Usafstingray

Need a little help on two carb adjustment issues. 1) What's the best way to set mixture on an L76? Stock Holley, recently cleaned and rebuilt. With the 30-30 cam, it only pulls 6 lbs of vacuum at low idle and doesn't seem very responsive to adjustment. At high idle, it pulls 22 lbs steady and seems more responsive. And, there seems to be a wide range of increasing mixture before the rich drop in vacuum. Is it better to err on the lean side or rich side? 2) sometimes it just doesn't want to drop to low idle. I drove it for 30 minutes his evening and it just wouldn't come down. When it has come down on other rides, it settles in at 750 rpm and everything feels just right.

856666

Ray,

I attached a paper I use written by Lars. - follow it

In my opinion you should have around 15 in/Hg of vacuum at idle - so check for a leak at the base plate.

Technically, vacuum is measured in in/Hg

After resolving the low vacuum issue - set the idle mixture per Lars.

My L79 is set 1 1/8 out per side.

FWIW - After reading Lars paper I discovered that there is a specific order to tuning the Holley.

Phil

JohnZ

Not with the L-76 and "30-30" cam - the best you can expect with that cam is 9"-10" Hg. at 800-900 rpm.

Usafstingray

I get 10" at 900. Thanks for paper. And thanks to Lars.

Usafstingray

Thank you Lars! Here's what I figured out. 1) My mechanical advance messed up. I had the wrong springs on it and the weights were either the wrong ones or too worn out. The limiter bushing was also slipping off. Fixed all of that - used the light springs from the accel kit to get reasonably close to recommended advance on the RPM curve. 2) The vacuum advance can was the wrong one for the L76. It was a B25 instead of the B28. Switched it out and tested it to specs. 3) Wrong power valve in the carb. With vacuum at idle ranging between 6 and 9", I swapped in a 4.5". 4) Primary and secondary idle out of synch. I set it up per Lars' paper in the earlier post. I generally followed Lars' paper for the procedure/order for initial setup and tuning on the engine. 5) Secondary opening seemed too late, but was in fact too early based on reading the Holley book (HP Books), creating a flat spot in acceleration. I increased the spring weight by one on the Holley color scale and got a beautifully smooth acceleration. With all these adjustments, I took the car out for a nice long drive and couldn't stop grinning!

Lessons learned: 1) timing issues can be confused for carb issues; 2) consult several sources; 3) be patient and diligent and you'll get the awesome performance these wonderful cars are capable of.