Michael Frank was experiencing rough running on his E-type. Basically, the car started running rough gradually and got to the point that he couldn't make it back up the hill although the car would seem to idle fine. He posted a message to this list and here are some of the suggestions that were offered as well as his final solution to the problem.
Tonight I will begin by checking the electrical system again by the numbers, just to be sure. First, a new set of plugs. Next, I will dress the points. I will inspect all the wiring. I will also try new plug wires. I expect this will not be fruitful, so it's on to the fuel system. First thing I will do is temporarily disconnect the suppression condensor from the fuel pump. If this doesn't't do it, I will drain the tank and check the pickup (this will be the second time, but who knows?). Next, I will replace the fuel filter. If all this fails, it HAS to be the carbs, and they will have to wait until I get new gaskets.
I'll share one interesting thing I have discovered. I wanted to see if there was a high-resistance short to ground in the coil primary. So I blocked the points open and attached an ohmmeter to the positive side of the coil (let's not get into a discussion of coil polarity). When the ignition switch was 'on', the reading was infinity, ie, no short :-). What was odd is that with the key in the 'off' position, the meter read 3.5 ohms, ie, the coil was now shorted to ground. Not sure if this is to prevent theft, or an indication of a problem (ie, it's not a bug, its a feature)- any thoughts?
I have some great clues, thanks to all of you! Here were some of the responses, and my evaluation:
I have been concentrating on the ignition, fuel system is next
I had this problem a while ago. Found and fixed. It tended to cause erratic performance, and backfiring, since the timing would change on its own.
Ballast resistors were introduced on 1970 Jaguars. Otherwise, this would have been my guess too.
This wire has been repaired by PO. To be sure it was ok, I disconnected and jumpered around it.
I have a Mallory distributor. The cap is so tight, it can hardly be removed or installed. They are prone to cracks, but I have checked it thoroughly
One better: I used a Colortune. Looks to me like the spark is intermittent, but you would be surprised how hard it is to be sure. It seems that the cylinder goes 'black' just before the engine cuts out...no spark, no fire. But this happens just as the engine is dying, so it is not obvious whether I am seeing cause or effect. Wish I could film it in slo-mo.
This was a great suggestion. As it happens, I crushed one muffler on a speed bump a couple of weeks ago. I don't think this is the problem, since I seem to have good exhaust pressure at both pipes. I have a spare muffler which I will install if nothing else works.
Air filter and fuel filter are brand new. I will change the fuel tomorrow, on the chance that something is blocking the flow.
This is a pre-charcoal cannister car. Tank is vented thrum the cap, not a lot to go wrong. I will check the cap to be sure.
I will order up some new gaskets and check the carbs.
They are now south. As the problem has gets worse, there is plenty of carbon fouling going on. Looks more and more like a fuel problem.
I will check this capacitor tomorrow. I suspect that it is original to the car. Good tip.
Been there, done it.
Fuel system comes next.
While I was checking pressure, one of the temporary fittings 'popped'. I had 1/4 tank of gas on the driveway before I knew it. Still could be something intermittent, tho.
Done this summer.
Not an octane issue, this I am sure of.
As I mentioned, I have a Mallory dual point. This has two flimsy brown wires that connect to the points. These will be inspected tonight.
Hmmmmmm. Don't need gaskets to check this, either. I will look into it tonight.
Yup. That was me...first time I had a problem like this, it was a blob of solder stuck in the intake pipe. The difference is that this time the problem is progressively growing worse, last time, it was binary: either I had the problem, or it was fine. The solder had a shape which allowed it to intermittently block the pipe.
Just a can of Diet Coke....sorry, couldn't resist. The sump is coming off again tonight. We shall see.
Will check this tonight....Mallory dual point = twice the probability that this will happen...and let's not start up the debate about vacuum advance again!
I should have done this first. I know I should have, but didn't.
I put in a new set of plugs tonight, cranked the engine and.....nothing.
Bypassing a bunch of steps, I replaced the fuel filter. I turned the key without cranking, and listened to the click, click, click of the fuel pump, until it stopped. I then looked at the fuel bowl, it was full of .... air. This is actually OK, as it indicates that the fuel system has integrity, and there are no leaks. Those Grose Jets are working well. I then cranked and watched as the fuel bowl quickly filled up. This told me that the fuel system was basically OK.
Then I tried an old trick. No timing light. No Colortune. Just a spare spark plug. I plugged this into a cable, and set it down on a suitable surface. I then turned out the lights in the garage, and cranked the engine. It is amazing how clear the problem became at this point. The spark was very weak, and frequently non-existent. Bingo! Back to the distributor. I removed the points, dressed them down, washed them in alcohol.
Bill Lyon's Sixth Symphony! :-).
I think that the Mallory distributor has caught a virus from all of the Lucas components which surround it. Any thoughts on electronic conversion?
Thanks again to everyone who responded!