If you have read the '69 400 Engine Talk thread then you know my Q-jet is contributing to my engine running poorly.
I bought this particular Q-jet because it was date correct (I'm an originality guy) and had it completely restored...redyed, everything. The engine has been running badly and most people point to the carb as the main source of the problem. It seems like most of the problem comes from fuel leaking down. This would be a problem with the bottom plate of the Q-jet. I've also had a problem with the top plate (horn) being bent and therefore not sealing all of the vacuum and fuel lines correctly.
My question is...could I just buy a new off the shelf Q-jet from someone like Autozone and use the top plate and bottom plate from the new one? Where is the part number stamped on the carb?...hopefully the middle section of the carb
Unfortunately, the bottom plate only houses the throttle blades and is called the throttle body assembly or more commonly the base plate. It does not do any sealing of fuel in the carb. It's really not that hard to seal the plugs on the bottom of the main body (float bowl assembly) while you have it apart. Taking the base plate off the bottom of the carb is easier than taking the top off. And there are differences in air horn assemblies (top), so if you still want to swap parts around, you should bring your other carb with you to make sure they are the same. Does your top have four tubes sticking out or six? (Did they put them back in correctly after machining it flat?? - maybe this is where your bogging problem is). Check to make sure both have secondary fuel discharge ports just above the secondary air valve as well.
I took the problematic Qjet off today and replaced it with the original Qjet that was on the car when I bought it (late '70s qjet). When we pulled the carb off there was gas everywhere. I pulled the carb with a mechanic friend at his shop and he couldn't believe how much gas was leaking out of it. I'm going to send this carb to Cliff Ruggles and let him work his magic on it.
The carb we put on has the car running pretty darn well. We dialed in the carb, set the timing, and then dialed in some more and it seems to be running well. I'm interested to see how it starts up in the morning and to see if it smokes or not.
Here's a tip for anyone who buys a rebuild off the shelf. Before you trade your carb in, open it and get the primary jets. The little brass, screw--looking things in the bottom of the feul bowl.
You also want to take the secondary rods and their hanger. It's held on place by that tiny screw right over the secondaries. Yes, that screw, if you removed it while the carb was on the engine, you'd lose the screw down the carb. The hanger and rods lift right out.
The reason why you want to take them is that federal law requires rebuilds to be detuned for emmision purposes. They do that by using small jets and low lettered rods and hanger.
If the carb doesn't give you the coal as your old one did, put your jets, rods, and hanger in/on the new carb. You'll know how to do it because you have already been in and have found out that a monkey can make such a replacemnt.
