I have a 1965 model 270 dart with a 170 slant six what holly 1920 carb on it. It's getting about 8-12 MPG. I've only had the car for two months and I don't have any idea what was done to it before that and I've only changed the oil. It runs good and starts very easily but my last slant six ('72 valiant 170) got around 20MPG and I'm looking for suggestions as to what could be wrong. I've been told it's probably something wrong with the carb and I should replace it with 2bbc with a prime and a secondary. What do you think?

Tackle

nas7@Po.cwru.edu

Before I went as far as a two barrel swap I would change the ignition to electronic instead of points, install a higher voltage coil, gap the plugs to .045, gap the pickup in the distributor to .18, rebuild the carb, install a K&N air filter, adjust timing for the best vacuum at idle, make sure your muffler isn't clogged up (if it is go ahead and install a 2 or 2 1/4 inch exhaust line), do a trany fluid and filter change (if applicable), and make sure your timing chain isn't stretched. Also make sure your valves are adjusted right.

All these will help both your performance and MPGs and are easier than a whole two barrel swap.

Reed

reed@seanet.com

Also check that the power valve in the carb is working correctly. You did not mention what carb you have. Those Holley model 1920's use a diaphragm operated power valve. Diaphragm could be stiff or ruptured. Also if someone installed it goofy it may cause the powervalve to be stuck open all the time using much extra fuel.

cfield@ll.net

Where do I look on the carb to tell more about it than Holley model
1920? And how do I check the diaphragm.

Tackle



nas7@Po.cwru.edu

I also forgot to mention another reason why I think the carb is the problem. I can usally start the car without pumping the gas. This is something people have told me means it's running to rich. It also floods the engine if I even pump once before I try and start the car.

Those all sound like good ideas. Do you have any suggestion as for the order? I am also wondering if there are any books or something that can get to learn about the carb rebuild stuff. I have a chillen's dart & Demon tune-up and repair guide for 1965-1972 and that covers the tune-up type stuff but doesn't go into to much detail about carbs. I was wondering how to check the really obvious things like float isn't working or is full of gas or there is a vacuum problem or choke isn't working. I think what I want is a general older fuel system book.

Tackle


nas7@Po.cwru.edu

Being able to start the car without pumping the gas makes me wonder if your choke is working correctly. Verify that the choke coil is attached to the buterfly valve and that the choke pulloff diaphragm doesn't have a hose. Does you car jump up to high idle when it is cold?

Reed

reed@seanet.com

Tackle,

After reading the other posts, it certainly looks like you have a carb problem. I have a sense that your car really needs a complete tune-up. I would do the following:

Rebuild the carb and make sure it is properly adjusted. Before you rebuild make sure it is rebuildable by checking for a loose throttle shaft, which is a common problem with 35 year old carbs.

New points and condensor. While you are at it make sure the vacuum and mechanical advance are working, and that the cap and rotor are in good shape. Set point gap to specs and set timing to 5-10 degrees BTDC.

If the ignition wires are old (or if you don't know how old they are) replace them. Also be sure your coil is working OK.

Be sure the air and fuel filters are clean.

Other things to check: low tire pressure, dragging brakes or a speedometer out of calibration. The first two reduce rolling resistance, and a slow reading speedo will give you false MPG calculations.

Best wishes

Pete Vanderlaan
Virginia Beach, VA

pmvdlaan@picusnet.com

I"m not sure what a butterfly valve is but the choke vacuum diaphragm has a hose attached to it. The choke seems to work. IE choke valve works. When the engine is cold the choke closes the valve and it opens once the engine warms up. I also opened the thing that lets me peak at the float and it was floating so maybe the carb isn't the problem. I'm going to try and do a tune up on it this weekend and check the compression on the cylinders and see how that turns out. The speedomiter/odomiter both don't really work that's why I gave a range for mpg. Speedomiter is about 15 mph fast and the odomiter is about 30% fast or so.

Tackle

nas7@po.cwru.edu