Leaky Holley 3810 help needed

[William F.]

Re: Leaky Holley 3810 help needed

Believe I'd quit aggravating myself, ditch the carb you have and buy a new one from Holley's source for vintage carbs-place in Alabama-Ho;lley can give you their number.Even then may have to beware. I bought a new one, flooded until I found out it had a pin hole in secondary float.

[William F.]

Re: Leaky Holley 3810 help needed

Are you saying there are some internal differences in Holley 3810's even though '67 Corvettes used 3810's in 300 and 350 hp SB's and in the 390 hp L36 BB? Thought they all had same jets, metering blocks, idle air bleeds, etc. from factory.

[John M.]

Re: Leaky Holley 3810 help needed

Scott,
Not to change the subject but just curious as to what your compression ratio is. The 14 and 39 at 2800 sound a bit aggressive to me but I don't know anything about LT-1 cam either. No detonation? I remember trying to get the 3810 tuned in right on my original 67 327-300 with modified cam. It was a similar struggle but it ran really sweet when finished.
John

[Joe C.]

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.

That's odd that you had to elongate the slot...........it's usually the other way around. 39 degrees BTDC may be too far. The ideal range for old school SBC with older wedge heads is between 36-38 degrees. Sometimes the sweet spot falls one or two degrees either side of this range, but the only way to know, for sure, is with a dyno, or clocking top speed at the track. If it were me, I'd start at 37 degrees @ WOT and work from there. Of course, if your WOT mixture is on the lean side, then 39 might work better, but if it's on the rich side, then 35 might work better. What you ought to do is to have the cent adv come in as quick as possible without detonation. If you could have it all-in by 2200, that would be better still.

The tech at QF gave you a bum steer. You're correct that it's bass-ackwards. With an 8.5, you'd be pulling it open if you idled down to 700 RPM. Carbs with larger primary mains use lower numerical PV's........or none at all. PV's are primarily an economy device.

John,

The amount of WOT advance is not only a function of cylinder pressure (ie: SCR, DCR, ICA, etc etc), but if an engine doesn't detonate with, say, 45 degrees WOT spark advance, does that mean that the engine is tuned correctly? NO. An engine can have TOO MUCH spark advance, and the ideal amount is determined by the situation where maximum cylinder pressure is reached at about 14 degrees ATDC. If too much advance is dialed in, then the max pressure occurs too soon, resulting in less than optimal torque.

[Scott M.]

Re: Leaky Holley 3810 help needed

Thanks Joe, I may have had to elongate the slot because this is an early 70s smog distributor, it only allowed for 17 degrees of advance. These are also Brodix heads, the engine doesn't like to idle well until 12 degrees, better at 14.

[Timothy B.]

Re: Leaky Holley 3810 help needed

The number on the power valve is simply the vacuum level the valve opens and enriches the main well, all you are doing is turning on the extra gas switch earlier when going to a higher number P/V.

Best way to tell which number is to use a vacuum gauge and drive the car at 25,35,45,65 mph and make sure the power valve is opening one or two inches vacuum lower than the lowest vacuum reading that way during cruise the valve is closed giving max fuel economy.

[John H.]

Re: Leaky Holley 3810 help needed

Are you saying there are some internal differences in Holley 3810's even though '67 Corvettes used 3810's in 300 and 350 hp SB's and in the 390 hp L36 BB? Thought they all had same jets, metering blocks, idle air bleeds, etc. from factory.

William -

The 3810 (P/N 3906631) was only used on the 327/300 and 327/350; the 427/390 used a 3811 (P/N 3906633), calibrated differently.

[William F.]

Re: Leaky Holley 3810 help needed

John, You're correct-forgot L36 used different carb than SB's. Thanks.IMHO Sounds like person who started this thread has got things too complicated with too many variables-non Holley parts, etc.

[Scott M.]

Re: Leaky Holley 3810 help needed

UPDATE: Thanks for everyone's help, on-line and off. Tim your comment about the baseplate made me pay careful attention when I removed the carb. It had a slight wiggle carb to intake. I thought I had sanded every surface flat but somehow I didn't get the bottom of the baseplate flat, it was off .015". Applied machinist blue, sanded on a slab of granite till smooth and assembled it. I also went back to the .031" IFRs and it runs great now. Air mixture screws work!