3810 holley

[Gerard F.]

Re: 3810 holley

Tim,

Had my 67 base engine car out yesterday for a 90 mile run in rolling foothill terrain and thought I'd pay particular attention to the idle, off idle and acceleration. Also testing out the replacement fan clutch.

In the morning just after coming off the fast idle cam, I set the mixture screws 3/4 out and adjusted the idle. First to get to about 550. The idle was very lopey and unsteady ranging from 500 to 600. Then I set it up to 650 and it smoothed out, finally decided to set it 600 with the Vintage Air AC on.

The car ran very smooth for the trip, up and down hills, no stumble on off idle, or accelerating, plenty of power. Had a passenger for the trip and was really proud how the car performed.

But, I have the original cam, distributor, timing at 8, the 3810 to factory specs.

The one thing I noticed, is that as the car gets hot, the idle goes up to 750 anyway. By hot, I mean over 160. With the new fan clutch, I didn't even get near 170 yesterday. (I'm running a 160 stock thermo).

[Timothy B.]

Re: 3810 holley

Clem,

I blocked the PCV port with my finger and the motor stalled immediately (no air). I could have opened the blades a bit to allow more air but decided not to mess with the PCV system. I may revisit this later.

Jerry,

You may want to consider a 180* thermostat for your car. As to the idle consider this, when the engine and manifold are cool gasoline is slow to vaporize so there is inefficent combustion, as the intake manifold warms to operating temperature the gasoline liquid turns to vapor when entering and the combustion efficency increases with the same mixture settings and the idle speed rises slightly.

[Joe C.]

Re: 3810 holley

Clem,

I blocked the PCV port with my finger and the motor stalled immediately (no air). I could have opened the blades a bit to allow more air but decided not to mess with the PCV system. I may revisit this later.

Jerry,

You may want to consider a 180* thermostat for your car. As to the idle consider this, when the engine and manifold are cool gasoline is slow to vaporize so there is inefficent combustion, as the intake manifold warms to operating temperature the gasoline liquid turns to vapor when entering and the combustion efficency increases with the same mixture settings and the idle speed rises slightly.

Timothy,

You might already know this, but the PCV valve should barely be pulling when the engine is at idle. The high vacuum signal pulls the pintle against the spring to fully closed position, bypassing only as much air as its calibration allows. I assume the PCV is clean and sealing correctly on the inside. Just for "fun", why not try another PCV valve. Whenever I block the PCV valve with my thumb, I have NEVER encountered a case where that small reduction of air flow would cause the engine to stall. Another test you might want to try is to make a temporary orifice block, similar to that used for 1964-65. Use a 3/8" diameter dowel and cut a short length to make a plug. Drill a .090" hole thru it, remove the PCV and insert the orifice in its place.

Remember, it FEELS like it's pulling HARD when you block the valve with your finger. What you're feeling is the high idle vacuum........in your case, probably about 16 in-hg, but the flow is actually VERY low against the calibrated restriction designed into the valve.

Joe

[Timothy B.]

Re: 3810 holley

Joe,

Thanks for that suggestion, I will take the valve off to clean, inspect and try to eliminate that as a problem.

[John S.]

Re: 3810 holley

Tim & Jerry,
Just thought I would tell you guys that after I returned from a trip this weekend I decided to play with the idle. I had it set at 650 originally as always had a small miss occasionally at idle. With car fully warmed up, I reduced it to 500 rpm and to my surprise I think it idles a little bit better! Took it for a drive and it runs great (just like before) I think I am going to leave it there and see how it runs in different situations. I also wanted to confirm that the 5oo 55o is the proper setting for the 67 300 hp car?

John Seeley
67 black/teal coupe
327/300 3 speed

[Timothy B.]

Re: 3810 holley

John,

I have the GM restoration package that states 500 RPM manual transmission and 500 in drive for automatic.

Sounds like you are doing better than the rest of us, is the base plate original to your 3810 and did you look inside the primary to see if the bottom of the transfer slot is visable above the blades at idle?

Before touching my carburetor base, I am going to check my PCV and take the timing out (put it back to 6*) just to be sure I have eliminated my changes. I fell comfortable 10* BTDC is OK for this engine though.

[John M.]

Re: 3810 holley

Tim,
I've had this carb on and off so many times that I'm not doing anything until I hear your results. BTW, blocking the PCV port at the carb only caused a 100 RPM (lower) change in my idle speed.

Jerry, can you see the bottom of the transfer slots from above with the throttle plates closed?
John

[John S.]

Re: 3810 holley

Tim,
Carburetor is original to the car I believe (Hank Lapcheck restored the car in 93 and the date matches). There are no bushings in the throttle shaft holes and even with my glasses on I could not see the holes in the plate while it is on the car. I will try and look at it with a flashlight and head loop when I get home. Like I said, I am going to keep it at 500 rpm for a while and see how she does.

John Seeley
67 black/teal coupe
327/300 3 speed

[Gerard F.]

Re: 3810 holley

John.

I can't see the position of throttle with respect to the transfer slot with the carb on the car, but I don't think it is revealing any part of the transfer slot when I am smoothly idling at around 650. (This is from looking at a replacement 3810 which I have off the car.)

When I adjust the idle down to around 550, I get this variance in idle between 500 to 600. I think what it is, is that I am not getting enough air down the primary barrels and the mixture is too rich. Fuel is probably just dripping from the hole below the transfer slot or from the hole from the mixture screw. By adjusting the idle up a little, you are allowing more air in and leaning out the mixture, until you hit the transfer slot.

I have no stumble at all on accelleration, and the engine runs very smooth going through the gears. But again, that's with my original base engine cam, distributor, and the 3810 to factory specs.

[Timothy B.]

Re: 3810 holley

I had some time to run the car today and checked the PCV valve after removing it from the oil fill tube, the valve is clean inside and seems to be working fine. I noticed there is a restriction in the valve and the motor did not quit when holding my finger over the end.

Retarted the timing to the original setting of 6*BTDC. This setting did not result in getting the throttle blades closer to the transfer slots so I put it back to 10*.

I decided to adjust the air/gas emulsion screws a different way according to what I read on another forum. Start with the screws 1 1/2 turn out and run the engine at 850 RPM and turn the screws in or out to achieve the highest RPM. Adjust both sides equally and keep adjusting the idle to 850 so you can tell if RPM's are increasing. This resulted in screws out 1 1/8 turn with no stumble but when lowering to idle RPM 550-600 it smells rich (burns your eyes a bit).

Seems like this method tuned the transfer slots but I am not sure it's the correct way to adjust air/gas screws.

All comments are appreciated.

[Gerard F.]

Re: 3810 holley

Tim,

I think your mixture adjustment is too rich. You'll get the same lopey variation at slow idle, as you get when you are very hot and have percolation or a stuck float. Just too rich and the idle lopes around until it dies.

I'm a pretty happy camper with accepting 650 idle as the minimum with my old engine.

[Timothy B.]

Re: 3810 holley

Jerry,

Try the lower idle with the emulsion screws out 1-1 1/8 turn. Let me know if the seeking stops, mine seems to like 600 RPM set like this but the idle may smell rich.

I think the pin hole below the primary transfer slot is holley's attempt to expose the slot to lower RPM. Like you stated in a previous post, the slot above the blade is atmospheric pressure so it acts as a air bleed feeding air to mix with emulsion from the idle circuit and then through the lower slot (pin hole) exposed to manifold vacuum.

Seems like all our problems arise when the blades are rotated above the pin hole but before the slot. This small blade rotation lets air but no fuel until vacuum finds the slot for more fuel. There is a lean spot at this point and is covered by either raising the idle and or opening the air/gas emulsion screws.

I am starting to think this 3810 holley is not calibrated to idle this low, and the fix would be to block the small pin hole in primary and lower the slot just a bit for proper blade/slot position, it may only take .060 or so to get it done. Like I said earlier, the AFB's will idle a engine down and when the blades are completely closed there is slot exposure.

[Gerard F.]

Re: 3810 holley

Tim,

I'll give that a try, but I think you are sucking gas through the pinhole, not air, with the throttle blade just above the pinhole. And I think you are too rich with the mixture screws out 1 1/8 turns.

The variation one gets at low idle is very similar to that drip, drip, drip of gas into the air horn when you are percolating or have a float stuck. The variation begins to increase, and then finally the car dies from too much gas and too little air.

At high vacuum below the throttle plate you are sucking gas through both the pinhole and mixture hole. With too little air to mix with, you get that dripping. By adjusting the blade between pinhole and the slot, you are adjusting the air and leaning out the mixture.

Just my theory

[Timothy B.]

Re: 3810 holley

I wanted to post my progress with this 3810. The only thing that makes this engine idle low with increased throttle blade/transfer slot exposure is to take timing out. When plugging the vacuum advance the idle lowered and required blades opened more. Ported advance would work in this case but then more heat is rejected to the coolant.

I removed that nice advance curve 0@900 2@1000 11@1500 16@2000 20@2500 25-26@3000 (inital 10 BTDC) and installed original distributor parts and 355 vacuum control, timed the engine at 6 BTDC and the same problem unless the engine is idled at 650 RPM. Also installed a NOS 726 PCV valve thinking my original could be passing more air because it's old and dirty, no difference.

I am back to believing the issue is transfer slot length.. Before modifying the slot, I am going to put a piece of wire in the idle air bleed to see if that helps. I don't think it's going to help this issue because I am not sure the transfer slot is lean and if made richer the curb idle A/F ratio will be richer also (same circuit).

Right now the car is set to idle at 600+ and air screws are approx 7/8 turns out. If set further out the idle gets dirty and eyes burn but no sputter. The transfer slot mod will require removing the base but I don't think it will take much in length to expose the slot to vacuum at low throttle blade position, I will be very careful here. There are no air leaks in this carb, throttle bushing etc worked out great..

PS.. Please don't ask me why I did not remove the timing by retarding the distributor 5-6* in paragraph two...

[Timothy B.]

Re: 3810 holley

I wanted to update interested members on the progress with my 3810 Holley carburetor. Long story short, making the transfer slots about .050-060 longer did the trick, they are cut on a angle and just exposed under the throttle blade in a closed position. At any engine speed the idle screw can be increased and the engine does not sputter like before and will increase in RPM very nicely.

I plugged the rear curb idle holes but removed the plugs because that change did not make any difference. I also plugged the small front constant feed holes located below the transfer slots because when exposing the slot to vacuum the idle mixture may have been to rich with the holes left open. I had to grind the set screws to about 1/8" so they did not interfear with the slots when installed.

The idle emulsion screws don't seem to effect the engine as much as they did before and I believe that's because the transfer slots supply more fuel than the constant feed hole located under them. The manifold vacuum is about 19" with the screws about 5/8 turn out.

At this point the car seems very good, idle is at approx. 550 RPM. I think the IFR and IAB is good so AFR in the idle circuit is good. I am going for a drive soon and want to try # 63 main jet to lean main circuit at cruise and light load then start checking vacuum readings so I can taylor power valve timing. After I am happy with the cruise jetting I will enlarge power valve channel restriction so WOT A/F mixture is the same as factory.

The last thing I will do is check the accellerator pump shot, right now when the throttle is stabbed a slight black smoke so I think it's good to go.

I think if I was to do it over again I would try to modify the throttle blade like a Carter primary blade. The Carter blade is cut so transfer slot is exposed, I will post picture. I am not positive this will work on a Holley but I think it will.

Great leaning experence and since I removed the throttle blades and plained the top and botton of the throttle plate flat with 220 wet paper on my table no more gas leaking on the intake manifold after overnight. The hot slot is open with no problems associated with that, I believe the oil sludge built up on the manifold under the splash plate held heat after shut down so this did not help with fuel perculation, it seems fine now.