I have been working on a problem that I can’t seem to isolate. I’ve been at it for a month now and I am at the end of my rope. In an attempt to give as much detail as possible, I have laid out the whole story below. It is very long, but if you have the time, I would appreciate a third party opinion.
Crower Stainless Steel Roller Rockers
MSD Ready-to-Run distributor w/MSD Coil and Wires
BG 850VE Speed Demon
Holley “Blue” Electric Pump with Fram canister filter
Boesch Platinum Plugs
Power Source 140 Amp Alternator
After pulling the car out for the first time this season, the engine ran fine. I have always had a rich idle circuit, but I had resolved to just live with that. I burned about ¾ of a tank of the fuel that was in it during the winter (which had Sta-Bil in it), and filled up with fresh fuel.
Shortly thereafter, I started having problems with the engine running rough and dying at temperatures over 180 degrees. It acted very much like the carb was flooding out (black smoke out of the tail pipes). It was almost like a switch, very consistent as soon as the water temp reached 180. I considered vapor lock, but that was never a problem I had in the past. After speaking with BG, I decided to rebuild the carb and look for any debris that would have stuck in the floats. I also checked the fuel filter, and replaced it even though it looked clean. The fuel tank is only 3 years old.
After disassembling the carb, I found that one of the idle fuel feed holes in the base plate was mis-machined so that it did not match the main body. It baffles me that I was able to see any change at all in that idle mixture screw. Even thought the carb was three years old at this point, BG took it back and sent me a new 850 VE with annular discharge boosters, believing this carb should work better on the ZZ502.
New 850VE with Annular Boosters:
This carb, to my confusion, had a Secondary Accelerator pump squirter installed, complete with “needle” check valve. I questioned BG why a Vaccum Secondary carb would have a secondary squirter. At this point, the BG tech said that the main bodies between a VE and Mech. Secondary carb are the same, so it should not be a problem because it was a dead circuit without an actual accelerator pump. At this point I was skeptical, but gave them the benefit of the doubt.
I installed the carb (with fresh spark plugs), started tuning it for base idle at about 170 Deg., and to my dismay the engine started to stumble and die above 180 deg.
So now I start think I lost something in the ignition. So I try the following, one at a time (I had these new parts on the shelf for another project):
- New Coil
- New Coil Wire
- Different MSD Distributor with 6AL Box
The engine acted exactly the same! As a last ditch effort, I decided to drain the tank and put in 5 gallons of fresh fuel. Problem 1 Solved!! I could idle at 180 degrees without any issues. I even took it up to 210 by disconnecting one of my electric fans, and she idled without mishap. Now, I still seemed to be rich at idle, but I was not about to go drilling out idle air bleeds at this point. I put my original MSD coil back on.
Enter Problem 2:
As I start to re-check base timing and other operations, I notice I had a no-load miss throughout the rpm range. Now what??
Tried new distributor cap and rotor – ran the same.
Now my base settings are:
Idle speed 800 rpm
Base Timing Mech: 16 Deg Adv.
Base Timing Vac. Adv.: 36 Deg Adv.
Total Timing Mech: 36 Deg. Adv.
Total Timing Vac Adv.: 56 Deg. Adv.
Idle Vaccuum: 14 in Solid
Transfer slot exposure: Primary 0.020”, Secondary 0.005”
(New BG procedure has secondary blades closed 100%, but I had to open them slightly to smooth out idle a bit).
Idle mixture screws: All four out between ¾ and 1 full turn.
(Any leaner it would stumble, any richer it would not run well and vacuum fell off).
During the miss:
Vacuum stays steady in the high 20’s depending on RPM.
Timing remains steady. There is no jump or bounce. I put a timing light on every plug wire looking for a timing fluctuation but found none.
BG had sent me a 1” spacer back when we thought Problem 1 could be vapor lock. Grasping at straws, I installed it. This allowed me to back out the idle mixture screws to about 1 and ¼ turn, but the no-load miss was still there.
Believing my problems were still carb related, I attempted to find out if it was a lean or rich miss by slowly closing the choke. By doing this, I could make the engine run smooth at a particular rpm, by varying the choke position. It seems like I am lean at some RPM’s, and rich at others, to the point which causes the engine to misfire. At the extreme, I started playing with primary jet size. I could “tune” the car under no-load to run smooth in a 100 rpm band by changing the jet size, but either side of that RPM window I would get a miss, sometimes rather severe.
Now, my observations are:
- Fuel is not pulled through the main boosters under no-load conditions until 3000 rpm.
- When it does come through the main boosters, it comes out as large liquid drops. This is very easy to see with the annular boosters.
- At no time do I get fuel through the secondary boosters or squirter, which I pretty much expected.
- When I pulled the carb off, I find that the base plate gasket is saturated with fuel.
- Fuel pressure is a steady 6 pounds under all conditions
- Voltage to the electrical system is a steady 12.5 to 13 Volts (Using direct ignition source, not factory resistance wire).
After working with BG now for a month, they are starting to doubt that secondary squirter, and are sending me a new carb. I will hopefully get it by next week.
However, last night I decided to bolt on a fairly new 750cfm Holley with a 4 corner idle circuit as a test. Same rich idle, same damn no-load miss.
My next test would be to but the original distributor back in, but now I feel I am just blindly changing parts.
I have also plugged of every external vacuum sorce, including the brake booster, without noting any change in behavior whatsoever. I have sprayed down the intake/head seal with starting fluid and have not noted a vacuum leak in that area either.
Has anyone out there had a similar experience? Any diagnostic tests I’m missing? Due to the rock solid and high vacuum I had initially eliminated a mechanical issue (such as sticky valve or flat cam lobe), but I am now not so sure.
Please, any suggestions would be greatly appreciated. I feel as if I am in my own little automotive hell.
Thanks and Regards!
'69 RS/SS Camaro 502/TH400/4.11 Best 12.10 @107mph
'69 Z/28 Clone 383/TH400/3.73 Done! 996 Points out of 1000 at MCACN 2009
'72 Chevelle 540/TH400/4.11 Best [email protected]
137mph - 11/07/10