Fresh engine won't idle

[Seff]

It runs pretty well with the mods to the '77 carb. Allows it to idle decently if not super smooth.

Now I have a strange sound, though. Comes from the front of the engine, it disappears (but may still appear) at moderate throttle but is there at idle. I disconnected PSP, ALT and water pump, and it's none of those three, as the engine makes the same sound without those connected.

My old engine had the same noise after a timing chain change, and I assumed it was due to the cheap timing set. But nothing other than the carb carries over to this engine that hasn't been ruled out already in the above paragraph. So I'm perplexed, and of course worried that it's a rod bearing or something.

Video of the noise: http://youtu.be/2usEjphiR-w

[Seff]

Turned out to be the hose running from the valve cover to the carb baseplate. Replacement eliminated the sound.

The engine runs at 180-190 F when cruising, starts decently, but idles a little rough, at least until it's warm (crossovers blocked, so that's to me expected). When cruising it gets very "loud" and sounds like it's sucking a lot of air at anything below 1100-1200 RPM. A lot happier at 1500 RPM. Downshifting in all gears results in choppy motions at around 1100 RPM, like the engine's stalling (which I guess it technically is, when you downshift hard enough?).

Thinking about getting a wideband O2 sensor to aid me in tuning.

The only modifications I made to the 77 carb was drilling out the upper idle air bleeds as prescribed by recipe #3 - everything else was already up to size or bigger than suggested.

[Seff]

I'd look at recipe #3 for idle fuel, for what you are doing.

I take it this means I shouldn't worry too much about the rest of recipe #3? I did the idle system mods, and the only part I identified that wasn't on spec for a #3 was the main body main air bleeds, which are close to 0.030" than the prescribed 0.070". Should I go ahead and open them up?

As for roughness and vacuum leaks, I went over the choke assembly again and noticed that the housing was out of round, meaning the E-choke didn't hold air. So, I glued the little plastic tube shut instead, fixed the problem that way.

I drive the car mainly between 1000 and 1500 RPM, should I still be adjusting my APT at 2200 RPM?

[Cliff Ruggles]

I'd leave the MAB's alone.

When converting to E-choke, the vacuum to the choke housing must be blocked on the suction side, as the e-choke grounds directly on the housing without a gasket......Cliff

[Seff]

I'd leave the MAB's alone.

When converting to E-choke, the vacuum to the choke housing must be blocked on the suction side, as the e-choke grounds directly on the housing without a gasket......Cliff

So you'd ONLY modify the idle system? Well, then I'd better bring the rest of the carb back to specs. I modified everything to third recipe specs.

Right now the fuel economy is pretty lousy - could that be because I'm working at too low RPM? What kind of vacuum should I be expecting at idle with that cam?

Thanks.

[77cruiser]

That cam should idle with a min. of 14 inches maybe even 15.

[Seff]

Gotcha, thanks. I'll let you know what it idles at.

When should I be considering idle bypass air? The book says "larger camshafts", but doesn't specify how large.

[Seff]

The engine idled at 18-19" when I put on the gauge, and now idles at 19" after adjustment. Are you guys SURE this engine needs that many carb mods? I had a vacuum leak back when I initially tried to start it up, mind you.

[blazer74]

What's your idle rpm? Seems like a lot of vac for a 221 cam.

[Seff]

It was 900 at that time. Any lower and the engine shakes and gets rough. Or, it did. I've since added idle bypass air (0.080" both sides), and have yet to calibrate the idle mixture and idle speed since.

[77cruiser]

Is your timing stable or does it drop off below 900 rpm?

[Seff]

Ugh, forgot to check timing. Anyway, dropped it to 800 RPM and vacuum decreased to 17-18.