scottyp99

Hi, everybody!
I have a question about Holley carbs, and since it's the carb in my '80 'vette, I figured I would make use of the wealth of knowledge on this forum. I have a 1850 Holley carb (standard 600 cfm Holley four barrel, vacuum secondary, 4160 type carb) It has a secondary metering plate instead of a secondary metering block. I would like to convert it to a secondary metering block, in order to be able to adjust secondary enrichment using jet changes. The conversion kit from Holley,

http://www.summitracing.com/parts/hly-34-6/overview/

contains basically a secondary metering block, a longer fuel transfer tube, and some gaskets. Could I save a few bucks by just getting the longer fuel transfer tube,

http://www.summitracing.com/parts/hly-26-114/overview/

and using a primary metering block from another parts carb, with the idle mixture screws screwed all the way in? Or does the secondary metering block need to be a dedicated secondary metering block? Feel free to get fairly technical with your answer, I know the basics fairly well, just not sure what the differences are between primary and secondary metering blocks, I've never dealt with them at all. Thanks,

Scott

glackore

I dont have a technical answer, BUT if it was me I'd just buy the kit and be done with it. The corner cutting method usually results in a carb that doesn't function at 100% thus leaving everyone who trys to tune it scratching their head.

keithinspace

I'd agree with Mr. Glackore. It's tough enough to "get it right" when dealing with any carb. And have you seen how many little holes and pathways there are in one of those widgets?

Even if they WERE the same, I'd probably just get the 'right' part with all the new gaskets and stuff and take the $40 on the chin.

Of course, if I was being TOTALLY honest, when dealing with my carb the last time, I just bypassed the entire question and bought a new 650 Double Pump QuickFuel. That has the metering blocks on the secondaries...problem solved!

gerry72

You can use a secondary metering block from another Holley, but the emulsion circuit will not likely be good enough to not cause you any issues.

A simpler solution is the metering plate kit from Quick Fuel with just replaces the Holley plate with a plate for jets and includes a new float to clear the plate.

What indicators are you using to suggest the secondary is lean? Most times, you just end up with a block or plate that happens to correlate to the fuel flow capacity of the original Holley plate. They try to make these carbs as simple and out-of-the-box useful as they can.

scottyp99

After thinking about it for awhile, I have realized that the primary metering block cannot be easily substituted for the secondary metering block on vacuum secondary carbs. The back of the carb body is flat, no room for a power valve plug, so the metering block would need to be modified by blocking off the pvcr circuit. I think you guys are right, best just to get the kit and be done with it. Thanks for the input, though. Have a good one!

Scott

keithinspace

Good call. Would have been money and time burned chasing after a $30 savings.

johnt365

There are other options also. Adding a metering block will make the carb longer and possibly cause it to interfere with the vacuum port on the back of the manifold. Regardless, you could also...

1. look at something like Quick fuel 34-2 which is a plate that accepts jets.

Or

2. Take your metering plate out, plug the holes on the bottom and then drill and tap it for jets. I just went and bought the tap for about $3.

Are you using an A/f gauge ?

johnt365

Scotty,
Here is a link to a thread that helped me. http://www.hotrodders.com/forum/seco...lp-150145.html

I have not made the conversion because my A/F ratio turned out to be around 12.5-13:1 at WOT. My motor is a 350 with a similar carb as you.

Have you seen this conversion chart? www.holley.com/data/Catalogs/Holley/90.pdf

My carb has the metering plate 134-39 which shows to be equal to a 69 jet. I basically have 69 jets in front and back.

scottyp99

I went out and bought a tap and modified my metering plate according to the first link. It has turned out to be a buncha BS. The jets interfere with the float. It would probably work well on a dual feed Holley, like a 3310, with the center hung floats, you can buy a float with notches cut into it for jet extensions. I have not been able to find a notched side hung float, so I have just decided to go with a new metering block. Sometimes, this is what happens when you try to save a few bucks, but at least I have learned something from the experience.
The engine in question is a relatively stock L48, (block-hugger headers, 2 1/2" dual exhaust, Performer intake) but I am planning a cam and head upgrade in the near future, and I am trying to look ahead at the tuning process after the switch. The vacuum port should clear just fine, I have a 1", 4-hole, phenolic carb spacer under the carb.
Just ordered the kit from Summit, so the point is moot, now! Still, thanks for everybody's input. See ya!

Scott

johnt365

Cool.

I was surprised at the a/f ratio readings i got from the factory metering plate considering all the mods I had made. Holley had the stiff black sec spring in and I swapped to the lightest.


Happy tuning

7t9l82

i wouldn't do anything without changing to center hung bowls, and for that money you'd be better off to get a new carb. unless you can find a swap meet carb you can pirate what you need. nice thing about holleys