Sputters at high RPMs around 55 mph

[6t6mstang]

'66 200 I6, C4, autolite 1100 (newly rebuilt), new fuel tank, filter and pump, DUI dist upgrade with full 12v feed (has manifold vac & the carb ported vac from SCV is capped off), timing advanced slightly (peppy and no pinging), plugs gapped at .045 (all plugs burn color is good), tuned with vacuum gauge at 20 steady. It runs really well until i get above 55 mph and it sputters. I can let off and it smooths back out after a couple minutes just cruising around 45.

Could the advanced timing cause this? New fuel cap not vented properly? Not enough fuel in carb bowl which would need a float reset? Is the dist, being hooked up to manifold vac correct? Any ideas will surely be appreciated.

PS I am leaning toward a float level reset for more fuel in carb bowl

 

[wsa111]

Check fuel pump pressure & volume.
How many degrees initial advance are you running??
A lot of stock cam engines idle better with ported vacuum. You can modify your SCV carb to ported vacuum.
There are instructions in the tech section on this forum how to do this. Too much advance at idle could cause a flutter in the engine.

 

[chad]

"...SCV is capped off..."
and LOM dizzy is...?

https://fordsix.com/ci/Loadomatic.html

 

[bubba22349]

"Its a DUI hooked up to manifold vacuum".

 

[6t6mstang]

Fuel pressure is 6 psi. Factory manual calls for 4-6. Haven't check volume yet. Manual says 1 pint in 30 seconds.

 

[B RON CO]

Hi, it sounds like you are running out of fuel and it sounds like you suspect it.
Who rebuilt the carb?
Was the jet cleaned out really well, were all the passages sprayed clean, and are you sure the check balls are in the correct places. Good luck

 

[wsa111]

Either modify this SCV carb. to a ported vacuum unit. Another option is get a carb from an application that is not a SCV carb.
Get one with more flow. CZLN6 can recommend one.

 

[6t6mstang]

Just now made a couple of adjustments. Earlier today the car was surging which is in addition to my original problem.

Float was originally set at 1-3/32" which is specs for the brass float.
I set it at 1-1/32 to allow more fuel in, (float is set inverted), which caused flooding so
I set it up at 1-5/32 and idled great with shut down and re-started with a key bump.

I was looking at the power valve. At higher speeds, the engine vacuum drops which causes the power valve to open and allow more fuel to flow. The tension on the power valve is controlled by adding calibrated shims for more tension or subtracting shims for less tension. When I rebuilt it a few days ago, i made sure the power valve, spring, and shim was free and movable and I was spinning the shim in the process. It turns out the the power valve in my carb, which I never noticed, has one shim that is on a threaded power valve rod. Upon spinning it, I seemed to have caused too much tension on the spring not allowing the power valve to function properly.

I unscrewed it back down and then closed everything back up, took it for a test drive, and so far so good.

 

[wsa111]

Great news. Nothing worse that an engine that has flat spots & does not respond on acceleration.