tgilligan

Hey Everyone,

Looking for some feedback/advice on whether what I'm experiencing on initial/cold startup is normal for my application.

Bit of background:
1970 350 with #6 heads. Machined and updated with Comp Cams adj setup, rockers, lifters, rods.
Forged pistons .030 over, block decked and honed.
Comp Cams flat tappet camshaft (mild).
Holley 750 DP
MSD R2R distributor, MSD plugs, wires and coil.

After the above upgrades, it's an amazing ride and I am in love with all the work I've done so far but I've noticed on cold startups, the first few seconds run a little rough which I assume is the mechanical fuel pump pulling in fuel. However, after those first few seconds (say 15-20 seconds), the engine will increase in RPM's but nothing crazy, almost resembles a vacuum leak and will stay until I burp the throttle and then it will settle in at its normal idle. It only does this on initial cold startup and not on any hot starts. I haven't hooked up my tach yet so I don't have the exact range but as I stated above, it's not that it revs up a crazy amount but certainly a noticeable amount.

I've checked for any external vacuum leaks from hoses, seals, intake, carb, etc. and haven't found anything. It's odd that it's only on cold startup and only until I let it climb up in temp a bit (130-150 range) and then burp the throttle. Until this point, I chalk it up to just how it is based on what the engine likes. Any input or any others that experience this?

Thanks
Tom

classicmuscle442

Sounds normal, if idle is too high on initial cold start on choke, you can adjust high speed idle on the choke side of carb. Just back the screw out a bit.

oldcutlass

Check your choke on the carb.