FE Misfire

[Bruce Botti]

Hello to all. I've got a question for you FE experts. I've got a 406FE from Southern Automotive with iron heads, aluminum intake, Holley 750cfm carb, turkey pan, and a Crane fireball ignition box and coil.

I've had problems with it misfiring. I readjusted the accelerator pump and it now accelerates fine, but if you are just loafing along, it misfires. The timing is set for 36-38 degrees advanced at 3000rpm (about 12 at idle). It starts instantly and idles smoothly. The plugs look as if it is running a bit lean (the color is between white and tan). Where else should I look?

Thanks in advance,
Bruce

[chopper]

OK, I'll take the initial shot. First a few questions: (1) Did it used to work OK but then this developed suddenly? (2) Any recent work around the time this problem developed? (3) What condition is the carb in? (4) Mechanical or vacuum secondaries? (5) Is the engine actually misfiring or are you instead experiencing small "popping" out of the sidepipes? (5) Are you sure the ignition system is operating properly, no loose connections, distributor advance operating OK, etc? (6) What condition are the spark plug wires in?

Now, a couple of suggestions. (1) If the plugs are white to tan, I would agree that you're probably running a little too lean. You might want to pull the primary jets and try one to two sizes larger. (2) Run a vacuum check on the engine with a good quality vacuum gauge to see what your idle and cruise vacuum readings are at stabilized engine speeds. Your power valve should be selected to be 1.5 to 2.0 inches lower than your lowest steady state reading (this normally occurs at idle but not always). The standard rule of "1/2 of the idle vacuum" does not always work with these high duration camshafts. Improper power valve opening can possibly cause erratic fuel mixture through the power circuit in the Holley. Most of the Holleys seem to come with 6.5 power valves. but Holley sells them in increments from 2.5 to 12.5 so you need to be sure you have the correct one. (3) If the problem is manifesting as an occasional "popping" out the sidepipes, check to see if you have any leaks in the exhaust system; this is the most common cause of exhaust "popping" at cruise and especially during deceleration. (4) If you have the vacuum secondaries, try to determine when the secondaries are opening. This is sometimes difficult, but if the secondaries are opening too early, this will also affect the fuel mixture getting into the cylinders. Holley sells spring kits to tailor the opening point of the secondaries. They also sell "quick change" kits which replace the top of the secondary diaphragm housing with a plastic cap which can be easily removed (without disassembling the rest of the carb) to change the springs for tuning purposes. (5) If all else fails, call Bill or Lewis at Southern; that's what I do. Hope this helps.

[Bruce Botti]

Chopper,
Thanks for the reply. To answer your questions:

1. It has been like this from the start. The engine has less than 2-hrs of run time (other than at Sothern Automotive).

2. I did have to change the turkey pan as there was a mixup and I received a brushed rather than a polished one.

3. The carb is brand new.

4. It has vacuum secondaries.

5. I suspect it is a misfire as it is down on power.

5. The ignition system is fine with about 12 deg at idle and 38 at 3000 rpm.

6. The customer spec'd out yellow wires so Southern Auto used "Mallory Super Wire Silicon Suppression Core".

I will try some of the items that you mention.

Thanks,
Bruce

[wilf leek]

Do you have a vacuum advance on the distributor? If so, try ruinning with it disconnected, see if it clears up the misfire at light throttle operings.
had this problem on another engine, drove me mad 'till I figured it out.

[chopper]

Bruce:

Sorry, I didn't realize this was a brand new installation.

IMHO, running the engine a LITTLE lean shouldn't cause it to misfire. If anything, it will cause it to run HOT but it should still run without misfiring. However, if your plugs are running towards the white side, this is a relatively sure sign that the carb is running lean and that's a relatively easy thing to cure. I believe Holley recommends changing jets by two sizes per attempt, then when the best setting through this iterative process, try one size on either side to arrive at the final jet selection.

Not to beat a dead horse, but the power valve can be a source of some odd problems. In an earlier thread, I stated that I believe it is helpful to have one of the power valve testers which are available through Jegs and Summit. It costs about $40 and you have to get a small hand vacuum pump to go with it, but it allows you to verify that the valve is opening when it's supposed to and will eliminate the valve as a source of potential problems. I check the valves I put in my carbs because I have found them off by as much as 4 inches from the rating stamped on the valve. This can lead to an assortment of little problems. Of course, you can also just get a couple of replacements (about $4.50 each at the speed shop) and just swap one out to see if it makes any difference. Word of advice here: get one of the special tools to remove the screws which attach the metering block and secondary plate to the carb body. If you try to remove them with a standard screwdriver, you'll be successful the first three or four times before you strip out the head of the screw. It's a bear to remove them after you've done this (data point accumulated on this one).

What type of ignition system are you running? I know Mr. Parham likes to use his modified Ford system. Since it is a new engine, there is always the possibility that there may be an infant mortality problem with the ignition system which didn't show up while Southern was running in the engine on their stand. Again, Bill would be the best person to check with to determine any troubleshooting procedures for his modified system.

If you are running an MSD system, they have troubleshooting procedures on their website:

www.msdignition.com

and click on Troubleshooting.

I assume the other ignition system vendors have similar information posted on their sites.

Hopefully, once you get the mixtures set up correctly, that will resolve the misfire. If not, I would start looking at the ignition system itself. My $0.02.

[Bruce Botti]

Thanks for the help!

Wilf, it is mechanical advance only.

Chopper, I tried a few things:
1. Checked the vacuum, and I only had 10" at idle. I changed the gaskets on the carb-turkey pan-manifold from thin paper to Mr Gasket (thicker material) ones. Haven't checked it yet (see #2).

2. I pulled all the plugs and they were all light brown except for #3 and 4 which were dark and wet. Checked the compression and all cylinders are 135-150. A few of the ends came off the wires, and a few of the boots were deteriorating. I called Southern Auto and they said that they would send out a new set that day (thats what I call service).

3. After you mentioned an exhaust leak, I paid close attention and noticed an area where the header gasket was leaking. I changed to a higher grade gasket. Whew, what a job! It took about 6 hours. I thought all I would have to do was take out a few bolts, loosen up the others and then reinsert the new gasket. This would have been fine except that the gasket was stuck to the block. This is with only 35 miles on it. That necessitated taking off the side pipes and removing all the header bolts. What a job getting in there and scraping since you couldn't even move the headers more than an inch or so. I'll start it as soon as I get the new wires.

Bruce

[chopper]

Bad plug wires will definitely cause the problem you describe. I'm surprised that Southern delivered the engine with wires in that shape, but mistakes to occur and I'm also sure Bill had no problem with replacing them for you.

Since your engine is new, some fouling on the plugs will be normal until the rings seat. I talked with Parham after I received my engine and he said it's normal to take about 2000 to 2500 miles for the rings to seat. Bill uses chrome-moly rings, which are much harder than the standard iron rings. Chrome-moly rings do not seat like the iron rings; it's more like the cylinders wear to match the rings than the other way around. I have had a couple of other engines (Chevys) in which we installed chrome-moly rings and they also seemed to take forever to seat. Until they do, you will find some oil residue on the plugs. MY current engine kept burning oil until just recently when the #7 ring finally seated. After that, oil consumption went down to normal and the plugs seem to be maintaining color. For these types of engines, I consider a quart every 1000 miles to be normal. Other opinions will vary, but that's what I use as a rule of thumb. Bill suggests using Valvoline 20W50 oil, and that's what I've been using. I'm debating whether to switch to synthetic but haven't made the plunge yet. Incidently, my brother tells me that WalMart (the one he goes to is in Buffalo NY) periodically sells 5-gallon jugs of Mobil 1 for around $17. I haven't seen this around here but I'm sure going to start looking. This isn't an endorsement of WalMart, either, I just haven't heard of this at any other store.

FWIW, my engine runs about 10.5 inches manifold vacuum at idle. I'm running a 484 stroker kit, Crane cam and dual 600 cfm Holleys. I hooked up a vacuum gauge from the rear carb, ran a vacuum line into the cab and duct taped the gauge to the dashboard. I then stabilized the car at 1000 rpm intervals in each gear and recorded the vacuum readings. The lowest reading was, in fact, at idle and all of the others were higher. I initially selected a 5.5 power valve based on the old "1/2 of the idle vacuum" rule of thumb and had all sorts of bog-down problems. I went back, bought two 8.5 valves and installed them and the bog went away. Actually, I bought FOUR 8.5 valves because when I tested the first two, they actually opened at 4.5 inches rather than the 8.5 stamped on the valves. This is why I recommended getting a tester and checking the valves before installation. My experience, anyway.

[Bruce Botti]

Chopper,
Bill sent them because yellow wires were spec'd. They had sat on the shelf for years.....and like you said, these things happen. Bill always works to keep his customers happy.

After making the above changes and still having the misfire, I got a set of wires that I know are good, and I changed the power valve and set the accelerator pump and floats to Holley's specs. It still misfires. Today I will change the cap and rotor. I'm also curious about the Crane ignition unit. They mentioned connecting a capacitor from the main 12 volt line to ground if the battery is mounted in the trunk. I'll give that a try.

Thanks for your help!
Bruce