I've just swapped a rebuilt carbureted 300-6 into an '85 F250 4x4 replacing the old 302 efi problem child. This 300 has about 200 miles on it and runs great. Got some questions,however, regarding vacuum, timing, and mpg. Vacuum: all emissions were previously removed except PVC and breather setup. The vacuum seems excessive as some of the caps on the carb are sucked in and the PCV makes a lot of noise. Does this sound right?
Timing: I do not know the year of the 300/ carb set up and I am using a '78 ignition module. Manuals reference a timing spec ranging from 6 to 12 degrees depending on calibration number. There were no calibration stickers on the motor when I got it and the underhood sticker is obviously of no use. I timed it by ear and it runs/accelerates smooth, no spark knock. Is there a typical timing spec for this motor setup such as without emissions? Is there more than one timing mark on the crank other than the square notch?
MPG: Currently getting 13.5 mpg which is unsatisfactory. Hopefully, with more miles I'll get better mpg. Any other suggestions? Thanks for any input.

 

Check to see if there is a timing tab bolted on the timing cover. It should be by the water pump inlet hose. The timing marks are stamped on it and there is usually a slight bigger jagged notch. And that notch is usually marked at 10 degrees. Most of the 300s I've seen have been set at 10 degrees. To get a 300 to pass emissions, i'll set it at about 6 or 8 degrees.

 

I recently put a rebuilt 300 in my '86 F-150. My mileage was around 10 mpg until about 3000 miles, and then started going up. Now with about 5000 miles on the motor, I'm getting 17-18 mpg. Your's should go up as you get a few miles on it.

 

[font size="1" color="#FF0000"]LAST EDITED ON 09-Aug-00 AT 09:48 PM (EST)[/font][p]Thanks, for the input Re: mpg. I'm also known as rosco (its my office alter ego, otherwise known as timekill). I'm wondering if there isn't a better way to check MPG.... I've used the same gas station, same pump, pump setting, same time of day, same 62-66 mile commute over the same bumpy Maine roads, but my mileage has flucuated from day to day. Motor has about 600 miles on it with 1 bbl carb. Ranges from 12.5 to 17.5 MPG day to day. Is there a better way to check MPG?? Can't think of one. ALSO, what about the sporadic sucking (vacuum) sound I get on accelaration? I've had to time this motor up to 4 degree BTDC and I'm still getting a hint of spark knock at the bottom of 2nd and 3rd gear (its a 4spd). Think I should retard another degree or so but all the timing specs don't go this retarded. Also getting some "run-on" when shutting down now and then. Any comments....anyone?
Thanks.