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About a month ago I posted with a question regarding proper jet sizes for a Holley 4150 on my 65 L78. I had mentioned that it had been rebuilt with #72's in both primary and secondary. I believe the correct sizes are #70 for the primary and #76 for the secondary. Many of you gave me good information pro and con. The car runs great now. I am just curious if there would be a substantial and noticeable difference at WOT if I replaced the secondaries with the correct #76's?
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Re: C2- Holley jetting
Rob,
Strange that the rebuilder did it that way. It should be much more susceptible to detonation @ WOT because of the lean mixture.
If it were me, I would jet it per Holley specs. Normally, the spark plugs will tell you the story. Find a suitable test area, preferrably a flat and level highway with low traffic volume, lower cop volume, and wide shoulders. Get the engine to op. temp. and give it a good blast @ WOT. Then immediately shut down the engine, coast to the shoulder, and pull the plugs. Examine them, and they will likely show too white.
Joe -
Re: C2- Holley jetting
Joe,
Slightly different question:
If I had 62 jets on a 3810 holley (65 is the Holley spec) would I tend to run hot with high speed accelleration. The secondary has the #22 holley spec metering plate although one high speed vent is intentionally blocked. One of the high speed vents on the primary side is also intentionally blocked.
Just put this restored Holley on, and it runs hot going uphill at high speed but then goes to normal just cruising along downhill.
Jerry Fuccillo
#42179Jerry Fuccillo
1967 327/300 Convertible since 1968Comment
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Re: C2- Holley jetting
Jerry,
If it were me, then I wouldn't try to re-engineer the 3810. I would re-install the stock pri jets, and unblock the air bleeds. If all is well internally, then I would think that the engine will be happy..........unless there is a problem somewhere else.
Signs of lean condition are detonation and "surging", which is a cyclical variation in pulling power at cruising speed. Elevated operating temp. will also result, but I don't think that it should be more than a few degrees, or so. Of course, the spark plug insulators will show too white, rather than tan.
I think that if your temp variation is moderate-to-severe, you ought to look at your cooling system.
JoeComment
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Jerry:
If the air bleeds are blocked, then there will be a gross imbalance of the fuel distribution. 2,3,5,8 will be rich and 1,4,6,7 will be lean, or vice versa, depending on which side is blocked. If you continue to run like this, you are likely to burn an exhaust velve.
JoeComment
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Re: C2- Holley jetting
which side drivers or passenger has the undrilled air bleeds? i have a call into my contact,not tech service,at holley about this.Comment
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Re: C2- Holley jetting
Clem,
On this 3810 dated 751, on the primary side, the passenger side high speed vent is blocked. The 4743 3810 stamped primary metering block has the corresponding vent hole in the track, blocked or never drilled. There is a place for the hole but it looks like it was never drilled.
On the secondary side, it's opposite, the driver side has a blank or undrilled high speed vent. The secondary side has a standard #22 metering plate.
All other idle and high speed vents are to Holley spec.
Clem, I really appreciate you looking into this for me.
Jerry Fuccillo
#42179Jerry Fuccillo
1967 327/300 Convertible since 1968Comment
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