cscotto

I bought a 1984 Z28 HO L69 as a project car. The car has had the ECM removed. The engine has a Holley 4160 (80457-2) 600 cfm carb and a Wieand xcelerator manifold. The distributor is a GM HEI. I don't think it is the stock distributor because that one would have an ECM connector on it. It does have vacuum advance, but I know some cc carbs did have vacuum advance. The engine runs and sounds good.

Problem: the engine would not idle at at a reasonable rpm (800-1000). It was idling around 2000 rpm. If I tried to lower the idle, the engine would stall. Carb has electric choke that was not working. I hooked it up and it works, but the fast idle kickdown does not appear to be working. The engine seems to be simultaneously flooded and starved for gas. It seems to take quite a few pumps to get it started. However, if the carb is primed well, the engine starts right up. The starved part occurs when I try to manually open the throttle. If I do it to fast, the engine struggles as if I flooded it. I checked the fuel level in the site plug, and at least according to the Holley videos, it looks like I need to lower the float level. Also, the timing was way advanced. I think this is how the previous owner kept the engine running.

Fixes I have done: I found a few vacuum leaks and plugged them. I could get the engine to idle at around 1500 rpm, but the idle is not steady, surges up then goes down. I readjusted the timing. The lowest I can get it is around 14 degrees BTDC. The idle with adjusted timing is around 1000 rpm, but not steady. The odd thing is that if I try to adjust the idle with the vacuum hose to the distributor disconnected and plugged, the engine immediately dies. Hook the vacuum hose back up, car runs.

So, is this a distributor problem, carb problem, or both? I have a feeling that the bad idle is the mechanical advance not working. If this was a cc carb, the advance at low rpm was controlled by the computer. I am ready to scrape the distributor for an MSD. I think the carb needs to be rebuilt as well. However, before I do all this, I was hoping I could perhaps get a little insight from the great folks at Thirdgen. Thanks

midias

A few things. These cars tachs often go bad so I would double check the RPM reading.


Are you disconnecting the vac advance before you adjust the timing?

Any intake gasket leaks?

cscotto

thanks for replying. I am using the tach on my digital timing light. The tach in the car is, as you said, bad.

I have to adjust the timing with the vac advance connected because if I disconnect it, the car stalls or won't start.

I have not checked for intake gasket leaks, but I will. I don't hear any whistling. I guess I could spray some WD 40 along the gasket when the car is running to see it is get sucked into the manifold. Is there a better way to test for leaks? when the car is idling, I have hooked up a vacuum gauge. The pressure was steady at around 16 in HG. However, the needle fluctuates with the fluctuating idle, so it is hard to tell if there is a leak. Thanks in advance.

midias

I would suggest advancing the distributor then disconnecting the vac advance and see if it runs then. You seed to set the base timing with the vac advance disconnected.

I would also remove the cap and rotor and see if the weight and spring assembly moves freely.

cscotto

OK, I will do both in a couple of hours and report back what happens.


EDIT: I see you are from Henrietta. I moved from Rochester NY to Tampa five years ago. Stay warm!

cscotto

OK, I removed the cap and the rotor. As far as I can tell, the weight and spring assembly moves freely. I can use the plate the rotor is attached to move the springs and the weights. The one thing I am not sure of is the vacuum advance mechanism. The vacuum canister has an arm that connects to a slotted plate at the bottom of the distributor. Should you be able to move the arm?

After starting the engine, I went to adjust the timing. As soon as I removed the vacuum hose from the distributor and plugged it, the engine stalled. I turned the distributor counter clockwise to advance it quite a bit. The car started with the vacuum advance off. The rpms were around 1200 but would fluctuate between 1000 and 1200. I set the timing as as close to 12 degrees BTDC as I could. I got it to around 18. Any lower and the engine would start to stall. I reconnected the vacuum advance and the car idles fairly steady at around 930 rpm. It still revs up and down. Again, I do not know if the cam has been changed, but the idle certainly reminds me engines I have had with hotter cams. Part of the problem is definitely the carb. It really does not return all the way to a closed position. The previous owner had a whole bunch of springs attached to the throttle arm and the front of the engine. I read in another thread about problems with the mechanical advance causing problems similar to mine. Any further thoughts would be much appreciated.

Ozz1967

iTrader: (4)

Vacuum at idle in a stock form car should be around 20-25HG.

I would pull ALL hoses off of your carb, plug ALL the holes, and then start the car. Pull one port off the intake and check the vaccuum. This will isolate the engine from everything else except maybe the brake booster if you don't disconnect that. Then connect one hose at a time and watch for vacuum fluctuations. This will tell you where your leaks are. Fix them one at a time.

cscotto

Thanks. I will try this later. The engine is not totally stock. It has a Holley 4160 600 cfm carb, a Wieand Xcelerator manifold, and Hooker Headers. The only access to manifold vacuum is the connection for the power brake booster. The only hoses on the carb are for the PCV valve and the vacuum advance on the distributor. All other ports are plugged. I will disconnect the the power brake hose and hook up my vacuum gauge to it. I will report back.

midias

Thanks, I am doing my best

The vac advance should move. You can try sucking on the hose and see if it moves.

Personally at this point I would rebuild the carb.

cscotto

I am leaning towards both rebuilding the carb and replacing the distributor. I read in another thread that a faulty mechanical advance would caused similar idle problems. In spite of that, the problem with the choke on the carb is enough to justify rebuilding it.

Jonesyfxr

iTrader: (2)

I'm betting an intake leak from a slipped intake gasket, sucking through the lifter valley. You can check this easily by removing both valve cover breathers and put your hands over both of them. If it's sucking from the lifter valley, your fingers will suck in. Hope this helps.

Good luck!

cscotto

I will give it a try. I did check the manifold bolts to see if they were loose, but everything is fine. Nevertheless, you are right that a gasket not seated well could cause a problem. Thanks.

Jonesyfxr

iTrader: (2)

I was chasing my tail for a week on an 80 ElCamino. Ended up being the intake the whole time.

cscotto

OK, I pulled both breathers off the valve covers, and I did not feel even the slightest bit of suction. I replaced the power brake check valve and hose, and the pcv valve and hose are also new. Everything locked down with hose clamps. The car started right up after priming the carb quite a bit. It ran pretty steady at around 930 rpm. Vacuum reading was 17 HG and very steady. I then hooked the vacuum gauge to the port on the manifold for the power brake. The only two vacuum lines on the carb are for the advance and pcv valve. Blocked both ports. The engine actually ran with the vacuum advance disconnected. Vacuum reading stayed the same. Reconnected the hoses, and it stayed the same. Engine still revs up and down, but not as severe as before. If there is a vacuum leak, I think it is coming from some part of the carb. I also think the erratic idle is still the distributor although it was a little better. Maybe moving the mechanical advance around freed it up. Also, no motion on the vacuum advance, seems stuck.

midias

Time to rebuild the carb and distributor.

stroken85z

maybe you already checked this but is the carb to manifold gasket in good order with no leaks

cscotto

Hi,
Yes, i have checked the manifild gasket, and everything is fine. I pulled out the distributor because i bought a new msd distributor for the car. It turns out, the distributor in the car was an Accel not a factory HEI. Just from things i read about this model (a direct replacement for a factory HEI), the module and other parts have been prone to failure. I think, for example, the vacuum advance has either been locked down or incorrectly adjusted. I have also read that the mechanical advance has problems as well, which could account for the erratic idle. I have some wiring to finish that runs behind the distributor, then I will install the msd and report bsck. I also have a carb rebuild kit, but I am going to do one repair at a time so I can tell what fixed what. Thanks