Wierd Holley issue
 

Hi guys. I have a really wierd issue with my 600 cfm Holley (vac secondaries, elec choke) in my '66 Mustang. Engine details: 289, mild hydralic cam, aluminum heads with roller rockers, flat top pistons, performer RPM dual plane intake, full length headers, timing set and re-set at 31 degrees full advance. The fuel level in the bowels has been checked, the power valve has been replaced and I am now running #67 primary jets.

No matter what primary jets I use (tried as low as #62 or 63 but the car ran like crap with those smaller jets) the gas mileage is really bad with about 9.5 to 10.5 mpg while most of the plugs are snow white. The timing was backed off but that didn't help so it was re-set at 31 degrees. Right now I am running #67 primaries and I just pulled all 8 plugs with these colours: cylinders 1 & 3 are off-white, 2,4,7,& 8 are snow white, and 5 & 6 are black.

With a duel plane intake I would expect 1, 4, 6, & 7 to be similar and 2, 3, 5, & 8 to be similar but that is not the case at all. Remember that I have all of these white plugs and really bad gas mileage. There are no gas leaks anywhere and the exhaust doesn't smell terrible. I have spoken to my engine builder (he put the 289 together for me) and he said that he has never seen plugs like mine. Any ideas? :confused::confused:

Sounds like valve timing...........is the firing order correct....
How about New wires........

Timing should be closer to 35-36 at max advance. Squirt some carb cleaner in the brass air bleeds near the base of the Venturi boosters. Make sure the choke is fully open when engine is at operating temprature.

Intake gaskets leaking. How many miles on engine ? Did it run this way since rebuild , or is this a new problem?

I'd go with Rick and Motorhead, 31 degrees is to retarded and the plug colors and milage would also make me look at intake gaskets. You said that 31 degrees was all in; what ignition are you running? What is your idle/low speed advance?

Rick, I tried more advance and nothing really changed, less advance made the car run like crap. The choke is definitely fully open after the engine has run for about 5 minutes.

CHANMADD, the firing order is correct 15426378. The engine runs fine and the car will just burn the tires if asked to do so.

Jac Mac, I will check the head gaskets but the fellow that put the engine together is a pro so I would be very surprised if he made that kind of error. I believe that I have the correct NGK plugs but I will check the number and indicate it here later.

lovehamr, I am not sure about the low speed advance. I have a stock Ford distributor with the vaccum advance disconnected and a Petronix module instead of points.

MOTORHEAD, the engine was rebuilt a couple of years ago but the heads were just changed this spring. The engine was using oil through a couple of the old valve guides so instead of having the cast heads rebuilt, I went for a set of Edlebrock Street aluminum heads. The engine no longer uses any oil. Total mileage on the engine is 5,000 miles since being rebuilt and 1,000 miles since the heads were changed. You ask if this is a new problem and I have to admit that I am not really sure. It runs well but I happened to pull a plug just to take a look and it was white so I started messing with it. It was at that time that I noticed how much gas it was using which was a complete contradiction of the plug color. Really bad gas mileage and white plugs don't make sense.

Once thing I forgot to mention earlier is that the idle speed changes by 50 or 100 rpm on occasion. This usually happens when the hot engine is restarted after sitting for a half hour, it will idle at 500 or 550 in drive instead of 600 rpm. The car has a C4 so a slight change in the idle speed is more noticable than with a manual transmission. I have also changed the power valve just in case that was the problem. Thanks guys.

Jac Mac, The plugs are NGK FR5. There are tabs visible on the lower front part of the head gaskets. Just to double check the firing order, I followed the plug wires and there is no mixup.

All very good points.

Other things to look at are the colour of the outer shell (exposed to combustion), since the porcelain picks up little colour from unleaded fuel.

With cylinders 5 and 6 side by side, I'd be concerned with their darker colours. I'd say do a leakdown test.

I took some pictures of the plugs which I will try to find and post. The car is sitting in the garage for the winter so all I can do right now is try to diagnose the problem and come up with a solution by spring. I am not overly worried about the high gas comsumption because I don't put a lot of mileage on this car but it sure does seem to be strange that a small block in a light weight car can burn this much gas while appearing to be running lean. I had pulled plug #1 quite a few times when I had cast heads and it had some decent colour but cylinder #1 had a bad valve guide so some of the colour was coming from buring oil. I will check the rotor and get back to you.

Plugs are not the easiest thing to photograph. :( Here is a picture of #6, #7, and #8. 6 is black while 7 & 8 are very white.Attachment 23219

The base of the outer shell looks ok on 7 & 8.

6 looks like low compression, weak valve spring, or small internal oil leak (guide, inlet manifold).

How many miles on these plugs?

What model Holley do you have?

I think you also need a better carburettor, like a QFT.

this link has good pictures of plugs and how to read them.

sparkplugreading

Dwight

Gaz64, The plugs have just under 1,000 miles on them. They were installed with the new aluminum heads. The heads were complete so all new valves, springs, etc. The only parts added were new roller rocker arms. The carb is a Holley 4160, 600 cfm, elec choke, vac secondaries. I bought the Mustang 9 yeras ago and completely restored it from the ground up. I had the engine rebuilt at during the restoration since I had it out of the car at the time. The engine builder said the engine was in good condition but we changed the pistons, rings, cam, bearings, oil pump, etc, etc. I installed the new Holley when the engine was put back in the car.

Jay Mac, the #1 cyl had the worst valve guide and of course #1 is the easiest plug to pull on an old Mustang. The engine was using about 1 qt of oil per thousand miles so it wasn't really a lot. The engine did not take any oil (or anti-freeze) since the aluminum heads were installed this past spring.

Dwight, I am going to take a look, maybe I will learn something. :p

Thanks all.

Hook up the vacuum advance. The Ford distributors have a very lazy and long advance curve. Your engine is running with the spark timing way retarded at cruise RPMs. This is killing your gas mileage. Also as a side note, the main jets have a very small effect at cruise speeds. Get an O2 meter and tuning your carb will be much easier.

First---you need to address advance curve of your dist and the intial/total timing------the vacume needs to be hooked up and on fords they use the port off the venture of the carb---not manifold--- total timing on fords over the years was around 38 btdc but with todays gas probably 36---------the centrifugal is slow to come in and needs to be modified, the vacume is critical to economy and cruising response-

Your issues with oily plugs on one end of a head and lean on the other is because of intake manifold/cylinder head fit up-------could be a combo of 2 or 3 things--------poor manifold, poor heads, uneven tightening during install???????anyway, its sucking air at one end and oil from the valley at the other end-------

You didn't mention if the block was bored/honed for the new pistons??????????

Find somebody who has a similar carb and try it.

Gerry & Tom, thanks, good points. I will look at hooking the vacuum back up on this dirtributor. The block was bored and of course honed. The engine did not take any oil or coolant in the 1,000 miles since the new heads were installed.

vector1, I am going to try the 750cfm double pumper from the Cobra on the Mustang. The gas line will be a pain but I will work out something.

Dwight, that is a very interesting article on reading plugs. I was only looking at the porcelain which according to that articlke, is all wrong. I am going to pull all of the plugs and have another look at them. Unfortunately I had to run the engine at idle for a minute or two putting the car in the garage.