I went for my weekly cruise past the lake,Starbucks then home.
After 4 or so miles the engine began to stumble at any acceleration.
around 1500 rpm's or so.
I ckecked all plugs gaps .Changed the fuel filter.Checked the dual points.Check the gas filters going into the Holley carb.

A few weeks ago it only did this when I kicked it to open the secondaries.
I have a accel dual point distributor. No vac adv. installed on distributor.

Its a 350 LT1

Any suggestions?

Mark

 

I would address the basics first. Check that the accelerator pump(s) produce a good squirt of fuel when the throttle is opened, check initial advance and centrifugal advance to be certain everything is normal and no changes or sticking. Plugs could also be fouled. How did they look when you regapped? Maybe just put in a new set and see if things improve. They could be fouled/glazed.

If you have a timing light that has the inductance pickup/trigger, you could also move it to each cylinder to make certain each plug is getting good spark and the wires are functioning properly.

Next steps will call for more drastic actions.

Larry

 

The bad news about your problem is that there may be lots of things that can cause bogging under loading (accelerleration)

Spark:
Coil
points
condensor
cap, rotor, wires, plugs
Ignition resistor
timming
Bad connections

Fuel:
carb,(power vavle, float adj, warn out jets etc,)
fuel pump, filters,
bad gas
Other:
Head gasket starting to leak ( not allowing gas into cylinder) Try IR heat gun for cooler
or hotter cylinder then others, pull 1 plug at a time and watch RPM drop
Compression
valve lash

 

my '64 used to do that all the time until it got warm, but when I went to the side exhaust and took out that exhaust valve that "helped the motor warm up" it runs great every time.

 

How long does your stumble last? Does it backfire out the exhaust? If more than a momentary issue, I suspect the condenser. If only while moving the gas pedal, check accelerator pump.

Use a dwell meter or electric tach to check primary side of ignition. Any failure will show up as erratic tach operation. Also,try another coil wire.

 

As already stated, a lot to review. One simple check is to verify if you have fuel. Suggest removing Holley bowl sight plugs to make sure there is fuel in the rascal. Could be a bad fuel pump????....

 

Sounds just like mine last year. I took on the simplest/cheapest first...replaced the condensor and bingo, it was fixed.

 

I checked all the plug wires with a ohm meter.All are reading between 12 and 16 ohms.
I will go buy a condensor.Im going to borrow a Buddies timing light to check the timing next.

Plugs wires

fuel pump

I will do one step at a time

Thx,Mark

 

I have a dwell meter, vacumn gauge, and timing light. If you need to borrow any of them.

Also, check the carb. and make sure its not loading up. Could be as simple as a bit of trash in it.

 

IMO when anything is off tune wise and the reason is not known always eliminate all things regarding the electrical and timing end of things before moving on to the carburetor. Then being as your stumble is not until 1500 I would not spend much time looking for a vacuum leak..... if it was at "just off idle" that would be another story

Then if the linkage adjustments such as accelerator pump and secondary openings are right with the carb then it is time to go to the rich / lean side of things.

Something lean will cause a stumble and there are different reasons that a carb can be either temporally or permanently lean. Torn gaskets or wrong gaskets can cause lean situations..... easier to get a wrong gasket back in than one might think it is. Diaphragm in the accelerator pump could be bad but if you already checked to make sure you are getting fuel through the discharge nozzles at the slightest linkage movement and the fuel stream is good you are ok there.

Any smell of fuel?...... easy for the bowl screws to leak or an old rubber line to deteriorate.

Make sure your rich lean screws are set right and they should all be turned the same amount and just down to the point where you do not get smoke when you give the rpm level a quick hit.

With all the advice given to you in the preceding posts and the couple of checks I mentioned I suspect your problem will be solved

Good luck

Doug

 

I got lucky. I went down to the local Auto Parts.Paid 1.99 for a condenser andnow it is woking fine. Thanks for all the help .

Now it appears that the secondaires are not opening up on my Holley double pump.Guess I need to find another Mustang !!!

Mark

 

I figured your problem would be the condenser.

To test your vacuum operated secondaries, with the engine shut off, hold the throttle wide open and blow compressed air down the passenger side primary bore. This simulates wide open throttle. If working, the secondaries will open almost immediately. If they don't, make sure they are not stuck. If they move freely, you need a new diaphram. Rich

 

Double-pumpers have mechanical secondaries; do you have a large vacuum diaphragm housing on the passenger side of the carb?

 

DUH, I missed that double pumper part...never mind.