online170

Ok, so i bought this carb used last summer, and drove with it for a year. It was really good to me, except i couldnt use the secondaries because of the #70 square jetting. It ran pig rich. Its been rejetted now, but recently had some problems developed, so im just gonna thow some new parts in there and be on my way. Need some help identifying parts, and picking parts.

Holley 4150 750 Cfm DP.
Model # 4779-6

Primary:
Jets: 70
PV: 45-37 (see pix)
Float #: 2 16R-587A - center hung.

Secondary:
Jets: 79
PV: 45-37
Float # : 2 16R-587A - center hung

Pink Accelerator pump cam.

Im rebuilding the carb, because it started spewing gas like a fountain out the top, plus i dont think this is normal. What would cause this to happen? (only the primary seems to be full, the secondary float seems empty. But i am going to replace both.

Primary:



Secondary:


While im in there, im going to replace the PVs (just incase) and regasket it all. I dont know what power valves these, are, can some one help? I read the digits 4,5,3,7 all the way around. I dont know if its a 45, 53, 37, or 74? Probably a 4.5 since they dont make other sizes, but thought id confirm.







Also, while driving the lowest i can get my vacuum reading to go, while driving normally under load in high gear is 9.5 in-Hg. Occasionally it will dip below that, at cold start up, but not after its warm. There was a bog on part throttle to WOT when i first had the carb on my car, but the bog went away after i rejetted the secondaries. Should i replace the PV with the same number PV or throw in an 8.5?

When i bought the carb, i was told it was being used for drag racing on a 383 motor. It was definately square jetted, and i noticed this today. Im not sure what is capped off here, and how it would affect the carb. I wasnt able to figure it out using the exploded view sticky. What does this mean? (See pic)

Primary: Looks like a rough "cap" like it was welded on after the carb was produced.


Secondary: A much smoother looking cap, almost looks factory.


Heres a view of the "front" of the metering block. The cap seems to be blocking that long straight diagonal passage. What does that do?


So in a nutshell:

1) What size PV do i have currently?
2) What is that hole thats capped off?
3) What size PV SHOULD i get considering the behaviour i pointed out?
4) What would cause the float to sink?

Thanks for any help.

greezemonkey

iTrader: (14)

I`ll try to help, the power valves you have are 4.5 inch, I would stay with that size for a street car, unless you like to add 8-10 jet sizes on a part throttle cruise.

I`m not 100% sure on the passage that is capped, possibly the acceelrator pump passage? I`d need to pull a book or see the other side of the block and matching main body side. don`t worry too much on how the plugs look as long as they are not leaking anything.

As far as the float sinking there`s only one reason, it starts leaking and takes on gas, you can usually hear the fuel inside it if you shake it, to test it drop it in a small container of fuel and be sure to pin it down under the fuel, bubbles or the float filling will tell you. More than likely the needle and seat have failed to seal and fuel keeps entering the bowl until it overfills, there is also a external float adjustment and sight glasses or plugs to properly set these levels.

Glad to see someone tackling the problems instead of bad mouthing the carb or maker

online170

Why would i need to add 8-10 jet sizes when stepping up to a higher number power valve? I thought that only happens if you block off the power valve circuit all together.....

It wont be sending any more fuel in, it will just be sending it in sooner. From the holley tuning sticky, they recommended to go 1 PV size numerically smaller than the lowest vacuum the engine will produce under high gear, load conditions. That was my only reasoning. The worse case scenario would be i would just develop a bog right? I dunno, maybe i shouldnt mess with it, if its good as it is.

Secondly, i know the float has sunk. Primary definately has fuel in it. But i was asking what caused it, as to be able to prevent it in the future. If its just because of age, then thats ok, its just a replacement item. But should i look for something that could have caused it?

Also, i dont really care about the quality of the caps, i just care if they are blocking something Holley intended to be open from factory... Maybe its capping something thats popular to do in a drag racing application, but not such a good idea for street? I dont know.

Heres some pix of the other side. The passage leads to an orifice directly above the power valve.

five7kid

iTrader: (14)

The cap is there to block off the end of the passage. Since you can't drill around corners, you have to drill through places you don't want to be open in operation. So, after you're done drilling, you cap off the hole you don't want to be open during operation. If that cap wasn't there, it would leak where you don't want it to leak (in your photo, it's the accelerator pump circuit).

4.5 PV is pretty low for a street car. 6.5 is typically closer; since this was on a race engine, 4.5 makes sense. You never square jet unless the primary and secondary PV is operating the same - i.e., if you have a primary PV and secondary PV, or both primary and secondary PV are blocked off, jet square. If you don't have a PV, either primary or secondary, you need to jet up 6-8 jet sizes to make up for the lack of PV flow (Proform recommends 12 jet size difference with their main body when you have primary PV and no secondary PV). So, if 70 primary gives you good cruise characteristics, 79 secondary is just about right, and you maybe could go up another two sizes on the secondary.

The lower the PV number, the lower the manifold vacuum has to be before the PV opens. So, if you have a large PV number, like 11.5, it will be more likely to open under cruise conditions than a 4.5 would be. If you have a dead spot off of idle, you need a larger number PV.

The Holley tuning sticky is a lot better way to go about picking a PV than using vacuum. Note that the PV is the last thing you tune.

If you are sure your float has fuel in it, that means it has a leak and needs to be replaced. If you know for a fact that it has never been abused in its life, that means it simply had a slight defect that finally caused its demise.

online170

What do you mean by abused?

It was used quite a bit in my possesion, and it sat for a couple of months dry. Mayb it caused a crack. In any case, ill just replace it and take it as a defect. It worked great for me for about a year before i started noticing issues with the float.

I have a PV on both primary and secondary at the moment, and both are 4.5 in-Hg. The lowest my vacuum will go under normal load in high gear is 9.5 in-Hg. As per the sticky, ill go 1 size lower than that (8.5), and throw a 6.5 in the secondary size.

Also i wont mess with the caps then. Did Holley have caps from the factory, or is that something that would have been done later on?

I also need help finding the float. I thought 16R-587A was the PN, but i cant find it on holley's site, or summit... SHould i just go by the description? ie: center hung, nitrophyl, etc...