Fast305

Anyone converted from Q-jet to TBI?? What would it do to gas mileage. I am getting 10 mpg now no matter what I do.

Brent

iTrader: (1)

I don't know how much duration that cam has but if its close to stock you can do much better than 10mpg with the qjet.

My '85 L69 made 26mpg on the highway. I suspect your part throttle timing needs tuning and the carb needs some attention also.

Fast305

I am running a 204-214* @ .050" cam, 700r4, 3.42:1 gears, and very little changed. The factory carb was non cc, as is the distributer. The carb is setup with .072" jets, .050M rods, 7 in/hg power spring, f hanger, DR rods. The distributer has 10* initial, 22* centrifical all in @ 3,000 and 10* @ 10 in/hg vacuum advance. It has lots of punch and seems to run good even @ 1900 rpm cruise in OD but gets crappy mileage. Nothing has changed it, rebuilt carb, cats, cam, heads, tune-up etc. I checked the leakdown and got 7% in the worst cylinder. I also have 185 psi cranking compression in every cylinder. I burn no oil. Seems to run fine except smells rich and guzzles gas!! I am thinking it is the APT screw in the carb but don't know. Edelbrock sets their 1904 @ 2 turns and mine is at 3.5? Is this the problem? By the way it got 10 mpg before I touched it and it still gets 10 mpg. Nothing I did made it get better mileage, only more power, and more vacuum @ part throttle cruise.

RBob

iTrader: (1)

The rich exhaust smell is something to go on. Check the fuel pressure to see if it is too high (sorry, don't know what it really is supposed to be, but I'd SWAG 6 psi or so).

Check the float level. And if the carb has the black plastic-like floats (nitril foam ones??) they can absorb fuel and sink, causing a high fuel level in the bowls. Just replace them.

Another thing to check are the round plugs on the bottom of the carb. I can't remember the size and location, but I do remember that they tend to leak fuel into the intake plenum. Epoxy is the recipe there.

I did swap a LG4 ('85 305) to TBI, but I never drove it with the QuadraJet on it. The same time I swapped the engine in it got a TBI setup on it. Runs nice, much better then the 2bbl carb that was on the previous engine.

RBob.