Head Scratching Problem - Suggestions?

[rt_hawley]

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.

 

[b_body_hopeful]

rt - question I have is what was your starting and ending jet sizes for the altitude adjustment? Is your vac advance connected? did you disconnect when turning and checking timing?

 

[Bruzilla]

Rotating the distro doesn't advance or retard your idle, it's the timing that's changed. Your idle is adjusted using the carb. You should feel a slight change to how the engine runs, right up until it runs like crap, but I don't know that you would call that a change of idle speed.

You said it was an 80 mile drive? What type of terrain are those 80 miles? I had a similar 360 in my 74 Road Runner and I was getting very slightly better mileage but that was 50% city/50% highway and over totally flat real estate.

 

[Mooky]

I have never been to CO, but what was the change in elevation during said 80 mile round trip? go down the mountain or up? and as stated by Bruzilla...moving the dizzy only changes the way the idle feels when you go way to far..might notice a little rump or sputter down while doing but the idle is changed by adjusting the front mix screws on the carb..as well as the idle screw in front of the throttle cable pull....wish i knew more on how the carb was jetted for the elevation...did it smell rich during the travel? run warmer than normal?

 

[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.