I've had several drivability problems with my Q-Jet, it seems to act differently every time I open her up.This is a 455 that sometimes misses, sometime bogs, and sometimes runs great. It's like a crapshoot, you never know what your going to get. The only thing that is consistant is the idle which is always bad, sounds like its got lots of cam but it ain't. Put a Holley on it and it seems to have cleared up all my problems. Now this carb has issues and probably needs a major overhaul, but my question is about the idle. I've read in David Vizards book on carbs and induction systems that if your running a 500 lift cam with more than 225 degrees of duration you may need to modify the air bleeds and idle screw hole. He also gives specific info on how to do this. Has anyone ever done this and did it help??? Dave Berry
How much cam do you have? And what Q-jet do you have? I doubt you are in need of those kinds of modifications. Personally, I'd send your carb to John Osborne and be done with it.
My cam is a straightline 226/238 and the carb is a 800 cfm, the number what I can remember offhand is 70**240. John Osborne rebuilt it about two years ago, although I don't think its anything he did just something gone wrong along the way. Dave Berry
Dave, I went through some trial and error but finally found a solution for my idle problems. Check this link for the story... http://www.v8buick.com/showthread.php?t=81581 My carb. and carb.'s history looks to be the same as yours!
I am not sure that the problems involved here are fully understood. The fuel dripping from the main circuits are due to the increased throttle necessary to make the engine idle with this cam. I am not sure of the cranking compression, but the requirements here include maximizing the timing advance, and possibly enriching the idle and off-idle circuits in the carb. Once these circuits are addressed, the choke can handle the rest. The concern here is simply the cranking compression. Check that first, being sure it is above 150 lbs. This will help immensely. What do the plugs look like? A widewr gap on the plugs may help here as well. Let me know... Ray
Ray My cranking compression is below 150, it's in the 135/140 range. I know a lot of guys swear by the Q-Jet and last year I was one of them. The Holley seams to have really woken the car up, it's running better than it has for a long time. The plug gap is set at .035 with a HEI ignition. I assume that Barrett is your last name which is an interesting coincidence the company I work for is Barrett Heating and Cooling. Dave Berry
Dave and Ray There is no possible way to make any Q-jet work correctly until you un-warp it and install the right throttle shaft bushing kit. mrqjet.com has the tool and the bushing kit, then the other defectis can be worked out pretty easy.
First, you are correct regarding my last name. It is Barrett. Since the carb at times runs well, I suspect an intermittent problem, which could include the ignition. If the power piston is sticking, it could well cause the problems you are experiencing. I suggest trying this: using a straw, place it on the power piston, through the front vent of the bowl. With the engine off, the piston should be in the up position, and gently pressing down should allow some movement down; it should then spring up again. With the engine running, it should be completely down, and should rise slightly when the engine is revved. These carbs were noted for the sticking power piston syndrome; it could frequently be fixed without removing the air horn. The dripping main system tells me that the throttles are open enough for them to feed, which may require other mods. Let me know... Ray
Ray The fuel dripping problem you keep mentioning was in cray1801s post, I never mentioned that problem. Although I don't know that I do have that have the problem, I may. I have checked the power piston and it's up when the motor is shut off and down while it's idling. I even cut a coil off the spring in case it was opening to early. It's kind of hard to check right now since the carb is not on the car and won't be until I make a trip to the dragstrip with the Holley. Anyway thanks for the ideas I'm sure I'll be back in trouble as soon as I put it back on. Dave Berry
Dave and Ray One of the worst places for warpage is in the middle on the bottom of the float bowl assembly due to the front 2 bolts when they are tightened, they pull down the out side edges, thus pulling up the middle. That thick soft gasket between the float bowl and base plate allows the pressure from the front 2 bolts being tighten the space to pull the float bowl down. Being warped the power piston is deprived of enough vacuum to operate correctly at all times. Un-warping the Q-jet is always the best place to start to correct any problems.
Though there are always reasons to be sure of any sealing surfaces before continuing, I am still concerned about the assumption made that the carb is warped. Though I have seen this situation, it is not the rule. It depends on the torque applied to these screws and the heat applied. Ray
