Has anyone ever had a problem with a quadrajet spilling fuel out of the secondary metering rod holes on a car that launches hard? I plugged the main vent at the rear of the choke horn and I have a piece of fuel line extending the front vent higher. This solved most of the problem but if I use a .145 needle and seat and/or raise the float above 13/32 the problem comes back. I only run a 1.72 60' time when it's working right but it hits the front stops pretty hard and when it hits it shutters from fuel splashing out and the only place left it could be coming from is the secondary metering rod holes.
a .145 needle and seat may require less fuel pressure, i think 5.5 psi. max on a q-jet with the big needle and seat is correct. i know 9 second chevy superstockers run the q-jet with much quicker 60 ft. times. good luck
I have the block in there. I also have a stg 1 pump so fuel pressure shouldn't be problem. I put a 750 holley on it last night to see how it runs Friday in Columbus. I'll do a couple runs and then switch back to the Qjet to compare. I also took off the shocks and adjusted them down from 90/10 and I took the Monroes off my other Skylark to bring with me if I need them. If I can keep it from smacking the stops so hard it will probably not splash the fuel. When you look at a Qjet the holes are at he very back of the fuel bowl. I have no idea how some of these cars do such huge wheel stands without spilling fuel out......
Q-jets are known for their ability to draw fuel DIRECTLY from the bowl whebn the secondary air valves opened. Rochester installed what is called a sail directly behind the primaries, using two of the air horn screws. It is quite possible that the original sail has been lost, and also quite possible that the sail may be retro-fitted to your carb. The incoming air flow, especially at intial opening is capable of tremendous force, and the draw is capable of drawing in small, low-flying birds. It was this capability that created the characteristic whoosh when the secondaries open. I would consider this possibility before pursuing other action. Heads-up! Ray
Doug, The way I get around this is to install tape on the gasket surface of the air horn (like packing tape) to completly cover the 2 holes that the secondary rods pass thru. Carefully trim the tape to fit casting and cut an "X" in the tape in the center of each hole. Reinstall airhorn as you normally would and carefully insert the sec. rods thru the "X". This seems to solve the problem.
My carb guy has fixed this problem for stock and s/s guys for years. He does the same thing in principle a Greg, but he uses a brass plate instead of tape. He machines the bottom side of the airhorn to accomodate the thickness of the plate. The end result is that raw fuel is blocked and the rods never bind-up either. He even gave me a tool to straighten the plate each time before you re-instal your sec. rods. This guy does complete re-builds as detailed as ANYONE and he is pretty reasonable too. He is also argueably the best in the business @ making them work better through midifications. His fastest customer has a single carb. QJ car that is in the 8's in the quarter. The only one we are aware of in the 8's. He built me a street carb with a choke and all and it the best $ I have spent on performance and drivability. Here is the guy Danny Ashley 765 674 5102 Tell him Randy Franklin sent you!
I was installing tape on the air horn like Greg suggested and I had an idea. I cut a piece of foam from a fuel cell to the shape of the well in the airhorn that the metering rods pass through. I poked the metering rods through the foam. Between the foam and the tape it should work.
For hard leaving cars you MUST address every potential point in the airhorn that could purge/slosh fuel out of the float bowl. This includes the round hole in the early carburetors in front of the air cleaner stud, the bleed holes over the POE wells, and where the metering rods go down thru the gasket. Some Pontiac q-jets had machined airhorns and a metal plate as described above. This idea provoked several "builders" to copy the deal. It is effective, but complicated/time consuming. A peice of 3M electrical tape across the gasket will work equaly as well. Lube the metering rods well and poke them thru the tape. Replace the tape every couple of years, no worries. Not a bad idea to back it up with a peice of foam either. If the POE holes are blocked, (some builders use epoxy/screen here, we tap them for set screws and lock them in the threads backed up by red loctite), the wells must be internally vented back to the fuel bowl. Keep in mind that there are quite a few different configurations (airhorns) used thru the years of production, some units having no potential leak points, and some having quite a few. Everything rear of the front vent should be sealed off on a really fast car, or it will be pulled out like a waterfall, and mistaken for incorrect tuning of the airflap, hanger, rods, pull-off release time, etc. It also helps to install a taller front vent, slashed facing forward, which can be made from a peice of steel brake line available at just about every auto parts store in existance. Keeping the fuel pressure low is a wives tail coming from the piss/poor float fulcrum position used on very early models. This problem was corrected in 1969, and improved again in 1975 (but continued to see use on Olds carbs to 1974 and Marine applications all years). These very early models with a .149 fuel inlet seat can be very troublesome at nearly any fuel pressure, even with the large float it's a "hat trick" to run 6psi fuel pressure with a .135", 4-5psi is about max. The later designs are fine to 7psi with the small float, some racers use 8-9 psi. The .135 fuel inlet seat will easily support 600hp at 6.5 psi fuel pressure. If you find yourself running out of fuel on hard runs at lesser power levels, get a better fuel delivery system. Fuel delivery is of the greatest importance for fast cars. Don't think for one second installing a carburetor with one quart fuel bowls on each end is the solution. Any carburetor placed in service must be kept full on a hard run, for tuning to be effective and predictable. I've back to back dyno tested our 1977 q-jet against HP950's, 850 Demon's, custom 1000cfm units, etc, and there isn't 1 hp difference between any of them, once they are correctly calibrated. At the track, if we see more than about .02 ET and .30 mph, one of the carbs was off just a bit for tune on that particular day. One last note. I continue to see folks tossing the smaller "750" cfm units aside for the larger ones. We always get inquiries to the shop about "upgrading" to the larger carburetors. I have one customer using a smaller unit on a legal Super Stock car, running deep into the 9's over 150mph! Right at the track on my own daily driven car, 600hp, running low 11's over 120mph, there is very little if any detectable difference in ET or MPH between a smaller unit vs a larger unit.......Cliff
Yeah, so I'm reading back over this thread and I thought "I" sounded like an asshole with the ANYONE part of my post. It was not, and is not my intention to come-off that way. With that being said, I'm pretty happy with my carb. I guess we all have our guys and this board is overflowing with helpfull and knowledgeable people. I don't want to discount any of those people. This is a good place to hang-out and learn.:TU: Randy
Randy, I stick to posting the most accurate information that I know, keeps me out of trouble most of the time. No hocus-pocus going on with building a q-jet for any level of performance, but you MUST take into consideration the items mentioned in my first post for really FAST cars. For cars that barely outrun Honda Civic's and Neon's, a decent stock rebuild with a Jiffy kit is usually good enough! Seriously, I would certainly hope that anyone you hire to build your carburetor or anything else with your car knows what they are doing and pays strict attention to detail in all areas? Kind of funny story, couple of days ago I was racing at Norwalk, and had arranged to meet a customer to pick up a TH-400 to build for him this fall. I took the quad over to the parking lot to pick it up, and there were a couple of guys drinking beer close-by who offered assistance. One of them mentioned to the owner of the transmission that his "builder" charges $150 to "go thru them", and is known in his area as the very best transmission "builder" available. Kind of interesting, as the last time I looked at my parts bill for a TH-400 the smooth drum, 34 element sprag and 4L80E lock ring cost me more than $150! Bushings, thrust washers, bands, low sprag, torrington bearings, steels, frictions, sealing rings, gaskets, seals, filter, shift kit and modulator will be more than $150. Leaves me wondering how you can get an entire TH-400 "built" for $150? No wonder I see units come in all the time with nicely sanded steels in them in several thicknesses and waffled, smooth and radial cut frictions packed in the same drum!......Cliff
Cliff, You sound like a man after my own heart. As an engine performance specialist, I hear all the time how this corner can be cut, or that corner was ignored, and my response EVERY time is that "Maybe that is why we are speaking." Any time I listen to these stories, I am amazed at the results of these horror stories, and the additiuonal expense required just to undo someone else's mess. Those having me do the job right are always VERY pleased with the results, and it is those results that are my signature. I tip my hat to those concerned with doing the job right, and letting the results speak for themselves, with no excuses. Ray
Ray, I cringe these days when I hear the component being brought to me was just "rebuilt". In more cases than not, it was better off worn slam out before the "builder" got hold of it! We don't do a lot of engines these days, but do end up building up to about half a dozen a year. Without exception, every single engine I get in here that was "rebuilt", is more work than taking one with couple hundred thousand miles on it right out of an old car and starting from scratch. That's one thing that hasn't changed in this industry in the past 3 decades, is that the term "rebuilt" doesn't mean the same thing to everyone, at least when it comes to engines, tranmissions, carburetors or most anything else I end up getting in here for repair(s)......Cliff
Cliff, I completely agree. I specialize in the process of making a performance engine really perform. The necessary ignition, fuel delivery, including fuel injection, and carburetion and electronic and electrical aspects are vital to the performance of the engine. When a customer brings me a vehicle with a problem, it typically is losing compression, or has other problems directly related to the "rebuild." Knowing the "process" requires having an engine first, it is the first thing I check. Same with electrical issues. Too many times parts are replaced without a thorough check out, and getting back to square one is typically more expensive than the original repair would have been. ANY time I get a hold of something I can work with, making the changes that work is both fun and rewarding, for both me and the customer. Knowing that there are others who understand the "reality" of the situation is gratifying. Thank you for standing up for the reality. Ray
Ray, good to hear that there are others who still pay strict attention to detail and do their best to make sure their customers get what they pay for. When we set up q-jets here, I look at all of the engine/drivetrain/vehicle specs, most specifically the engine cid, static CR, and cam specs. The carburetor MUST be set up for the idle characteristics of the engine, if not, no amount of tuning anywhere else is going to have a good end result. If the customer is drag racing, and/or the power to weight ratio dictates, we seal them up if/as needed so they don't throw all the fuel out of the bowl on the launch. As it relates to this thread, not all models have as many leak points rear of the front vent, some none at all. If/when drag racing is part of your vehicle's portfolio, it's a good idea to at least take a look at the carburetor you are using, and make the needed modifications BEFORE you find that the engine pukes all over itself on hard runs and no amount of tuning does anything to help the situation!.....Cliff
Thanks for the input y'all. I had the 60' times down to 1.70 (13.00) without a fuel splashing problem then I switched motors last month and now get 1.60, 60' times (11.60's) without a fuel splash problem. Not bad for a worn out Qjet!
