TheBigBlueBoat

Background: Personally rebuilt 455 giving me grief. Engine had definitely been sitting for awhile. Fuel pump was borked, replaced with a spare I had. I have good pressure and flow getting to the carb. Carb is a late model Quadrajet of unknown status. I don't see any fuel squirt when I manipulate the linkage to WOT. It does start and run (briefly) if you pour your flammable fluid of choice down it.

Now it's been a few years since I've monkeyed with carbs, but it seems like all signs point to a carb rebuild, do they not? It clearly has the air/spark down if it runs on fluid, and it's getting the fuel to the carb.

If that is the case, are there any tips or tricks short of a rebuild? And any recommended sources for getting rebuild parts quick locally? Seems like the selection of carb and distributor parts at the big parts stores are long since gone.

oldcutlass

No tips and tricks, you cannot band aid over a bad carb. Get a kit its not that hard, they can be had at your local auto parts store.

Quadrajet Power

We may not be local to you, but we ship parts and kits daily.
www.quadrajetpower.com

shiftbyear

Besides a rebuild, the choke may need adjustment to keep running when cold. Are you breaking the engine in or was it running before it sat?

TheBigBlueBoat

Looks like I can get it locally but it's not in the shelf- it will take a day or two.

Choke will definitely need adjustment, but it's warm out and it won't so much as pop on its own.

This will be breaking the engine in after a rebuild.

TheBigBlueBoat

Well I rebuilt it. It was full of crap, accelerator pump was busted, power piston was all gummed up. Everything was cleaned and replaced.


...now she doesn't want to start. It'll pop and run briefly if you spray into it or keep working the pedal for the accelerator shot, then sometimes backfire and die. I can see the accelerator pump working so I know it's getting fuel into the bowl. I've tried adjusting the choke from closed to open. I ran out of battery before I got to mess with the idle adjustment screws much.


I don't think it's timing because it ran before the carb rebuild when the needle stuck open (until it overflowed the vents and flooded.) So if I'm not mistaken that should narrow it down to fuel- and since we know it's got fuel in the bowl that should narrow it further down to just the idle circuits, right? Any tips on that one, or just set it to 1 1/2-2 turns from seated and back it out until it starts or surges? What if that doesn't do the trick?

scottv442

sounds like your engine is getting spark and you say its timed correctly enough to run as before so.....

I assume this is a qjet?

back the idle screws out 2.5 times from seated and leave them alone. The engine will start and run fine at that setting once the other issues are fixed.

from your description it sounds like the float level is too high or the needle is not seating under the float pivot. have someone do what you described above ...using the foot pedal to keep the car running .....while you look down the barrel of the carb throat. you will probably see alot of raw gas spilling into the engine from the primary venturi's and eventually flooding the engine out.
this shows the engine is "flooding"

take the top/airhorn off the carb and readjust the float and or clean the needle and seat. this should fix the issue.

caveat....your full supply must be clean and filtered so no dirt can re-enter the carb.

oldcutlass

If the fuel came out the vents, its flooding. Check your float level. The engine will not start with wet plugs.

TheBigBlueBoat

Yes, it's a Quadrajet, although apparently it's from a 1977 Oldsmobile. More on that below.

Didn't get anything at 2, 3, 4, or 6 turns out. It wanted to start at 6.

Needle and seat are brand new from the rebuild. Float was set at 11/32" per the guidelines in the rebuild kit.

Plugs were dry. I wasn't sure if it was lean or rich, so I had tried it yesterday with the throttles open in case it was flooding, but no dice.

Same as previous, carb was just rebuilt this week.

Fresh gas and new filter.

That was what prompted the rebuild. Opening it up the needle/float were stuck due to deposits. Needle and seat are new, float was checked.


Today I seemed to confirm my theory. I put it on full choke, started with 2 turns, and walked it out to see when it would start. 2, 4, nothing. 6 I got a few pops. 7 and it would start to pop, then run, and stay running if you kept your foot in it. 7.5 was as far as I was daring to go, and it would start without any throttle input and run without any throttle input, at least for awhile.

So it seems to boil down to the idle circuit. With it being a 1977 carb I'm not sure if it can deliver enough idle fuel for a big block. I'm hesitant to turn them out any further. The carb was soaked and I checked every passage to make sure they would flow. Is it worthwhile to enlarge the idle discharge ports?

oldcutlass

I agree your idle circuit may still have some junk in there. You might want to take it apart again and reinspect.

scottv442

some 1977 qjets have a secondary/automatic idle circuit under the air horn in a pot well. this was a failed attempt at emissions control and was discarded in later qjets. does your carb have this? if so remove it or find another carb.

backing the idle screws out allows more air in the mixture. air that it can't get thru the closed choke. this should indicate the car is running too rich.

wish i was there to smell or see the exhaust when the cars running.

TheBigBlueBoat

The question is if it's obstructed, or just plain too small. Being a 77 would mean that it would have to be a 350 or 403, and a post-emissions one at that. Would that be enough to run a pre-emissions 455?


Any clue as to what that would look like? I don't immediately recall seeing anything of the sort, and I couldn't find any readily available pictures.


Wouldn't the idle screws primarily allow fuel, as well as a little air through the idle air bleeds?


It's acting like it wants both more air and fuel. Fuel based on the fact it won't even start without them turned way out and the choke on, and air based on the fact it's got the notorious primary drip of pulling too much air through the venturis at idle, rather than the bypass.


It seems like my options are either do some drilling, or get an actual pre-emissions big block carb.

olds 307 and 403

The 77 carb will be a 800 cfm carb, the best Qjets but very lean from the factory. All I did was increase the compression 1.5 to 1 and the rocker ratio from 1.6 to 1.72 to 1 on my 350. It was basically the same carb, just ran awful. I got the idle circuit opened up for a larger cam and compression, idles and transition are both about perfect. Get Cliff Ruggles book open up the idle tubes yourself or get someone like Everyday Performance or Quadrajet Power to do a rebuild and tune for your motor, Ken from Everyday was very reasonable.

TheBigBlueBoat

You would be right.

Based on my previous conclusion I ripped it apart again and pulled out the idle tubes/restrictors. I drilled them and the idle adjustment ports out a little more than stock based on what other people had work for their combinations. (Punched, soaked in PB blaster, heated a bit, then extracted with a #6 stainless sheet metal screw in case anyone needs recommendations.)

I put the carb back together, set the screws at 2 turns out, and she lit off perfectly. I was going to use one of the capped vacuum ports for bypass air, but it didn't seem to need it once it got enough fuel. Runs like a top.

Never thought I would have to tweak something so specific with a carb, but it sure did the trick.