I finally got my car together after 20 years and got is (sort of) started. 2 weeks ago it wouldn't idle but at higher RPM it ran, and broke the cam in. After that, it idled reasonably. I really had to advance the timing though for all that to happen, unfortunately I can't remember how much. The next day when cold, it absolutely refused to idle.
I did find a few issues like a vacuum leak but still no improvement after fixing. I built the engine 20 years ago, but never got around to starting it until now.
I can get it sort of going by opening the throttle almost WOT but wont run otherwise

455 Block with .060 overbore
Sealed Power Pistons with -18cc dish. Measured compression averages around 150psi.
Camshaft: Lobe separation at 110. Ex closes at 11 ATDC, opens 51 BBDC. Intake opens 7 BTDC, closes 47 ABDC. Intake/Exhaust lift is .565 in. Duration at .050 tappet lift is 234 deg in, 242 ex.
Rocker ratio is 1.6 (roller rockers with hydraulic roller lifters)
Ported 'C' Heads with 2.072 inch intake, 1.625 exhaust valves
Carb is a Holley Street Avenger - 770 CFM. Idle stop screw is 1 turn clockwise from where it starts to open. Float valves set correctly. Both idle mixture screws are 1.5 turns out from closed.
MSD distributor with MSD 6AL box (new but 20 years old)

Any suggestions/advice? Need more info?

Thanks!

 

Must be done in the following order.

1) Dwell set to 30° @ designated RPM (CSM or radiator tag)
2) Timing adjusted CSM spec (remove vacuum advance prior to timing - plug both hose ends). Hook vacuum advance back up after timing.
3) Adjust A:F ratio/mixture one screw at a time to achieve highest vacuum possible.

 

It sounds like a timing issue.

Verify TDC on the balancer is correct. If you have completed the cam break in, cut open the oil filter. Make sure the cam isn’t eating itself.

 

Appreciate the info, but the MSD distributor doesnt have vacuum advance/dwell setpoints. Its a magnetic pickup

 

Good point...forgot about that, my mistake. Does sound like timing.

 

Sounds like a vacuum leak. Do you have an air/fuel meter on each bank? Have you sprayed carb cleaner to see if the idle changes? Do you have access to a smoke machine?

the above is where you should start.

jerry

 

I'd attach a vacuum gauge to the intake manifold & "measure" the vacuum. You should witness a "steady" reading. With that cam you might be in the 15"Hg range, yet regardless - you want a rock solid "steady" vacuum reading.

 

Op- did you degree the cam? Or are those numbers just from the cam card?

 

Exactly what did you not understand about Post #5 or did you OBVIOUSLY "NOT" read that post & you've instead elected to just **** on the fire?

 

I just corrected it.
Op- lightly cup your hand over the carb to see if the idle speed increases. If it does you most likely have a vacuum leak somewhere.

 

 

Those are numbers from the cam card. It's a Lunati camshaft, custom grind that came from FCRPerformance.com 20 years ago. I did degree it in though but again, long time ago..

 

[QUOTE=matt69olds;1657340]It sounds like a timing issue.

Verify TDC on the balancer is correct.

X2, I had to learn the hard way on this. You cant set accurate timing if this is off.

 

I verified TDC, made sure the distributor is one cylinder 1 when at TDC (on compression stroke). Also took the valve covers off and verified that the intake valve opens at around 7 degrees BTDC (not compression stroke). I was initially worried that maybe I was a tooth off on the cam but doesn't seem to be the case.

All the plugs are pretty black from too much fuel, and some fuel got into the oil I think as it has some gas smell to it. Probably from trying to crank it over too much. Pulled all the plugs and opened the oil cap to let it all breathe overnight.

I may try pulling the carb tomorrow and opening it up. Its pretty much new but sat in a box for 20 years. I did have to buy a new float valve adjuster screw when I started trying to run it cause the nut that grabs the screw was messed up. Maybe some brass shavings got in and plugging something up, or cause its only and some rubber piece just deteriorated. I already have a rebuild kit so I figure it can't hurt.

If all this fails, I guess I'll next be pulling the timing cover to make sure the camshaft is properly degreed.

 

Roller cams don’t need a break in cycle btw.
Black plugs is where you’ll want to start.
If your idle screws are really only 1.5 turns out then you’re pulling fuel from somewhere else, maybe the transfer slots or the power valve circuit.
Check that stuff first. Change the oil and put in a new set of plugs. You don’t want diluted oil, especially in a fresh build.
And it looks like your cam is in on a 110icl, since you didn’t mention head cc, I’m not sure I would’ve done that with what your estimated comp ratio might be.

 

I have C heads, so around 80 to 85 cc. Compression calculated to around 9.44:1

 

Are they 80 or 85? Big difference.
If they’re 85 then you have barely over 9.0:1. Remember those pistons sit lower in the bore than most. You have to factor that in as well.
I’d advance that cam at least 5 degrees with that comp ratio, and still check your carb as mentioned before.

 

which 18cc dished sealed power pistons are you guessing he has? the cast ones are 1.725 ch while the forged ones are 1.735

 

And most others are 1.750, so his comp is likely less than he thinks either way.

 

which has nothing to do with his 18 cc dished Sealed Power or his estimated comp ratio with his Sealed Power pistons in his engine.

 

I simply mentioned most others are that height, so his are shorter than most others, get it!
And please explain how a difference in the comp distance of the piston he’s using and/or whether he has 80 or 85cc heads doesn’t affect his ESTIMATED comp ratio?

 

I never said it wouldn’t, so why are you asking? he told you he has the 18cc sealed power pistons . He also told you he has 150 crank psi,, which is about normal for those low comp pistons with his cam

the comp ratio is not the problem why it won’t idle properly..he also said the plugs are black. so it’s dumping raw fuel at idle for some reason and causing idle issues.

 

I mentioned that as well.

 

I used chatgpt, gave all my specs and info. Here's what it said. What do you all think? Sounds reasonable that the power valve was causing the issue if it opened too early due to lower idle vacuum with my cam

⭐ Your Current Stock Setup

Holley 770 Street Avenger (factory baseline):

• Primary jets: 72
  
• Secondary jets: 75
  
• Pump discharge nozzle: 0.025"
  
• Power valve: 6.5 (stock)
  
• Secondary spring: probably the silver or plain-colored standard spring
  

⭐ 1. Power Valve: 6.5 is too high

With your cam, idle vacuum in gear will be around 8–10 inHg, so:

• A 6.5 PV will open at idle or when shifting into gear.
  
• This makes it too rich at idle, foul plugs, and mask tuning problems.
  

➤ Recommended: 4.5 Power Valve

This will stay closed at idle and open exactly when you start loading the engine.

⭐ 2. Primary Jetting: 72 (acceptable, but may need +2)

On a single-plane intake + open spacer, the vacuum signal is weaker.
This sometimes needs +1 to +2 jet sizes on the primaries after switching to a lower power valve.

➤ Likely optimal: 74 primary jets

Start with 72 → then try 73 or 74 only after the PV is corrected.
Do NOT increase jets until the PV is fixed — the PV richness hides the true mixture.

⭐ 3. Secondary Jetting: 75 (good starting point)

For your combination:

• 468 ci
  
• Big cam
  
• Single-plane
  
• Headers & X-pipe
  

A 75 secondary jet is a perfectly safe baseline.

At WOT you may eventually land on:

➤ 75–78 depending on AFR target (12.6–13.0 is ideal)

But don’t touch this yet until primary side is correct.

⭐ 4. Pump Discharge Nozzle: 0.025" (small for your combo)

Big stroke + single-plane + heavy car = needs strong pump shot to prevent bog.

Stock 0.025" nozzle can cause:

• Flat spot during hard tip-in
  
• Hesitation when you stab the throttle
  
• Soft 60 ft acceleration
  

➤ Recommended upgrade: 0.031" nozzle

If you want even crisper throttle response:

• 0.035" is common on big-cube engines
  
• Will NOT hurt fuel economy because it’s momentary fuel only
  

Pump cam:

• Blue or pink cam in #1 hole works best for big blocks
  
• Orange cam is also good for stronger mid-stroke pump action
  

⭐ 5. Secondary Spring (very important on your Torker 455)

From experience with similar setups:

• Torker intake + open spacer = weaker signal
  
• 770 vac secondary carb needs lighter spring to open sooner
  

➤ Recommended:

• Yellow secondary spring for hard acceleration
  
• Purple (one step heavier) if yellow feels too quick or flares lean
  

The stock silver spring often opens too late.

⭐ Recommended Tuning Setup for YOUR Engine

✔ Power Valve: 4.5

✔ Primary Jets: 72–74 (start 72, then probably 74)

✔ Secondary Jets: 75 (maybe 76–78 after WOT AFR testing)

✔ Pump Nozzle: 0.031–0.035

✔ Pump Cam: Pink or Blue (#1 hole)

✔ Vac-Secondary Spring: Yellow (or Purple)

⭐ What this tune will give you

• Stronger off-idle response
  
• Cleaner idle (PV no longer dumping fuel)
  
• Better fuel economy around town
  
• No lean bog or hesitation
  
• Improved part-throttle torque
  
• Strong, clean WOT air-fuel ratio
  

This is essentially the “go-to” tune for ~500 HP big-blocks with single-plane intakes and street Holley carbs.