3810 holley IFR and IAB factory specs

[James H.]

Need help in finding factory specs on the original old carb on a 300 327. I need the factory specs on the idle circuit air and fuel orifices
to check what I got . The rear plate is a 134-21 Carburetor does find accept at idle, runs rich.
Thank you for help

[David H.]

Re: 3810 holley IFR and IAB factory specs

Need help in finding factory specs on the original old carb on a 300 327. I need the factory specs on the idle circuit air and fuel orifices
to check what I got . The rear plate is a 134-21 Carburetor does find accept at idle, runs rich.
Thank you for help

James

Link below may help. Holley has significant information on their web site.

Dave

https://documents.holley.com/techlibrary_carb_numerical_listing.pdf

[Timothy B.]

Re: 3810 holley IFR and IAB factory specs

James,

Holley 3810 IFR= .031 IAB= .070 Rear metering plate 134-22

[James H.]

Re: 3810 holley IFR and IAB factory specs

Thank you very much

[Ralph E.]

Re: 3810 holley IFR and IAB factory specs

Tim,

The 134-22 rear metering block doesn't come up on the Holley site??

Look forward to hearing if James Henry resolves his rich running carburetor.
I have the same issue with my 67 327/300 and 3810 carb.

[James H.]

Re: 3810 holley IFR and IAB factory specs

To All
I've been dealing with Holley Carburetors for over 50 years. After 10-12 hours of research and watching videos of seasoned mechanics, I finally understand how Holley Carburetors work. It's all in the front metering block and the 3 fuel air circuits. Every motor has its own factory combination or orifices to make THAT motor run the way it is supposed to run. Most all of the old carburetors that I dug up had been altered because we used to alter the motors back in the 60's. Now we are dealing with stock motors and we have to go back to the stock metering block specifications. For example if your 327 is a 300 horse you have to set up your idle circuit for that motor. The air and fuel orifices has to be right for that motor. I found that a .031 IFR and a .075 IAB made my 300 horse perform correctly. Also both front and rear butterflies are completely closed using the idle circuit at idle. Remember, that idle circuit is at 100% the way you set it up the entire time that motor is running. Hope this helps, James

[Timothy B.]

Re: 3810 holley IFR and IAB factory specs

James,

Sounds like you have a good understanding of the Holley carburetor. The idle circuit is active anytime there is manifold vacuum present but much less so when the vacuum is acting on the boosters (throttle blades open) creating air flow through the carburetor. The air flow through the boosters creates a low pressure around the nozzles (venturi vacuum) which draws fuel out the nozzle.

The 300 and 350hp engines both use the 3810 and as you have discovered slight tuning helps our 300hp engines run a bit better.

I bet you can go down even further to a .029 IFR with a little accelerator pump tuning. Less fuel available may need a bigger fuel shot, (.028 vs .025 pump squirters) I think mine is currently set up with .031 IFR and .076 IAB and I'm certain I can go leaner on the IFR, just been to busy with house things and no time to play lately.

Ralph,

The #22 metering plate specs should be in the archives here, I can't remember the IFR, it may be .028 and the main jet is a .076 orifice, the rear air bleed specs are also in the archives. Make certain the power valve gasket is correct and the P/V is securely tightened, and the main body surfaces are flat along with a flat metering block. Manifold vacuum can pull fuel and air from other holes if surfaces are not flat causing all kinds of head scratching things.

James is so right about knowing the factory specs for these carburetors and they are the starting point for any carburetor repairs. I modified mine with 3/16" brass set screws (6-32 and 8-32 size) so you can change and go back if needed.

[James H.]

Re: 3810 holley IFR and IAB factory specs

Tim
Thank you for the info.
The car is running so good now that I am taking a 250 mile trip Monday to see how it is doing.
The metering plate that has been in the factory carb for 12 years was stamped correct but someone had drilled out the fuel to around .060 (I did not know ) The car has always run rich. Thank you again and will try a plate with a smaller IFR. If better, then will try the drill out and replace in the original meter plate

[Ralph E.]

Re: 3810 holley IFR and IAB factory specs

Many thanks to Tim and James.

The R3810 on my 327/300 has been running rich for years and I hate the smells.

My plan before I try and modify anything is to re-check the carb with a vacuum gauge and make idle adjustments as needed. Maybe something changed from the last time I did this. Then I will check the transfer slot to see if it is a square or rectangle. Check the vacuum to verify the correct power valve and if necessary re-adjust the floats in the float bowls. Since this is a 3810 it does not have a site screw so adjusting the floats is not fun. Then since I will have the float bowls off I will verify the IFR and IAB bleeders and make changes as suggested.

Tim, not clear what you mean by "I modified mine with 3/16" brass set screws (6-32 and 8-32 size) so you can change and go back if needed."

[James H.]

Re: 3810 holley IFR and IAB factory specs

Ralph

I worked on a 3810 style carb a while back that was acting like the power valve had ruptured letting gas through. The problem found was fuel sucking straight from the front bowl through the small port in the center of the front metering block the runs through the block that supplies the path for the accelerator pump gas. The problem was the metering block was warped enough the not let the gasket seat on the little ridge around the hole in the metering block that faces the main body. That camber is the vacuum chamber for the power valve. When you pull the plate off look to see if the old gasket has that little "O" impression for the seal.
Could be the running rich problem.
It is always something simple. Good Luck
James