Tuning new engine, trying to getting it dialed in...

[madmike]

Hello, all...  Long time lurker, looking for some help or advice...  Last fall I rebuilt the 440 engine.  It's a 0.060 over bore, flat top pistons, stock stroke, with a Howards roller cam (0.545/0.540, @50 231/236.6), Edelbrock aluminum heads with 75cc chambers and right around 10.6:1 compression.  It has an 850 Holley mechanical double pumper on it, and a Mopar Performance electronic distributor.  It's bolted to a four speed, and the rear end ratio is 3:23.  I think the engine alone is a pretty good package, but the cam choice might not be ideal with the 3:23 gears, which I may change out later.

When I first fired the engine, and drove it, it seemed pretty responsive, but ran rich.  You could smell it in the tail pipes, and the plugs were pretty black.  The car also seemed to 'surge' at lower rpms, but as soon as you got into the gas a little bit, it would smooth right out and feel pretty powerful.  The carburetor was a used unit, which was cleaned up and rebuilt.  When I got it, it had 80 jets in the front, and 76 jets in the back, along with 6.5 power valves.  So, I reduced the jet size down to 78 and 74, and reduced the power valves down to 4.5.  Still ran rich, dropped the jets to 72's all the way around, and at the advice of my neighbor (a Ford drag race enthusiast, and more knowledgeable than me) he suggested putting the 6.5 power valves back in.

Right now, there is less than 500 miles on the engine, and it actually runs worse now, than it has since new.  It surges in any gear at any rpm, doesn't start so well (I had it close enough to where turning the key fired right up, now it cranks a bit before igniting).  Just off idle, it bogs out pretty bad, and I never did have it adjusted well enough to kick in the back barrels properly.

I bought the carburetor used, and even though my neighbor rebuilt it, I don't know what changes were made to it by the previous owner, or even if that matters...  I don't know if my problems are ignition related either.

I guess what I'm looking for, is some advice on where to start on jetting and power valves.  Also, I'm no expert on mechanical advance, vacuum advance, and how they relate to each other.  All I know, is that I had it running better before, than I do now, and every change I've made, it seems to run worse...

[70 sublime]

Can you swap parts back to the way it was orignally running and get back to that point ?

If you do swap and still running the same bad that might not be your main problem

Vaccuum leak ?

[b5blue]

https://www.ramchargercentral.com/threads/the-best-way-to-tune-a-holley-carburetor.326226/ and  https://www.motortrend.com/articles/how-to-custom-tune-holley-vacuum-secondary-carb/  may help  Pull plugs as they may be foul.

[metallicareload99]

Definitely keep an eye on the plugs in case they get fouled up.

Make sure the accelerator pump squirts fuel as soon the throttle linkage moves.

Leave the vacuum advance disconnected for now and cap off the carburetor port it was connected to.

What's the timing set at?

Do you have a vacuum gauge?

[madmike]

Yep, gas fumey smell from the exhaust, and the black plugs were give aways to richness.

The front accelerator pump lever arm does NOT move (or just a tiny bit) when actuating the throttle.  The lever arm does move fully, when more throttle is applied, but it doesn't seem soon enough...will look into that.

With vacuum advance unplugged from distributor, I think it was 10-12 BTDC.

Yes, I do have a vacuum gauge. At idle, I think it was reading around 12" of vacuum, not rock steady though, (fluctuating slightly).  I think that might be because of the cam?

[armor64]

i would also recommend a wideband 02 gauge. back before i gave up on tuning my old trucks 350 (311k on the odometer), i had a cheap wideband gauge and sensor, and drilled/clamped it onto one of the pipes to help out, and the tuning was was easier to track for me (i was using an edelbrock 1406 though). After getting it dialed in, i sold the gauge off for basically the same price as new, so it was a good investment at the time.

[metallicareload99]

If those cam duration numbers are @ .050" I would expect more than 12" of vacuum...

First thing I would do is increase idle advance to @ least 16° OR hook up the vacuum gauge to manifold vacuum and advance timing until vacuum stops increasing, then back it down a hair and get a reading. You will probably have to adjust your idle back down to where it was

Next, adjust the idle mixture screws. Since it runs ok, you might have to screw them in OR out. I do each side a quarter turn at a time each side. Again you are looking for max vacuum here. Again you'll probably have to reset idle speed.

Depending on what particular distributor you have, advancing the idle timing might (almost certainly) result in too much timing when it's all in/full throttle. IF you have the Mallory built MoPar Performance distributor they are pretty nice and easy to modify the curve using this kit:

https://www.summitracing.com/parts/sum-850535-1

After all that bring the engine up to @ least 3,000 RPM and get a reading on what the timing is

[John_Kunkel]

With the engine warmed up and idling, grab a flashlight and look straight down the primaries and secondaries...if you can see fuel dripping from the boosters, the float level might be too high.