Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Another wet airhorn gasket thread...
Cliff Ruggles:
The problem is a poor fit between the airhorn and main casting plus adding a thick gasket. Lacking clamping force the "wicking" is only worse with that configuration.
Warping of the parts isn't a big deal unless you are trying to sell something to flatten things or making Youtube video's trying to convince the rest of the World you weren't successful at your day job and certainly not much better at carb building.
All that is needed here 99.9 percent of the time is to very gently flatten the front of the airhorn slightly and let it re-conform to the main casting when you bolt things down. Even though the two parts pretty much warp at the same rate the LONG BOLTS bolts tend to "hump" up the airhorn just a tad more than the main casting between them and the CENTER FRONT SCREW.
I would flatten the airhorn or I could do it for you, then bolt things back together with a thin OEM type gasket (denser material) so less "wicking".
Not sure where you got all the parts to date, I'm showing a couple of sales last year and you mentioned getting the N/S from Quadrajet Power.
The correct seat should be .135" and no "windows" in it, I have them in stock.
Replace the float with a new one if you are still using the original.
Also make sure the divider is in place between the fuel bowl and accl pump well as this reduces "splash" in that direction.
"K" metering rods aren't that great for fuel control with the APT system and you need to make some adjustments there with the larger main jets.
I'd add a set of my 45C rods, new PP spring for the engine/cam combo, and 3/8"-16 set screw for the airhorn for quick access to the APT for fine tuning. I would also get one of my accl pumps in there. It has a lifetime warranty for a reason as the seal is NOT the same as the cheap POS blue ones showing up everywhere else, and those "soft" blue seals will NOT hold up in this new fuel no matter what some uneducated folks lurking around on the Forums will try to lead you to believe.......FWIW.......Cliff
nUcLeArEnVoY:
Thanks for weighing in, Cliff.
That makes a little sense, but I still don't understand why mis-fitting between the airhorn and main casting causes the gas to wick. The fuel should never even be reaching that high unless it splashes, especially at my float level. I know that fuel is constantly touching the gasket as part of the idle system, but that's all I can think of.
Interestingly, when I first got the carburetor, it was using a thinner airhorn gasket; but photos I found from at the time showed that it was also wet. Maybe not as much. I wasn't aware that the thinner OEM-style gaskets were made of a denser material. Do you stock those?
If I send it to you, will you need the main casting as well as a reference, or is there just a general amount you can plane off the front of the airhorn that should work?
The seat I'm using is .130 windowed from Quadrajet Power. I thought .130 was the stock seat size. The original part number for the needle and seat is 7035148, and NOS Delco units on eBay do verify that it's solid/non-windowed, so you're right there. I actually HAVE one of your .135 solid seats already from an order last year - can I re-use the metal sealing rings? If so, then I'll drop your .135 solid seat back in after vac-testing it with the needle. I don't drive my car hard, I prefer to cruise in it so honestly I didn't notice any difference in performance between the .135 and .130 seat. Is there a document somewhere that lists all of the factory orifice sizes for my carburetor? That would be like a holy grail for me.
By divider plate, you mean that thin metal strip separating the main fuel reservoir (located right next to the needle and seat) from the accelerator pump bore? Yeah, it's in there.
The float I put in is new. Maybe 3 weeks ago. Nitrophyl late-model type. When I got it, I weighed it and tested it in water. Came in at 6 grams and floated just fine.
Kenth:
To flatten the airhorn i don´t like removing material from it, i prefer to use my shop press, add some heat on end needing straightening and some washers under screw holes and press the thing straight.
For inlet seat sizes i compiled this chart, it contains all Rochester inlet seats:
30-1 0.083
30-3 0.086
30-5 0.098
30-6 0.098
30-7 3.098
30-8 0.093
30-9 0.101
30-11 0.125
30-13 0.118
30-14 0.057
30-15 0.084
30-83 0.098
30-89 umbrella
30-93 umbrella
30-96 0.130 Buick 1967, Cadillac 1967-68, Pontiac 1967-68 OHC6 + V8
30-97 0.135 Buick 1968, Oldsmobile 1967-68
30-98 umbrella
30-99 0.125 Chevrolet BB Late 1967 –68
30-130 0.108 Chevrolet SB Late 1967 -72
30-132 0.120
30-133 0.106
30-134 0.135 Buick BB HP 1970 + Buick BB 1971-Later
30-140 0.125 Buick SB, Chevrolet BB 1969-, Chevrolet SB 1973-Later
30-142 0.135 B BB –1970 (not 1970 HP), Cad 1969-Later, Olds 1969-Later, Pontiac 1969-72 (1972 RA, MT)
30-143 0.090
30-144 0.101
30-145 0.083
30-148 0.135 Pontiac 1972 (not RA, M/T)-Later
30-150 0.125
30-152 0.120
30-156 0.090
30-157 0.110
30-158 0.116
nUcLeArEnVoY:
--- Quote from: Kenth on March 28, 2021, 07:32:42 AM ---To flatten the airhorn i don´t like removing material from it, i prefer to use my shop press, add some heat on end needing straightening and some washers under screw holes and press the thing straight.
For inlet seat sizes i compiled this chart, it contains all Rochester inlet seats:
30-1 0.083
30-3 0.086
30-5 0.098
30-6 0.098
30-7 3.098
30-8 0.093
30-9 0.101
30-11 0.125
30-13 0.118
30-14 0.057
30-15 0.084
30-83 0.098
30-89 umbrella
30-93 umbrella
30-96 0.130 Buick 1967, Cadillac 1967-68, Pontiac 1967-68 OHC6 + V8
30-97 0.135 Buick 1968, Oldsmobile 1967-68
30-98 umbrella
30-99 0.125 Chevrolet BB Late 1967 –68
30-130 0.108 Chevrolet SB Late 1967 -72
30-132 0.120
30-133 0.106
30-134 0.135 Buick BB HP 1970 + Buick BB 1971-Later
30-140 0.125 Buick SB, Chevrolet BB 1969-, Chevrolet SB 1973-Later
30-142 0.135 B BB –1970 (not 1970 HP), Cad 1969-Later, Olds 1969-Later, Pontiac 1969-72 (1972 RA, MT)
30-143 0.090
30-144 0.101
30-145 0.083
30-148 0.135 Pontiac 1972 (not RA, M/T)-Later
30-150 0.125
30-152 0.120
30-156 0.090
30-157 0.110
30-158 0.116
--- End quote ---
Incredible. How did you come up with that list?? Collecting parts, or is there an actual document somewhere?
Cliff Ruggles:
If you need to do anything at all for poor fitting components 99 percent of the time all that is needed is to remove a small amount of material from the corners where the long bolts go thru. Done correctly it will be just a tad flatter than the main casting under it and re-conform nicely when you tighten things back down.
I have the fixture to flatten airhorns and unwarp castings but rarely use it. I've found it much less intrusive and no risk of cracking either part using the method described above.
I work on a LOT of very valuable and difficult if not near impossible to replace carburetors. The best method is always the least intrusive with lowest risk of breaking something. A 30 ton press and heating up 50 year old metal castings doesn't fall into that deal.
I stock a really nice .015" thicker gasket for the early carbs that is made of an excellent material, and it seals them up most of the time without doing anything at all to either part.
The good thicker gaskets for the later 4 MAB models were unavailable for quite a while, but I just got some of those in about a week ago.
Most of the later variety thicker gaskets will wick as the material isn't that great. I have a lot of them here, but in almost all cases I'm going to make the parts fit better and use the stock high density gasket for those units.
As far as the N/S assembly you should be using a SOLID seat with a .135" hole in it. They flow equally as well as a windowed seat and will NOT allow the carb to drain back nearly as far after shut down IF you are using the clip on the needle in the first place.
I have found ZERO negatives anyplace using the larger late style solid N/S assembly in any application.
Currently available rebuild kits are showing up mostly with .110" thru .125". Some are solid but most are windowed. Occasionally I'll see a .130" seat in a kit or in a carb sent here that was just "rebuilt", but in most cases it will be smaller.
Kind of interesting but at least 80 percent of the time one of the complaints about the "new" build and why it was sent here was LOOSING power at higher RPM's, and guess what? Without exception every time that complaint was on the list the carb had a small N/S assembly in it.......FWIW.
Anyhow, as a reminder to anyone reading this thread I sell COMPLETE rebuild kits, the most complete in this industry for $45.95. I will also put together "custom" rebuild kits with tuning parts for any application so it's basically just "plug and play" for the builder/owner.
It will include a high flow N/S assembly and complete accl pump assembly with a lifetime warranty. The accl pump comes with new spring, stainless return and chrome vanadium spring wire upper for improved performance. There is a garter spring under the seal to keep it in constant contact with the pump bore and a retainer to keep the pump from pulling apart. It is currently the very best accl pump available for these carburetors and dating back almost 20 years now ZERO failures and never had to replace one. IF you want a larger .140", .145" or .149" N/S assembly and/or an HP accl pump just ask and I'll upgrade those parts at no additional cost.
....continued
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