LT1 stroker tuning issue - help

[VintageMusclecar]

Assuming everything else is right, I have never needed more than a .028" squirter and the #218 pump cam (which is stock on the 4053) on a 780.

Make sure your pump arm isn't bent/tweaked which limits travel. The end that rides on the cam sometimes gets bent upwards. If everything's set right, the pump arm should move immediately upon throttle opening. FORGET that old wife's tale about .015" clearance at WOT, that's a myth that needs to go away (along with that crap about picking a power valve that's 1/2 of idle vacuum, but that's a rant for another time).

If that checks out, make sure the ball isn't stuck in the pump well on the bottom of the bowl, and that it doesn't have too much clearance--.~.015" is sufficient.

*EDIT* get rid of that locked out distributor set-up. 16°-18° initial and ~36° by 3000 rpm should work nicely.

[earntaz]

[aaronkl84corvett]

Originally Posted by VintageMusclecar

Assuming everything else is right, I have never needed more than a .028" squirter and the #218 pump cam (which is stock on the 4053) on a 780.

Make sure your pump arm isn't bent/tweaked which limits travel. The end that rides on the cam sometimes gets bent upwards. If everything's set right, the pump arm should move immediately upon throttle opening. FORGET that old wife's tale about .015" clearance at WOT, that's a myth that needs to go away (along with that crap about picking a power valve that's 1/2 of idle vacuum, but that's a rant for another time).

If that checks out, make sure the ball isn't stuck in the pump well on the bottom of the bowl, and that it doesn't have too much clearance--.~.015" is sufficient.

*EDIT* get rid of that locked out distributor set-up. 16°-18° initial and ~36° by 3000 rpm should work nicely.

all of the checks out - and I find the same issue with 2 different carbs -

as for the timing - i've had it everywhere from the stock Z28 curve to locked out at 36- it does very little to solve this issue - with or without vacuum advance.

[seventieshow]

Originally Posted by aaronkl84corvett

all of the checks out - and I find the same issue with 2 different carbs -

as for the timing - i've had it everywhere from the stock Z28 curve to locked out at 36- it does very little to solve this issue - with or without vacuum advance.

If you are sure it's not a carb or timing issue you could spend some time looking for an air leak elsewhere, maybe the intake. I think a .031" is the largest squirter I've ever used. Not crazy about locked timing on a street car with a relatively mild camshaft.

[aaronkl84corvett]

i will say that the idle mixtures on a stock 4053 do little to nothing.

i will look for leaks and see if I can find what gives.