[firstyearta]

I'm not positive if this is the best place to post, forgive me if it's not.

I've recently put my 1973 Firebird Formula 400 (4 speed) back on the road after a many-year restoration. The engine was not rebuilt as it ran fine before.

The symptoms are a bit hard to describe, but I'll try my best.
It will start right up and run but it does not run smooth, though the engine sounds like it's running on all 8 cylinders the exhaust sounds like something is amiss. The exhaust almost has a sputtering sound do it. The though has crossed my mind that maybe it's the muffler but I really am not sure.

The carb seems to be adjusted fine and function fine but not sure if after all that time sitting, it has issues. The timing is also set. Points have been converted to Pertronix.

When you take the car out and drive it, it has a slight surge to it. It never seems to have a nice constant rpm. Now don't get me wrong, this is not a violent bucking surge, you can just tell as you're driving it's not running smooth.

Again, this is one of those things that is rather hard to explain as it's sort of minor, but just not right. I'm hoping something I've said here might sound familiar to someone and maybe give me a direction to go and/or what to look at.

Let me know if I can provide more info.

Thanks!

[1967Tempest]

What is the timing set to? Also what kind oh heads does 400 have? Carburetor type? Spark plugs and gap ?

[A.W.Dille]

From the sound of it, since it sat for several years I would start with a teardown, cleaning and rebuild of the carburetor. Gas can turn to varnish after it sets for a period of time, which in turn will create blockages in passages. Also I would suggest having the gas tank flushed out along with all the fuel lines and possibly installing a new fuel pump.

[rohrt]

I would start simple and just pull the distributor cap and make sure your advance is springing back. Then check your timing at idle and on up and also verify your vacuum can is all working.

Have you messed with the idle mix screws?

No crossed plug wires?

[Grand73Am]

I'd try some new spark plugs first, if you haven't already changed them.

[Doug]

The Nascar driver who has a comfortable lead late in the race starts hearing his car making all sorts of weird sounds and acting like it has started to miss.

Seafoam the tank, get some good gas and drive it hard!

[gtofreek]

Besides the suggestions already made, if it has an EGR valve on it and it is not functioning correctly, the engine will run rough, but will run on all 8 cylinders. If a little piece of carbon gets stuck in the valve, that's all it will take. A good cleaning of the EGR valve could fix that.

[firstyearta]

Thanks for the replies!

The engine was rebuilt by the previous owner but appears to be an unmodified '73 400 with stock heads and Q-jet. I did have the carb rebuilt by Cliff Ruggles about 10 years ago when I first bought the car. Plugs are new AC Delco R45TS gaped at 35. The timing is set at 12dBTC. The wires are also new. The car has a brand new gas tank and all rubber fuel lines were changed. There is no EGR valve, it was removed before I purchased the car. I have played with the mixture screws and that helped some but did not eliminate the problem. No crossed wires. I'll give the distributor springs a good look and check the vacuum can. Sounds like the carb might need to come back apart.

[Old Tin Indian]

pull the distributor weights right off and see if there sticking. clean them and clean where they sit in the distributor. obviously you'll pull the spings off doing this. check them and reinstall. if you have an outside vacuum source(mity-vac) apply vacuum to advance cannister to see if it is working. holding vacuum and pulling the advance plate.
with todays crap gasoline, i would be willing to bet the carb needs a deep cleaning.
with crap carb cleaner. isn't it great how eveythings best for the enviroment, but not for the consumer. sorry, on a roll here.
keep us posted on your progress.

[firstyearta]

I just wanted to update this.

After trying various things (even replacing the carb with another), what finally cured the problem was ditching the Pertronix ignition and putting the points back in. I really have no idea what its issue was but getting rid of it cured my miss.

[Old Tin Indian]

points. adjusted properly, they run good. but, that's the problem. you will be constantly adjusting them. if your dwell is off, your timing will be off. plus, if you don't use a good set of points, they could bounce on you at higher rpm. and, if you put a good set of points in, they wear the rubbing block out quicker because of the higher spring tension, again causing your timing to go out of spec also. this is one of the things that i was glad to see go in the early 70's.
you could put a set-up hei in it and make life easier for yourself, or if you don't like that fat looking distributor cap, get another pertronix system and install it in a points style distributor, retaining the stock look. i've been running the pertronix for 20 years now with no problems. also, many friends doing the same.
sorry so long. it's more than my . best to you on whatever you continue to run.
tony

[LATECH]

Originally Posted by firstyearta

I just wanted to update this.

After trying various things (even replacing the carb with another), what finally cured the problem was ditching the Pertronix ignition and putting the points back in. I really have no idea what its issue was but getting rid of it cured my miss.

read post #13

http://forums.maxperformanceinc.com/...d.php?t=734804

[salem1912]

Any chance at one point(no pun) did you leave the key on engine off for a while?

[gtofreek]

Originally Posted by firstyearta

I just wanted to update this.

After trying various things (even replacing the carb with another), what finally cured the problem was ditching the Pertronix ignition and putting the points back in. I really have no idea what its issue was but getting rid of it cured my miss.

Did you have a tach hooked up to the Pertronix? I saw a tach mess with them before.

[RamAirIV28]

Watch out for stuck valves, usually the result of chit gas left in the gas tank for a million years.

reving up the engine does not cure it.

[steve25]

The first thing you want to do is confrim even compression, to do so put a full charge on the battery, kill the spark to the plugs and crank the motor for 8 seconds and listen close for any changes in cranking rpm that would be a indicator of very uneven compression.
If that checks than my moneys on a gummed up power piston in the carb from it sitting,

[gtofreek]

He said he tried another carb and that didn't help. He said it was fixed by putting points back in. How is that carb or gas related?