Engine: 10 mpg

[jff]

1962 Lark Daytona, 6 cylinder. It feels like it runs pretty ok, but I've been getting only around 10mpg when, I've heard, you're supposed to get 18+. Sure, it's an old engine, but I guess I'd expect a little better.

So my question: If this was your car, where would you start out looking for problems? It's running an aftermarket Daytona carburetor with a manual choke, which means the little tube for the original automatic choke is just kind of hanging out there. I guess it's supposed to be sealed off from the exhaust but if I put my finger up to it, I can feel puffs of air so there may be a leak.

I've done a basic by-ear idle mixture tune, turning the screw inward until the idle changes then backing it out a little again, nothing proper with a vacuum reader. Didn't see much difference before or after.

I've tried running regular and premium gas for the heck of it, no discernible difference.

Is poor mpg just something I should expect from a clapped-out engine? Is an exhaust leak wrecking the mileage? Do I just need to adjust the mixture properly?

[Warren Webb]

Your aftermarket carb may be running rich. Do you have a tach & dwell meter? Personally I first set the idle speed, then the idle mixture. Are the points new? If not file them clean & set your dwell angle, then set the timing. With the timing light on see if the centrifugal advance is working, then reinstall the vacuum line & see if the vacuum advance is working. If the vacuum advance isn't working it alone would give poor fuel economy along with the others. After that is all done remove the valve cover, torque the head & adjust the valves. Is it an automatic or stick? If its an automatic, it may be slipping & require changing trans fluid & do a band adjustment.

[christophe]

[Xcalibur]

"10 mpg" ?!? Something is DEFINITELY WRONG!!!

[jclary]

"10 mpg" ?!? Something is DEFINITELY WRONG!!!

Yeah...especially with a six! Years ago...I owned a huge International Travelall with the huge 401 V8 they sourced from AMC that ran the law enforcement version with the high lift cam for pulling heavy loads and it got better mileage than that! (although not much)

When the car is sitting without running...do you smell gas? When it is running...Is there black smoke? It's difficult to believe one of these little engines can "burn" that much gas without leaking raw gas or smoking and running real crappy.

[jackb]

how are you measuring mpg's ?? Aftermarket carb = ?????'s

[jff]

It might be running rich, I'm not at all confident that the idle mixture is set well. I'll try to do a proper adjustment.

jackb, I am measuring mpg by noting the odometer at each fill-up.

Warren, I'm not familiar with all the techniques you mentioned but I'll do some research and see what I can figure out.

Thanks!

[rstrasser]

The screw you are turning on the carburetor has negligible effect on your gas mileage. It only controls the idle speed air fuel ratio. If the engine idles correctly the mixture is set close enough. Without a exhaust gas analyzer use a vacuum gauge and by adjusting the idle speed screw and the mixture screw, adjust the engine for the highest vacuum reading at the correct idle speed.
I doubt that the carburetor could be running rich enough and the car still run; to reduce the gas millage to 10 on a car that should be getting around 18 in non city driving. Even a non working vacuum advance should not reduce the gas millage to 10.
I would start with a compression check of the engine to determine the condition of the engine. While the spark plugs are out; their condition will also be a indication of the engines condition
Ron

[Mike Van Veghten]

No one mentions the ignition timing...!

1. Carburetor jetting, mixture setting. Check the spark plugs, they should be clean, dry and light sand color. Darker to black indicates too much fuel (and or excessive oil consumption).

2. Raise the ignition timing a few degrees. Your note about running regular and premium kinda tells me that the timing is low. Along with this and as has been mentioned, make sure your points are gapped correctly before setting the timing. Add about 4 degrees to the "stock" setting value. You might be able to go another few degrees before detionation sets in, then back off about 2 degrees.

3. Tires low on air.

4. Brakes dragging.

5. Manual or auto trans. ? If manual, what are your shift points/rpm's ? If auto, is the shift point adjusted properly ?

And the list goes on.

Mike

[skyway]

FWIW that choke tube sticks out of the manifold both top and bottom, and yours has rotted out within the manifold.
Its a press fit, and with the correct sized punch you can carefullydrive out the old pieces and drive in a new one.
The originals had little bumps on them, perhaps to slow down the airflow so that the air to the choke got a bit warmer? Nonetheless, when they are bad, I usually replace them with a piece of stainless.
Probably not a bad idea to do this with the manifold removed so's you don't lose a piece in the manifold.
If you are not gonna use the choke stove, you could just seal off the openings?

[altair]

rich carb

That kind of mileage for a six could be because the float level is too high or a plugged up air cleaner/filter. Confirm the jet size to a standard stude carb, it may be too big. All the adjustments may have some effect but not that much to reduce it to 10 mpg. Also be sure that somebody is not helping themselves to your fuel at night. Locking gas cap? Dave B.C.

[jff]

Well, it's been a while, but I finally got a little bit of free time this evening and checked the timing.

I disconnected the vacuum line, capped it, and adjusted the idle to 550 rpm as specified in the manual. WOW. That engine is turning over slow, and the AMP light is on.

Anyway, I hooked up my timing light and saw that at 550 rpm, the pointer is more between the I and G of the "IGN" mark. Am I correct in reading that as meaning the timing is too advanced? I had noticed that before I lowered the idle, the pointer was still on that side of the IGN mark, just much much further along.

So it looks like the timing might be slightly advanced. I'm not hearing any pinging; should I adjust the timing anyway? Where the heck is the distributor clamp screw, anyway? What direction would I rotate the distributor, and how far?

It got dark pretty quick so I had to come in, but tomorrow I plan to check the vacuum advance. I was planning on just sucking on the carburetor end of the vacuum pipe. I've seen two ways to test it: 1) apply vacuum and see if the advance plate inside the distributor moves or 2) apply vacuum while the engine is running and check timing / listen to the engine for any change. Do you recommend one of those, or some third option? I can also try and borrow a vacuum pump from Autozone if sucking on the vacuum tube is a stupid idea

[Tom Bredehoft]

Setting advance....Find the T mark for Top Dead Center. It may be something other than the T. The next mark in Ign. Set your timing beyond the Ign as far as the T is the other side. You should not experience Ping with this advance, but if you do, back it down 1/4 of the way to Ign.

Good luck.

[Bob Andrews]

I always doubt the accuracy of these old odometers.

[jff]

This isn't from my car but it looks very similar to what I've got. I annotated it, the red arrow shows where the manual says the pointer should be, and the blue arrow shows about where the pointer actually points.

http://i.imgur.com/queKnIu.jpg