When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
here is one of those instances where trying to save money cost twice as much .i thought it would be easy enough to rebuild my quadra jet for the 455 i have. it turns out it had a hairline crack in the top section and it leaked .no big deal ! got the top off a spare my buddy had but was a chevy version and newer version so it wouldn't fit .the matching carb top i did have as a spare i ended up breaking off the ear that holds the accelerator pump lever ! just bought another off a member here for a good price but that has the wrong top as well.this of course is completely my fault for not checking the numbers on the carbs . i should have just bought a complete rebuild right from the start.(which is what ill do now)pictured is my pile of junk that i likely couldn't give away UGH!
Way back in the 80s I broke one of the accelerator pump ears (the outer one) and I was able to keep using the carb. What I did was instead of using the roll pin to attach the pump arm, I tapped the hole in the remaining ear and used a machine screw with a suitable size washer to hold the pump arm on. To make sure the machine screw stayed in place, I put a nut on the backside (where the threads came through the pump ear), tightened it up against the ear, then used a drop of Lock Tite to make sure the nut stayed in place.
Could you post a close up picture of the cracked area of the top section? I'm thinking maybe file and epoxy the section from underneath if it isn't near a fastener. Hate to see a good carb get scrapped for a small repair. I like to use Marine Tex on qjets. Shop for best price ebay, amazon, ect.
There is a repair part for your situation. I'd also order a new pump lever that uses a clip at the top, that way you if you have to take the airhorn off it's just a simple clip instead of having to mess with the pump lever. I don't know why the web page didn't download the pics but just click on accelerator pump repair( #5 on the list) & it should come up.
These are good suggestions but I must admit I got pissed and tossed the broken one . I’m just going to bite the bullet and have one built to my specs . I’ll try to sell off what I have here .Dragline I’ll try to post a pic but honestly I can’t see the crack at all until the gas starts seeping out if it
okay, after regrouping i did find a nice carb core with a good top on it and proceeded to clean it and installed the carb on the 455. started and ran fine but didnt have time to take it out for a test drive .im running .070 primary jets with .049 primary metering rods with DA secondary rods we will see how it performs once i get my throttle cable bracket and electric choke conversion. one thing i notice people dont talk about when rebuilding a quadrajet is the warpage in these tops nearly every one i have is pretty warped but with some light filing and sanding you can get these much flatter. no doubt this is caused by over tightening the carb bolts.
okay, after regrouping i did find a nice carb core with a good top on it and proceeded to clean it and installed the carb on the 455. started and ran fine but didnt have time to take it out for a test drive .im running .070 primary jets with .049 primary metering rods with DA secondary rods we will see how it performs once i get my throttle cable bracket and electric choke conversion. one thing i notice people dont talk about when rebuilding a quadrajet is the warpage in these tops nearly every one i have is pretty warped but with some light filing and sanding you can get these much flatter. no doubt this is caused by over tightening the carb bolts.
Some say that they were warped as soon as they came out of casting when new. Check out your other main casting 'cores'. You will see the main body is warped also. Usually at the notch where the divider is under secondary air valve flap. Tops are thin enough castings that even if you get them flat they will still conform to main body when assembled. Be carefull swapping tops. There is differences that could make things not work unless you have the top off a same number carb.
Mine was warped better than a 1/16. I machined up a jig to straighten it. It works for both the top and main body.
A thicker air horn gasket really helps to seal it properly. About 10 years ago I bought a reman QJet from Holley and it had the wrong accelerator pump, so I called and talked to their tech support to have them send me the right accelerator pump and I convinced the fella to send along some extra air horn gaskets as well. They are definitely thicker than the gaskets in the rebuild kits,.
A thicker air horn gasket really helps to seal it properly. About 10 years ago I bought a reman QJet from Holley and it had the wrong accelerator pump, so I called and talked to their tech support to have them send me the right accelerator pump and I convinced the fella to send along some extra air horn gaskets as well. They are definitely thicker than the gaskets in the rebuild kits,.
Yes sir, use the thicker top gasket. Nearly all quads are warped at the front two mounting screws. Probably not a good idea to sand the top flat while the bottom is still warped. Best idea is to leave it alone and use a thicker gasket.
Also, you can't just go sanding the top of the main body flat either. That opens up a whole new can of worms with power valve and needle length.
If you want your quad to run like fuel injection, you must start with a good core (try to pick up an Edelbrock repop that was made late 90's to early 2000's). Buy Cliff Ruggles quad tuning book and measure out all of your orifices, needles, etc. Then, call up Cliff, tell him your motor, cam, gears and quad specs. He will sell you the necessary power valve springs and brass/aluminum plugs to resize the orifices to match your quad to your engine. It will still take a little trial and error, but eventually you will have a carb that starts hot or cold, idles perfectly and has great response and economy. Anyway, that's how I do it.
One more suggestion, if you have a hot air choke, replace the choke assembly with a later electric choke. Those hot air chokes never worked well, and don't work at all if your exhaust heat riser valve is inop or removed. Electric chokes are great because they are not dependent on the intake manifold design. The old divorced chokes work perfectly, but reliy on a bimetallic spring mounted on a manifold pad heated by exhaust. Very few aftermarket intakes have this pad.
Waiting on the electric choke for the carb now , I have one on my 76 and it works perfect . And no I didn’t just go grinding away at the top with sand paper the carb works good so far and no leaks with the standard gaskets . Over the next few days I will test and tune . I’ll say it has a tall order to fill after using that avante Holley I had on it !
Those hot air chokes never worked well, and don't work at all if your exhaust heat riser valve is inop or removed.
I agree with you on everything except this, and that may be due to geographic differences. The hot air choke on both my 70 and 71 Supreme 350s worked perfectly, with factory manifolds (no heat riser valve) and with headers. The only reason I went electric was the Performer RPM doesn't have the hot air port.
Glad to hear you got it sorted out. I used to think electric choke was the way to go. Really the hot air choke is better. You can't over adjust and have too much choke with the hot air choke like the electric one. I am switching my 350 back to hot air since I am putting the Performer back on. The 70 will have filled crossovers and and the RPM intake so the electric can go on it.
Hot air choke uses a port to allow some bypass air. When switching to electric, plug passage. Unless using healthier cam than stock. Sometimes a little more bypass helps with idle tune. Depends too on whether carb already uses bypass. To much will cause a possible 'too high' idle. Basically a small vacuum leak. Only tunable by size of holes.
I don't see a need to block the air bleed in the choke. Think about it - if you kept the hot air choke, the air bleed would still be there and the engine would run fine, so the engine doesn't know what type of choke is being used.
Hot air choke uses a port to allow some bypass air. When switching to electric, plug passage. Unless using healthier cam than stock. Sometimes a little more bypass helps with idle tune. Depends too on whether carb already uses bypass. To much will cause a possible 'too high' idle. Basically a small vacuum leak. Only tunable by size of holes.
Actually, this guy is spot on. I had a big block carb on a 305 Chevy. Would not idle down, so I drilled, tapped and put some plugs in the idle bypass,. Now it runs well, but could run great with some additional changes in air bleeds. Pick up the Ruggles book. You will be rewarded with excellent power and manners.
Just sayin on some applications, if your on the ragged edge, it could make a difference.
Think of it as pulling a small vacuum line and creating a vacuum leak or the opposite. Finding a small vacuum leak you have to fix. Something to be aware of when you are chasin your tale on that fine tune and cant seem to find the issue.
Got a chance to drive the car today with the quadra jet on it and it works pretty well but not perfect.it doesn't seem to want to low idle very well.i have it set at 850rpms in park,and about 650 in drive with brake applied,much lower and it wants to stall .im getting 17inches of vacuum and the idle screws turned out 1 1/4 turns equally .the electric choke works pretty good its the first time ive started it and didnt have to warm it up for ten minutes like the no choke,(milled air horn) holley.a quick stomp of the throttle and it kicks off high idle so that seems good as well.i think im getting close but called it a night ,back at it tomorrow.
You can buy an air sensor test system for the tail pipe to check the exhaust and adjust the carb mixture. Worked with my Quadra jet and small block in my 69 Cutlass S.
same sensor as is used for fuel injection system
Last edited by spate51; September 13th, 2019 at 08:32 PM.
Reason: Additionally info
Take a look down carb when warmed up and idling. Check for nozzle drip. Fuel being pulled from transfer slots. Could be idle speed screw set to far open. Causing a rich condition from nozzle drip. In turn causing idle mixture screws to work best when set lean. If no nozzle drip. Could be APT set to far up. Causing rich condition.
You can buy an air sensor test system for the tail pipe to check the exhaust and adjust the carb mixture. Worked with my Quadra jet and small block in my 69 Cutlass S.
same sensor as is used for fuel injection system
Where did you get yours from? I need to learn more about adjusting theses carbs, mine is definitely running a little rich. Not sure if it's an adjustment issue or jetted to large. As a kid I had no patience for this. The older I get the more I want to understand the issues instead of ignoring them.
Deadeye: Years ago I found Hoggly carbs were only good in 2 positions, idle and WFO (Wide BEEP-ing Open). Went back to Q-jets and never bothered with them again. Have no clue what they've done over the years or what they offer and never had an interest due to my early experience. I know we aren't driving around in Prius's but if I can cruise with 2 small primaries rather than 4 it helps increase fuel economy. Easy don't laugh to hard. I ran Q-jets on a boat I had in my late 20's early 30's. Four Winns 241 Liberator with twin 350's (100 gallon tank) and if I didn't open the primaries I could cruise all weekend. My friend had a BaJa 251 Froce with a 350 & a Hoggly (80 gallon tank) and no matter what he did he was stopping for fuel more often. And not just 20 gallons more often.
Last edited by zeeke; September 14th, 2019 at 05:37 AM.
i spent a good part of this morning working on this carb and dont see how i could get it much better (key word "I").it has good part throttle response ,idles well at 800rpms drops to 700 in gear ,will roast the tires punching it from a dead stop with no hesitation ,secondaries are opening up nicely, one press of the pedal and fired right up on high idle when i first started it.has 18 inches of vacuum@1000rpms.for now im calling it good! i would be interested in this air sensor test system as well .Zeke i too am trying to become educated as much as possible about these quadrajets,i think they are an excellent carb once figured out .thanks to all for the advice definitely helps me learn about these things
Inability to lower idle is usually a vacuum leak or too much idle bypass air. Idle bypass is larger in big block calibrations. If know you have a 455, so idle bypass may not apply. But, too much air needs more fuel = high idle.
Last edited by bry593; September 14th, 2019 at 07:42 AM.
Inability to lower idle is usually a vacuum leak or too much idle bypass air. Idle bypass is larger in big block calibrations. If know you have a 455, so idle bypass may not apply. But, too much air needs more fuel = high idle.
i wouldn't really say i have an inability to lower the idle at this point .i can back out the idle speed adjustment screw until it disengages with the little tang(dont know what to call it)and that brings my idle down to 500 rpms and at that point the motor stalls . Without proper testing equipment how would i know if im getting too much air?im pretty happy with it right now but always striving for better.
Good to hear tune is getting there. Look up Lars Grimsrud. He has some good stuff on quads and lots of stuff pertaining to timing.
Some good tips on checking rich/lean conditions. He puts a lot on digitalcorvettes too.
Crankshaft coalition has a bunch to. On all kinds of subjects. If your like me every time you drive it you think 'it could be better' thus always tweakin things.
If you can back the idle screw out and rpms drop, then it sounds like idle circuit is not delivering enough fuel. Turn your idle mix screws out until it either starts running rough or there is no change. Next turn them in (cw) until idle drops. Then back out (ccw) 1/2 turn.
This basically richens the circuit and then leans it out and then puts it right before lean. The idea is to make it close to lean for optimum performance and efficiency.
If that doesn’t work, you may need to get serious and use the other tricks Ruggles has up his sleeve.
And yes, Lars info on tuning the distributor is also very useful. You’d be amazed how much hp and mpg you can unlock just by doing a serious tune on carb and dizzy.
Last edited by bry593; September 15th, 2019 at 08:08 AM.
Before I put this thread to rest I just want to mention I bought the ruggles book and read it from cover to cover twice now . Still trying to digest all the info , as well as a ton of Lars stuff . I’ve made slight adjustments here and there and the motor runs really nice , I will now start fine tuning the timing . I picked up a dial back timing light so I’m going to mess with that and see what happens . I have a spare 73 455 Quadra jet on the bench that I’m going to experiment with And try some mods I learned from all the reading I’ve been doing . But that’ll be next spring before it goes on .i guess I can change this thread from quadrajet woes to quadrajet goes
👍 I’m impressed. Most guys just whine about quads and then buy a holley. You are taking the initiative to learn how they work which sets you apart from the herd.
Once you have all your sizes recorded, you might send cliff an email or give him a call. He can make recommendations on the phone and will sell you the brass plugs to make bleeds smaller if necessary. If you take it seriously, your quad will run almost like fuel injection.
Deadeye I read that book too about a year ago and my head is still spinning. I'm afraid to read it again, it think my head would explode second time around. When I see the detail in these things it amazes me that anyone could come up with a design like that to begin with. I guess what I'm not taking into consideration is the failure rate to get there.
Good luck with it. Hopefully I see you at the ADK nationals next year. This was my first year there and didn't know what to expect. I use to pass it on my way to Port Henry for years and think "I need to go to this show". Glad everything is working out.
Thanks Zeke,im amazed as well how they built these things.I could only attend the car show one day this year but had a great time.Im going to do 3 days next year hope to meet you there.
August 30th, 2019, 02:46 PM
. I’m just going to bite the bullet and have one built to my specs . I’ll try to sell off what I have here .Dragline I’ll try to post a pic but honestly I can’t see the crack at all until the gas starts seeping out if it
the carb works good so far and no leaks with the standard gaskets . Over the next few days I will test and tune . I’ll say it has a tall order to fill after using that avante Holley I had on it !
I ran Q-jets on a boat I had in my late 20's early 30's. Four Winns 241 Liberator with twin 350's (100 gallon tank) and if I didn't open the primaries I could cruise all weekend. My friend had a BaJa 251 Froce with a 350 & a Hoggly (80 gallon tank) and no matter what he did he was stopping for fuel more often. And not just 20 gallons more often.
