I'm a new member with a '67 E block original 4-4-2. I just rebuilt the engine, .30 over, for the second time within maybe 10k miles due to issues with the first rebuilt. I changed only ONE thing on the stock rebuilt this time around and that was I used the hotter W-30 Cam for that year. The car now has a pretty bad 'surge" or I call it more of a "******" at a constant speed. Not under acceleration. The plugs look like they are burning extremely lean. I've been told its the primary jets needing to be swapped out, so I just swapped the Q-Jet .071 primaries for .073, but really don't feel a difference. Does anyone know what Carb changes or other changes are necessary to make this hotter cam work in my 4 speed car? It sounds great and accelerates ok, but just very "jerky" at any constant speed in any gear. It really ran better with the stock 4-4-2 cam, before I had issues with the valve guides moving around, thus requiring the second rebuild. Feels like a vacuum leak somewhere but mechanic says its not leaking.

Thnx much.

 

My feelings are if the plugs look lean that would be a good clue, you could go to a larger primary jet to see if you went big enough. I would also go over the ignition system to be sure there are not anything wrong that would cause a miss or perhaps there is a condition of lean misfiring going on. I assume your fuel delivery is strong enough to carb. Was the carb rebuilt? Maybe something has gone sour with it? I really dont think the cam change caused the problem you are having. When I did my stock 400 rebuild I also used the 67 W30 spec cam and it runs just fine, 4spd. The carb was used shortly on a stock 425 and performed the same. The carb was rebuilt and was original to a 67 Toronado. I dont know what primary jets it would have come with.

 

This is a very helpful reply - simply the fact that you also changed the W-30 cam into a stock 4-4-2 setup and things ran fine tells me a LOT. I have the Pertronix Igniter III for ignition and it seems to be the same before and after the rebuild - plus I've checked its ground wire. Still, this is a key part of the puzzle. Thanks much!

 

Richer jets, rods and rod adjustment would be my first take.

 

Hello and Welcome!
I had the same thing with my '67 E block. W30 cam. Vacuum leak. I took out the bolt that is in front of the throttle on the carb to replace that check valve. I didn't put the check valve back on, and that bolt goes to a intake runner. Put the bolt in and ran a lot better. Plain site but missed it.
Mike

 

Does sound like a vacuum leak with the surging.
I'm not an expert here, but also with the change in vacuum with cam should also be a change in the power piston spring. Or considering it is a more radical cam anyway, get rid of the spring spring altogether.