idle problem

[mustangman1974]

ALright all it seems I am plagued with weird issues. Yesterday I took my car to a charity car show. When I arrived my car started idling a bit rough no biggie sometimes it does it when the air is on. I shut her down registered and drove it to my spot. When I was backing in it started to die. Like it was starving for gas. Well the day went on and I just sat there shoot the poop like normal. When I went to leave. Damn thing would not idle. It was missing bad. This is the odd part when I reved it above 2.5k no problems and the missing disappeared.

Got home start checking.

I can pull 2 3 5 8 wires off with no idle change 1 4 6 7 it almost dies.
I can screw in the right idle screw all the way in with no change. Very little change all the way out.

If I unplug any vacuumed item, such as pvc, or trans mod leak causes car to die.

Changed carburetor from edlebrock to holey same problem.

Check timing gap on breakerless pickup. fine .010 - normal

Timing at 8 degrees. - normal

vacuum is barely 10 in when its normally 19.

checked for vacuum leaks around manifold and carb.

Check plugs all looked good but 8 and 6 they had major carbon deposits. I changed them and noting changed.

If idle is held above 2250 it smooths. at freeway speeds no missing or surges. anything below 2200 it hesitates both carbs. holley works fine on 68.

I find it funny its all the same venturi on the carburetor. The only issue is I changed the carb.

Oh and I changed coils, resistors, and primary wires.

What could it be.

 

[rbohm]

torque the intake down to 30ft/lbs. that should cure your leak.

 

[bnickel]

yeah, i think you hit the nail on the head with vacuum leak, that's definitely what it sounds like. i also agree it could be the intake causing it as well.

 

[mustangman1974]

Just out of the blue like that? I'll try tomorrow and let you all know. I also noticed that bank on the manifold was oily inside while the other side was clean as a whistle. Could the intake gasket be bad under the manifold?

 

[paintballtommy]

thats a good possibility. take apiece of vacum hose hold it agains your ear and run it along the edges of the intake while its running. listen for a hissing sound. also check the carb gasket. and try plugging the vac advance lines as well as checking all your vac lines.
but it deffinitely sounds liek a vacum leak

 

[mustangman1974]

retorqued intake 22 ftlb - same rough idle.

changed all plugs gaped to 45 - same

Changed MBI brain - same-

should I take the manifold off and try that?

 

[mustangman1974]

Alright problem is still here.

change intake. Now a ford 4 barrel cast iron.

same carb

still no idea.

To keep it running I have to pump the throttle to keep it running. LEft side of carb sounds like its sipping the last of gas.

Checked floats all good.

One goofie thing I put carb on backwards and engine started smoking white smoke.

I sprayed around throttle shafts and engine speed up. (will rebuild solve this?)

Did compression test all cylinders are 155-160. (no burnt valve i guess)

New plugs are now completely carbon fouled. only about 20 minutes run time on new plugs.

Alright any other suggestions?

 

[mustangman1974]

Ok new update. Rebuilt 3 times. Last time I soaked carb in acetone for 3 days. Seems to have cured the rough idle, however I have very little throttle response compared to before problem.

Idle still varying between .5 - .75 in hg.

I am kind of hoping the combination of summer gas and deep cleaning might have returned carb to new.

What jet sizes are is everyon one running in so cal?