10mpg

I get around 20 MPG plus or minus that is imperial gallons so US gallons I suppose around 17 MPG . My ccpu likes to cruise at 45 MPH and I get up to high gear when I can . I do have a 28 phaeton with the AF 3" bore engine 28 BHP at 2600 RPM .the rear axle is 4.55 to 1 and it gets the same gas mileage but not the performance . 10 MPG seems too high to me if you can borrow another carb from someone who gets better mileage give that a try something is wrong somewhere . IMHO .

John in Suffolk County England .
 
eamonford said:
So, I did a few test drives today with different GAV settings, and it turns out I still get about 10 mpg even with the GAV at 1/4 turn and all the way closed. I know the GAV is doing something, as it instantly affects the engine power when I change it, but I’m confused as to why closing it all the way doesn’t seem to improve the mpg at all. I should note that I was driving with the gas pedal all the way down in order to maintain 40mph. I did order an infrared temperature gun, so that I can check for drag as John Neilson suggested. Other than that though, why would my mpg be unaffected by closing the GAV all the way?
Click to expand...

That definitely doesn't sound good. I don't need full throttle to go 40 mph up a moderate hill. My car is all stock. I run non ethanol 93 octane fuel.

Is your fuel fresh? Tire pressure correct?
 
If the GAV is making a big difference, it could be that the main jet is clogged or the wrong size. Try a different carburetor.
 
Remember, model A gas mileage and speed stories are similar to fish stories, Trust but Verify. However 10 mpg seems somewhat low. Don't pay attention to where others have their GAV, it varies greatly per car, especially since you have a different carb. Set the GAV for smooth running and best power. Run the car around 45 mph for a tank, in reasonably level terrain and then check the mileage. Don't set the GAV any leaner than what runs the best. Advance the spark until it just starts to ping on acceleration, then back off a click or so. If you havent tuned your ear to what ping sounds like you can go to youtube and hear it in videos. Some people with enough hearing loss can't detect it. Take a young person with who can hear well, teach them what to listen to. If it still doesn't give you the mileage you're looking for then swap out the carb with one from a tested car. Let us know how it goes.
 
Be careful that you are not going too lean and losing power and thus gas mileage because you are on the lean side of the power curve. Your spark plug pictures suggest a good fuel mixture with a little oil usage so this probably is not the case. However, try less than full spark advance (3/4 of travel) and a little more than 1/4 turn (3/8) on the GAV to see if your engine wants just a little more to give the power necessary. I once tuned in a Harley carb that was giving poor gas mileage and power until I went richer and suddenly hit the sweet spot that gave both power and gas mileage.
BTW, at 55 mph you are entering the speed where air resistance is the overpowering driver for poor gas mileage. The Model A is as aerodynamic as a brick. Try some 40-45 mph mileage tests to see if there is a step improvement in your gas mileage.
I have been consistently disappointed with my mileage as well at 15-16 mpg but I drive a section of highway at 60+ mph going to and from work.
 
Alright, so you guys really got me thinking... Eagle, you suggested to advance the spark until my engine starts to ping, then back off a little. Starts to ping? I’ve never heard my engine do that when advancing the timing, and I always drive at full spark advance because it feels way underpowered otherwise! So, when you said that, I thought maybe my distributor cam is too retarded, since I can’t advance it far enough to get engine pinging. (Big Hammer also mentioned earlier that 90rpm at idle sounds like spark is too late). So I advanced the cam by 15-20 degrees, and wow — now I’m getting 15-17mpg instead of 10mpg, and I barely have to press the gas pedal to get to 40mph. What a huge difference! I still don’t think I hear a ping when I run at full spark advance, but now at least it feels like I stop gaining extra power when I go to a click or two before full advance, which means I’m probably hitting the top of the timing curve. I think I can probably get a few extra mpg’s by finding the right GAV setting now that the timing’s more optimal, fixing the exhaust leak between the exhaust pipe and the manifold, and staying between 35-45mph.

I’m not sure why I had to advance the cam 20 degrees to be able to get the optimal timing... spark plug gap too wide maybe? In any case, I’m happy that it works and don’t want to look the gift horse in the mouth. Thanks everyone for all your help on this!
 
Sounds like you got her fixed. I would, however, learn what ping sounds like. Ping is destructive and you just dont want to go there.
 
Good news Eamon. Thanks for the feedback. You may not hear the ping if you have any hearing losses at higher frequency. But if you are at the top of the ignition curve, as you say, then you have the right timing. I call it the knee.
 
You must log in or register to reply here.
Back
Top