Thanks good idea. Used to having to remove steering locks mandated in many racing bodies.

 

Thanks folks for all of the replies, I have checked for vacuum leaks by restricting the carb and spraying wd40 and carb cleaner around the intake, everything seems okay. The steady vacuum is around 9-10. I have no egr, truck did not have it and I did not pursue getting it. I am going to purchase a distibutor, just cant make a choice between a rebuilt from NAPA, a rebuilt from Madman???, or a MSD. Could my issues have anything to do with valve action timing? The carb is only three weeks old. The air mixture screws are functioning. I am also considering changing from a 180 to a 160 degree thermostat. I noticed the piston knock is less when the engine temp is lower.

 

Something tells me it isn't your ignition timing that's the problem. Not sure what, but it doesn't sound like it.
I could very easily be wrong because I am not there to hear it run, but it doesn't ring true that ignition timing is the problem.

I think it is in the camshaft (don't know how to interpret your numbers), or your timing chain or cam gear is off a tooth or two. Or a keyway perhaps.

Just a thought.

 

I agree with banjopicker, 9-10" of vacuum is way to low and is the reason the engine won't idle. Normal is 15-18" of vacuum with a stock or close to stock cam. What are the specs on that Comp Cam? If it has 336° of duration, you will never have an idle below 1600 rpm if you are lucky, more like 1800.

 

What are the cam specs? What compression? My engine pulls 19 to 20 with 87K on it. Even when things went south for a bit. Do you have the retarded crank sprocket?

 

Hey folks, the cam specs are .560 int and exh, duration @ .006 tappet 292 int exh, valve timing @ .006 int: open int 40 btdc, close 72 abdc...exh: open 80 bbdc, close 32 atdc.... Specs installed are duration @ .050 244 int and exh...lobe lift .3235 int and exh... lobe separation 110. Saturday when I pulled in the driveway the idle was high...linkage problem is my first guess. It turned out to be the vacuum advance, I diconnected and plugged it and it is running much smoother. I am going to get a new distributor...any suggestions? Also, any ideas on how to check the valve timing without a disassembly? Sorry this is so long folks.

 

No need to apologize for being long! We learn too, when these issues crop up and get solved.
Sounds like you have the distributor advance connected to manifold vacuum, instead of port vacuum.
Find the right port on the carburator, and reconnect the hose - and I think you will have solved your problem!

 

Thanks, I have it to the port on the carb above the air mixture screw. I think the advance mechanism is faulty. I have read that I really dont need the vacuum advance anyway...is this true?

 

No, that is not true.
Witness that the engine would run only at high RPMs with a high advance.
The "advance" is just that - it makes the spark plug fire earlier, as measured in degrees of rotation.
It is a matter of simple physics and chemistry.
It takes so many milliseconds for the fuel in the cylinder to burn. It doesn't explode, but burns in the form of a wave. That wave needs to push down on the piston to drive the engine. If the burn starts too soon, then the wave pushes down but the piston is still too far down on its way up - and you get a detonation effect, called pinging.
If the spark comes too late - or retarded, then the piston starts down after passing the most optimum time, and you don't get the full effect of the wave, and you have a loss of power.
Keep in mind that the advance is BTDC - Before Top Dead Center - which means the piston is still on the way up when the plug fires and the burn wave begins.
Now for the chemistry part.
It takes time for that burn to propagate across the combustion chamber and push down on the top of the piston. This time never changes - whether the engine is going fast or slow, the chemical reaction still takes so many milliseconds to propagate across the combustion chamber. You cannot make it burn any faster.
Therefore, when the engine is turning at high RPMs, the burn must start earlier to get to the top of the piston at the optimum time.
In other words, the piston is moving up to the sweet spot faster, but the burn rate is still the same pokey speed it was when the engine was at idle. To overcome this, the burn must start earlier - that is, it must be advanced.

The vacuum advance gizmo uses engine vacuum to increase the advance as the RPMs go up. If you have full-time manifold vacuum, you have set the advance as though the plugs must fire extra early. That only works against the pistons because the burn wave starts too early, and pushes the piston back down before it can get to the top.
Look for a port on the carb that has no vacuum at idle, but has vacuum as the RPMs go up. You can find it by checking vacuum ports with your finger at idle. When you find one with no vacuum at idle, put your finger over it, and raise the carburator off of idle. If you now get vacuum, you have found a ported vacuum source. If that doesn't work, you 'll need to check it out somehow else.
Since I don't know Holleys, I can't point out where it is on your carb, but I bet the manual does - and you might find it on-line.

 

Thanks for the explanation. A lot of this stuff makes more sense when the deeper meaning is put forth. I know Holleys well enough to know that I am on the correct port. I am thinking that the idle is turned up to the point the the port is functioning correctly. I am replacing the tach tomorrow. This will help with my settings. I also have a 400 in my 1979 F350. I might pull it and see if it helps the 460. Thanks again, all of the input has helped a lot.

 

I like the MSD
Bill

 

Vacuum advance should not increase your idle speed if connected to the ported vacuum source (and that is where it should be connected to). If it is to manifold vacuum it will increase idle speed. Are you checking the initial timing with the vacuum hose disconnected. If not you should be. Vacuum advance increases you gas mileage at light throttle while cruising down the road. You do want it unless you are rich enough to have someone else work on your truck, at least with todays gas prices.

 

That is the timed vacuum port and is were the hose to the distributor should be connected, it should be coming out of the metering block.

If the idle speed screw is turned in to far it will uncover were it gets its signal from and you will have vacuum to the distributor full time.

You need to pull the carb and look at the idle feed transfer slot in relation to the throttle plate. There should be only 1/4 of the slot uncovered below the throttle blade.

There will be a small hole near the idle transfer slot on the side the timed port vacuum for the distributor. If it is uncovered vacuum will be present at idle.

With 244* of duration at .050 a Holley carb may need mods to correct low vacuum at idle.

Your power valve might be opening at idle also depending on what came with the carb and your idle vacuum readings.

Your cam selection is a bit much for tow applications.

The air flow in stock heads poop out around .530 on intake and .560 on the exhaust more than that isnt value added it will just bring the RPMs up like 20 HP for top end but losses of like 30 or 40 at lower RPM.

Duration at .050 should be more around 210 intake 220 exhaust. Unfortunately there are no flat tappets that span this range without using 1.8 rockers or a hyd roller with 1.73 stock ratios. Also if you use aftermarket roller rockers most all are only 1.7. So you dont get full advertised cam lift.

The cam shoud have a split duration and lift due to ford poor air flow on the exhaust side.

Your cam would build up cylinder pressure to some extent because the equal duration on the exhaust kind of makes it harder for the exhaut to leave the cylinder.

 

I tried a Crane cam in my 460 but went back to a stock grind. I did leave the Crane roller rockers in and added the MSD ingition with the variable timing option. I set the static timing at 10 degrees with the controller at minimum. This way I can run 18 or 20 degrees while going down the highway for a little extra mileage. When I start pulling a long hill or get pinging from overheating I can pull the timing back to 10 degrees right from the cockpit. This makes towing heavy loads a lot more comfortable.

 

Thanks, I am not towing with this truck. It is a 1978 F100 shortbed I intend to use for a street/strip application. The heads have been re-worked and I am running the Crane gold series roller rockers. I played around a little more with the distributor and the vacuum advance adjusting screw and I have my initial timing at 14, thats as low as I can go. The idle is turned up to the point that the vacuum port is pulling 5lbs at idle. I have checked again for vacuum leaks and cannot find any. I am almost to the point of tearing it down and starting over, but not quite yet. The truck runs so strong with the advance turned up, but the detonation is too risky.