Just posted another video of it acting up. Got a close up if the motor too

 

No PCV on the truck ?

 

Trust me, I understand it. Excessive output pressure of even a few psi will require setting the float extremely low in the bowl. This is a "tell". The only thing holding back the fuel is a tiny chunk of Viton.

Take a look at a carburetor in action, it will become immediately apparent that they don't really operate like a toilet tank as popularly supposed i.e. draining all the way down and then filling back up.

The idea with a carburetor, is that the fuel level in the bowl is constant at all times, under all conditions, from idle to wide open throttle, and everything in between. This is the reason for setting the "wet height" to specification in the first place. There are slight variances normally in a given fuel pump ouptut pressure, volume, line size, filters, and float weights or bouyancy, materials (brass or plastic) etc. The siphoning action, column height pressure, and fuel atomization through the venturis and tiny orifice and high speed air bleeds and all that stuff is calibrated from the factory on a very specific amount of fuel in the bowl itself.

There is naturally going be some variance in the float height when adjusted on the engine to achieve the correct fuel height specification, but when the float needs to be cranked all the way up or all the way down out of the nominal settings, the fuel pump output is obviously flaky. In the case of excessive output it will accelerate the erosion of the Viton needle tip.

As far as I can tell that little guy is the ONLY thing keeping a carb from flooding over badly. If I'm wrong, that's fine too.

 

You're right, the float might be able to be raised or lowered at the extremes to compensate for a defective fuel pump either on the high side or the low side.

But I figure the engineers put those specifications in the book for a reason. Measuring the fuel pump output is as basic and simple as it gets, and only takes about 30 seconds.

Measure, don't guess!!

I don't really care who made the pump insofar as if it's defective, it needs to be replaced with a serviceable unit, that's all.

 

even if it’s a mechanical fuel pump?

 

what’s the easiest way to measure the output?

 

You are going to have to TEE into the output line and install a gauge.

If you are not flooding any need to worry though. When I was at FMCofC and we tested the impact of variations of mech fuel pump pressures as the stock pumps could vary 5 psi or more as there were concerns about the impact on emissions with the change in fuel level, It was determined that the impact was not worth worrying about and as long as it did not overpower float it had no real measurable impact on operation this is in part why the switch was made to Viton needle seats higher cost yes but more reliable fuel control with pump pressure variations. Since you have a sight glass you can see if your fuel level is correct. The specifications in the book are ideal but not written in stone

 

well im not spilling fuel out of the overflow, but i cant figure out why the motor is doing the stuttering and dying. Did u watch the video of it?

 

Yes I have watched the video and it looks likes an Idle air issue. You need to set that to rule it out before anything else. And the Idle seems way high the engine should idle at 750RPM unless you have a lumpy cam in it. Also, do you have a PCV on the truck ? As those carbs are calibrated for a PCV from the factory. not having the PCV will make for a rich Idel air.

 

Are you sure it is not a vacuum leak? Have you pulled the carb and visually inspected each port and cap? I say this because I was sure I didn’t have a vacuum leak. All ports plugged. But when I pulled the carb, one huge port had a rotted out cap. Looked OK from top side when carb was on, but it definitely was leaking. Also when the carb was off saw a jukey vacuum tree that had a port unplugged. Fixed all that and truck ran perfect.

That said, it sure seems like an ignition thing with that tach dropping to zero so fast and then back up. You would think if it was carb it would not go to zero as fast...

 

yah i made sure all the plugs weren’t dry rotted.

 

id be lucky to get it to idle at 925 because of the cam. An no i dont have a pcv. Also this idle drop occurs when you drive it too. Not just at idle.

 

So it cuts out when you are driving.....

 

yes and then it acts like its flooded

 

Would it be to much to ask you link the video's here. Can't find anything with the motor on Youtube