I know this question has been asked before but here goes.
My 74 has a 650 Holly DP Carb, new distributor(no points) aftermarket cam and Hooker Headers.
Also, has roller rockers and as far as I know (no suspected vac leaks.)

I have adjusted the carb until my hands got tired and had to idle it up to 900 RPM's to smooth out the idle a bit.
Car still has a rough ide, could this just be the cam.

As I mentioned before I have no idea what cam it is.

The only thing I think might be causing the proble is my Headers with 3" collectors reducing down to 2" stock exhaust causing plenty of back pressure.

Thx,
Schoon

 

Lets start with the basics, like spark plugs, plug wires, timing and so on....

How old are the wires? Headers have a funny way of burning them up. The plugs may be fouled, incorrectly gapped or just the wrong application.... Is the firing order correct? Spark plug wires that run close to each other could be cross firing too. Has the timing been set or checked? How much vacuum are you getting?

Lot's of questions - I know.....

Anyway - if the carb ain't responding then it probably ain't the carb.....

My .02 worth, I hope it helps!

 

Plugs and wires have less then 5k on them.
Timing was set when new distributor was installed 500miles ago.
Vac must be okor my power brakes would not be working good.
I will check anyway.
Ben think about putting insullated sleves on wires by headers, have them on my camaro and they work well.

You don't think it could be the back pressue or just a nasty cam?

 

Did the idle get bad recently without any other changes or was something worked on and then it went bad?

Another thing to check would be stuck vacuum or mechanical advance.

 

The idle has been very rough since I got the car 3 years ago.
It was really bad then until I rebuilt the carb and that helped some.
Then I replaced the distributor and that helped a little.
Yesterday I sprayed starting fluid looking for vac leaks, no luck.
When I get on it it runs very strong in first and second gear.
Cruises very good @ 60+

I am begining to think it's just the cam doing this?

 

2" exhaust should be OK. Do you have catalytic converters? Sometimes they collapse internally and block the exhaust flow. A restricted exhaust would limit top end speed and you would hear the pressure building up in the exhaust and leaking out someplace ( a hissing sound).

It still sounds like a vacuum leak to me.... or an ignition miss...

How is the oil level? Low oil pressure will not pump hydraulic lifters enough to give good valve opening/response and will result in a rough idle too...

Keep us posted!

 

No converters, oil pressure is very good.
The stock 2" exhaust is connected to 3" collectors on the headers.
I bought new plugs today and will set the gap wider then before, 40 instead of 35


Stay tuned!

 

Watch your engine vacuum @ idle. Sounds to me you have a lot of valve overlap (big duration cam) tall lift, big duration means rough idle because the intake and exhaust valves are slightly open at the same time during idle.

 

When you say watch engine vac at idle, what am I looking for?

 

Pulled plugs today, 2 were wet with gas.
Put news one in and car has a lot more power then before, idle still on rough side.
Now the question is what made the plugs wet?

Schoon