing the valve off even though there is no fuel in the float chambers.

I am going to assume that if it's starved for fuel that the pump is not at fault and the glass bowl is full of fuel when the problem happens. I know it's difficult to run out side the car and observe the glass filter bowl when the problem occurs.

This probably isn't it, but the main pistons in the carburetor move freely up and down _ not sticking ? Is there oil in the damper tubes _ this helps to lubricate the pistons.

 

I had forgotten to mention it has Lumination.

 

Temporarily put your points back in and see if the problem doesn't go away.
I've had a number of Pertronix units over the years in different cars and they all gave troubles.
One failed in my TR7, the car ran fine then suddenly one morning it was only running on three cylinders, then 2 then one _ then it just died.
It had good spark, but would not start.

The Luminition unit in my Bentley just stopped working and left me stranded.

I'll never go back to these after market ignitions again.
Points have been used for decades, they're not that unreliable, they just require a bit of yearly maintenance _ and I can live with that.

I'm betting your unit is about to fail completely.

 

ive had this happen on carborated cars before, last time it did, I changed the in line filter with no results, spend a lot of money on solutions that didnt work, then while taking the carb off to rebuild it, discovered a secondary filter on the carb itself. changed that out and it ran like a dream.

same symptoms as you describe, runs fine then dies suddenly, come back after a few minutes and it fires up and drives fine again for a short distance.

 

Hello Mr. Blue, Just discovered fuel pump leak, very slight, but who knows, I've fixed it but haven't had time to take it for a good run. (here's hopping!)

This car has two carbs, so if one filter were clogged I wonder if it would produce these
problems?

Do the carburetors have to come off the see this filter?

 

The SU's have a filter when you remove the banjo bolt where the fuel enters the float bowl.
That's the only other filter that I'm aware of within the carb itself.


So no, to access this filter, the carburetor's do not have to be removed.