I have a 72 vette with a stock 350 200 hp when the secondaries start to open it bogs and then it kicks in but not like i think it should it has the stock Q-jet on it and im not sure is it is the carb or the vacume advanse also whats the best way to adjust the jets. Thanks for the help.
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Sounds like vacuum advanse check the vacuum at the distributer and also check to make sure the plate is not stuck in it as well... Had this happen to an old nova, rebuilt the distributer and all was well...
Might be the same but was the ol Nova running today's fuel? Take the carburetor down and clean it, reset the float levels and update the rubber parts, plastic float (metal is better), and the inlet filter. Look for corrosion on the internals and replace any of them that you can that are bad.
To adjust the jets take the screws in until they just touch the seats and back them out 1 1/4 to 1 1/2 then balance them at idle.
Also you may be chasing a problem with today's fuel that you'll need to live with. Remember it's not injected and it was not designed to run on today's fuel.
REPLY: Before tearing apart the carb, try putting some SeaFoam down the carbs vent tubes so it goes thru the passages and cleans them. It might be the vaccuum advance but then again the carb could be gummed up.
Is this a new problem? I had a similar problem when I first bought my 72 Vette back in 1984 (long gone now). I rebuilt the carb. I live at 3500' above sea level and changed the accelerator pump lever to give a bigger shot of gas. If it worked fine before, then carb rebuild time - could be the accelerator pump is worn.
The purpose of the accelerator pump is to provide a shot of gas when the butterflies are opened quickly. It takes the Qjet carb a little time to "catch up" as normal operation works off of engine vacuum.
chevyman84 wrote:
Good point Eugene. One thing they changed on the new rebuild kits beside the elastomembers is the spring loaded accelerator pump. It is now one piece, in other words a direct injection of fuel versus a softer dispense. Must be they know it needs it now and all it can get of today's fuel.
probably cheap quality/high priced fuel :-) try an octane boost to see if there is a difference....
my2¢
A bog problem can be difficult to track down sometimes. Timing advance curve "can" be an issue, but you mentioned the problem occurs when the secondaries are opening. You should be well into the advance curve at that point, I'd think......
If memory serves, on a Q-Jet there is a secondary air door spring that can be adjusted, plus there are secondary metering rods that can be changed out for different ones to adjust the fuel flow.
Maybe do a Google on "Q-Jet Secondary Air Door Spring Adjustment", at least that would be something free to try.
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