Pontiac Owners Club UK

4 barrel Holley carb was put on my 400 when engine was put in last year. I took the air filter off today to measure it (another story) and noticed that the rear 2 'secondary' butterflies don't open at WOT on the front 2. Looking at it there's a small rod that connects 2nd butterflies to the primaries that would perhaps need to be bent to hook around the slotted V shape plate on the end of the shaft that turns them? At the moment nothing is attached in a way that would turn that, it just slides in the slot.

I wonder if it may have been set it like that to stop any hard accelerating as I'm running it in? Effectively running as a 2 barrel?

When I press the secondaries lever (engine off) with my finger, they'll open up fine but unlike the primaries there doesn't appear to be any fuel going in there? Or is it just that the little nozzles that are only in the primaries actually feed the rear ones somehow when the air gets sucked through? (Venturi?)

I just want to make sure it's all as it should be (no point in having a big carb only to use half of it eh!)
(As you might guess, the last carburettor I looked at was a single butterfly on an 1600 capri!)

You won't usually ever see the secondary butterfly valves opening when revving at a standstill.

They only open under hard WOT driving when the engine is under load. I'm assuming here it's similar to a quadrajet - no fuel will be delivered by the secondaries unless there is vacuum to pull the fuel through the jets and so you won't see that either.

To put your mind at ease you could speak to Robin.

That makes sense to me with the fueling. I didn't have the engine running while looking but assumed pressing the throttle linkage to WOT would have a physical connection that opens the secondaries at that point? Going to Robin for service and MOT next week so will pick his brains then. I just like to understand these things.

the secondary barrels are vac. operated (bit of a miss-name as they open when there is no vac.) so at WOT and higher revs they open

ah, so if I've got it right, there's no need for a physical connection cos if the engine is working hard when at WOT it'll create enough suction to open the butterflies?

Well on a quadrajet the secondaries are mechanically operated, the secondary throttle valves are below the air valves you can see at the top of the carb. They open with the linkage but if no vac present the air valves above stay closed. Not sure if a Holley is the same or similar.

First pic shows the whole thing.
Second pic shows WOT - the V shape part with the slot in is to the right and doesn't move at this point.
3rd pic shows it with secondary barrels open with finger pressed on it.

What model carb is it?

No idea. I just know its a holley 4 barrel. Lots of tiny numbers on front but no easy id.

don't recognise it from photo's

Well I'm no Holley expert but I've just read a tech manual for one of their 4 barrel carbs and they are vacuum operated secondaries and will not open visibly. There is a vacuum diaphragm which controls them and it's calibrated to open only when the demand for air and fuel is high enough.

I think yours will be ok you just won't see them open on the driveway. My quadrajet only opens it's secondary air valves if I hold WOT for more than a few seconds and it's risking engine damage doing that.

Get Robin to check it over he will know!

Yeah I'll leave it to the experts - obviously more to these things than I thought. BTW, I think it looks pretty much the same as this one:

http://www.ebay.co.uk/itm/Holley-0-1850 ... 0762526981

Although with older looking Holley logos on front and rear.

yeah looks like a 1850 i have one fitted on mine

mine has a holley the old owner has told me it suffers with hot starting if its left a while and tonight i see it for my self as he delivered it and i tried to start it after he left.

i read its the fuel boiling any one else had this and how do you cure it. the spacer kit ? or fit standard carb ? i have not even looked at it yet to be fair as it was dark when it got here.

a decent high volume fuel pump should help, insulator may help. check choke adjustment (is it fuel starvation or flooding?)

no choke. i think i need to look at it in daylight flooding i think. due to heat holley carb

or get a fuel injected car

my 78 had a Rochester carb. and that used to do the same thing, if it was hot then left for 15 minutes it wouldn't start sometimes
I found out the choke was coming on and flooding it. found the answer was to wedge the choke open with a screwdriver then it started ok. was going to fit a cable but sold the car before getting round to it

so the best way to start is foot on the floor and crank ? i guess i will learn the technique eventually.

depends if its flooded or evaporated
trial and error really

fired up lovely from cold couple of pumps and she was off. its very loud

flooded would be foot on the floor
other wise its pumping the pedal i guess

if one dose not work, try the other

any one used one of these to help with fuel boiling after a hot run.
http://www.ebay.com/itm/1-2-phenolic-op ... 0877617289

i can only go half inch max or lose the shaker and i dont want to do that.

i suffered with hot starting today after the meet on a 10 minute or so stop after the run i believe this could help you can see the fuel boiling on the fuel filter its a holley anyone have trouble with a rochester ?

thirdgen wrote:any one used one of these to help with fuel boiling after a hot run.
http://www.ebay.com/itm/1-2-phenolic-op ... 0877617289

i can only go half inch max or lose the shaker and i dont want to do that.

i suffered with hot starting today after the meet on a 10 minute or so stop after the run i believe this could help you can see the fuel boiling on the fuel filter its a holley anyone have trouble with a rochester ?

Me personally....no.

If the fuel is boiling it could be due to a number of things. Is the engine bay too hot due to headers/over advanced ignition timing? And is the fuel return line present and not blocked or crushed?

i dont think there is a return line its a holley mechanical fuel pump system. no headers.

i have read other forums about 400 pontiacs having trouble with holleys thats why they fit the spacer as a insulator to help maybe its just holleys that suffer ? i have ordered a half inch one to try

its only with s short stop after a run it does it. the previous owner had told me it was a issue also. i have a inline fuel filter you can see it boiling in on top of the inlet