Page originally created by MRHZV8 January 27th 2005:
Additional info by T and Munromad Apr 2nd 2007:
Back to Fuel System Section
==Rochester Quadrajet Carburettors:==Rochestor carburettors were made specifically for different engines and transmission types.
They also changed throughout the models/years as well.
===Troubleshooting:=== ===Flooding Rochester:===
Don't know if you'll get this but…………….. for all those others searching,...
"Been there done that" , in the endThe needle is Cock-eyed when it gets too low on fuel in the bowl, 'correct your float level', it should be reasonably high to the eye, the spec requires a 5/16 gap from the top of the flange to the fuel only. "Been there done that"
Check list would require you to ensure the Fuel does not drain back to the pump first.
When is the needle not closed so it drains back you may ask? During fill when the engine is stopped. Because the fuel pump was faulty valved, allowing fuel to drain back down. , I had to ensure the fuel line approach to the carby was from on high, not from low as the fuel drained back from the carby to the pump, lowering the float so low it Cockeyed the Needle, then you need to undo the Horn of the carb and adjust the needle. AARGH! Why you may ask, the Basket PUMP! Valves failed to seal and the fuel drained down hill from the carb.
Now that I’ve finished my gripe that perplexed me so long, the other reasons are thus;
I just raised the float, but of coarse, that’s no good if you’re going to Duel Fuel and you have this problem as this would require the Fuel being switched off when going to GAS and then Causing the fault, OK if you’re not going to run Petrol ever again, but, if you want to the float must be restricted from falling too low, allowing the needle to come up from its seat too far.
The Needle must have a smooth Point seal on it, (I think its rubber) mating with the Seat which itself must visibly be cut smooth, check for damage and grime.
Ensure the Pivot spring is held correctly in place by the horn when clamping it down, if its spring hinge is below the horn flange the it’ll raise up underneath and flood the bowl.
Fun Carb aren’t they?
End of Submission by Holden Fan -Q-Jet master. (not verified) on Sun, 27/05/2007
===Rebuilds:===Vanman's Qudrajet Rebuild
===Tips for Quadrajet Carburettors:===Submitted by campbell on Sat, 07/07/2007 - 05:41.
Before you blame the carb(and especially if changing the carb doesn't fix it).Make sure the ignition is tip top. New cap, rotor, leads, and plugs. Then do the timing correctly.
First tip: Get the float level correct.
Second: Have patience lining the rods up, and make sure the primary rods are in the main jets.
Thirdly: When you are pulling the carb apart. Be sure to screw the APT adjustment screw all the way in, counting how many turns it takes. Then when you reassemble the carb. Screw it all the way in, then back it out the required number of turns. This screw sets the height of the Primary rods when the engine is pulling strong vacuum.
Another thing with Quaddies is the power piston spring. They need to be matched to the vacuum of the motor. If the motor has low vacuum, due to a worn, or lumpy cam. The standard spring may over power the vacuum. This will make the carb run rich on the primary side.
The opposite is that a weak spring(or sticking power piston)will create less power(and/or flat spots).
On a standard 253, 70 mains, with 49p secondary rods, CX secondary rods, the correct float level, and the APT adjusted right, will give great fuel economy and power.
Stick with it, they are a great carb.