Clouds of smoke

[Gregtx]

Hey guys, hoping you can give me some more ideas here...

I'm getting clouds of smoke from my exhaust after the motor warms up and at idle. The smoke is very stinky (strong fuel smell) and it hangs in the air and doesn't dissipate.

The motor is an FE 390, fresh rebuild. Cam is a mild Lunati. The cam has been degreed and is on the money. Motor makes 10:1 compression and the compression check comes back with 150PSI on all cylinders, cold. Leakdown test shows no leakage past any of the valves. Lash is good, no bent pushrods, all the valvetrain seems to work fine.

Carb is a QFT Brawler 670 with vacuum secondaries. I've also tried this with a QFT Slayer 600 and got the same results. Intake manifold is an Edlebrock Performer 390, dual plane. Fuel pump is Holley electric with a regulator and runs at 6PSI on the gauge. Float levels are both good.

Ignition is TSP ready to run disty, Accell super stock coil (new), MSD 6A (have tried without as well). Timing is set at 18 deg and I did check the marks on the balancer against TDC. New plugs (autolite) and wires (Accell 8mm). I also recently added an ignition relay to ensure that I'm getting a strong 12V to the MSD and the coil.

I've checked for vacuum leaks, tried replacing the PCV (and removing it altogether), planed the intake faces and checked the intake gaskets multiple times. Heads are freshly rebuilt, and the springs match the cam.

I've tried adjusting the secondary butterflies on the carb, changing out the idle air bleeds, changing the power valve, still nothing. The power valve is an 8.5 4 window and that should match the 17inches of vacuum I'm getting at idle in gear. I've tried a 6.5 as well.

I thought that maybe it might be a water leak, but all the signs point to fuel/air. My plugs are sooty (not oily), the smoke isn't a steam, it's more of a fuel smoke. Thing is, it's not black... It's more white/grey. I'm not loosing any coolant though, so I don't believe that it's a water leak somewhere. It's also eating gas like a top fuel dragster. I even tried pressure testing the cooling system and, other than a pinhole in my radiator, I'm not seeing any pressure loss there. The other oddity is that if I introduce a vacuum leak, it idles way up and stops smoking. But then, of course, I can't set my curb idle below about 2000 RPM.

Any ideas as to what could be going on here?

[1972hiboy]

It sounds like you are running rich, what jet sizes are you running? It wont idle below 2 grand? is that because the cam is that extreme or you just physically cant? sounds like some more carb tuning is in order. If you introduce a vac leak and it cleans it up then it really points to needed to lean it out.

[Gregtx]

Oh I can get to idle at 750 with no vacuum leaks, it just smokes like crazy there. But with a vacuum leak, it clears up but won't idle below 2000.

The jets are the stock jets that came with the carb.

[tnlprt]

Your timing should be between 12/14 advanced

How did you plane the intake on the head face?

Dual exhaust ...Both sides equal on the smoke

Plug gap should be around 35

[Gregtx]

Plug gap is 35. Intake was planed .030 per side on the faces to match the geometry once the heads and deck were cut down. It was done at an automotive machine shop. I've tried the timing set anywhere from 12 to 22 deg, no change. Dual exhaust with headers and H-pipe. Smoke is even on both sides.

[colnago]

Stupid question, but you're not 180 degrees off on the distro, are you?

Joseph

[tnlprt]

Sounds like you may need to try a 3rd carb

introducing a vacuum leak and the smoke quits is a sign of fuel mixture

White smoke is water or possibly trans fluid

[Ranchero50]

OK then... You are running pig rich by your description so stop worrying about the rest.

Pop the air cleaner and look down the carb for fuel dripping or puddling either front or back. If so, sort it out. Secondly, lower the float levels a lot as a test. This will increase the emulsion signal needed to pull fuel. Your idle mixtures should also change the mixture. Shut them down as a test (should be obvious).

We had to back off the secondary butterflies a lot on my friend Demon to get the blower motor to idle down correctly.

report back.

[Gregtx]

Ranchero, I think you are on the right track here. I backed WAY off on the floats and the smoke is definitely far less (although not gone entirely). This carb has sight glass on both bowls, and the factory setting is in the middle of the sight glass. I backed it down to just UNDER the bottom of the sight glass and saw a vast improvement. I also noticed that my fuel pressure went way up, so I've adjusted that back down. I would theorize that the increased restriction I introduced at the floats caused an increase in head pressure ahead of the regulator resulting in in overall increase in pressure in the line.

I hooked up my vacuum gauge again and now I'm seeing less manifold vacuum that I was before. It's looking like around 14 inches in gear now, so my 8.5 power valve may be too big. I guess I should go ahead and change that out because I'll never get my idle set correctly if I've got my power valve opening up at idle. I've got the stock 6.5, so that should be sufficient to get my idle set right.

I may also be proactive and buy another set of plugs for when I get my mixture close enough. I'm sure that the ones that are in there are toast if I was running that rich.

[Ranchero50]

Don't worry about the plugs, they'll sort themselves out once the mixture isn't burning your eyes. Float level should not effect the fuel pressure. Set it around 4 psi and make sure the gauge reads 0 when off. Sounds like your pressure is pushing fuel past the needle and you mid set float is borderline on emulsion.

Are you seeing fuel dripping or puddling in the carb bores? Need this answer...

Vacuum will change with RPM and idle quality, concentrate on eyes burning first and get the idle under 1k, preferably 700 in gear.

[Gregtx]

I'm not seeing any dripping or puddling in the bores. I set my pressure to 4, and then 3. I do see improvement there with the lower pressure, but it's still burning my eyes a bit and there is still a good bit of smoke, although I wouldn't call it a cloud anymore. It does drop to 0 when it's off. If I run the motor with the fuel pump off altogether, it runs pretty clean.

I did replace the power valve back to a 6.5.

[Gregtx]

Holley just said I should change out my idle air bleeds... they think they're too small. I've got some laying around, so I guess I could try that.

[Ranchero50]

Did you shut the mixture screws completely first?

[Gregtx]

I did, and it dies before I get them turned all the way down. The motor dies at about 1/4 turn out.

[Ranchero50]

Then you idle bleeds should be OK. It's been a while but the wrong bleeds will nullify the idle mixture's ability. Next up is make sure the throttle plate is closing enough to get off the main jet circuit. I think you'll need the PCV hooked up to help keep the idle up with the plates closed.

No puddling means it's just a basic tune problem.