Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - Poor fuel mileage
View Single Post
  #16 (permalink)  
Old 11-06-2004, 07:37 PM
Pantload Pantload is offline
Registered User
Join Date: Nov 2004
Location: Warren, MI
Age: 58
Posts: 8
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I feel your pain

I just bought a junker mid-eighties Camaro that has the same problem. The previous owner let me have it real cheap because he couldn't get it to run worth a darn. The person he bought it from went to the hot rod store and put one of every single thing in that store on the car. I bought it because it has a fresh engine with all kinds of internal goodies, I figured I can sort out the rest.

The thing was getting the mileage of a top fuel dragster, until yesterday. Here are the problems (see how many match your setup).

1. Square bore Edelbrock carb. Mine isn't a 750 cfm, but it would run a lot worse if it were. Since the things are adjustable, that means you have to adjust it, properly, or it will run like doggie doo. I had to re-jet the thing to run leaner on the primaries and a lot richer on the secondaries. Made a big difference. Next thing I'm going to do is put a Quadrajet on it. Better mileage, much better street performance, and just as much horsepower, on every one I've ever had. The Edelbrock is pretty, so maybe it'll bring a good price on Ebay.

2. Cam. Loping idle, doggy acceleration below 3,000 RPM. I don't know what cam mine has (still haven't gotten the info from the original builder yet) but I thought at first it must be way overdone. But that wasn't the case. If the idle is loping badly, you have two things happening, most likely. Timing (I'll get to that in a minute), and idle adjustment. You will have to advance the base timing to smooth things out some, then adjust the idle mixture and idle speed. If you get the combination of too lean idle mixture, to wide throttle opening, and too retarded timing, the thing will lope and gallop and sound great, but it won't run worth a darn. This is because the vacuum falls off, and the carb enrichment circuits think you are trying to accelerate, so the metering rods pull out and let gas through. The result, you are not running on the idle cicruits at all. The thing lopes because it is chugging gas. So, advance the timing, get the vacuum up a little, then adjust the idle properly. It might get you through until you can get yourself a nice Quadrajet (or at least a 600 CFM something-or-other, if you must).

3. Timing. Mine has a gorgeous top-of-the-line MSD system on it, complete with the box, rev limiter, coil, and billet distributor (pretty wires, too). The guy paid over $600 for all of it. And it didn't help it run any better. The guys at the speed shop probably ought to be shot for selling anyone a distrubutor without vacuum advance on it for street use. First, I recurved it. (meaning lots more advance, sooner). That in conjunction with the jetting on the carb made the thing develop power for the first time since it was rebuilt several years ago (tee hee). Lots of power! It still chawed gas like a hungry dog, though. So, since there is no vacuum advance on it, I ended up running the base timing way up there, off the scale, to a point I never would have tried on a stock setup. Still no pinging or detonation, but the idle smoothed out, the pep came back at low rpm, and now it sips gas. This car WILL get a vacuum advance distributor, before it gets the Quadrajet, so that I can set the timing up properly, don't want any holes burnt through the pistons, right?

Bottom line; that carb might be too big to get tuned properly, but you can almost count on it not being jetted properly. If you set up the timing and jetting, you should be able to make it drive around town without drinking up your paycheck. You might have to advance the timing far enough that you can't floor it because of knocking, if that happens, you need to swap out that carb. If the distributor is a pretty aftermarket one, it is probably curved wrong, get the kit and set it up for 35 degrees at 3000 to 3500 RPM, as a starting point. And if it doesn't have a vacuum advance, it will never get very good mileage or throttle response. You can reach a compromise, like I have going on now, but the vacuum advance was a pretty well engineered feature, in my opinion.

Yep, you got something that is all adjustable, now you have to adjust everything.

Once the thing runs right, then you can decide whether overdrive will help.

I came upon this forum looking for information because this car I bought, they completely jacked the transmission around, too. Sorry if my first post here is off topic, guys, and sorry for giving amateur advice (I'm not a professional tuner or anything, hehe), but I found this guy's problem here and so I'm trying to help here.

Good luck with that 327.

Last point -- I've had a few muscle cars in my life, they all outran my buddies' muscle cars, mostly because they put double pumper whatchamajig carbs on, while I kept my Quadrajets. Mine had more pep in normal driving, better mileage, just as much all out power, better cold starts, less flooding, less backfiring, and better reliability. I still laugh about that bogging sound! Anyone wanna buy a nice shiny Edelbrock 1405 with no choke, so I can get a rebuilt Quaddie?
Reply With Quote