Car falling on its face at 55-60 mph

Hienkel429

Hello all, 

I am open to all ideas.   I just finished restoring the car last week and it is now legal!  (EIGHT years in the making)  Car is a 1951 Hornet sedan with a single range hydramatic and original rear end. The engine is a 55 308 crate engine from JC Whitney with factory Twin H.  Car is running with a new fuel system with a carter rotary vane pump (p4070) and a diaphram fuel pump delete.)  The carbs are correct and rebuilt with kits from Daytona.  I set the timing by vacuum.  Car starts the moment you touch the button and is perfect around town.  Getting on the highway it pulls very nicely on the on ramp up until I am about to merge around 55-60 mph.  Then it loses power, seems to be missing or flubbering (is that even a word) and can't get out of its own way.  Different throttle positions don't help.  It will maintain the speed but it is not a comfortable ride.  

I am at a loss and am open to suggestions.  Thanks all. 👍

Ray

50C8DAN

There was a similar issue a few weeks back and it turned out the fuel filter was clogged (second filter that the owner did not know was there).  Not sure what to say about electric pump issues?  Was the dist. rebuilt and new coil?  Pertronix or points?

One other issue that you may want to check.  Did you clean the fuel tank and reseal it or just dump out and refill with new fuel?  If you are using the old tank it could have lots of rust and junk.  Not trying to be a smartass, but throwing out a potential issue.

Hienkel429

Thanks Dan, 

Running two filters. One before pump and a see through before the carbs.  Filter has fuel running through it.  Distributer was NOS with engine.  New points with correct gap, first new condenser I put in was bad out of box, new good condenser.  New cap and rotor as well.  New Pertronix 3 ohm Flamethrower coil with a new set of points. 

Maybe something something mechanical advance?  That is something I have not messed with.

Ray

50C8DAN

Check the prepump filter that is what the other poster found was his problem.  Is that filter see-through or metal.

lostmind

It doesn't matter if it's see through, could be bad. I would bypass both filters, one at a time and road test.  Side of the road experience .

Hienkel429

Just tested fuel pressure after replacing the rear. I have 7 psi at front carb, even with both filters.   Also cut open old rear filter, clean as a whistle. 

Geoff

Check the coil voltage.

Hienkel429

Both windings are good. 👍

ratlee2

Isn't 7  pounds too high.  I thought I remember someone saying fuel presseure was arounds 3 1/2 psi.

Hienkel429

Checked the rear-end.  Seems I have a 3:55. 🤷‍♂️

Hienkel429

The book says 3.5 to 4.5 psi.  

rusty_apache

Sometimes capacitor manufacturers make several bad batches. 

Find one from a completely different manufacturer if possible.  Just another wild guess, is the condenser matched to your flame thrower? 

D7fever

Check your points, last time I put in points, I put the spring on the wrong side of the hold down.  Did the same as yours, checked, and discovered, put in the right way and it runs good. Could also be weak spring on the points.  Do you have a hose between your fuel pump and the tank? If so it could be collapsing at higher suction.

Geoff

The windings may fine, but if the input voltage is low, then you will run out of puff at high speeds.  You must have full battery voltage at the coil.   

Hienkel429

Geoff voltage is good.  

Could it be the vacuum advance? I put a tac on it and it does its whole stumble /sounds like a popcorn maker around 2000-2100 rpms.  And the true speed this happens is right around 49-50 mph.  I evidently have the incorrect speedo gear.  

Thanks all!

Geoff

Vacuum advance only works at high vacuum, i.e. when cruising or going downhill, so no, it will not affect the top speed if not working.  Sounds like fuel starvation to me.  

Hienkel429

Geoff...

You are 1000000% correct.  Pulled the plugs and from looking at the ends this thing is LEAN!  Twin-h with wa1s and code 2113s tags.  
From reading I've been told to check float level and metering rods. On meter rod tab bend down to richen and upwards to lean.  Also to raise the float which means a shorter distance between the top of the float and the inside of the top cover when inverted.   
I know there is more that can be done but I am very limited in time and equipment after a valve spring cracked in two on a long trip. 

I am learning.  Thanks all!