Smokey idle, and surging at cruise speed.

[Mudsport96]

Well, my hand got forced and I had to turn my project into a running vehicle over night. So I'll give the symptoms and hopefully somebody can point me in the right direction.

Recap the setup 76 Nova, 355 8.5:1 compression, comp high energy 268 cam 218@.050 on both lobes .488 lift with 1.6 rockers. Ported stock iron intake topped with a 17057229 carb. Has Cliffs HP kit in it with orange PP spring. Car pulls 14 to 16 inches mercury at 900 rpm.

SMAB .050
IDLE TUBES .035
DCR.050
MIX SCREW HOLES .077
Upper IDLE BLEEDS .074
LOWER IDLE BLEEDS .063
BYPASS .125
JETS 69
RODS 36B
SEC. RODS DR
HANGER H
SEC. FLAP SCREW @ 3/4 TURN

I had it out and cruising in drive at 35 mph around 1400 rpm it has a surge that I thought was a lean surge that seemed to get better turning up the APT. But I got to max adjustment, so I went to my parts bin and looked for some smaller rods and didn't have any. So I swapped out the 64 jets for 69 jets and left the 36B rods in place. The "surging" seemed to get a little better, but the idle is Smokey now and I can't tune it out. Do the main jets affect idle???
The surge doesn't fully go away while cruising at higher speeds either. It's noticeable at 55mph doing 2500rpm as well.

[Mudsport96]

Ok, I put the 64 jets back in and the Smokey idle went away with no other adjustment.
So that leaves the surge at cruise.
Now, if I remember correctly, this carb originally had the 64/36B combo. And my engine is fairly mild so it shouldn't need much more than that I wouldn't think... right?

[Mudsport96]

Alright, didn't get much done today with work, and.... the daughter driving the car into the garage door.
BUT! I wanted to try something, so I disconnected the accelerator pump and started the car. And I found that in park, from 800 rpm idle I can whack the throttle open and it revs super crisp to redline.
I have no visible nozzle drip at idle.
So I'm going to take a guess that my rods are too small. Any opinions?

[Cliff Ruggles]

Yes, 36B rods are too small if you are using larger main jets in that carb number.

Verify that the power piston arms are level and EXACTLY even.  Call the shop when you get a moment and we'll get some larger primary metering rods headed your way. 

With a working APT system in one of those carburetors all you have to do is determine the most ideal jet size by doing some heavy part throttle driving, then fine tune the APT system for best light throttle/light load operation.

Are you using the vacuum advance?  How much timing is it adding at cruise?.......Cliff

[Mudsport96]

The vacuum advance is adding right about 10 degrees. So all in total at cruise it's around 41 degrees.

But I think I have another problem. I checked the well plugs when I rebuilt it, and had no leaks. This weekend I disconnected the acc.pump and opened the throttle to look down into the manifold. And fuel was pooled in the manifold.  Removed the airhorn, and the bowl was empty, and there is fuel on the walls of the secondary bores along the bowl side.
So I took note of that and disassembled the carb and checked the well plugs again, no bubbles when pressurized.
Is it possible for fuel to leak out of the bowl to the manifold any other way, perhapse porosity? This was just 8 hours after the last time it was driven. So it is leaking down rather swiftly, and may be part of my idle tuning issue.

[Cliff Ruggles]

The bowl can syphon dry if you are missing a pair of upper idle airbleeds. 

I have ran into a couple of bad castings that leaked down as they were defective internally, but that is very, very rare and would show up if you filled the fuel bowl with fuel on the bench with the needle sitting in the seat......Cliff

[Mudsport96]

Have it apart right now, and found FUEL in the idle air bypass chambers on each side of the primaries. And when I pulled the pcv hose off there was gasoline dribbling out of that port too.  I will try the thick gasket that came in your kit to see if that helps. Unfortunately I can't seem to get my pictures small enough to fit in the post so I'll work on that as well

[Mudsport96]

Still cant get picts to post, but, I got the idle a little better. Took it for a 30 mile drive today after putting the thicker airhorn gasket on the carb. Had zero problems the first 15 miles no surging, and zero problems until i got back to town and stood on it to ooen the secondaries. Wound it through first, and for to the too of second gear and she started fumbling and stumbling. And wanted to doe if I let off all the way, so I kept it half throttle till it cleared up and then stood on it and she pulled to 5000 in high gear.
Got home and pulled the pcv hose off the base plate and had fuel in it again. And fuel in the side chambers where the bypass air flows through.
I'm about ready to get a rebuild kit for the old 1901that was on the car before, even with the base plate needing bushed she didn't have these problems haha. I'm betting the bodies warped on this one. I didn't have a good straight edge when I did this carb build.
Thoughts?

[Mudsport96]

[Mudsport96]

Ha, got them. As you can see. Remnants of fuel, where fuel shouldn't be.

[Cliff Ruggles]

Sounds like your fuel pump isn't keeping up if it's fine in low gear then developing issues at the top of 2nd gear.  Slowing down allows the bowl to re-fill then fine once again. 

Being a little wet in the voids really doesn't tell us much.....Cliff

[Mudsport96]

Well, between working 15hour days six days a week and remodeling the basement, I was able to get a pressure gauge on the fuel line today. It isn't a liquid filled one so it was shakey, but at idle the needle jumps between 8 and 15 psi. When I shut it off, it settled in at 12psi.
Revving the engine just made the needle more erratic so I'm going to get a better gauge to see if it smooths out. But, if this gauge is right, this may be a big part of my problem. Including the stall after wot, maybe its pushing the needle off of the seat and flooding. Like I said I'm going to get a better gauge and retest.

[77cruiser]

If the gauge is right that's way too much. 6 psi would be good.

[Mudsport96]

Right, heck 12 to 15 is where GMs TBI runs for pressure haha

[Cliff Ruggles]

For sure a spike in pressure will cause what you are seeing.  Those carbs will take a lot of fuel pressure, but I've had issues with mechanical pumps because the flow isn't smooth and pressure inconsistent. 

Years ago I bought a Carter 120gph pump to help solve fuel delivery issues with my Ventura.  It was fine most of the time, but every once in a while it would flood in similar fashion to what you are seeing.

I finally got fed up with it and installed a gauge. Pressure was pretty steady most of the time at 9 to 9.5psi, then it would occasionally spike to over 12psi.  I got rid of that pump and went to an electric pump with a regulator and it solved both issues, fuel delivery and flooding......Cliff