CarbHelp

I'm flummoxed. I do a lot of carbs, this set has me puzzeled. These carbs are original ford 406, 3 X 2, holley type 350cfm w/side hung floats. My customer has been having nightmares with them and brought the center to me for rebuild - this was a month ago. He called yesterday and said he still had problems so i went out to have a looksee. The center carb and the carb nearest the firewall had float levels out of whack and fuel coming up thru the vent tube. I took the rearmost carb off and looked at the float. They had adjusted the needle & seat all the down tight and i was puzzeled why it had fuel at all. I decided it best to take all 3 carbs back to the shop. I rebuilt all 3 carbs, pressure tested the floats to 8lbs and all was ok. Put them back on the car this afternoon, turned the fuel pump on (holley red, no regulator nor pres gage) the rearmost & middle carb again sent fuel thru the vent. I took both carbs back off and checked the floats thinking something happened in the traveling. All looked normal. I put them back on, retested and adjusted the rearmost flao down and it is now ok. I did the same with the center carb and it was ok. We started the engine and the center carb started dumping fuel thru the vent again. I replaced the needle and seat thinking trash, retested it ok. Started the engine and it starts dumping fuel out the vent. The front and rear carbs are ok, just this center carb. When testing i let the pump run for an extended period. I also replaced the flaot in the center carb, they were br*** and i thought perhaps there wasn't enough fuel volume to close the needle and seat proper so i replaced the br*** with nytroprofyl (the black plastic type, not the white to yellowish type).
In summary, 3 carbs all see same fuel pressure via common fuel log. The center carb has had float, needle & seat replaced; tests ok up to 8psi on a flow bench but cannot shut fuel off when engine is running. All three carbs ***embled & adjusted by the same hand, all parts/pieces & rebuild procedure consistant with all three carbs. It would have been a good idea to exchange the entire float bowl ***embly, just swap it with another carb - but that didn't occur to me until just now. I can't exchange carbs as the center one has the choke. Linkage is not progressive, all 3 carbs in giddyup mode. Ford intake with common plenum.
I have the center carb back here in the shop and will give it an autopsey when i finish this. Any thoughts what is going on or what to test? Thanks, oj

 

Pump on car making too much pressure ie more than the 8psi on your test bench? Good fuel filter after pump? Any signs of dirt/**** when you pull the bowls?

 

I just connected carb to test bench and ran it up to 9psi, it is fine.
JohnEvans, it has a fram cannister type filter located high on the fenderwell so you don't have to drain tank to checl it. It is clean. When i took the carbs apart the front and rear carbs' metering blocks had a reddish clay-like deposit on the floor, i ran them thru the 'cooker' and then a chemicle bath that i recently added and they are absolutely spotless. I had gone thru the center carb last month and it was clean.
Is there any way you guys know of that the engine can pressurize the carb? I mean, it is vented to the atmosphere and all but what else can force fuel thru only one of three carbs when the engine is running?
Throw up any idea, stupid sounding or not - toss it out there. I am sure we can all learn something from this. Thanks, oj

 

Oj. I do not know of any way the engine can pressurize the carb.
The holley electric pumps have an internal spring and needle to allow excess pressure to reciraulate around the pump. It sounds like you are getting too much pressure to the carb. The excess pressure will just overpower the weakest link. I have had good luck running a return line from a tee near the firewall with a resriction in it back to the tank.. This helps pressure and any vapor lock problems while making life easier on the pump..

 

Yup, i know what you mean. I have converted many 'red' pumps to teh 'blue' pump by changing the byp*** spring and trash can bind that little poppet up and run up the pressure, but i have two other carbs in line with the center one and they are as good as can be. All three carbs get fuel from a common log that runs along the carbs and has a short 3/8 hose going to each of the carbs. Good thought Dale. Can you dig a little deeper? Again, with the pump running all three carbs are happy, soon after you start the engine fuel comes thru the vent of just the center carb.
I gotta go home and hook up a bush-hog to the big tractor, i'm gonna puzzle this tonight and won't be until tomorrow i can answer questions or make observations. Later, oj

 

are all the machined surfaces on the carb/carbs flat
>>>draw file them to see<<<
quick fix use two quailty gaskets on metering blocks
sounds like your customers are heavy handed they may have warped the body by over tighting?

trouble shoot pinch line shut to carb..........

 

have you put a psi gauge on the car? curious as to what actual pressure,maybe pumps gone wild? just asking i figure you already checked

 

You'll have to check the fuel pressure on the car. I've had a lot of fuel pumps going crazy lately due to the ethanol in the gas. We had a dodge 318 manual pump put out 20 lbs. of pressure making the carb flood.

 

Bttt

Any ideas fellas? This morning i added a second gage to confirm pressure test and i have run pressure to 9psi, needle & seat hold.

 

Which way are the carbs mounted?

 

Ford backwards. The bowls are rearward facing.