Let start by saying I know nothing about carburetors. I have a Q Jet on my 455. The engine was built by Mike Phillips. The Q Jet was rebuilt by a professional West coast builder. It had a stumble on WOT from day one on the dyno. It was sent back to the builder and he made some changes. It functioned better upon return but it still doesn't seem right. I will try to explain. The engine fouls plugs not all just 2 or 3. the plugs are black. If the car sits more than 24 hours it seems as if all the fuel has drained from the carb. It takes a lot of cranking and throttle pumping to get gas back to the carb. So is the gas draining out of the carb into the intake? Is this fouling the plugs? Is this bleed down causing what I think are problems? I am thinking about sending it out to another builder to be reworked. Your thoughts and suggestions please. Thanks in advance Jim
The main well could be emptying, maybe evaporating, which might cause the hard starting; I wouldn’t think that alone would foul plugs though. You may have more than one carb problem. Personally, I wouldn’t trust anyone other than our Buick (and some Pontiac) people with a Qjet. Also, beware of anyone with a guarantee-you know what happens when you put your trust in the ‘Guarantee Fairy’. Patrick
What do you have for an ignition system? How do you set the timing? What are you using for spark plugs? If the ignition is not correct, no carb will work correctly.
Bottom plug leaks are actually not that common on 1969 and later Q-jets despite what every single "guru" and self proclaimed Q-jet expert tells us on every thread related to difficult starting issues after sitting a few days. The worst symptom caused by leaking bottom plugs is the fuel bowl draining into the engine after a hot shut-down, then being flooded after 15-20 minutes or so of sitting. You can verify this problem by simply removing the lid from the air cleaner after shutting the engine down when it's fully warmed up and well heat soaked. Within a few seconds you'll see vapor coming up from the primary side of the carb indicated that it is draining into the hot intake and vaporizing the fuel. A "professional" rebuild should have involved pressure testing the main casting and bottom plugs and making repairs if/as needed anyhow. 99.9 percent of the time difficult starting after sitting for long periods of time is either a bad accl pump seal or fuel not returning to the bowl with a few short bursts of cranking by the operator. This assumes the choke is hooked up and working like it should be. Put it this way, even if I completely/correctly rebuilt your carb and you installed it bone dry the engine should fire right off within 2-3 short cranking and pumping the throttle a few times cycles. Fouling plugs could be a number of things from the carb being too rich to the distributor not adding enough timing when it needs to, or a little of both........
