Need some advice - 1965 L78

[Joel T.]

Guys;

I have a situation which I have never run into before... and I am not quite sure what to do next.

I just finished some upgrades to my L78.. some for more judging points the others for better drive-ability.. the judging point stuff include a water pump/pulley/fan clutch replacement and is not the issue here.

The drive-ability changes included: replacing the base of my "dated" carb with the one off my service replacement so as to get manifold vacuum versus ported vacuum; replacing the TI coil with a "correct" reproduction from TI Speciality; and installing an adjustable VAC so as to get to that 2" rule which we all know about (I'm running a non-stock cam so idle vacuum is lower than spec)...

Here's the problem... The car will run after initial start up although I cannot get it to run at high idle upon start-up although the high idle cam is set.. I can drive the car and it will drive just fine.. decent idle and nice power... the car will run fine for as long as I do not shut it off... If I do shut it off it will not start again and appears to be flooded. If I hold my foot to the floor and crank it (the thing to do for a flooded engine) it will backfire up through the carb.... big time... Yesterday I got a major explosion out of it... scared the crap outta me! If I let the thing sit and fully cool off it will start and run again.

Can't be very many things because I have not changed many things..... I don't have much experience with Holley carbs... Could this be a power valve issue?

I appreciate any thoughts....

Joel

[Carl N.]

Re: Need some advice - 1965 L78

Joel,

First thing I'd check is float level on primary bowl. Threads on here tell how or goggle how to adjust float level on Holly.

Sounds like it is a carb problem - it's been a few years since I've had mine apart and I'm at work but I belive there is a "check valve" (may be called something else) that is not seating on the new base. Does not sound like a power valve issue - but could be,

Others like Duke may have better suggestions.

Carl

[Carl N.]

Re: Need some advice - 1965 L78

Joel,

Try this site

www.holley.com/TechService/FAQ.asp

Carl

[Duke W.]

Re: Need some advice - 1965 L78

The hot start backfiring makes the distributor installation suspect. It could be caused by cross firing due to improper cap/rotor alignment. Check wire indexing on the cap and cap/rotor alignment.

Is the VAC near or at the interference points? Some aftermarket cams appear to have improperly indexed gears, which may require the dist. gear to be installed 180 out from OE.

I'm not a big fan of aftermarket adjustable VACs. What do you adjust - the total advance or the vacuum that it maxes out?

Depending on your idle vacuum either a B20 or B28 should conform to the Two-Inch Rule.

Duke

[Joel T.]

Re: Need some advice - 1965 L78

Duke;

I did put new wires in however I replaced them one at a time so as to avoid potential crossing... The car runs fine on the road... I've run it at WOT for short spurts and it is totally smooth and strong.. I will double check the wires just to be sure however... but I do not think there is anything there...

The VAC is in the center of the run... I replaced the can while the distributor was in the car so I know there is no chance of being off a tooth... This can you adjust the vacuum levels for initial pull and full pull. My cam makes about 9 to 10" of vacuum at 600 RPM. I have the VAC set to start the pull at 6" with full advance at 8"... per the 2" rule.. I tried a B28 a while back but I required more vacuum than I had at idle, at least by MightyVac testing.

At this point I need to begin retracing my steps...

Thanks guys.... will keep you posted.

Joel

[John H.]

Re: Need some advice - 1965 L78

My cam makes about 9 to 10" of vacuum at 600 RPM.

Joel -

How do you get an L-78 to idle (without a lot of shakin' goin' on) at 600 rpm?

[Joel T.]

Re: Need some advice - 1965 L78

Joel -

How do you get an L-78 to idle (without a lot of shakin' goin' on) at 600 rpm?

Hi John,

I can get her down to 600-700 RPM, with the VAC, disconnected and source plugged to set the basic timing... It actually does not shake all that much... I've set the basic timing to 10 degrees vs the "book" 8 degrees which gives me a tad more vacuum. With the VAC plugged back in I set her to 1000 RPM curb idle which is pretty smooth...

Joel


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