Popping cutting out at WOT

[Kerplunk]

So this weekend I picked up a rebuilt 750 edlebrock from a buddy to replace the 600 eddy on my 440, the car is a 67 Belvedere.

Went for a test drive, and it pops and cuts out at WOT, I took it apart checked the floats and the metering rod and jet numbers and went for another test drive and same thing. So I put the 600 back on and now that Pops and cuts out at WOT too. Could I have screwed something up running the other carb?

Any ideas on where to start and troubleshoot?

Thanks!

 

[70rr-brian]

I would look at fuel filter and fuel pressure from pump. I know it doesn't make any sense given what you did...but sounds like it may be starving for fuel when you floor it.

 

[68gtxman]

Carb Trouble

2 things to check - first is try pushing in on the secondary top plate to see if it is stuck. Sometimes when you stomp on the gas and then drop it off, this plate shuts so hard it gets stuck in the closed position and won't open the next time you floor it. The 2nd thing to check is total timiing. Take off the distributor's vacuum hose and plug it. Then take it for another test drive. If that solves your problem, then do some trouble shooting of the distributor if you can. You should always run with vacuum advance on the distributor (see Mopar Muscle articles on this).

Good luck!:hello2:

 

[Cranky]

Check your base gasket. Did you use a new one when replacing the carb?

 

[amike95]

Check your base gasket. Did you use a new one when replacing the carb?

Good point. I tried reusing a base gasket once and the same thing happened to me.

 

[Kerplunk]

Yeah, I reused the old base gasket. I'll try a new one and report back, thanks guys!

 

[plymouth67]

Is it floating the valves?

 

[theman440]

A flat cam will do it too.

 

[scotts74birds]

Any thought of installing an O2 sensor and fuel/air monitor? Rich at the end could mean the ignition is cutting out. Lean would mean a fuel shortage.

 

[Kerplunk]

It runs beautifully as long as I keep it under 3000rpm, anything over that and it pops, either in gear or neutral.

So I installed the new base gaskets and checked the carb, still pops. I checked the plugs and wires they look good. 7 out of 8 were light brown, one looked a little carbon fouled, but not really bad, I changed that plug and she still pops.

Tomorrow Im going to change the fuel filter and install an inline fuel pressure gauge, double check the timing. I would love to have an o2 sensor, it would definitely make tuning easier.

If that doesn't work I think I'm looking for a broken valve spring or flat cam.
Im guessing if thats the case I should start with the plug that looked fouled?

Thanks guys for the help.

 

[67 B-body]

Did you get the vac adv hose plugged into the correct port when doing the swapping back and forth? Sounds like your telling us that it didn't miss and pop before you started changing carbs. I doubt the cam went bad while the engine was not running, and I bet the valve spring didn't break then either.
I hope you find it's nothing major!

 

[Kerplunk]

So looks like Ive got an issue with the exhaust side of number 6, doesn't seem to have the same movement as the others, but the pushrod is still spinning.
Is the cam toast? Its the same cylinder as with the fouled plug.

 

[70rr-brian]

If the backfire is only happening at higher rpm's it could be a broken valve spring. Could be cam lobe or lifter.

Put a mark (white,yellow or something easy to see) on the pushrod. Mark the bad exhaust valve pushrod and an expected good one. Bump the motor and see if each are moving at least 1/4" or about the same. If not, remove the rocker assembly and try again. If they now move the same it is likely the lifter that is bad. If it still isnt moving as much then it is likely the cam lobe.

 

[Kerplunk]

Here is a picture of the lifter from the rocker without movement, its about 1/8 inch concave, Im assuming this isn't a good thing. I cant just replace the offending lifter correct?

If I need a new cam for the 440, what else should I replace while Im in there?
Timing chain? Valve springs, I'm thinking about the MP 509 cam.

Thanks guys!

 

[67 B-body]

did you just perform an oil change about the same time you swapped carbs around?

 

[Kerplunk]

No, but It did have the occasional tick.So Im really not surprised, I guess the carb was just coincidence, or my test and tune was the last straw.

 

[67 B-body]

Anyhow,,, todays oil will cause this very thing,,,, Happened to me too!
Only problem is that you now have all the metal that's missing shoved in all kinds of bad spots! I had to tear mine down, Inspect bearings, and clean it all out then re-assemble. I ended up pumping about 4 gallons of Kerosene through the oil passages with a new filter stuck on the pump to make sure all of it was out! then I ran some cheap oil through to get all the Kerosene out!
Make sure you use some good oil and get the RPM up right away to make those lifters spin during breakin,,,,,,, Brad Penn is what I went to and worked great!

 

[70rr-brian]

Maybe consider a total rebuild to match that big of a cam. Get head work done and compression and intake to match. Otherwise just replace like for like would be my opinion.

 

[Big Jim]

After seeing the lifter I know this isn't the problem BUT if you're running a points dist. you could very well be seeing points "bounce" @ high rpm. Used to be a common problem back in the day with cheap parts. Seen more than 1 car with vacuum tubing behind points to cure it.

 

[plymouth67]

We just pulled out my buddies lifter from the same exact hole and it looked the same. 300 miles on a brand new rebuild..... replaced the one lifter and within 10 miles it did the same thing. We pulled the cam out today and that lobe is toast. If you replace that one lifter it will most likely do the same thing.