bmankin

Found TDC, Installed distributer at 8 degrees BTDC. The engine started like it was fuel injected. After it warmed it started missing at idle almost like it was backfiring through the exhaust. Very low vacuum at the carb. Less than 5 in. I can advance the timing and get a little more vacuum. about 15 in. at the intake. Somethings wrong but I don't know where to look.

OzzyTom

First thing that comes to my mind is intake manifold leak....

If you used gaskets between the manifold and block at the front and rear, that may be where your leak is.... I've given up using gaskets, and use an appropriate high temp oil resistant silicon sealant... much more reliable.

tom

427Hotrod

Pull valve covers and check valvetrain.

JIM

Durango_Boy

Does it still run good when it's cold and only starts missing once it warms up?

If it now runs poorly even when cold I would suspect valve train as well. Check your oil for metal too.

bmankin

No obvious vacuum leak. When you try to start it, it sometimes backfires through the carb. Edlebrock performer. do you think thats doing any damage? I have never been as sick of a project in my life...
I did not install the rockers, do you think they could be to tight? There is nothing clicking like they are to loose. Comp roller tip 1.52 ratio. this motor only has about 120 miles on it and it got something (red Loctite) under the first bearing cap so I had to pull it back out. I just started it yesterday again but I did not let it warm up until today. I Think it might be a vacuum leak but if a valve was cranked down to tight it could doe the same thing, right? If I find metal in the oil I'm selling it for a parts car.
BTW, It runs fine when cold and the only problem when its hot is the backfire but I have not road tested it yet.

weimer20

Backfiring through the carb can really only be one of two things (I think). First and most obvious is timing. I've seen mixups with harmonic balancers where the timing mark is "off".. If true TDC is not checked (properly), it could be off.. The thing that gets me is its only happening when the engine is warmed up. That leads me to the only other possibility that I can think of which is valves. I'd check valve adjustment first then progress with the degree wheel to verify true TDC. Just my 2 pennies. Anyone else thinking along these lines?? Shoot, I could learn from this!

bmankin

I'm sorry, I wasn't clear. When it backfires through the carb. it is when I first try to start it. When it warms up it starts a strong miss through the exhaust. When I first started it yesterday it was real gassy smelling but thats cleared up. If it is a timing problem it seems like it would be a little harder to start but I'm no expert. I can advance the timing and the vacuum starts to come up. This is with the vacuum advance disconnected. That sounds kinda like the harmonic balancer is jacked up don't it?

73, Dark Blue 454

Agree with the above,..start with a static set of the timing.

1) Turn the engine by hand to TDC (or close to TDC) as you watch the valves on the number one. You want TDC just after the compression stroke.

2) Turn the engine by hand an additional 8-10 advanced on the harmonic

3) Pull the number one plug wire and install an old but working spark plug in the boot

4) Loosen the distributor tie-down bracket

5) Turn the ignition key to the "on" position

6) While grounding the plug (away from the carb) rotate the distributor back and forth and stop where you get spark

7) Turn the key off, tighten the distributor tie-down bracket, reinstall the valve cover, and reconnect the number one plug wire. (Note...you don't want the key to stay "on" without the engine running for long but the step above, #6, doesn't take but a few seconds).

The timing is set. Fire it up and see if that solves anything.

As mentioned, if you have a mismatched harmonic and timing pointer, the above won't work.

Let us know what transpires and good luck!

Bob Onit

This can also be done with an inductive timing light on the plug wire.
Just watch for the light to flash while rotating the dist.

bmankin

I set the timing with a dial type light. If it is off it is because of the harmonic balancer. I think I read or heard that edlebrock performers are "backfire proof". Is that a true statement? It didn't backfire hard or at least it didn't appear to. What about a wiped cam lobe? I've heard about it but I just pulled that cam out and it appeard to be broken in OK. The guy at the machine shop thought so too. He assembled the motor the second time just to make sure it was right.

SIXFOOTER

Put a vacuume gauge on it and see what that tells you
Mechanically check the timing by verifying TDC
Go thru the valve adjustments, with the valve on the base circle, back the adjuster til you can wiggle the pushrod up and down with your fingers and then turn it down til you can't wiggle it and then 1/4 turn. You will have to turn the motor over a couple times to get this done

73, Dark Blue 454

Backfire-proof intake manifold? No,..bad info

If you're confident the timing is close and you have the correct harmonic/timing tab combo, then it's time to look at the valve train. Could be a valve spring(s) or bad lifter(s).

TJ76

If you have solid lifters, you need a bit of clearance to compensate for push rod and valve expansion. If too tight, the valves will hang open after warm-up. Same can be true if you have hydraulics.
Good luck.
TJ

rcread

Did you double check to make sure the spark plug wires are routed correctly? This is a pretty common and easy mistake to make (and easy to correct).

bmankin

You know I thought about that but didn't want to mention it. I'll let you know.

Duke94

or Timing is off.

bmankin

You know I'm gonna feel like an idiot.

Duke94

Don't feel bad, we've ALL done it.

LXXVIII

I had a motor once where I had few miles on it and it was doing close to the same thing. Valves were adjusted correctly and so on, but a cam lobe was worn down. It was a new cam so I did not check it until many days of frustrations. You can verify it by placing a dial indicator on the rocker and rotate the engine.

Also, I have also had to time an engine in the woods by bringing the RPM's up to about 2000 and rotating the dist. to the highest rpm. Works the same as the static timing when starting a new moter, but will help if the balancer is off.

bmankin

The #1 and #3 wires were crossed. I started not to even tell yall but I figured I owed it to you. Thats what happens when I get in a hurry. Why did it idle so smooth? Why am I so stupid?