3810 holley

[Clem Z.]

Re: 3810 holley

how about a PCV system not functioning correctly and allowing to much air thru the carb? try blocking off the PCV system.

[John M.]

Re: 3810 holley

Clem Tim,
I did have a gasket leak earlier, so checked all this and it turned out to be just the gasket. I will block off the PCV and let you know what happens.
John

[Joe C.]

Re: 3810 holley

Were you ever able to get it to idle at 500 without tip-in stumble before the carburetor surgery?
Is it possible that the carb is drawing air through the new bushings? Not probable, but possible.
Take some timing out of it if it bothers you.
1st post said 10 initial........I thought that the low horse motors were "supposed" to have 8 degrees initial.
If it bothers you, make initial timing less than what its "supposed" to have, lengthen advance slot or remove nylon bushing to make up the difference, and lighten the advance springs (if the engine will tolerate it). Then, the car will pass PV with a nice, sleepy, lullabye and manure smooth idle of 500.
The "square", or .020" transfer slot is only a guide...........it can and does vary widely from that. Your secondary plates should be open slightly if your sec idle stop screw is not screwed up. If you hold carb up to light, you should see SLIGHTLY less light coming from the gaps around the secondary plates as from the primaries.
Maybe somebody installed an idle air bypass port (like Demon's "Idle-Eze") in the baseplate when you weren't looking.

Joe

[Gerard F.]

Re: 3810 holley-Let's analyze this

Tim,

Been thinking about that pinhole below the transfer slot, and I think it maybe unique to the 67 carbs, maybe only for the 3810.

If you a look at John H's picture above, it doesn't have the "pinhole" below the transfer slot, and the slot by my eye seems to extend further down than ours. Both mine and your original 3810 base plate have this mystery "pinhole" below the transfer slot just above the larger hole which comes from the primary mixture screws and tracks in the top of the base plate.

My measurement of the pinhole indicates that it is .020 diameter (#76 drill bit butt fits nicely). So I think on those carbs with the pinhole below the transfer slot, the pinhole is your main idle feed and that there is no need to reveal the bottom of the slot unless you want a faster idle.

With the throttle plate just slightly open below the transfer slot, vacuum is sucked through the transfer slot, mixes with gas and then goes through this small orifice and mixes with air. A basic idle feed and on all 4 corners.

As you raise the angle of the primary throttle plates, you are introducing more air, and leaning out the mix, that is, until you expose the bottom of the transfer slot where you would then introduce more gas. Introducing more gas at a higher angle would seem to be great at part throttle operation.

The larger mixture holes which go through the mixture screws on the metering block are just what they are called. The screws and feed through these screws, enriches the basic idle feed. Remember the mixture adjustment, turn them out, then in to a lean roll, then slightly back out again.

Maybe I have over-analyzed this, and I'm all wet But I don't think I'd screw with the engineering and lower the transfer slot if you have a pinhole below.

Maybe on a brand new stock engine and 67 gas, they could get down to 500 rpm idle, but with a 42 year old engine and the new gas, I don't think you are going to get there. Maybe close.

[Gerard F.]

Re: 3810 holley

Joe,

Actually the initial timing on a 67 base engine with the stock distributor (30 d mech. advance) is only 6 d.

[Joe C.]

Re: 3810 holley

Joe,

Actually the initial timing on a 67 base engine with the stock distributor (30 d mech. advance) is only 6 d.

Absotively. I knew it was at least 2 degrees less than the L76, so guesstimated 8.
There, Homer, is his problem. Those 4 degrees will loar the idol stubstabitably.

[Clem Z.]

Re: 3810 holley

checked the length of the idle transfer slot on a couple of holley i have here.a 780 CFM #3247 the slot is 15/64 long and no extra holes. a 390 CFM #6299 has a slot 9/32" long and had the little holes in line with the slot

[Timothy B.]

Re: 3810 holley

When the car was timed at 6*BTDC I could idle at 500-550 and had the same approx throttle position and problem, that's not the problem. I realize that taking timing out will cause the idle to slow but the efficently of the engine is not as good. The PCV valve is stock and of course changing the air flow with a different valve will slow idle, that's not the problem. I am quite sure there is no problem with the throttle shaft bushings and air as I think it's sealed better than any new holley, 19" steady vacuum at 500-550.

The car seems to like 10* inital, centrifugal starts at approx 900-950 with 25* in at 3000-3200, total WOT timing approx 35*. The vacuum is very good to the point I installed a 163 vacuum can with 16* pulled to the stop at 16.5" vacuum and comes off quick with the throttle.

Everyone please keep in mind that increase in idle to 650 there is probably no problem, I know at 700 there is no problem. As I said before, I think this 3810 is calibrated for the 350HP car also. I would almost like to try to plug the rear curb idle holes to see if throttle blade position needs to be moved open more and this would solve the tip in stumble.

It's obvious I am not the only person that's been down this road with the idle issue. The Carter AFB carburetor on 65/ earlier is a better carb.

Sorry for the long winded post and thanks everyone for there suggestions, keep them coming!!

[Robert B.]

Re: 3810 holley-Let's analyze this

Tim,

Been thinking about that pinhole below the transfer slot, and I think it maybe unique to the 67 carbs, maybe only for the 3810.

If you a look at John H's picture above, it doesn't have the "pinhole" below the transfer slot, and the slot by my eye seems to extend further down than ours. Both mine and your original 3810 base plate have this mystery "pinhole" below the transfer slot just above the larger hole which comes from the primary mixture screws and tracks in the top of the base plate.

My measurement of the pinhole indicates that it is .020 diameter (#76 drill bit butt fits nicely). So I think on those carbs with the pinhole below the transfer slot, the pinhole is your main idle feed and that there is no need to reveal the bottom of the slot unless you want a faster idle.

With the throttle plate just slightly open below the transfer slot, vacuum is sucked through the transfer slot, mixes with gas and then goes through this small orifice and mixes with air. A basic idle feed and on all 4 corners.

As you raise the angle of the primary throttle plates, you are introducing more air, and leaning out the mix, that is, until you expose the bottom of the transfer slot where you would then introduce more gas. Introducing more gas at a higher angle would seem to be great at part throttle operation.

The larger mixture holes which go through the mixture screws on the metering block are just what they are called. The screws and feed through these screws, enriches the basic idle feed. Remember the mixture adjustment, turn them out, then in to a lean roll, then slightly back out again.

Maybe I have over-analyzed this, and I'm all wet But I don't think I'd screw with the engineering and lower the transfer slot if you have a pinhole below.

Maybe on a brand new stock engine and 67 gas, they could get down to 500 rpm idle, but with a 42 year old engine and the new gas, I don't think you are going to get there. Maybe close.

Jerry -

I was looking at the list 3814 carburetor off my '67 300HP engine (it's a K19 California car) and noticed it has the very small holes under the transfer slots in the primaries that yours does. Not sure what they do, although to some of the earlier posts, I can get that engine to idle pretty well at 550 to 650 RPM. Problem is I'm fighting an off idle hesitation, and what appears to be a lean surge at speed. I think I need to have it rebuilt and recolored -

Bob

[Timothy B.]

Re: 3810 holley

Bob,

The small holes under the transfer slots are located well below the throttle plates and exposed to engine vacuum at idle speeds. These holes are a constant feed of idle fuel from the bottom of the transfer slot well. There purpose on the SECONDARY side is to feed the engine with a small flow of fuel and keep the fuel fresh in the secondary bowl if you have a light foot.

The idle circuit on these carbs consist of curb idle ports (controled by the side screws) and transfer slots so the idle well in the front metering block feeds both areas. With a 300HP engine the idle calibration is rich IMHO and requires closing the throttle blades to a point where there is a incorrect alignment of the blades to transfer slot. When tip in of the throttle this incorrect position exposes itself as a lean spot (stumble).

To go one step further, at low speed light load when the circuits in play are idle (transfer and curb), and main there is a lean mixture feeding the engine and you feel a surge in the engine. The idle circuit has to be correct before you can tune the main circuit (jets). You can't try to cover up one problem with another circuit of the carburetor.

If your car is a AIR car where is your inital timing set? Mine is 10* BTDC but the car acts the same at factory setting of 6* BTDC. If you increase the idle like so many others have done the position of the throttle blades to transfer slots is much closer hence no stumble and the air/gas screws can be made richer because the idle is faster.

It's a one carburetor fits all from Holley, but I feel it can be tuned to be very efficent. As I said above, I feel that blocking the rear curb idle holes thus reducing idle fuel may allow primary blades to be opened closer to the bottom of the transfer slots. It's a modification that can be done in the snake like channel of the base plate shown in one of the above pics.

[John M.]

Re: 3810 holley

Tim, Just to add a little more to this, I was working on my newly assembled 327-300 when I came upon your original post and was having the same exact problem. In addition the car would surge a little at any RPM and I tried a bunch of things with out much success. I changed the primary jets from the stock 65s to 67s and it was amazing, no more surge at all. But still the stumble. Tried a more aggressive accelerator pump cam and different power valve which didn't do much, if anything. So, unless you guys find the cure I'm going to turn the idle up to 700 any drive it like I stole it.
Great thread.
John

[Clem Z.]

Re: 3810 holley

Tim, Just to add a little more to this, I was working on my newly assembled 327-300 when I came upon your original post and was having the same exact problem. In addition the car would surge a little at any RPM and I tried a bunch of things with out much success. I changed the primary jets from the stock 65s to 67s and it was amazing, no more surge at all. But still the stumble. Tried a more aggressive accelerator pump cam and different power valve which didn't do much, if anything. So, unless you guys find the cure I'm going to turn the idle up to 700 any drive it like I stole it.
Great thread.
John

i posted above the reason for the stumble.
if the idle transfer slots are not exposed at idle you will have a hesitation because they cover the time it takes for the fuel to get down from the pump shooter to the base of the carb.

[John M.]

Re: 3810 holley

Hi Clem,
Yes, I learned about the slots from this thread but with this carb on this engine those slots are not exposed under the throttle plates until 1000 RPM. I set the plates so that a "square" slot was visible under the plates and when I put the carb back on and started the car it was at 1000, choke disengaged. The carburetor is the original, unmodified rebuilt with Holley parts. It's a mystery that's only a little bit annoying. I wonder how many other 327-300 w/Holleys have this problem. Maybe Tim could do a poll?
John

[Clem Z.]

Re: 3810 holley

Hi Clem,
Yes, I learned about the slots from this thread but with this carb on this engine those slots are not exposed under the throttle plates until 1000 RPM. I set the plates so that a "square" slot was visible under the plates and when I put the carb back on and started the car it was at 1000, choke disengaged. The carburetor is the original, unmodified rebuilt with Holley parts. It's a mystery that's only a little bit annoying. I wonder how many other 327-300 w/Holleys have this problem. Maybe Tim could do a poll?
John

there has to be excess air getting into the induction system for it to need the butterflies closed down below the idle transfers to get the proper idle speed you want.

[John M.]

Re: 3810 holley

Clem, I haven't had the chance to block the PCV port yet but will tonight.
The engine has a steady vacuum of 18-19", could it still be getting excess air?