Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Edelbrock 850 performer RPM Q-jet
Cliff Ruggles:
You can NOT use the original posted dated for the 1910 for float level recommendations unless the original float is being used. They used a larger float in the 1910's with more leverage than the replacement variety.
I've set up several hundred Edelbrock 1910's at this point and have only ran into issues a couple of times. Coincidentally it was from customers using high output mechanical fuel pumps to them without any type of return. One in particular was pushing past the N/S assembly no matter what he tried for float level (or size of the float) or fuel inlet seat diameter. He was also using a "pusher" pump to his high output mechanical pump. He refused to install a return (been doing things that way since Moby Dick was a minnow), until I showed him that the carb was fine with my fuel system past 10psi.
For most "high performance" applications I've used the smaller .135" seat at 9/32" and recommend 6-8 psi fuel pressure. That will usually get it done with an good fuel delivery system to at least 500hp.
For really high HP applications, like one of customer and good friend uses with their 735hp engine pushing his car to 9.80's over 136mph we use a larger .145" seat, same 9/32" float level, fuel cell, electric pump fed by 10AN, then 8AN to the nose of the carb with a return style regulator in between........Cliff
bry593:
Cliff,
Are you saying they had a special float, just for Edelbrock? Now I know there are two off-the-shelf nitro-floats that can be used in the 170 series. The first is slightly larger, but has the heel closer to the fulcrum (what my 1903 had stock), the second is slightly smaller, but has the heel farther away from the fulcrum (what I'm running now). I tested both in my open bowl at 9psi and was shocked that they shut off at the same time when set to the same level. I really thought the bigger float would shut off sooner, but it did not.
Cliff Ruggles:
No, they weren't special just for Edelbrock, but they used the larger variety in their later style APT units. The larger floats showed up randomly in post 1974 later style q-jets, but I never kept track of exactly which carb numbers I found them in.
The hinge pin location is excellent on the later carbs and they are fine with the smaller float.
I've been running a later 1977 carb for quite a few years, small float, .145" seat, 9/32" float height and 7.5 psi fuel pressure. It will NOT flood clear up to the 14psi rated pump pressure and has been absolutely FLAWLESS for over 20 years with the current fuel delivery system.
The ONLY time I had issues with the carb was way back around 1988-1990 when I installed a 428 into the Ventura and a Carter 120gph mechanical pump at the same time, dead-head. It was OK most of the time but on occasion, especially hitting the brakes really hard it would flood momentarily. I had a .149" seat in the carb at that time.
I also noticed the gasket was wet all the time and I'd see fuel laying at the top of the accl pump hole at times. So I decided to check the fuel pressure at one point and it was fluctuating between 6 and 10 psi with an occasion "spike" even higher. I was NOT using a return and to this day suspect the HP Carter pump just didn't like to be dead-head even though Carter says they are OK in that configuration.
Jump ahead to 1999 when I installed a larger 455 making 1hp/CID. I ended up sumping the factory tank, 140gph electric pump behind the tank, and going 8AN lines/fittings everyplace with a return to the tank from the regulator to cure fuel delivery issues.
Since then I've moved on to two more powerful 455's and have never once had a fuel delivery or any other problem, and no flooding, wet top gasket or fuel laying around the accl pump hole.
I see some folks get away with less, but that's what it takes to support the power level of my engine and performance of the vehicle at the track with good traction. In full street trim the car runs low 7's at 95-97mph in the 1/8th mile. 60' times are in the 1.59-1.64 range for most runs.
I don't run 1/4 mile because it's well below the legal roll bar rule of 11.49. I have made a few 1/4 mile blasts before being asked to leave and the car has went really low 11's over 120mph and that was in pretty hot humid weather.
I did not dyno the current engine but did dyno one very close to it, just lower compression at 10.2 to 1. It was also a 455 with the same heads and cam, and made 552hp/604tq, so mine will make at least that and probably a bit more since the compression ratio is 11.3 to 1.......Cliff
bry593:
Nice. Sounds like a pretty awesome Poncho.
Cliff Ruggles:
Thanks.
The current engine was about 30 years in the making. I started out with a low compression 400, TH400, stock converter and 2.73 gears. It ran 14.0's around 99-100 mph in that configuration with a best ever 13.87 @ 101mph.
Two 428's and two 455's later, 10" custom converter and 3.42 gears it's running quite a bit quicker, but remarkably just as mild and easy to drive as the "little" 400 was way back in the mid-1980's........
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