Good day gentlemen,

i´ve got a 318 from '75 sitting in front of a 3-speed auto-tranny. When i bought the car, the Holley carb was fitted with 71 jets, the power valve is stamped with a 7. With this setup, the engine is running waaaaaaaaaaay to rich (fuel consumption is around 10 mpg, and the car stinks like hell of gasoline), this goes as far as i can start the car at -10°C without choke, just with a little push on the throttle.

Before i start messing with the countless setups, i like to ask if someone runs the same carb on this engine and maybe could give some advises for in which direction i should go.

I also wondered if the accelerator pump cam can make such a big difference in fuel consumption.

Please help.

 

My first guess would be a blown powervalve.
My second would be an incorrect float level.
My third would be a too-big idle circuit.

If the engine stumbles when you step on it [like fast] then the accelerator could be too big or too small. If it dont your ok.

 

Well, powervalve doesn´t look like its blown, the diaphragm is not ruptured in any way. I also checked the float level before i took off the bowl and it was perfectly level with the bottom of the sight hole.

Apart from running too rich, the engine behaves quite good. I just wondered because when i moved the throttle lever, there is really a lot of fuel squirting out of the nozzle.

I don´t know much about the idle circuit. Could you give me more info on that topic?

 

Go to a smaller jet.

 

your jets just seem to be too big

 

Yeah try changing the jets and see how small you can go.
I was assuming your jets were in the ballpark.
Holley idle circuits were set large on some carbs {for racing}.
You could place a small piece of wire [.012-.017 inch diam.] in the idle feed channel [in the metering block].
Accelerator circuits were set large on some holley carbs also, they sell different cams and squirters to reduce if needed.
BTW, the 4412 is a popular carb of the circle track racers.
Hear is a site that gives alot of info on carb tuning. It even tells how to use a single wire O2 sensor and a cheap voltmeter to tell your rich/lean [like to help figure out your jetting.]

http://www.bob2000.com/carb.htm

 

I always worry about the small piece of wire in the idle circuits, I have found some people are not as gentle as they should be and actually plow up a little aluminum with the wire, blocking off the idle circuit and making matters worse. I am a big fan of the lacquer thinner 24 hr soak and a little compressed air.

 

I´ve installed a pair of 67 jets yesterday and also switched to a 8,5 pv. I drove 60 kilometres home and back to work today and then filled her up again with 8 litres, making for about 18mpg (measurements are likely not accurate, but it definitely takes far less fuel than before). Not that bad at all, it still smells a bit of fuel, but not so much like an oil refinery as it has done before. I *think* it also accelerates a bit faster now, but that could be just imagination as well.

Only one problem occured: It started very hard this morning. Before, a slight push on the pedal was enough to fire it up right away, but today i needed almost 3 minutes to get it running. When the engine was finally approaching operating temperature, it ran fine though. Any suggestions on that?

 

Oh, and i have read Forgnone´s stuff before. Pretty interesting, but i think i have to get more familiar with carburetor technology first before i can make use of all this info. Since this is my first attempt on a carbed engine, this stuff is a little too scientific for me now

 

How cold outside when you had the hard starting?
Im thinking the choke malfunctioning obviously.

 

Yesterday, it was around -5°C in the morning. Today it was slightly above zero, and it started a lot easier. The choke is basically operated by eye, since the lever goes from full open to full close without any set stop. And i dont know how to adjust the choke properly. But it seems that it doesnt make any difference, the engine starts and idles the same regardless if the choke is applied or not.

I also threw new spark plugs in, then checked them today. There is some sort of white coat building up on the side electrode. Does that indicate a too lean mixture?