I have a slant six from a 74 Aspen in a D100. This motor is in good health and runs good, but when I am cruising at 55-60mph and open the throttle slightly (like to maintain speed up a slight hill) it begins spark knocking faintly and continuously until I either open the throttle a good bit more, or close it some. Some on another site have suggested that it may be a clogged or inoperable EGR valve. This sounds plausible to me, but I don't know where the EGR valve is located on a mid seventies vintage slant. Where is it?

On my motor I DO see what appears to be a 5/8 inch steel tube that bolts to the head just aft of the rear-most exhaust manifold runner. This tube leaves the spot where it bolts to the head and comes forward over the intake and exhaust manifolds and ends about at the carburetor in a round looking thing that looks like it might be the EGR, but there is no port on it for a vacuum tube. A large rubber tube comes off of it and goes under the air cleaner housing, but I see no vacuum hookup at all. Is this the EGR? If not, where would it be? Davey

That would be the EGR valve you have found, althought I do not know how it hooks up to make it function because I have never had a /6 with this setup. There are probably other ways of getting around your problem though. I expect that the carb is lean at this piont you have detination, or that the timing advances to far at this piont. A older carb with a different calibration may be all that you need, or you may be able to rejet the carb that is on it. Also you can test the distributor with a timing light & see how much timing it has when you light throttle & can recurve it to fit your needs. Or it may be that all you need to do is set the timing down a little lower on the base than it is set.


There is other things that can cause this also, like there can be to much carbon build up in the combustion chamber & valves. One way to help this is by taking water and dribble it down the carb while you rev the engine up. You dont want to let to much water go down at a time. The engine will let you know how much because it will start dying down when you do this. The trick is to get it where the engine is slightly dying down while you are feeding it water ( while holding the RPM's at about 2000) , but not enough that it kills the engine. With the engine hot, the water will make the carbon bust loose and blow out the exhaust and leave the engine better able to run.

Also if the engine is running a little to hot it will tend to detinate easier. The spark plugs can be of to hot a range and give this trouble. All in all, a little cleaning & some close atention to tuning should be able to cure this with out to much a problem. Running a check on exactly what the timing is doing, the plugs, and some fuel corrections should get you there.

You may be able to get the EGR system working, but if it needs a new valve I think it would just be to much for me to be welling to fix. The thing is that it will probably run better if the engine is tuned to work without the valve anyway.


Jess

One way is......

Back off a couple of turns on the vacuum advance. It is kicking in too soon.
Use a 3/32 allen wrench in the nose where the vacuum line plugs in. I run mine about 3 turns out.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

that is the back flow valve for fresh air to the exhaust through the head that hooks to the breather, you need to look on the drives side of the ex/intake manifold just under the carb linkage, the round metal diafram with one vac line is the egr valve the passages are internal and if you want to block it you have to remove the two 1/2in nuts and block the passages behind it.