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340 6 bbl metering plates ?2

Posted By: calrobb2000

340 6 bbl metering plates ?2 - 04/01/20 06:04 AM


hi

i need 2 outboard metering plates for the 340 end carbs .

someone has drilled the originals ????

where can i get them ?

thank you !
Posted By: Cab_Burge

Re: 340 6 bbl metering plates ?2 - 04/01/20 06:25 AM

Have you tried Holley yet? If not do that first, if they don't offer them still try Chicago Corvette in Chicago IL scope
I don't have their phone number anymore, sorry blush
Posted By: 62maxwgn

Re: 340 6 bbl metering plates ?2 - 04/01/20 12:04 PM

You need # 41 plates,Chicago Corvette,(708) 458-2500.They are now in Bend, OR.
Posted By: Cab_Burge

Re: 340 6 bbl metering plates ?2 - 04/01/20 07:25 PM

Originally Posted by 62maxwgn
You need # 41 plates,Chicago Corvette,(708) 458-2500.They are now in Bend, OR.


I learn something new today, Thanks up
Posted By: Cab_Burge

Re: 340 6 bbl metering plates ?2 - 04/01/20 07:33 PM

I have worked on several OEM stock 340 six packs, they came lean from the factory and needed jetting to help them run as good as they can at WOT.
How does your car drive with those plates in the carbs?
I have seen a lot of those type Holley metering plates converted to removeable jetting by drilling and tapping the bottom fuel inlet holes to #6x32 thread size and then use #6x32 blank brass set screws and drill them to the size (with a good quality numbered drill set) you want up scope
Don't change the center carb jetting on the 340 carbs tsk
IHTHs
Posted By: John Brown

Re: 340 6 bbl metering plates ?2 - 04/01/20 07:56 PM

Originally Posted by 62maxwgn
You need # 41 plates,Chicago Corvette,(708) 458-2500.They are now in Bend, OR.



Al Firke sell Chicago Corvette to someone else? I know he buys and sells shows, didn't know he was no longer involved with CC.
Posted By: scatpacktom

Re: 340 6 bbl metering plates ?2 - 04/01/20 10:40 PM

Why don't you just fill in the holes and redrill them. Probably save a pile
Posted By: 62maxwgn

Re: 340 6 bbl metering plates ?2 - 04/02/20 12:34 AM

Originally Posted by John Brown
Originally Posted by 62maxwgn
You need # 41 plates,Chicago Corvette,(708) 458-2500.They are now in Eugene, OR.



Al Firke sell Chicago Corvette to someone else? I know he buys and sells shows, didn't know he was no longer involved with CC.


I talk to Al a couple times a month,have known him for years,Chicago Corvette is still Chicago Corvette,Al moved the whole operation to Eugene,OR ,that is where all his family is located.
Posted By: John Brown

Re: 340 6 bbl metering plates ?2 - 04/02/20 02:26 AM

Just asking. I have known him for years too. Just haven't run into him lately. May be a while to, what with area swap meets being put on hold.
Posted By: CKessel

Re: 340 6 bbl metering plates ?2 - 04/02/20 03:43 PM

I can't remember who it is but one of the aftermarket carb companies makes a plate that is set up to take jets. Does not make the bowls stick out any farther. Much easier to deal with. Yeah, not STOCK but who is going to pull a bowl to make sure its oe.
Posted By: 62maxwgn

Re: 340 6 bbl metering plates ?2 - 04/02/20 04:40 PM

Originally Posted by CKessel
I can't remember who it is but one of the aftermarket carb companies makes a plate that is set up to take jets. Does not make the bowls stick out any farther. Much easier to deal with. Yeah, not STOCK but who is going to pull a bowl to make sure its oe.


Promax makes a jetable plate but it will cost you $150 a pair,or you can plug the metering hole on the bottom of the plate,drill into the passage from the bottom front,tap and you can jet your own.
Posted By: 1DGEMAN

Re: 340 6 bbl metering plates ?2 - 04/02/20 07:30 PM

I bought Quick fuel plates and have full adjustability.
Posted By: 4406bbl

Re: 340 6 bbl metering plates ?2 - 04/02/20 11:56 PM

What should a stock set of #41 plates measure for idle restrictions, and main jet? I have a holley book but as we know the new 440 #34-35 plates made today are not the same as what was installed in 1970.

Holley book shows #41
.033 idle
.070 main jet restiction
Kinda find that main size small for a 1-3/4 holley barrel, and dyno tests I have saved thru the years show .079-.083 to net a 13-1 afr, still lean. An 850 holley, same barrels, uses a #80 jet, amd a power valve. So are new # 41 plates correct or too small?
Posted By: 62maxwgn

Re: 340 6 bbl metering plates ?2 - 04/03/20 03:13 AM

Originally Posted by 4406bbl
What should a stock set of #41 plates measure for idle restrictions, and main jet? I have a holley book but as we know the new 440 #34-35 plates made today are not the same as what was installed in 1970.

Holley book shows #41
.033 idle
.070 main jet restiction
Kinda find that main size small for a 1-3/4 holley barrel, and dyno tests I have saved thru the years show .079-.083 to net a 13-1 afr, still lean. An 850 holley, same barrels, uses a #80 jet, amd a power valve. So are new # 41 plates correct or too small?


I'm pretty sure it is in the old Direct Connection manual,I'll look tomorrow if not I have at least 3 sets of 41 plates,easy to measure.
Posted By: fastmark

Re: 340 6 bbl metering plates ?2 - 04/03/20 10:46 AM

Originally Posted by CKessel
I can't remember who it is but one of the aftermarket carb companies makes a plate that is set up to take jets. Does not make the bowls stick out any farther. Much easier to deal with. Yeah, not STOCK but who is going to pull a bowl to make sure its oe.


It’s Promax carbs. I just bought some for my customers 440-6 Bee. They sell the base for the rear carb that has the angled metering screws for easy access.
Posted By: 1DGEMAN

Re: 340 6 bbl metering plates ?2 - 04/03/20 11:09 AM

Originally Posted by 4406bbl
What should a stock set of #41 plates measure for idle restrictions, and main jet? I have a holley book but as we know the new 440 #34-35 plates made today are not the same as what was installed in 1970.

Holley book shows #41
.033 idle
.070 main jet restiction
Kinda find that main size small for a 1-3/4 holley barrel, and dyno tests I have saved thru the years show .079-.083 to net a 13-1 afr, still lean. An 850 holley, same barrels, uses a #80 jet, amd a power valve. So are new # 41 plates correct or too small?

Here is a list of the plates in my 340 carbs . The last 2 carbs are the replacement carbs. These were all pined.

LIST # DATE APP PLATE IAB HSB T JET D KILL BLEED IFR
4789 490 340 F 41 0.052 0.039 .086 .072 0.046 0.037
4789 500 340 F 16 0.052 0.039 .067 .079 0.047 0.028
4789 890 340F 41 0.052 0.039 .085 .073 0.045 0.037
4790 500 340 R 41 0.052 0.039 .086 .072 0.046 0.037
4790 850 340R 41 0.052 0.039 .085 .072 0.045 0.037
4790 3518 340 F 41 0.068 0.027 .086 .072 0.047 0.037
4790 3518 340 R 41 0.068 0.027 .086 .072 0.046 0.037


Posted By: 4406bbl

Re: 340 6 bbl metering plates ?2 - 04/03/20 04:15 PM

Thanks 1, that info is gold, it looks like the replacment generic #41 plates are incorrect just like the #34-35 generic 440 plates. It could be that just the book is wrong I guess. To the OP if you went by the holley book to determine if your plates are drilled, that printed info at least is wrong for a 6bbl.

Does anybody have this same info for the 1970-440-6?
Posted By: 1DGEMAN

Re: 340 6 bbl metering plates ?2 - 04/03/20 05:22 PM

The only 440 carbs I have and they have been modified, Some one had pluged the kill bleed and I had to drill them out and make them adjustable.
LIST DATE APP PLATE IAB HSB T JET D KILL BLEED IFR
4382 3149 70 440 F 34 0.052 0.039 .089 .089 ADJ 0.037
4383 2039 70 440 R 34 0.052 0.039 .081 .085 ADJ 0.037
4383 3149 70 440 R 35 0.052 0.039 .097 .086 ADJ 0.037
Posted By: Imrare

Re: 340 6 bbl metering plates ?2 - 04/04/20 04:48 PM

I have a 1970 340-6 rebuilt to stock specifications. Originally the engine would not run properly, I was unable to idle it down below 1,000 rpm. Eventually I determined the carburetor metering plates on the end carburetors had been re-drilled as well as an incorrect metering block (generic) for the center carburetor. After several conversations with Holley and the Technical Department they assureded me the 2300 series carburetors they are manufacturing (4789, 4790, 4791, 4792) are manufactured to the same exact specs as was manufactured in 1970. The tech was able to pull a metering block assembly for my 4792 center carb off of the line (Holley P/N 34R6611-4AM, $73.17) along with 2 #41 machined metering plates (Holley P/N 34R6153-41, $30.98 ea.).

I'm not sure what your problem is with the carbs., but check your center carb base plate for any sloppiness whatsoever. The slightest amount of play in your center carb base plate throttle body will have a significant effect on the idle characteristics. Also, check that the correct jets are installed, (#61 auto, #63 manual) as both of these were a problem with my set up as well. Another thing to check are the air/fuel adjustment needles. When I purchased my metering block from from Holley it came with new air/fuel mixture screws installed but when I still couldn't get a consistent smooth idle, I checked the needles on my end carburetors. Looking under a magnifying glass it was obvious all four needles had been filed or slightly bent or in some other way not perfect. I ordered 4 new needles from Holley (P/N 15-3QFT, $4.98) and that was the last piece of the puzzle.

After making these changes and of course a complete rebuild kit installed, the engine ran perfectly, just like it did and was supposed to in 1970. Unfortunately, this was a 2-year process (2 winters) in diagnosing the problem, eliminating all other potential problems like a vacuum leak, distributor vacuum advance, fuel, etc. etc. I even had the carburetors professionally rebuilt (twice) and the problems detailed above were not caught. It seems they put a nice dichromate finish on the carbs,installed a new rebuild kit, but never really "dug into" quality of the parts that made up the carburetors...

I guess what I'm saying is that if you are doing a stock rebuild on a stock engine...I would get the parts described from the manufacturer of the carburetors designed for that engine.
Posted By: 4406bbl

Re: 340 6 bbl metering plates ?2 - 04/04/20 06:31 PM

Originally Posted by Imrare
I have a 1970 340-6 rebuilt to stock specifications. Originally the engine would not run properly, I was unable to idle it down below 1,000 rpm. Eventually I determined the carburetor metering plates on the end carburetors had been re-drilled as well as an incorrect metering block (generic) for the center carburetor. After several conversations with Holley and the Technical Department they assureded me the 2300 series carburetors they are manufacturing (4789, 4790, 4791, 4792) are manufactured to the same exact specs as was manufactured in 1970. The tech was able to pull a metering block assembly for my 4792 center carb off of the line (Holley P/N 34R6611-4AM, $73.17) along with 2 #41 machined metering plates (Holley P/N 34R6153-41, $30.98 ea.).

I'm not sure what your problem is with the carbs., but check your center carb base plate for any sloppiness whatsoever. The slightest amount of play in your center carb base plate throttle body will have a significant effect on the idle characteristics. Also, check that the correct jets are installed, (#61 auto, #63 manual) as both of these were a problem with my set up as well. Another thing to check are the air/fuel adjustment needles. When I purchased my metering block from from Holley it came with new air/fuel mixture screws installed but when I still couldn't get a consistent smooth idle, I checked the needles on my end carburetors. Looking under a magnifying glass it was obvious all four needles had been filed or slightly bent or in some other way not perfect. I ordered 4 new needles from Holley (P/N 15-3QFT, $4.98) and that was the last piece of the puzzle.

After making these changes and of course a complete rebuild kit installed, the engine ran perfectly, just like it did and was supposed to in 1970. Unfortunately, this was a 2-year process (2 winters) in diagnosing the problem, eliminating all other potential problems like a vacuum leak, distributor vacuum advance, fuel, etc. etc. I even had the carburetors professionally rebuilt (twice) and the problems detailed above were not caught. It seems they put a nice dichromate finish on the carbs,installed a new rebuild kit, but never really "dug into" quality of the parts that made up the carburetors...

I guess what I'm saying is that if you are doing a stock rebuild on a stock engine...I would get the parts described from the manufacturer of the carburetors designed for that engine.


Did you happen to measure the idle feed and jet sizes of the #41 new vs old plates? I also know the qft needles are not the same as stock baseplates used, stock needles are longer and thinner at the needle end. The qft match the metering blocks, not the baseplates. I just wish we had a baseline of all the stock designed restrictions so we could tell what has been drilled or not. The book specs for #41-34-35 plates do not match what most find in their 1970 carbs.
Posted By: calrobb2000

Re: 340 6 bbl metering plates ?2 - 04/05/20 03:16 AM


holley , chicago corvette no got !

where else ?
Posted By: 4406bbl

Re: 340 6 bbl metering plates ?2 - 04/05/20 05:59 AM

Originally Posted by calrobb2000

holley , chicago corvette no got !

where else ?


I would drill and tap for the mains for 6-32 setscrews and drill what you need. If the idle is drilled solder them up and redrill. What size are they now? You could buy the quick fuel plates also.
Posted By: Imrare

Re: 340 6 bbl metering plates ?2 - 04/05/20 06:37 PM

The Power Valve Channel Restrictions (PVCR) on the new Holley metering plates were measured as follows: Drivers side, .086; Passenger side, .073. The prior plates that the Holley plates replaced measured .084 Drivers side, and .072 Passenger side. These plates were probably okay but these plates probably replaced the "drilled" plates by the last rebuilder to handled the carburetors. I went ahead and installed the new Holley plates I had purchased since they met the specs exactly (see attachment) that I had on the 340 2300 series end carburetors.

Not sure what you meant in your response by "qft". However, if you remove the old needles and inspect them, you should be able to tell if they are "true" or not (for the minor cost, I would just replace with new). Also, closely inspect the end carb "seats" on the base plates and clean the seat that the needles screw into. Make sure no debris gets between the needle and seat. The new needles are a little longer than the OE needles from 1970 (and easier to adjust) and you will not be able to reinstall the small "caps" that fit on the base plate and go over the needles heads to prevent further adjustment. I believe when you buy the new needles you will also get new "cork" seals that go around the needles to prevent inadvertent movement of the needle once set. Tip: install the seal in the needle channel first and then screw in the needle.

Attached picture Scan0002.jpg
Posted By: 62maxwgn

Re: 340 6 bbl metering plates ?2 - 04/05/20 08:47 PM

Originally Posted by Imrare
The Power Valve Channel Restrictions (PVCR) on the new Holley metering plates were measured as follows: Drivers side, .086; Passenger side, .073. The prior plates that the Holley plates replaced measured .084 Drivers side, and .072 Passenger side. These plates were probably okay but these plates probably replaced the "drilled" plates by the last rebuilder to handled the carburetors. I went ahead and installed the new Holley plates I had purchased since they met the specs exactly (see attachment) that I had on the 340 2300 series end carburetors.

Not sure what you meant in your response by "qft". However, if you remove the old needles and inspect them, you should be able to tell if they are "true" or not (for the minor cost, I would just replace with new). Also, closely inspect the end carb "seats" on the base plates and clean the seat that the needles screw into. Make sure no debris gets between the needle and seat. The new needles are a little longer than the OE needles from 1970 (and easier to adjust) and you will not be able to reinstall the small "caps" that fit on the base plate and go over the needles heads to prevent further adjustment. I believe when you buy the new needles you will also get new "cork" seals that go around the needles to prevent inadvertent movement of the needle once set. Tip: install the seal in the needle channel first and then screw in the needle.




I'm a little confused with the PVCR for the end carbs as there is only the secondary metering plate with idle feed restrictions and main metering restrictions,PVCR is in the metering block unless you are referring to the mechanical set where each has a metering block.Also, you will find the longer screw you are referring to does not have the correct taper as the original..
Posted By: 4406bbl

Re: 340 6 bbl metering plates ?2 - 04/05/20 11:46 PM

Imrare, just pointing out the taper is wrong where the needle seats, I doubt the holley tech guy knew that, anyway just trying to establish a baseline of design specs for both the 340-440 setups, so guys don't keep buying parts that they do not need.
Posted By: GomangoCuda

Re: 340 6 bbl metering plates ?2 - 04/06/20 12:46 AM

That 6 bbl tips page has been messed up for many years. For the front and rear carbs it should say Main Fuel Restriction or Main Jet instead of PVCR. The sizes are ok but they are not pvcrs. And that Venturi nozzle is probably unobtanium. I think it just has a distribution tab on it.
Posted By: 62maxwgn

Re: 340 6 bbl metering plates ?2 - 04/06/20 01:48 AM

Originally Posted by 4406bbl
Imrare, just pointing out the taper is wrong where the needle seats, I doubt the holley tech guy knew that, anyway just trying to establish a baseline of design specs for both the 340-440 setups, so guys don't keep buying parts that they do not need.


iagree

I have talked Holley techs over the years and some didn't have a clue what I was talking about.On the needles,incorrect on left,main metering block screw used primarily on 71 and later plus current production,middle correct end base screw,no variation since initial production,right
main metering block screw that has been tapered,you can make your own if you have a drill press.

Attached picture P4051026.JPG
Posted By: 4406bbl

Re: 340 6 bbl metering plates ?2 - 04/06/20 04:54 PM

Originally Posted by 62maxwgn
Originally Posted by 4406bbl
Imrare, just pointing out the taper is wrong where the needle seats, I doubt the holley tech guy knew that, anyway just trying to establish a baseline of design specs for both the 340-440 setups, so guys don't keep buying parts that they do not need.


iagree

I have talked Holley techs over the years and some didn't have a clue what I was talking about.On the needles,incorrect on left,main metering block screw used primarily on 71 and later plus current production,middle correct end base screw,no variation since initial production,right
main metering block screw that has been tapered,you can make your own if you have a drill press.


Thanks for the needle pic, saved me digging thru my junk. Holley techs did not know the different styles in the the 80s, they would not, or could not give me any measurments, just sell the new parts.
Posted By: 62maxwgn

Re: 340 6 bbl metering plates ?2 - 04/07/20 03:11 PM

Originally Posted by 4406bbl
Originally Posted by 62maxwgn
Originally Posted by 4406bbl
Imrare, just pointing out the taper is wrong where the needle seats, I doubt the holley tech guy knew that, anyway just trying to establish a baseline of design specs for both the 340-440 setups, so guys don't keep buying parts that they do not need.


iagree

I have talked Holley techs over the years and some didn't have a clue what I was talking about.On the needles,incorrect on left,main metering block screw used primarily on 71 and later plus current production,middle correct end base screw,no variation since initial production,right
main metering block screw that has been tapered,you can make your own if you have a drill press.


Thanks for the needle pic, saved me digging thru my junk. Holley techs did not know the different styles in the the 80s, they would not, or could not give me any measurments, just sell the new parts.


Also,here are the jetable plates you can get without paying the price for billet plates that you are not going to see.

Attached picture P4071027.JPG
Posted By: 572B1

Re: 340 6 bbl metering plates ?2 - 04/07/20 10:08 PM

Originally Posted by 62maxwgn
Originally Posted by 4406bbl
Originally Posted by 62maxwgn
Originally Posted by 4406bbl
Imrare, just pointing out the taper is wrong where the needle seats, I doubt the holley tech guy knew that, anyway just trying to establish a baseline of design specs for both the 340-440 setups, so guys don't keep buying parts that they do not need.


iagree

I have talked Holley techs over the years and some didn't have a clue what I was talking about.On the needles,incorrect on left,main metering block screw used primarily on 71 and later plus current production,middle correct end base screw,no variation since initial production,right
main metering block screw that has been tapered,you can make your own if you have a drill press.


Thanks for the needle pic, saved me digging thru my junk. Holley techs did not know the different styles in the the 80s, they would not, or could not give me any measurments, just sell the new parts.


Also,here are the jetable plates you can get without paying the price for billet plates that you are not going to see.


That's great info 62maxwg. would you have brand and part number on hand. thanks in advance.
Posted By: doctor_mopar

Re: 340 6 bbl metering plates ?2 - 04/08/20 04:56 PM

I have previously installed the Pro Max metering plates in my 340 outboard carbs . So from what I am reading here , I beleive I was correct , to meet stock requirements in putting .086 jets drivers side , and .073 jets passenger side . Is this the correct conclusion ? Thank You
Posted By: 4406bbl

Re: 340 6 bbl metering plates ?2 - 04/09/20 04:15 AM

Originally Posted by doctor_mopar
I have previously installed the Pro Max metering plates in my 340 outboard carbs . So from what I am reading here , I beleive I was correct , to meet stock requirements in putting .086 jets drivers side , and .073 jets passenger side . Is this the correct conclusion ? Thank You



Yes, and .037 idle feeds from what others are measuring.
Posted By: formula S

Re: 340 6 bbl metering plates ?2 - 01/31/24 11:29 PM

I know this is an Old Post, I did a Google Search and found it so I decided to read it. I've used the Promax metering plates, there is an engineering problem with those plates. They do not seal to the body of the carburetor with the large cavity behind it, the guy at Promax says not to use the little thin plates, well they don't cover the Promax metering plate anyway, the last six pack I built I use AED jettable metering plates and they seal up fine, I saw on this thread someone posted about jettable non-billit metering plates, are those available, I've never seen them before?
Posted By: doctor_mopar

Re: 340 6 bbl metering plates ?2 - 02/01/24 07:39 PM

Formula S . Now you have me wondering . I ran with the Promax plates jetted like i said in my post . What would the symptoms be if they are not covering properly like you said . i did not use the thin plates under them. I am in the process of changing engines now to a 340 stroked to 418 . I planned to go to a 3310 750 holley on an LD340 manifold. I have felt like the 6 pack would be hard to tune with the big motor, and have intended to sell it . I may consider running it though, and some insight on what I should be doing with the jetting.
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