I'm looking for insight on a couple of problems I'm having with a '67 straight 6 automatic.

I just had the head rebuilt. Now that it's back together, there's a new noise. It's like a metallic clanking periodically. It happens more when the throttle is opened just above idle.

Another problem I'm having is a rough idle when the car is in gear. It's just fine in neutral and park. In drive, the idle gets quite rough and the motor starts to bounce around.

There are no vacuum leaks, including the line going to the tranny. The motor mounts and tranny mount are new. The timing is correct, and the problem happens at any timing.

 

ok, even tough you say there are no vacuum leaks i would do the following.

set idle timing to 8 - 10 degrees before tdc with the dist vac disconnected.

make sure there is no vac to the dist at idle.

disconnect all vac lines to the carb and plug them at the carb. pcv's and loose fitting pcv hoses are one common cause of this.

spray flammable brake cleaner using long nozzle gently at carb base etc.

turn fuel mix screw in 1 turn and out 1 turn from current position. if it has no effect your idle circuit is plugged.

if it does have an effect then turn it until the highest engine rpm is reached then reset idle using idle set screw.

hopefully this finds or fixes the prob.

if not it may be possible that your valves are no longer closing properly because the machinist did not grind the top of the valve stem to the proper height.

 

readjust your valves

 

Outstanding, thanks much for the advice. I believe the problems are both solved. I found a vacuum leak at the compression fitting where the hose from the distributor advance enters the carb. That has fixed the rough idle. The intermittent clanking noise is also gone, though I don't know if that was a byproduct of the vacuum leak, or something else that just went away with time. Thanks again.

 

ok, cool you're welcomer.



Ok, but now yiu have a new prob. there should be 0 - 2hg of vacuum to the dist at idle speed of 1000 or less. the fact that you have vacuum at idle means you have a prob and it is advancing your ign timing at idle which it is not supposed to do contrary to what some other less experienced people might think.

Do you have the orig distributor with a "pancake" vacuum diaphram and a carb with a thing that looks like a power valve on the outside of it?

i would remove and plug the vac hose to dist.

check timing at idle and 1/4 throttle or around 1600 rpm.

timing should be around 8 at idle and 22 at 16000.

if idle timing is not 8 then set it anywhere from 8 - 10. i would use 10.

reconnect dist vac.

if idle speed goes up or if timing at idle increases then we need to fix that, you might hsave a bsad spark control valve.

adjust fuel mix screw until engine reaches the highest rpm then turn it back in 1/16 - 1/8 turn.




if you have a flapper valve in the ex pipe and it is not frozen then that is most likely what it was. i know the sound well. it sounds like someone hitting a pipe lightly with a hammer. the irregular idle was simply sending irregular pulses to it instead of a nice constant flow of air, cool huh?

 

Good info. I'm going to check the timing advance tomorrow.

In the meantime, another problem has come up. The car stalled while driving, and now will not stay running. It fires right up, then dies immediately. I can keep it running by choking the carb hard with my hand, or by drizzling gas into the carb continuously.

I checked for vacuum leaks, and plugged all the vacuum connections at the carb. I rebuilt the carb with a complete kit. I checked fuel: plenty of fuel squirting out of the hose at the carb when disconnected. I replaced the fuel filter mounted to the carb. There's plenty of fuel in the tank.

Ideas?

 

man, no mercy, lol.

check the points to insure they are not burned up.

check the point gap, it should be .014" - .016".

check ign timing and dist vac hose as suggested.

if it still stalls it is possible your idle circuit is plugged.

try adjusting the fuel mix screw, if that doesn't fix it then take a can of flammable brake cleaner or flammable carb cleaner.

install the long nozzle on the can.

turn the fuel mix screw in until it just stops, count the turns.

remove the screw.

stick nozzle in screw hole and spray for 3 seconds.

look in top of carb and push nozzle onto the small holes and spray for 3 seconds each.

spray fuel mix screw hole again.

reinstall fuel mix screw to previous setting.

stat car.

reset fuel mix screw until engine reaches highest rpm.

turn screw in 1/16 - 1/8 turn.

pray that it is fixed.

 

Thanks, I'll try that. I've got the Pertronix unit, so no ignition points.

 

ok if that doesn't work try a different coil.

its possible your pertronix is bad.

 

I cleaned the fuel mixture screw and orifices. That helped, but still not there yet.

I suspect the throttle shaft bushing(s). The shaft has at least 1/32" of sideways play, if not 1/16". There's no end play, only side play. Is that much play excessive?

The carb says Motorcraft, but at AutoZone it was the Holly rebuild kit that fit the carb. The factory tag on the corner of the carb says "DOPF L".

I'm used to working on the old Volvos rather than Mustangs, and on the SU carbs that the Volvos use, that much throttle shaft play will make for a really poorly running car. But the SU's are fairly notorious for being touchy, so I'm not sure about what's normal throttle shaft play on Motorcraft/Holly carbs.