QuadraJet

[ejkob]

I have a small block 350 chevy that is fuled by a Rochester Q-Jet. Last season, I was having issues at near full throtle where the engin seemed to begin to miss or sputter. Could this be timing, or is there an issue with the Carb?

[redtech]

this could be a great many things as the answers come in
my shop rule is alway look at carberation last
start with the basics points, ignition, plug wires (often over looked) do you have good fuel pressure, and good fuel, (no E85), fuel filters then go ahead tear that carb down
don't forget engine condition a broken valve spring can cause high rpm missing too
i don't want to mislead you it's just there is a lot to think about

[ejkob]

Thanks for your reply and I have considered lots of things, but this condition basically started after I had the Q-Jet rebuild by a carb shop. Last year befor the boating season, I replaced all the plugs, wires, dist cap and electronics in the cap (points have been removed). The motor runs great up untill almost full throtle. Then it sounds as though the engin is sputtering nearly backfireing through the carb.

[tkinak]

Weak ignition and or wet dist cap will show itself at high RPM's. Quadra jet metering rods can get bent if care is not taken putting the carb back together. Pop the top off the carb and check them out. Look for water in the bowls and for vacuum leaks. A lean engine will pop.

TK

[pila]

You likely checked, but a fuel system can meter the flow to the carb, like with a filter that's restricted slightly. You could remove the line from the carb and turn the engine over to check flow from the line, into a clear plastic jug. The fuel pump may be getting week on output and not meeting the demand of wide open throttle.
Q-jets have a fairly small orfice that feeds the secondary well from the float chamber, and it doesn't take much debris to restrict them.
If the carb doesn't use a paper filter in the fuel inlet fitting like automotive types do, and uses an inline filter somewhere in the boat, disturbing the fuel line can cause particles to dislodge in the line and get in the carb float bowl.

Just trying to give you some scenarios to check out.