200 CI auto spark knocking under load- HELP!

[john tate]

My '66 is driving me crazy...haven't had this tough a problem in a while. Posted on this about two months ago and appreciate all the feedback to get me to this point.

Problem: It spark knocks under load and is the worst under moderate throttle- WOT reduces it.

I have done the following:

New harmonic balancer
Replaced distributor with original style Load-O-Matic from Mustang supply place (new vac advance, new points/condenser/rotor)
Set timing at 12 deg BTDC
New plug wires
New plugs
New fuel pump
New fuel filter
New PCV valve
Rebuilt carb (Motorcraft 1940 w/o spark valve)
Radiator rodded out- cleaned
Thermostat replaced with 160 (was 180 and car got very hot in traffic)
6-blade fan
Sea-Foamed the car twice to clean out carbon (seemed to work but after time no change)
No obvious vac leaks but haven't done too much checking

Car is approaching 200K (90K on rebuild) and it does seem to burn some oil but when it burned tons of oil 20 years ago it never did this.

Spark knock started when I replaced the vac advance unit.

Otherwise it starts and runs fairly well- the new fan and lower t'stat really help keep it cool in traffic compared to how it used to be.

Any ideas? I am out of them!!!!!!

 

[Mercury Mike]

"Replaced distributor with original style Load-O-Matic from Mustang supply place (new vac advance, new points/condenser/rotor)"

"Rebuilt carb (Motorcraft 1940 w/o spark valve)"

You can't run a load-o without a SCV. If you don't have the valve in your carburetor, your distributor won't work correctly, and that might be where your problem is coming from. =)

 

[fordconvert]

I would say to check the total advance, especially because you mentioned changing the dizzy and modulator. Easiest way to do that is with an advance timing light. Budget way is to mark off your crank pulley to around 40* using the orignal timing mark bracket to get the distance per degree. Most stock engines dont seem to like more than around 35* total from what I have read here. Mine is running at 48 somehow but we suspect the cam is advanced and also causing some other issues. Do a search here on timing curves or recurving dizzys those theads explain the easy and hard ways to check and change total advance.

Back the base down 6* and see what happens. Try running higher octane fuel. It may be a combo of carbon/octane/and timing.

 

[61Futura]

Too much total timing advance. Probably coming mostly from your vacuum advance. The ignition timing advance curve(s) needs to be planned and every component matched up to each other. The amateurs way is to get a matching distributor and carburetor with a ported vacuum source.

I'm guessing that you aren't using ported vacuum, but intake vacuum instead. My limited knowledge can't understand how straight intake vacuum could ever give a proper advance curve. I'm still in the planning stage of what I'll have under the hood. My current setup isn't quite right, but everything is being replaced next year. And then probably 1 more time to speed up the 200/C4 that goes in next. I hopefully will have Classic Inlines set me up with a matched DUI ignition for whatever else I decide to change.

 

[LaGrasta]

I'd say it's too advanced.

I run mine as advanced as possible. I turn it up until it starts pinging, then back off a bit. I then take it for a drive and under load, listen for ping. If it does, I stop, retard, and drive it again until I hear no ping under any driving load.

That's how it is now and has been for the past few years. I believe I'm in the low twenties (degrees).

 

[john tate]

Thanks for the tips- what doesn't make sense is that I've run the Holley for 20 years and never had an issue.

Also, I set the base all the way down to 3 degrees base and it still knocked under load, even using premium gas.

Guess I assumed the new return springs and distributor would be set up correctly so I will search more. Adjusted old springs but could never get it to stop.

If I'm setting the rough total advance to 40 degrees what RPM would I expect to see this?

Thanks.

 

[JackFish]

"Replaced distributor with original style Load-O-Matic from Mustang supply place (new vac advance, new points/condenser/rotor)"

"Rebuilt carb (Motorcraft 1940 w/o spark valve)"

You can't run a load-o without a SCV. If you don't have the valve in your carburetor, your distributor won't work correctly, and that might be where your problem is coming from. =)

:!:

 

[CZLN6]

Howdy John And All:

Once you go to WOT all vacuum advance should be gone/none. Try disconnecting the vacuum advance hose and plugging it. Take it for a drove. The vacuum advance should be there to improve off idle and steady cruise speed power.

If this improves or eliminates the knock, you've at least isolated your problem.

If you have a Load-a-matic distributor you will need a carb with a SCV for it to function properly. IF you've "run the same Holley without SCV, for 20 years" the SCV may not have been functioning, or the vacuum cannister may not have been working. New parts will sometimes reveal problems that did not exist with old parts.

"Spark knock started when I replaced the vac advance unit."
That should be your first clue.

Adios, David

 

[john tate]

David, Thanks for the info. I just assumed since this was the Ford replacement unit for the original carb that it would work.

Will re-verify but when I disconnected the vac line and drove it the knock was gone; only difference was it fell flat on it's face during accel under part throttle.

So I need to rebuild the old 1100 or cough up $400 plus for a Pony Carb rebuild, eh? Ouch.

Will do some more experimenting.

 

[john tate]

Acutally, thinking out loud here would it be easier to install a later '68 or newer distributor? If so would I connect the vac line as I do now?

Do they sell "spark control valves" that you can put on the vac advance? That might be another option.

"Preciate the help folks.

 

[cfmustang]

A newer '68 or later dizzy would work fine. That was what I did before I installed my Unilite. I can't remember exactly, but I don't remember it being too pricy from Advance Autoparts...

Anyway, with the non Load-a-matic, you can hook it up to the ported vacuum out of your Motorcraft (or full manifold if you choose).

 

[Mercury Mike]

The spark control valve is on the carburetor. It's a bolt-looking thing, with a 1" head. On the holley/motorcraft, it's on the front left of the carb, when the carb is mounted.

 

[john tate]

OK, sounds good.

On all the '68 distributors in catalogs there are two types- those with one vac connection and those with two. Which one do I need?

And would I hook it up the same way as my current dizzy?

 

[CZLN6]

Howdy Back John:

Glad to hear you're making progress. On the '68 distributor you will do best with the single vacuum hose fitting. The distributors with two fitting have both a vacuum advance and a vacuum retard for specific EPA/emmissions control for those years. You will only use the distributor with one vacuum advance connection.

If you were to rebuild the original Autolite 1100, a new SCV would be in the rebuild kit.

Your 1940 Service carb (actually made by Holley) should work well with the '68 distributor. Hook the vacuum line from the distributor to a ported vacuum source for best results on a mostly stock engine. If there are two taps, the lower one will be full manifold vacuum, the higher one will be a ported vacuum source. This is the one you will want.

Adios, David

 

[john tate]

David,

I only see one vac inlet on this carb which I assume is ported based on my spark knock response. I will go pick up the '68 and see what happens.

Running a stock setup- after I rebuilt the 1940 it seems to be running well so I'd much rather replace the dizzy instead of the carb.

I will see if I can dig up the old 1100 from my attic just in case.

Will let you know. Thanks a mil- John

 

[john tate]

Bought a '68 reman distributor from NAPA and it doesn't want to fit- it is about 1/8 of an inch from seating fully in the block. I don't see what is different- distance from the gear to the bottom of the shaft appears the same, diameters appear the same, hex drive may go in a tiny bit more on the old one, but not 1/8"!

Does anyohe have any experience with this?

 

[Mercury Mike]

Oil the dizzy gear maybe. And keep rotating it. Also, make sure it's going down straight. It will fall into place, most likely.

 

[addo]

The media blasting sometimes seems to enlarge the boss where it engages with the block. Check with Verniers, if necessary do a dry fit with the oil pump shaft removed; lightly sand/polish the dizzy as needed to fit. Don't forget the hex shaft when reinstalling.

 

[cfmustang]

I have that problem all the time when I try to install a dizzy. There are two places that have to mesh. The dizzy/cam gear and the oil shaft. The dizzy gear is the heligear and is easy to get to mesh. The difficult one in the oil shaft. I believe that is 6 sided so both have have to mesh for it to drop that last 1/8th of an inch. Look at the bottom of the dizzy and then down the hole and you will see what I am talking about.

Sometimes I get lucky after a few minutes, other times I have played with it for an hour before it will drop. I have yet to find a sure fire way to get it to work right off the bat.

 

[ludwig]

I never had that problem with the oil pump shaft. The ones I have gotten are pointed and slide in okay. Naturally it won't work at all if I HAVE to get it done by some particular time.