I've recently made a jetting change which has increased my fuel mileage by an EXTRA 3 to 5 miles per gallon. The stock accelerator pump feed check valve has a 0.5mm bleedback hole. I've installed 0.8mm ones. There is a slight hesitation now that happens every once in awhile at gentle takeoffs but not so much as to be a real annoyance. What this does is lessen the amount of fuel squirted in when ever there is a small opening of the throttles but at WOT it reduces the total amount by only a tiny amount. If you're driving such that constantly you're on and off the throttles and obeying the posted speed limits then the fuel saved will be quite noticable. Best I ever got out of a tankful when dry was 220 miles but now it's upped to 250 and I usually have another gallon left to go. The twos jets were $12 each from Pierce Manifolds. Roughly figured I've already payed for the jets in the fuel savings in past couple of months.

Better John?

So your previous mpg was only 2.???
John
(only kidding) :rolleyes:

Wow. Pretty significant change in mpg for a seemingly insignificant change in jetting. Nice.

Greg Z

My son and I have been doing power tuning on his muscle car for last few weekends. He also has to run the idling timing at nearly zero to prevent it from kicking back when starting and dieseling when the ignition is shutoff. This correlates well with the timing modifications I had to do to the twinkcam for similiar reasons. The static timing called for originally on his 383 was 12 BTDC with 26 degrees of mechanical advance. But those timing numbers were only okay back in days when 104 octane fuel was available. With today's 91 octane fuel that causes no end of problems. So if you've power timed your twinkcam and have not modified your dizzy to add another 10 degrees of mechanical advance then you're undoubtably down on power by at least 20 horsepower. It will run okay just it won't start to pull really hard at above 4000 rpms at WOT. This is valid for the California fuel only.

Be aware that the upgraded steel 4" diameter crankshaft pulley everyone has installed has the timing mark in the wrong place by 8 degrees. If you are timing using that pulley then you're automatically retarded by 8 degrees more than you think.

When doing any sort of timing never use the mark on the pully, there are always wrong. Find TDC with a dial gauge then you know for sure where you are.

Being wise to this problem I dialed in the true TDC to check the Romac harmonic balancer's indication mark I recently installed. It lined up perfectly with zero error. It's a well-made Lotus component for a change.

That steel 4" pulley has to be a Cosworth part which just happens to fit the twinkcam also I'm guessing. Sure saps the power of the unwary. I must confess I ran my engine retarded for at least 6 years before I got around to dialing in the TDC marks. I was plenty peeved off with myself to find it was wrong all those years.