quadrajet 455ho
 

hi working on pontiac 455ho stock eliminator with a single booster quadrajet that runs fat in first gear from 5100 -5900 afr 11-11.5 anyone know how to fix this. regards magnus

Re: quadrajet 455ho
 

May be over rich with the secondary metering rods. The smaller the diameter of the rod the fatter you will be.

Re: quadrajet 455ho
 

How is the carb set up,does it have primary rods and jets with the spring or just jets with no rods.Where's the float level?,fuel pressure?. gsa612

Re: quadrajet 455ho
 

I just noticed it was a single booster carb.I believe it's only legal on a few cars yours being one of them.The guy you need is Danny Ashley,he's a member here,hopefully he'll see this.I don't have any current contact info,maybe someone here does. gsa612

Re: quadrajet 455ho
 

There is a special system that the 1971 455 HO carb has , its called the POE system . Its purpose is to add extra fuel at WOT . You may want to get the Quadra Jet book by Cliff Ruggles , he has a section on that system . Most Q-Jets do not have that system , it doesn't meter fuel as well as having fuel go through the venturies . You say your engine only runs rich in 1st gear , are you running a Ram Air hood and air cleaner ? Which body style , GTO , Formula , or Trans Am ? Each has a different system .

Check Fig 11 https://www.gmcmi.com/wp-content/upl...ice-Manual.pdf

Re: quadrajet 455ho
 

May be sloshing fuel out of the secondary metering rod holes. Do you have them sealed with tape or anything?

Re: quadrajet 455ho
 

Danny is retired and living the quiet life, have to find somebody else.

Re: quadrajet 455ho
 

Try Dean Oliver #870-830-5470

Re: quadrajet 455ho
 

the car is a 1972 lemans no ramair hood no aircleaner no primary rods just jets secondary metering rod holes are sealed float level 1/2 in fuelpressure 6psi accelerating well tubes are blockt afr 12.5-13.5 in second and third gear. regards magnus

Re: quadrajet 455ho
 

What size jet in the primary? Are you leaving off the two step, and does the condition get better with rpm? Sounds like it may be rich from being on the two step then clears up after.

Re: quadrajet 455ho
 

the primary jet is 74 leaving off the two step att 2600 converter locksupp att 5100 condition gets better between 5900-6300 and in second and third gear

Re: quadrajet 455ho
 

Your primary jet is too large based on my experience for not using primary rods. I run a 65 jet and have gone to 63s on the primary side with a very similar combo. The pump shot puts a fair amount of fuel when you mat it on the two step and it could cause it to run rich at the start. Are the secondary vent tubs plugged when you remove the air horn? I do not run a two step but someone with experience may be able to help. Have you tried foot braking to see if the AFR is where it should be. The other thing to check is the air door spring tension. If the air door does not open fast enough it will run rich, if it opens too quick it will create a lean bog.

Re: quadrajet 455ho
 

That's way too rich if your running a fixed jet (no rods).The general rule is to be 5 steps leaner than with a rod.You should be around 67 possibly leaner.Your float level at 1/2" is too low,it should be around 1/4 ".I would think at that level it would lean out due to lack of fuel in the bowl. It's hard to keep the needle on the seat when the fuel level is that low.A q-jet has a small fuel bowl to start with.When you build your fuel system you should have a pump with good volume and 1/2" lines to keep the bowl full.And keep your pressure low (6-6 1/2 lbs) for a clean leave. gsa612

Re: quadrajet 455ho
 

Was the float level and the accelerator well tubes modified that way to try and fix this rich problem ? Not sure what you are talking about when referring to accelerating well tubes . Are these the tubes that are supposed to feed fuel into the secondaries as the flaps start to open ? Also when you are on the 2 step , are you flooring the accelerator pedal ?

Re: quadrajet 455ho
 

float level 1/2in accelerating tubes are the tubes that feed fuel into the secondaries when the flaps opens they were seald to try to fix the problem. yes the pedal is floored on the 2 step.

Re: quadrajet 455ho
 

Apparently you have some sort of data acquisition system , assuming you are measuring A/F ratio with a wide band O2 sensor . When on the 2 step , what is the A/F ratio ? Once you release the 2 step , what is the A/F ratio ? Is the A/F ratio consistent at 11.5 through out 1st gear , then goes to 12.5-13.0 after the shift to second ?

Re: quadrajet 455ho
 

yes we have a racepack. after releasing the 2stepp the afr goes from 10.5 to 12 att the first to second shift after that it varies between 12.5 to 13.5.

Re: quadrajet 455ho
 

What is hard to understand , is usually when your on the two step the O2 sensor is faked out , and will read very lean . This is because the two step interrupts the ignition which means some cylinders don't fire and the air passes right through the engine , and the O2 sensor reads that as excess O2 and therefore lean . Yours is reading rich , which is opposite from what I would expect . You may want to make a run without running the two step and compare the results .

Re: quadrajet 455ho
 

I firmly agree you have too much main jet. I think you should change the primary jets to # 68, then evaluate.

Re: quadrajet 455ho
 

I always thought the opposite. Unburned fuel from 2 step going out exhaust and making a rich condition. My bracket car has a O2 reader and on 2 step it is rich and gets right by second gear shift. Yes on to big primary with no rods.

Re: quadrajet 455ho
 

In a production car , when the engine misfires the O2 sensor reads lean , and then starts to add more fuel to correct . Most production calibrations will only allow so much correction , and once it reaches that limit , it sets a code . A misfire is similar to what a two step does only more controlled . I am surprised your engine reads rich when on the two step . Hopefully a few more folks will chime in with their experiences .

As far as running as big a jet with no rods , I agree , too big , but remember that this particular carb has the POE system , which adds even more fuel into the primaries at WOT . He might have to put a very small primary jet , or reinstall the power piston and primary rods .

Re: quadrajet 455ho
 

^^^^ Read an article on one of the Burton firebirds.They claim to run a 61 pri.jet,it does not say if that's in Denver or...So say if you ran at sea level and went to a 63,that would be 11 steps leaner than the 74 that's in it now.You would think if it's that far off it would be just flat off the line.What does the car 60' 330' and ET. gsa612

Re: quadrajet 455ho
 

when on the 2 step afr is 18-19 but afterreleasing the 2 step afr goes from 10.5-12 just before shifting to second gear. poe system blockt. best 60 foot 1.39 best et 10.69 in e/sa should change to 69 pri jet for the next race and but a gopro camera under the hood over the carburator.

Re: quadrajet 455ho
 

You may not be too far off , your et and 60 ft is pretty darn good . Tweeking the primary jets will let you see what the combo wants . Also , my 455 HO wants around 40 degs of timing , what are you running ?

Re: quadrajet 455ho
 

it likes 36-37 degrees best but we are using vp motorsport 109 are not allowed to use leaded fuel here in Europe. our goal is go 1.1sek under index to be a little faster than the other e/sa cars here.

Re: quadrajet 455ho
 

The VP 109 has plenty of octane for your engine , I would warn you that because that fuel has no anti corrosion additives it will rust the valve seats . You would need to fog WD-40 or some other spray lube into the intake after you are done racing for the weekend .

Re: quadrajet 455ho
 

What is the elevation of the track you run at ?. gsa612

Re: quadrajet 455ho
 

the track were we ran 10.69 is 682 ft over sea level and we had 1700 ft of air.