Engine missing (well, I know where it is)

[71Shortbed]

I've got a stock 307 with an Edelbrock 500cfm and performer manifold. It's been running great until yesterday. It started running rough like its got a plug wire off. I replaced the plugs, wires, points, rotor, condensor, and cap. Set the dwell to 30 degrees and timing to 8 degrees and it's no better. Checked all my vacuum lines. Still runs rough and sputters and backfires when I step on it.
Any ideas what it could be?

[krue]

Can u tell which cylinder is not firing? I had problems with mine until I replaced a cracked exhaust manifold of all things.

[71Shortbed]

I can't tell for sure but it appears to be on the drivers side. 1,3,5, or 7. Idles smooth and normal but pulling up my driveway it shudders and runs rough as hell. Should I do a compression test?

[larry may]

WATER IN FUEL? Blown Head gasket? Float in carb needs adjusted? Good luck . POINTS GAP TO WIDE ? Cam sprocket failing ? Good Luck

[krue]

May want to pull the plugs and check them. Any Haynes manual will have a TS guide for plugs.

[chops333]

take off rocker cover start engine see if all rocker arms move smallblock chevy notorious for wearing out cam hope this helps

[71Shortbed]

I pulled a few plugs. They are black and sooty and so are the pipes. Maybe its just running too rich. When I stand on it I hear the exhaust really crackin and it starts to cut out. I'll dig into the carb next and see if I can lean it out a little.

[4tiresngas]

71Shortbed, why did you set the timing to 8 degrees advanced? The reason I ask is because when I got my truck it was 8 degrees advanced. I set it back to 0...where I thought it should be. It fires right up. Was that wrong?

[71Shortbed]

My 71 Service Manual says 8 degrees for a 307 with automatic and 4 degrees for a manual. I was running it at 12 degrees with no problems. I went back to 8 just to eliminate that as a possible issue when it started running like hell yesterday. More advance should give you more power up to the point where it knocks and become a bad thing.

[truckdude239]

does it only do it when you step on the gas? if so it might be an accerateor pump in the carb

[71Shortbed]

I thought about the carb pump but it does it all the time. I thought about trash in the filter but generally that means it would run OK when it starts and die out when the bowl runs dry. Maybe its my mechanical pump going bad.

[larry may]

Like chops333 said . Also look for BENT PUSH RODS.

[71Shortbed]

Thats my next step. I'm going to pull the covers and make sure my rockers are moving. Thanks

[cdowns]

i'd set the timing at 0//the dwell needs to be 33-34//plugs gapped at .035

[71Shortbed]

I'll try it but why 0 degrees when the manual says 8? Do you think I'm getting too much advance at higher rpms? My vacuum line is on the carb port that only pulls a vacuum above 1600 rpm. All this was workin fine at 12 degrees until I went for that afternoon spin...

[jamesi20]

I don't think "0" degrees is going to help 8 degrees sounds more like it.you could have a cam problem as these were notorious for lobes wearing,that is if it is a stock motor

[chops333]

also did you disconnect vac at the vaccuum advance when you set timing just a thought

[71Shortbed]

I'm starting to suspect the cam. It's stock with about 140,000 miles on it. Dangit That's not a 3 beer job to replace a cam.

[motocrosschump]

Take the valve cover off that side and start and see how far the lifters are lifted.

[lloyd k]

timeing chain , cam and a good lifter puller

[mrein3]

Originally Posted by 71Shortbed

I'm starting to suspect the cam. It's stock with about 140,000 miles on it. Dangit That's not a 3 beer job to replace a cam.

Not a three beer job but if you're in a hurry you can be staring at a camless engine in about an hour. Of course clean-up of parts and reinstalling everything takes about 3 more hours.

Pull the valve covers first. Check for rockers that don't move as high as the others. Every flat cam I ever had was obvious with the engine running and the valve cover off.

The engine that was in my truck when I bought it stumbled and coughed when I was trying to make power (pulling the boat or passing on the highway). That time I had two exhaust valves that weren't working any more. A compression test will tell you about that if your cam appears to be ok.