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turr'ble MPG?

H

hbar

Member
So what kind of MPG's are you guys getting? For reference, I have a 66 289w/C4, Edelbrock Performer intake, Holley 600cfm, pertronix II dist., flame-thrower coil, and plugs gapped at .038. The carb & intake were done by the PO, and I don't know if anything else was done. I suspect not. Timing set to ~12deg BTDC. FWIW, the timing seems to "wander" by 1 or 2 degrees on each flicker of the light, but never *actually* drifts.

I just got the new distributor installed, and it fixed "something" (it kind of bogged when I hit the gas, if you feathered it, it would eventually come around and then take off), so I might be a shade heavy on the gas right now, but nothing too serious. I'm looking at about 10mpg. That feels pretty crappy, but I don't really have a point of reference.

Other symptoms: my garage smells like gas, and the radiator & hoses are still really hot, like too hot to empty my gano filter. The upper hose & intake are both ~140 deg. It's barely 70 here right now, but the garage is still pretty warm, and I pulled in about 2 hours ago. I feel like the heat & smell might be relevant. Or maybe that's just how old car go, to paraphrase Ron Washington.

I feel like tuning the carb might be in order, although it really seems to drive well, and has power off the line, despite having a 2.89 rear end. That, and I don't have a clue how to do that (yet).
 
B

blue65coupe

Well-Known Member
It definitely sounds like you're running rich. You should be getting much better than 10 with that gear. Check the Holley website for instructions on how to dial the carb back to manufacturer settings for starters. I know with the Edelbrock you just screw the a/f screws back in and then turn 'em out two full turns but I don't know about Holleys. A vacuum gauge is the easiest way to dial it in if you have one. FWIW, I'm running a very similar setup with 3.55 (c4 also) and am guessing (very closely) to 15 mpg. What did you set the timing at with the new distributor?
 
AzPete

AzPete

Well-Known Member
My 289, slightly built, MSD @8*, Edelbrock 600, AOD, 3:55 gears does about 14 around town, 13 with the A/C on. On the highway, it is about 20 but I have not had much open highway time. Car stays out of OD under 55 mph. I do play a bit now and then.

I learned a long time ago that the MPG is not a big thing in these as long as it is not real stupid......drive and have fun....tune it so it performs the way you like it to. As long as I have enough gas in the tank to reach the next station, I figure I am good.
 
H

hbar

Member
I added the timing info to my original post, but probably after you read/replied. I'm at 12deg. I was running at 6, but then I read somewhere that 6 is recommended for a manual, 12 for an automatic. I know how to set it to a certain #, but I don't know how to *really* determine what the best # is.

Do you have a pic of the vacuum gauge you guys are always referring to? I'm sure I can fix the a/f screws once I find them. One of my pet peeves is that any pages about tuning carbs might have a picture, but ever any circles and arrows and a paragraph on the back of each one explaining what each one was to be used as evidence against me....wait, hang on....the pictures never say "hey idiot, here is the screw I'm talking about". Instead it's just a picture of a carb with a zillion screws and tubes and whatnot. They assume the reader knows more than I do, but I'll overcome that eventually.
 
H

hbar

Member
"AzPete" said:
I learned a long time ago that the MPG is not a big thing in these as long as it is not real stupid......drive and have fun....tune it so it performs the way you like it to. As long as I have enough gas in the tank to reach the next station, I figure I am good.
Click to expand...

For sure. I'm concerned much less with the number than I am identifying some sort of tuning issue. If it's 8 or 20, so be it. I want it to run as well as I can make it run with the equipment that is bolted on.
 
AzPete

AzPete

Well-Known Member
The mixture screws on the Holley should be one on each side, a small sized head. You could look at a parts breakdown of the carb to learn the names. Should be able to find them on line as they come in a rebuild kit.

The vacuum gauge can be as simple as buying one for under the dash and hooking a hose to in and the engine. Any parts local house can fix you up.
 
guruatbol

guruatbol

Always on vacation!
I get 25 on the highway in the 67 and 23 in the 65. I am running the performer on both and the edlebrock 600 cfm carb on both. the 67 has a T5 and 3:00 gears and the 65 has a TKO and 3:53 gears.

I agree you are running rich.

Mel
 
R

RustyRed

Active Member
If the garage smells like gas I am assuming you have checked for gas leaks?

I only ask because a while back I was getting really bad gas mileage and could smell a strong odor of gas a few times when it was in the garage. Thought it was a tunning issue at first.

Then I noticed a puddle of fluid on the intake and turns out I had a leak. My culprit was the short piece of rubber hose that connects the steel fuel line to the carb. Mine only leaked when it was under pressure (i.e. the car running).
 
H

hbar

Member
There is only the *slightest* hint of a trace of "wetness" at the rear of the intake, on the passenger side. I just drove the car for about 30 minutes, and checked again, and I didn't see anything else. A better man would've cleaned it up before taking it for a spin

IMG00680-20101004-2223.jpg


I did notice that the gasket might not be the correct one. There seems to be a lot of excess hanging off...makes me wonder just how good a match it is underneath the carb.

IMG00687-20101004-2239.jpg



I found the 2 a/f mix screws. The Holley tech page said to warm the car up, put them all the way in, and then back them out one turn, and start the car. Their page didn't specifically say, but other pages I've read say to then put the car in gear and back them out 1/8 turn at at time, keeping them n'sync. I guess this means you need two people? The same Holley page said if you didn't have a vacuum gauge (I'll be getting one tomorrow) you could tweak it for maximum idle. Honestly, I couldn't hear any difference, but I didn't hook up my bench tach, either. Regardless, it ran fine (to my untrained ear) at the initial setting, so I left it. Car drove great, but it's running hotter than it used to. Used to be the needle pointed to M, but it was at P the entire drive. It's a cool 60 deg. outside now, but earlier today it was in the 80's and it was running cooler. I did put my laser thermometer on the intake near the temp sender while it was running, and it said ~165. Blast that stock temp gauge!!!! Give me real information!!! Could running to lean make it run hotter?

Anyhoo, I guess I'll get that vacuum gauge tomorrow and try this again in a more scientific manner. It did drive great though...I peeled out at a light, which I never do. Quite awesome. We'll see how it does in the cool of the morning, after sitting all night.
 
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S

Starfury

Well-Known Member
165F is not too hot by any means. The motor is designed to run at 200-210F. A good place to check temp is on the top tank of the radiator, right next to the inlet.

You definitely need to learn how to tune the Holley. The idle mix screws will only change the mix up to about 1200rpm. Above that you need to start looking at jetting.

That hose definitely looks like it's leaking. Crank down on that hose clamp, or replace the hose entirely.
 
AzPete

AzPete

Well-Known Member
Yes, lean can cause it to run hot.

As for the mixture screws in sync, just turn each one 1/8 to q/4 turn at a time, doing one and then the other.

Using the idle speed to adjust works but you must use a tach as we do not hear a 100 rpm change sometimes.

The gasket is most likely the only one you will find for fit...they are not that good.

I never adjust one in gear unless I have two people. You should be able to get it tuned and then put it in gear to see how it runs.
 
H

hbar

Member
I know 165 isn't too hot, but it's hotter than it was, and it's pushed the temp needle to the far edge of the gauge....meaning that now i have only 3-4mm of travel before the temp gauge is pegged. If 165 is nearly pegged, how will I ever know if it starts running at 230? I've got a gauge replacement project in the works, so I guess that's how I'll know. Also, wife doesn't mind coming out in the garage to help me, so doing it w/2 people is usually feasible.

That video was great, I don't know why I didn't think to look on youtube for that sort of thing.


"Starfury" said:
That hose definitely looks like it's leaking. Crank down on that hose clamp, or replace the hose entirely.
Click to expand...
What is that hose, btw?
 
AzPete

AzPete

Well-Known Member
From that picture, the hose looks like the one for the PCV valve going to the passenger side valve cover.

Getting a good reading gauge could be as simple as replacing the constant voltage regulator on the back side of the instrument cluster. Also, on my infared thermometer, the closer I hold it to the source of the reading, the more accurate it is. They tend to take an average of the area in the viewing area. Closer might give a more accurate reading.
 
H

hbar

Member
I actually just checked the voltage regulator last week, and it was giving a strong 2Hz pulse. For the life of me I can't figure out why the gauges weren't just engineered to use a constant 12V.

So many things I want to do to this car....but having reliable temp & oil press. might trump them all.
 
H

hbar

Member
Is this the vacuum gauge I'm looking for? And what vacuum port should I be connecting to? Sorry for the endless questions; this is my first foray into this level of tuning. I don't need to be an expert...I just want to have a foggy clue.

2




And who makes that gauge bezel? I think I just picked the same one up off ebay yesterday, but the mfgr wasn't clear in the listing. I just liked it because it was the closest thing I had found to the OEM bezel.
 
AzPete

AzPete

Well-Known Member
Yep, looks good. Attach it to a non ported source. That is one that is low on the carb.

Here is a pic of my previous car. You can see the dist. vac. line goes near the top. Look lower on the carb near the intake and you see a line going to the back...hook the vac. gauge there.

Silver66019jpg.jpg
 
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