Head Scratcher ...need help

[rt_hawley]

Re-posting in general tech threads hoping to get a bit more exposure.

I'm the first to admit that my mechanical knowledge is slim at best, but I've run into a situation that REALLY has me scratching my head. I'm in Colorado Springs and have been having trouble with my timing. I know that altitude plays a part in the issue and I've had the carb re-jetted for altitude so that should have solved the problem, however, last weekend, I made a run from Pueblo back to Colorado Springs (about 80 miles round trip) and burned half a tank of gas. I wasn't really coming on to the accelerator but just taking it easy. I know my car is hard on gas, but that seemed a little excessive. So...over to a buddy's place to see if we could find out what was going on. I suspected the timing was messed up again, but here's where things get weird...we loosened off the nut that holds the distributor cap in place and as we rotated the distributor left and right, advancing and retarding the idle, there wasn't any change in rpm whatsoever. Now, as I've already stated, I'm not overly mechanically inclined, but even I know that rpm should rise and fall as you rotate the distributor cap. Anyone have any ideas as to what might be going on? I've considered changing out the whole assembly and installing an MSD ignition system, but there's not much sense in spending $500 on parts if that might not be the problem. Timing issues and gas consumption aside, I'm very curious as to what might be going on that isn't allowing rpm to change as we rotate the distributor. My vehicle is a 74 Roadrunner with a 360 in it...Edelbrock 4bbl, (650 cfm), Edelbrock intake manifold, headers, mid-range cam. Any suggestions as to what the problem might be would be appreciated.
Thanks in advance.

 

[barnfind]

Have you popped the cap off and advanced/ retard the dist?
Checked for slop in the dist shaft?
how many miles on the timing chain?
youre right this doesnt make much sense....

 

[Speedbird]

Try moving the distributor with a timing light attached. A good purchase if you don't have one.
Since what you are observing does not make sense, that will tell you if the timing is in fact changing.

 

[idrivemopar]

Regarding your mileage, lets think about this for a minute with a couple if things to keep in mind.

First, average fuel consumption on a good day on the highway back in the day was estimated at 15 to 18mpg I believe on a stock motor. So going 80 miles one would think that you would use about 1/4 tank of gas.

Second, you have bumped up your cam a bit so that is going to decrease your mileage, maybe down to 12mpg and that would consume about 1/3 tank of gas in 80 miles.

Third, throw in that you are changing elevation by about 1,500 feet between the two locations, in one direction going down hill using less gas, and the other going up hill which requires more throttle to maintain speed which may change your average down to 10mpg, and this could translate then to be around 1/2 tank of gas.

Of course this also depends on what gears you are running in the rear-end, I am guessing 3.23's but if like me, I have 3.55's so I am about 3,300 rpm at highway speed so I am not expecting any great fuel savings when on the highway.

I used to go between Cheyenne Wyoming and Fort Collins which is a change in elevation of about the same from Colorado Springs to Pueblo, and if I remember correctly, I used about the same amount of gas or a little under a half of a tank. I have not yet made this run with my higher compression and bigger cam in the motor but I would expect to use about 1/2 tank.

One other comment, you say you have performance intake and headers which will certainly increase your flow in the motor which with the bigger cam can also translate to lower fuel economy.

If you still think this is not the proper mileage then I would check for fuel leaks in the line and on the tank, make sure your not losing it somewhere else.

 

[AMX364]

Maybe, post picture of distributor. Maybe it is something different. I will not say of all my errors made in my youth about car parts.

 

[Budnicks]

19-20 gallon fuel tank, 9.5-10 gal. {a 360 with mods in a 4000# car, getting 8 - 8.42 mpg, at elevations, it's not all that uncommon, if it's not tuned absolutely correctly, for your altitude or driving conditions, could be too retarded/ignition too, @ altitudes they like more ignition timing to run correctly & smaller/proper carburetor jetting too} if the gauge is actually even accurate, mine the 1st 1/4 consumption "off full" takes a while, then from 3/4 to 1/4 goes really fast, then back to about the same rate as the 1st 1/4 rate of consumption, remember these cars weren't digital they are old analog gauges & aren't as accurate as some of the newer stuff is... Edelbrock Performer carb not helping much either, I'm not a big fan, I'd get an original Carter AFB or AVS or Thermoquad {spread bore design with smaller primaries & larger secondaries, for better mileage, still have good performance} & rebuild that & run that, long before I'd run any Edelbrock carb, some people swear by the Edelbrock carbs, I'm not one of those people... Edelbrock makes some great products, their carbs aren't one of them... I'm not trying to start a debate on who makes a better carb, just my experience & my opinions.... Good luck with you project thou