I just finished a 69 SS camaro-- 350 zz4 crate motor came with the car-- 4-speed- headers-- 3.73 rear gears-- everything new except distributor--- new fuel tank- pick up, lines-- a new 69 camaro.

It initially ran like a raped ape-- very very strong. I felt it drop off and have tried everything i can possibly think of trying to find the problem. It comes out strong but as i pour the pedal to it-- it lays down-- wont generate any more rpm-- i let off and it is ok-- something is really crazy-- i put another HEI distributor-- no LUCK--- plug wires and plugs are new-- i changed oil thinking my dipstick was wrong and i might be losing lifters with aerated oil--no luck--- i ran an external gas supply in case something was clogging the new pick up at the tank, no luck-- i pulled the inline filter, no luck --- i found 4psi on the mechanical fuel pump and put a new one on, 9 psi but no luck. Timing is per specs for the ZZ4-- 10 degrees idle and 32 degrees at power. I have a new holley 600 cfm with choke unhooked cause its hot in florida and i dont need it. Its crazy cause for the first 50 miles it was full power-- now it wont give high rpm. Any clue or suggestion as to what i should try next? I am at wits end.

 

Welcome to Camaro Forums. I know you said your choke is disconnected, but did you check to make sure the butterfly is straight up & down, and staying that way?

 

I wired the butterfly for the choke so it cant close.

 

Here what I would do,

Step one: Verify your timing advance is working right. With a adjustable timing light make sure you are near 30 deg total timing when you rev the motor up to 5K.

Step two: Hook up a vacuum gage and watch the vacuum. If you have some aire restriction you should read high vacuum. If the needle starts to jump you are floating the vavle. If the vacuum reading is low (as it should be) and you are sure well timed spark and your exhaust is not restricking then you are could be starving the motor for fuel or running it too rich.

Step Three: Verify lean/rich you need to get the motor to boog down for 10 seconds or so and kill it. Then pull a plug. Do not let the motor run "normal" or idle as that could mask the issue. Inspect plug, black is rich, white is lean.

Carb based cars are easy to work on but once you have felt the differents a dyno tune can make you will take every engine you setup to a good dyno tuner. They can tweak the car and the timing advance arc and gain you a lot of hidden ponies. In your current state you can kill two birds with one stone. Get your car diagnosed and tunes in one trip.

 

What vacuum source do you have the distributor hooked up to?
Is the engine fine when cold, but gets worse as it approaches running temperature, or is it doggy regardless of engine temps?

 

Thanks Gorn-

Its timed at 10 at 750 rpm with vacuum to dist plugged (manual transmission). Revd up it advances to 32

I havent tried the vacuum gage yet but will do this--- sounds easy. I personally feel it is not getting enough fuel. I have revd it up and observed the secondary butterflies opening cause i thought this could be the problem.

I will pull plugs initially and inspect-- not sure how to get it to bog for 10 seconds before i check the plugs again though.

I really like the idea of the dyno tuning-- alot-- great suggestion

 

The car is great cold and hot-- and the vacuum source is a small diameter port from the forward base (adjacent to the big vacuum port i am have my PCV hooked up to)

 

Carb vary so much I can not remember them all. There are to types of Vacuum. Manifold and Carburator. On a ZZ4 motor I would expect 13-15 inch of vacuum at idle from the manifold vacuum and almost no Vacuum from Carburator port.

You can get a long hose and run the gage into the car while your driving. If your car is starving for air your manfold vacuum will go up with higher RPMs. That is the motor fighting to pull more air in. The 10 second thing is just a guess, If you can shut it down while it is doing it and coast off the road the plug will give you a clue what is going on.

 

The fact that it was fine for the first 50 miles means something obviously changed.
Could be you had a chunk of crud in your fuel line and it's restricting the fuel flow into the carb, or....
you could have a defective float (sank) or something went funky with your float settings.
Have you removed the sight plugs and checked both float levels?

 

Gorn and 69 Camaro--

I will check the vacuum next-- i really think my problem is something along the supply side-- i wouldnt understand how spark could change and i know the timing is right and i do get vacuum advance to 32 degrees. Will let you know how that works out.

The 10 second thing will be to hold it to the floor for a while then do as you recommend. I will do a plug check before and after.

The new 600 holly doesnt have adjustable floats-- so i will pull it off and check the float levels---

I will also throw a tach on it - been kinda picky on what tach to use-- the factory tach wasn't cheap and needed adapted to the HEI ignition. I plan on getting a small sun tach and mounting it on the steering column.

I am amazed this is happening -- this car is strong for the first couple thousand rpm then lays down.

I am pretty sure the distributor is perfect- but will double check the tdc and #1 firing position. I have heard talk of being one tooth off but i think that refers to the sprocket gears--- or could the distributor gear be one tooth off and still run as great as it does at low end and be timed correctly?

Appreciate all the help-- i wil load some pics of this car when i figure out how. Think i just did--