80TA

I have a 400 pontiac in my 80 ta. I sold it to buddy it used to run good and got it back when he didn't pay me like he was supposed to.

The symptoms it starts alright and idles not too bad. It has a xe274 cam and he took out my 2400 b and m holeshot but getting it put back this week.

So its a very lopey cam and think saw about 10 inches vacuum now and looked pretty steady. Car seems to really bog out off the line and if you go very light on the gas it drives not too bad but if you floor it it really pops and seems to make a weird noise hard to describe exactly.

I have newer fuel pump, fuel filter should be good and have brand new edelbrock 750 performer car and performer rpm intake. I have the xe 274
and have crower dual springs,moly pushrods,comp roller rockers and comp pro magnum lifters.
I have newer rotor and cap,newer mallory coil, new msd 8.5 wires.New delco plugs. None of the above has helped the problem. I am starting to lean to broken valve spring or lobe wiped off cam or something. The car had terrible exhaust leak for likely a long time from crappy old blackjack headers that were leaking horribly so wondering if that caused burned valves?
Also not sure what the syptoms of a wiped lobe are how you would even get one. I put in the cam myself and the cam seemed great for many thousands of miles. The car used to run strong before.

So is valve spring obvious if its say an inner spring. Which is more likey to break inner or outer? Does compression test show anything if just one spring is messed up?
Would one broken spring make the car seem really gutless like it is now.
The car blows zero oil out the back so at least that seems to be good.
I have not compression tested the car yet. Would ignition scope show a problem with broken valve spring? The problem seems worse when floor the car.
Timing is ok and did put in a bit of curve kit.

angel71rs

I know 2 guys that wiped lobes on XE268s installed on SBCs. There was talk on the boards of the XEs having bad metallurgy, but it might just be due to aggressive lobes combined with the zinc issue (search "zinc" on this board for more info). Would hear ticking noises due to increased valve train clearance.

Broken spring also causes valvetrain noise. A compression test will show problems if a cylinder has rounded lobes, not sure on a broken spring. Easiest to diagnose by just popping the valve covers and having a look. If don't see a broken spring, have someone crank the engine over with the coil unhooked and see if any valves aren't being opened as much as the others.

Rice Killer87

Agree ^.

Also check the valve lash....too tight could cause strange problems like that as well.

BUT....what kind of converter is in it now? A stock stall will cause to run really screwy down low...friend of mine has a .530-ish lift roller cam and a stock stall and the car will hardly idle in gear...no converter b/c hes a cheap *** SOB.

80TA

Update" I reinstalled my 2400 stall. It helped of course. I also got a new pontiac distributor off ebay and installed it double checking to make sure it was in correctly not 180 out. It has new cap, rotor, coil,module. I put on new msd 8.5 wires ,delco 45 somethiing plugs. I have timing at 16btdc. Think most guys said to run between 12 btdc and 16. I am not sure on mechanical advance of the distributor ,it also has adjustable vacuum advance.
The car seems to crank over a bit slowly even with new ministarter. I put in new delco battery a day or so ago and car got new alt a few years and maybe 10000 miles ago.
I checked alt, bat at local car parts place. It passed.

The car idles pretty good. The stall as said helps. I see about 10 inches of vacuum.
I still get the loud pop when step on it. But if go up gradually on gas think its not as often. If hammer it then it does it. Tried to run it on highway for a bit to maybe clean off plugs but haven't much do to some other problems with leaks from think stall install. Taking it back to tranny shop next week for that most likely.

So also might take it to speed shop. These are things I though should get checked. I also looked at springs under drivers side think they are ok. Didn't check passenger side yet.
Was going to check fuel pressure, maybe float in the new carb. Was going to have them check spring pressure if they dont' see any visible broken spring and set rockers as have those goofy comp r pro magnum type lifters. Can get run on scope too if necessary. Think do compression test maybe also if he thinks its a good idea.
.Don't think the timing is making it pop could try going down to 12 or so see if it turns over better. Not sure why it seems to turn over a bit slow. Mabye the rockers are too tight? I would try to set them but they are messy to set without clips or cut valve covers. Let my local speed shop pro do it. If the cam is gone then likely buy kit and put in new normal type lifters and milder cam. Dont need this wilder 274 and likely will switch makes to crane or crower. I am wondering if those crower springs would be too much for lower lift cams. Not sure which ones I went with ,might have the box around here somewhere. They are crower dual springs.
Anymore suggestions?

Rice Killer87

Sounds like a bad plug or a fouled plug to me,but then again im not hearing it in person so its hard to tell.

The float bowl level is easy to do and needs to be checked...check edelbrocks website b/c I cant remember how to do it them as ive only been doing holleys for a couple years now.

Also check the timing while having someone else rev the car from idle and gradually bring it up to about 3,000 which is where you'll want full timing advance in by. Make sure it not jumping around and goes up steady.