I picked up a replacement 3810 for my '67 L79. The carb leaked like a faucet when I first tried it so I followed the 3810 rebuild article in the Restorer, and using machinist blue, straight edge and a block of granite sanded all mating surfaces true. Assembled carb and it ran really rich. A search of archives turned up more information about replacement 3810s having incorrect air bleeds. I emailed Holley for correct sizes and my idle bleeds were almost .020" too small. Drilled out idle bleeds to .070" and tried carb again. Ran much better but still rich and I noticed that each time I remove the carb, the base gasket is very wet and sometimes there is some fuel accumulated inside the intake manifold. Also have noticed some occasional fuel vapor come up out of carb after shutdown. Obviously I have an internal leak somewhere. Can this be a power valve leaking or a main body to throttle plate gasket? I dropped the floats down to .250" to eliminate them and have fresh Viton needle and seats. Last time I had something like this happen I forgot to tighten down the power valve and it was flooding the intake. My plan is to install another fresh power valve and gasket along with a new body to throttle plate gasket but what am I be missing? I see good crush on the throttle body gasket so I do not think its that.
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Last edited by Scott M.; April 11, 2013, 08:57 AM. -
Re: Leaky Holley 3810 help needed
Scott,
There are two air bleeds for each barrel, (idle and main circuit). The main air bleeds are much smaller than the idle bleeds, I know the idle bleed is .070 and I think main is .026 but double check. Lots of info in the archives on this.
Did you remove the throttle blades and plain both sides of the throttle plate and the attaching surface of the main body, vacuum can draw fuel from these surfaces if they are not flat. Get a small drill bit set and check the idle feed restriction hole and emulsion holes inside the metering plate. Ifr hole is .031 and emulsion holes are (I think) .028. -
Re: Leaky Holley 3810 help needed
If the leakage is in the rear, check the metering plate for warpage. Common on that model.Comment
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Re: Leaky Holley 3810 help needed
Thanks Wayne and Tim. Sorry I forgot to add I eliminated the rear metering plate and went to the Holley jetted block kit for the rear of the carb. Yes the throttle plate was sanded straight top and bottom, and as I said I have great gasket crush between the main body and throttle plate. Looks like gas in the main well behind power valve, so that's either the power valve, power valve gasket or leakage past the metering block to main body gasket right?Comment
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Re: Leaky Holley 3810 help needed
Scott, Make sure you have the correct power valve gasket for the power valve you are using. The metering block could be warped, it the block stamped 4743, that the correct block. When the engine idles how far out are the emulsion screws and can you kill the engine if they are turned all the way in.Comment
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Re: Leaky Holley 3810 help needed
Nope, I can not kill engine with the screws. Another reason I worked on all mating surfaces to get a good seal. I checked metering block for warpage and even swapped it out with a quick fuel billet block, same issue. I'll double check PV and PV gasket.Last edited by Scott M.; April 11, 2013, 12:35 PM.Comment
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Re: Leaky Holley 3810 help needed
I just removed carb, fuel was puddled inside manifold. Removed front bowl and the darn PV was loose. Removed it and paper gasket was torn. This time I installed a Quick Fuel PV and their heavy duty blue gasket along with new metering block gaskets. Found some info in the archives with conflicting float settings Holley spec vs Chevy so I opted to lower the floats even further to the Chevy spec of .310 front and .340 rear. Torqued bowls down 50 in-lbs, installed carb and engine fired right up settling down to 875 RPMs. However those idle mixture screws will still not kill engine even though I am not past the .020" on the transition slot. No more fuel vapor cloud after shutdown either. Getting very close, now to figure out the mixture screw thing??Comment
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In Appreciation of John HinckleyComment
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Re: Leaky Holley 3810 help needed
Scott,
You may be able to idle your L-79 at 750, try to set primary throttle blade idle adjustment screw at approx 3/4 turn from just touching and set idle with the secondary throttle stop screw. This may allow the primary blades to close further against the transfer slot which will allow more adjustment with the emulsion screws.Comment
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Re: Leaky Holley 3810 help needed
Thanks Joe and Tim. Joe I also swapped in a new billet quick fuel metering block with new needle and seats with the same results. Tim I'm running a LT-1 cam, it will idle down that far, not well, but maybe enough to try it out. Besides this hickup things are rolling along well and I hope to actually drive this '67 in another month.
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Re: Leaky Holley 3810 help needed
Scott, Your car looks very nice, the LT-1 camshaft is a very nice set up for that motor. Does the quick fuel metering block have removable emulsion bleeds and idle feed restriction for carburetor tuning.Comment
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Re: Leaky Holley 3810 help needed
Thanks Tim. Yes the QF block has removable fuel feed restrictors. It came with .028" feeds installed and I went down to .025" feeds. I also have some .020" feeds I am going to try when I swap out the throttle body gasket tomorrow. Quick Fuel thought the .028" fuel feed restrictors were about right for a 600 cmf carb. I plan to call them today and see if they have any suggestions.Comment
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Re: Leaky Holley 3810 help needed
The IFRs are sized according to the amount of air flowing thru the throttles at idle. Therefore, a 427 and a 327 both using the same sized carb, and both idling at the same speed (and with the same VE
), will use different sized IFRs since the velocity thru the 427s throttles is higher and thus pulling harder on the idle fuel ports. As an alternative, if both engines use the same carb with the same IFRs installed in each, then the 427 might require the idle mixture screws to be backed out 1 1/2 turns (the recommended, or "mean/normal" amount), but the 327 might show highest vacuum (best a/f ratio @ idle speed) with the screws backed out only 3/4 turn.
The IFR orifice should have nothing to do with the fact that the engine won't stall with all 4 (or 2, in your case) mixture screws seated. What a larger IFR orifice WILL do is add extra fuel off-idle, so as to make throttle response crisper and will cover any lean spot in your accel pump shot.
Barring any leaks, I'd take another look at the secondary throttle plate adjustment.Comment
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Re: Leaky Holley 3810 help needed
Scott,
Keep in mind the stock 4743 metering block has a .031 IFR size. Changing that size smaller will not only affect the idle but will lean the transfer slot and thus the cruise.
IMO, the best way to tell is to rev the engine to approx 2000-2200rpm which is just before the main circuit starts feeding so the engine is running on the transfer slot and finger the idle air bleeds to see if the engine speeds up or slows down. That will give you a indication if the engine wants more fuel/less air or the opposite. At that point you may find .028 is lean, I think .025 will be way lean.
Get you timing right first and make sure the engine is warmed good so the plenum is hot.Comment
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Re: Leaky Holley 3810 help needed
Thanks all. I called Quick Fuel, they said to stick with the .028 or even the .031 with .070" air bleeds. However he thought I still had an internal leak either between the front gasket or the PV and suggested maybe a 8.5 power valve vs. the current 6.5 (seems backwards to me) but the LT-1 Holley used a 8.5 PV.
Duke helped me dial in the timing yesterday. I needed to file the advance slot to get more centrifugal and installed lighter springs. Now I am at 14 degrees initial and 39 degrees Total WOT advance all in by 2800.Comment
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