Posted by Brian in Oregon on Saturday, November 18, 2000 at 14:04:05:
In Reply to: Re: 318 poor gas mileage posted by Tom J. on Saturday, November 18, 2000 at 10:34:18:
Don't overlook a tired distributer. If the bearings are worn, the shaft wobbles and you get spark scatter (inconsistent spark ranging from full spark to weak). You have 8 cylinders, so if a cylinder or two and maybe three are not being fired off as well as they should, the problem could be masked by the others. With the distributer out, check the ends of the shaft, both upper and lower, for play. There shold be ZERO play. If you are getting wobble, the bearings and perhaps the shaft are worn.
Another problem is the breaker plate and centrifugal weights being sticky or rusty. This prevents proper advance, which would have the effect of you giving it more gas to make up for the power loss.
Some auto parts stores have machines that you can put a distributer on and see if it is up to snuff, though they are getting scarce these days. If you can't find one, and most likely you won't, at least take the breaker plate out and lube the rubbing points with a very light amount of white grease. If the rub points are rusty, sand them smooth with 400 grit. I prefer to finish with 600 grit, but thats up to you. Most folks feel 400 is enough. Check the counterweights and see it they move freely. Lube there pivot points with a couple of drops - no more - of Break Free (in liquid form - don't hose them with spray - too much lube is undersireable in a distributer).
Also check the vacuum advance. You can put a short length of hose on it and should be able to get some movement by just sucking on it. You won't get it to move all the way, usually. But it should move some. If it fails to move at all, it could be torn, which also causes a vacuum leak, or the pivot points could be frozen. Again, use Breakfree sparingly on the contact points and linkage.
You can either but a rebuilt distributer, or you can rebuild it yourself. There are very good rebuild instructions for the 273/318 etc distributer in "How To Rebuild Small Block MOPAR Engines" from HP Books $17.95US ISBN 0-89586-128-3. Anyone with a small block MOPAR should have this book anyway.