72 LS5

Swapped the drivers side header gasket - hopefully all exhaust leaks are fixed! Getting ready for our driving season down here - like the polar opposite of the last few posts.....literally!

Did the passenger side header gasket. Perfect storm of number 8 cylinder, 2 inch headers, and AC evaporator! I got the skinned knuckles to prove it. Trans mount replaced and wobbly PS pulley replaced.

Davey, I had the vacuum gauge with me and the lean stumble happens at over 10 inches of vacuum. Would a power valve have an effect on that b/c whether its a 5.5 or 8.5, it won't be opening at 10 inches. I was going to try this initially, but didn't once I saw the vacuum readings. It may be worth a try.

Thanks Scott. All those restrictors are fixed, so I'm going to try just running richer air/fuels for now. Thanks for the feedback!

So is it fixed?

Specifically which carb is this? Did you blow out all the air-bleeds with carb cleaner or compressed air? I always remove the air/fuel screws and blow out those holes as well. If it worked fine in May, and doesn't now, sounds like something is plugged or clogged, like the air bleeds. How is the idle? 2 1/4 turns seems a little on the rich side. Timing and spark are good?

I also have the 2" Hookers and they fit well, esp after reading what Dave wrote. Plenty of clearance with the steering, passenger side has all the room in the world and I can remove the starter too. But the drivers is really close to the perch and the collector on my particular set was not 100% straight, so it didn't line up with the Pypes exhaust which required me to take to a muffler shop to hook it all up.

I'm guessing that will chop some serious time off your ETs! I'm jealous!

Davey, I totally agree with it being a transition issue. I should have mention that the 4781-2 is not a 4 corner idle - its only got air/fuels on the primary block. I got the highest vacuum at 2 turns out, but I made it a little richer to help out with this issue and warm up (no choke). When I put the 50 cc pump on (which cured the stumble 95%), I set the lash of the pump arm at 0, since I needed most of the shot early as possible. I could try slight lash.... At very low speeds, like driving in a neighborhood, if I gently go off idle, I can *hear* a slight stumble but can't feel it. Since I thought it was not involving the jets or power valve, my only other choice (after installing the 50cc pump) is the air/fuels. Like I mentioned before, this carb was not designed to be "streetable" like today's custom carbs. An $800 carb is in my future but not at the moment. Maybe I should quit [you said a naughty!]-footin' around and just drive it harder already!

Scott, I ran this carb on my mild 454 for a short time and it was too much carb - it bogged with slicks. But now I have 509 cubes. Everybody I've spoken to says the 502 needs a lot of carb. I have a nice AED 750 HO that ran great with this motor, but I felt I may be leaving something on the table with that carb. I'm going to run them both at the track this winter, one right after the other, and see which is faster.

Sam - do you have the adjustable air bleed screws?

I have an 850 Holley double pump 4781-2 that is a fresh rebuild and bone stock with 80s all around and 6.5 power valves front and rear per the book. I was getting this off-cruise stumble....only when I give a very tiny bit more gas while cruising. If I give a decent shot, it would not stumble. I played with every pump cam in every position looking for the most shot as early as possible. Also spent $20 on a set of 37 squirters. Finally sprung for a 50 cc pump kit and using the most aggressive cam, the problem is 95% cleared up. But I'm still getting a VERY TINY lean stumble during the transition from cruise to main, one that you can't really feel, but can hear it ever so slightly if you listen closely. This is only under very light throttle from cruise. I thought an 8.5 pv may clear it up, but I drove with a vacuum gauge and the "stumble" happens at 10+ inches of vacuum. Then I thought of upping the primary jets from 80 to 82, but the plugs are perfect light tan as it is. Plus, it bothers me to have bigger primary jets than secondary (for reasons I can't explain). Air Fuel screws are 2 1/4 turn out for highest vacuum (11.5 in drive, 13.8 in park) The air bleeds are fixed. I betcha adjustable ones may do the trick. I understand that this is not considered a street carb per Holley. and maybe I'm expecting too much. The carb was not really designed for "tip-toeing" around. Any thoughts?

My first Monte had you same issue - long duration cam on a 350 with no low end torque. Timing is mentioned - did you get the initial and total timing specs? Make sure your total is 36-38 degrees and all in by 2500 rpms. I like to run vacuum advance too - makes the part throttle more responsive.

Put a dent in the top of my fender when a rattle can fell out of the overhead cabinet......arrrrgh!

Steve, you're coming to Florida tomorrow? A little short notice, but thats ok......bring your paint equipment. Did your wife find the folder of receipts by chance?

I've been breaking in the 502 with an AED 750 dp because my Holley 850 dp would not idle consistently and would spudder when I cruise part throttle. The 750 runs absolutely fantastic, but its just not big enough. After inspecting the 850 (for the third time), I finally found why it would idle inconsistently and surge randomly. I held it up to the light and discovered the secondary throttle blades were not closing all the way - they were cracked open slightly, and it was not allowing the primary air/fuels to function properly. I adjusted them so they close completely and slapped it on last night. Runs good - no surging! Still have some accelerator pump tweaking and tuning to do, but I'm hoping I have the cfms I need until I can afford a Pro Systems carb.

Nice times!

Just did an oil change with Amsoil 10/40 (engineered for older vehicles with added zinc). Even though I have roller cam now, the zinc has to do some good elsewhere in the motor, why not use it?

Last night I installed the GM Performance Part Wire Looms on the 502. This is the deal of the century - 12 bucks from the local GM Dealer! Finally, something priced below what I expected! And they fit right and look good. Part number 12495502. (Not sure if they will fit tall valve covers)

haul the "male", eh?

But now for the all-important question - did you get on it? if so, how did it feel?

So run the 850 vacuum for a while - it will give you the opportunity to upgrade later. It's never really done, we all know the story. And I'm with ya regarding the track - I want to see what the car will do, but can't do it on a regular basis. That 200r4 might last longer than you think if you run regular tires on the street with this thing!

Sounds great! Are you going to keep that 850 vac carb or is that temporary until the budget permits?

After reading all this, I'm anxious to hear how the car drives when its done! Davey advised me to spring for a cam when I was building my 502 and now I kinda wish I had - but the costs were spiraling out of control. When I do, down the road, I'll be giving Chris a call too. With that much lift, how much low end torque will be lost and what stall speed is needed?

We are all pulling for ya! Best of luck!