I just put a 800 CFM quad on my 455 from a 76 caddy (17056230). I was running a holley and wanted to build a carb of my own. It idles well for a bit then starts to stack up and eventually leaks fuel out of the accelerator pump shaft. I set the float to 3/8's. I know Cliff's book recommends 1/4 inch and I have even read about .420 settings for "late" carbs. I am running a "Stage one" pump and I put a regulator on it set to 5.5 lbs to see what happens and it stopped the issue but created a fuel starvation problem at WOT. Could my issue be the float setting or is the pump too much? I notice the float setting for a 70 stage one stock carb is 5/16 or .3125 inch oppsed to the regular 455 set at 3/8's. Should I try this setting? Will it make a difference? Thanks for your help.
What is the size of your needle/seat? I know they come in sizes ranging from 0.110"(factory) to 0.150"(huge). The size you choose will affect how well your float will act against the incoming fuel flow from the pump. If it looks like the fuel flow into the carb is overpowering the float action on the needle/seat, then I'd decrease the size a bit so that the float can better regulate the incoming fuel. I put the needle/seat size on my carbs at 0.125" since I don't race, and keep the float level at 9/32", just a hair lower than 1/4". No issues on my carbs with fuel flooding.
Thanks for the reply. I have to take out the seat to see what size, but I used the original, I have the one that came with the rebuild kit (from quadrajet parts) and I used the original because it was a larger orifice. I was thinking of changing it out and then adjusting the float down a bit closer to if not the stock for that carb ( 13/32 or .40). Am I thinking wrong or is that seem like the way to go? My buddy here seems to think that the issue is the Stage 1 pump, but that pump is a type stock so it should work? To add also my return on the pump is hooked up if that makes a difference.
The float level is critical for keeping the bowl filled to the correct level. Lowering it reduces the amount of travel it can go, and restricts the height at which the needle can lift out of the seat. The fuel pressure is a factor, but you indicated that you tried adjusting the regulator, and it ended up causing a fuel starvation issue at WOT. You don't want to limit the height of the float to where only a tiny amount of fuel flows into the bowl, even when the float is at its lowest point. 13/32" seems really low for a carb feeding a 455, especially for one which isn't burdened by emissions hardware. I'd take out the needle/seat, and compare it with the one in the rebuild kit. If the one you're using is huge, then I'd knock it down a size. If it is tiny, then bump it up a size. The volume of fuel which flows through the seat has to counter the action of the float and needle correctly, and if you're getting flooding at idle and starvation at WOT, something in that relationship is out of whack. The needle/seat modification is simple and painless, so I'd give that a try. Did you inspect the needle on the original needle/seat? It could be worn (groove worn into it), and that will also affect how well it regulates the fuel flow. If the kit from Gessler's was for a Stage 1 carb, I'd use what was in that kit. I think that one is 0.135".
Sorry I have created some confusion. The carb is a 76 caddy carb from a 500 engine, I set the float at 3/8's, the stock setting is 13/32, and the stock setting for a 70 stage one is 5/16. I looked it up for comparision. My fuel starvation only came with the adjustable regulator. Without it it begins to have issues idling after a few minutes, but driving around is great. No issues except idle. I will be taking out the seat which is the original one and try the one with the kit. The original was larger and I thought bigger was better. Should I try adjusting float with the change in seat? Thanks.... ---------- Post added at 02:01 PM ---------- Previous post was at 02:00 PM ---------- By the way I also used the small brass float instead of the plastic.
Skip brass to phenolic float and check needle-seat assy if it can hold vacum. I have found lots of seats can't hold it, if they can't they won't hold up fuel preassure and will flood at idle. What i do than is drop checkball in and punch it. I used acc pump ball and it worked great. Peace Kacper.
Thanks for the suggestion, will do. I hope to have this DONE tomorrow so I can finally enjoy. Ill post results, again thanks for the help.
Many of the later carburetors will have "low" factory settings. This was done in many cases because they used higher pressure pumps and return systems to circulate and cool the fuel. We use and recommend a 1/4" float setting for the later carburetors for most applications. They are fine to at least 8psi with a .135" seat, many racers run 9-10 psi with zero issues anyplace. I've done extensive street and strip testing with fuel inlet seat diameters, float height, float size (there are two different sizes for the later carbs) and fuel pressure. I use a 1977 Pontiac carb on my own engine, small float, .135" seat, 1/4" float height, 7.5 psi fuel pressure, zero issues anyplace under any conditions. I've went all over the place with seat diameter, fuel pressure and float level. I wouldn't use or recommend low fuel pressure on the later carbs, or float lower than 9/32", and the .135" seat is fine for big power levels if you have a good fuel delivery system feeding it.......Cliff
The brass float that I have is smaller than the stock float but it supposed to be the replacement. I used the brass because of the smaller size and the float was original from a original, never torn down, carb. I will mic out the seat and the replacement seat and then use the accel check ball to ensure a good fit. Thanks for all your advice.
I took the carb apart and the seat was not that great looking inside, and I also found a tiny sliver of metal on the tip of the seat, looks like a piece of a wire wheel. I used the seat that came with the rebuild kit. It was (if I remember) .127ish.. I put the float to 1/4 inch and used an old check ball in the seat and made a big difference. I vaccum checked it and it was sealed tight. I now have a harmonic balancer leak, so have to do that first. Thanks for all the advice.
The factory used nitropyl floats for all models, and for a reason. They are lighter and more bouyant than brass, and brass floats can develope leaks at the soldered seams, especially with this new fuel, which seems to find it's way thru everything......Cliff
I have the plastic float, but the brass is in right now. I will be trying to put it on tomorrow and see how it runs. That will be my next thing I look at.
Got it to work. Set 1/4 float level, and threw away the original seat and used the one in the kit. I punch it with an old check ball, then drilled the idle mixture holes to .090. It is great now, she idles forever and never has an issue, also the idle mixture holes cured the slight nozzle drip. Thanks everyone.
