Rough Idle

[BLAKEBRONCO]

Guys,
I have a 302 in my 72'; when I purchased from the PO, he had put a newer model 302 in (around a 1980) Years ago I put a Holley 4 brl carb on and couldn't believe how well the engine ran. Recently I did allot of work on my front end - nothing related to the engine. My Bronco suddenly developed a real rough idle - almost as though I had a racing cam installed. I don't know crap about engines.
Now my truck is running so rough that it will not hardly go. I'm not sure if the problem is electrical or fuel related. When the problem started, I thought it was a choke issue; but it spits & coughs almost like a timing thing.

Any ideas?

 

[68 Broncoholic]

That old of a motor has the old heads w/out case hardened valve seats which needs leaded gas. Now that we use Unleaded it burns them up. This happened to mine and had a rough idle. I did a compression test and it came up OK on all cyl. Then I did an air leak down test and found a leak. In #2 the valve was leaking. I pulled the head and found most of the other valves were recessed up inside the head about to fail also. I sent the heads in and got hardened seats and it ran like a new truck again.
Something else to look at is inside the distributor, check timing and maybe look at each spark plug. Pop the hood at night and see if you see sparks fromt he wires.

 

[BLAKEBRONCO]

68 Broncoholic - Thanks. I believe I just found the problem. While cranking it this morning, it spit, (to an idiot like me that is timing related. Apparently when I was doing all the work changing out my PS pump & hydro-booster, etc... I must have bumped my distributor - it was loose. Now my next question - how should this timing be set?

 

[broncnaz]

If you have a single diaphragm vac advance on the dist. use a timing light to set it around 10-12 degrees(stock is 6 degrees and if you have a dual diaphragm dist it will need to be set to stock specs) then adjust the carb to get a smooth idle. Then go drive it make sure you dont get any pinging if so back the timing off a little keep in mind you may have to readjust your carb each time you adjust the timing.