Bob Onit

Well I used some of the parts I picked up saturday to throw together a QJ for my 73 L-48

My original 1973 QJ float bowl which has stripped ball check threads was not rebuildable so I used a 71 float bowl with my original 73 throttle plate and original 73 air horn.

I cleaned it out the best I could with carb cleaner , (I dont know what type of solvent is used to soak a carb in, nor do I have the proper equipment)and blew it out with compressed air.

The throttle shafts were tight so I diddnt need to bother with them (good thing because I have no experience bushing them either

Long story short, I installed 73 main jets/43 pri rods and DR sec rods and a set of long tapered Idle screws.
Set the float @ 3 1/8" new Acc pump and put it together.

I honestly diddnt think it would run at all but Im trying to learn all I can about these carbs so I gave it a shot.

Keep in mind that I have advanced Lymes disease-over 14 weeks so everything is a major chore

Mounted the carb, fired it up and it was pretty good but a bit rich at idle as I could see the smoke coming from the exhaust tips

Adjusted the curb Idle with a vacuum gauge and it leaned out nice

TEST DRIVE!
The carb ran as good as the two others I have which run great and are set up with the exact same rod/jet combo (which made it easier for me)

Anyhow I was very impressed for about 5 miles
Then the QJ gremlin showed up
It started running rich, barely idleing but the top end was still ok...

So.... what happend?
Ill believe anything at this point.
Im learning!

Little Mouse

Holley has been in business since 1903 and still going strong.
Heres the plan run the holley and keep the original type Q-jet
for the day your car goes up more in value, then bolt the Q-jet
back on for the big original bucks. Keep the hood closed and I
promise I will tell no one you are non original.

Bob Onit

C'mon bud.. gimme a break
I have 2 Qjets and a Holley Street Avenger 670 that all run great
Im just trying to learn...too bad that my brain is just about full...

Little Mouse

well you have plenty of carbs one of the three should be able to keep the car going down the road, I guess pick one and stick with it.
Even if you like the design of the Q-jet all of them are old and on
the wore out side, its kind of like having an old car something to
always work on. The holley is all new front to back, it may allow
you to do a lot more driving of your car and enjoying it.

Bob Onit

I guess you dont understand my point

#1 First of all, they never wear out..the two QJ's that run great have re-bushed throttle shafts so they are basically like new

#2 Yes the Holley is new and I love it, its a great carb.

#3 It takes me less than 10 minutes to swap a QJ ... so I am just testing carbs.. and trying to LEARN something new.
Even though I have a 2000 Explorer V8, A 70 ElCamino SS 454. And the 73 Corvette, I never leave my cars at a point where I cant get in it in the morning and drive it to work unless of course there is a MAJOR problem...... basically, I can drive any of my cars anytime I wish

jotto

I guess Bob is looking for ideas and opinions as to what may have gone wrong with his rebuilt QJet. Yes he could use any other carb but he wants to figure out what has happend thus learning a little.
I have my original Q jet waiting to be rebuilt ( by myself for fun ) and my car is running fine with the Holley at the moment.

I too would like to learn about carbs, rods and needles etc...At the moment I know the carb mixes air and fuel and makes the car go...kinda basic I know but with help from you guys, a few books and the hands on rebuilding...hopefully I will learn to understand them more.

Good luck Bob.

SIXFOOTER

OK, I'll step up here with a swag. First, the stuff you soak a carb in that you talked about is called Berryman ChemTool. it comes in a gallon can with a basket in it and has some sort of other chemical floating on top of the cleaner, it is Great carb cleaner! That said, it is also some seriously nasty s%&t. Don't breathe it, don't get it on your hands and don't put plastic parts in it.
Next, the carb ran good for a bit and then croaked....does it run good again after cooling back down? Think choke, hot idle compensator, or maybe an errant piece of crud in a passage.
Curious to know what ya find

Little Mouse

Well I did not think you would have to be walking you have told me about all your cars before, one of the great running carbs is having
a problem or you have another carb I don't know about.

cooter69

it sounds like a power valve stuck open that is the primary needlevalve hanger in the front by the float. quads are the best carb for any street driven car . let the racers run holley. never replace a quad with a holley . unless you dont now how to repair a problem then go buy a cheap holley.

Little Mouse

Where can I get a cheap holley the prices are high and demons
even higher ?? I need two holleys around 600cfm ??
I bought a trypower used in 1974 that was originaly off a 427/435
car the hole thing bottom to air cleaner for $85.00 spent $15.00 for
three carb kits I was up and running. Now the same setup costs
$1500-$2000 the higher rise 67 trypowers are going for $2500-$3000.
and my old Z/28 cross ram the price on them makes $3000 look like
childs play. I may have to get a cast iron manifold and a Q-jet.
How much would a cast iron manifold with Q-jet cost me ???
I would rather just buy a brand new Q-jet I'm not that great of
a carb rebuilder/tunner where can I buy a brand new Q-jet ???

gerry72

If the choke is functioning properly, then I'd give the idle air bleeds a squirt of aerosol carb cleaner. The air bleeds are about the only thing that will suddenly cause a carb to go fat on the idle. My experience in bringing Qjets back to life (or any other carb for that matter) is that the fuel and air channels are never adequately cleaned out with just a quick dip or a run through with aerosol cleaners.

If I have a real cruddy one, I usually soak it for days. And if the carb has seen any water -like a junk yard carb- or if it was allowed to dry out, I'll use an irrigation syringe and squirt some acid in the form of an industrial toilet bowl cleaner down all the air and fuel channels. This will clean out any scale or mineral deposits. Then I hit it with the spray carb cleaner, then run a .020 wire ream through the passages, then more spray and then blow everything out with high pressure air. You can not get a carb too clean.

Most of the time, faulty performance is because the carb just isn't clean enough. Yes, it takes a lot of time but I have brought back some of the most pathetic carburetors you will ever see. I did one a couple months ago that you'd swear went down with the Titantic.

SJW

Also check to make sure the float isn't sinking. If it saw carb cleaner, it may now be absorbing fuel.

Be well,

SJW

chevygod

HI Bob,
TFNG here, but I have played with lotsa Q-jets, and have had no probs with them that I can say were "poor design" related. Poor care related maybe, but that's my fault, not Rochesters fault! Holleys are great carbs, but not for me. If I am gonna replace a Q-jet, it will be with Rochester TBI, so still in the family!

I posted this on a another Chevy forum:

If you want to learn all about Q-Jet carbs, buy the Doug Roe - authored book, "Rochester Carburetors". It is excellent at explaining how carbs in general, and Q-Jets in particular, work. After reading this book, taking my time, and working with the darn things a while, I would never remove one from a vehicle that was originally equipped with a Q-Jet.

Of course, one must start with a nearly correct, complete, intact (in otherwords, unmessed up!) carb. Doesn't have to be rebuilt, the book will help with that. Also, access factory adjusting info on your carb. Take your time, and you will be able to sort out whats wrong, and be proud that you could fix it yourself.

Never, never let anyone sandblast your carb, any carb. It just ruins them. My 71 Montes L48 carb is sitting on a shelf, to remind me of this. The only plave I have ever gently glass-bead blasted a Q-jet is on the 4 jets wells on the underside of the floatbowl, and then, everything else was masked off. Which leads to this:

Did you clean and JB Weld the 4 rod/jet wells on the underside of the floatbowl body? These can and do leak and cause a rich condition at idle, and at cruise.

Anytime I had an issue with a "running great, then running poorly at idle but nice at cruise" carb, it was a float problem, either stuck inlet valve or sinking float. As was mentioned use a new float. Also make sure inlet valve moves freely with the float.

As most of the carbs on my cars are pretty clean (Four Monte Carlos with Q-jets, and soon on my project Vette) I have always cleaned them by soaking in laquer thinner or acetone. If one I have rebuilt was really bad, I would use the 5 gallon pail of ChemDip, but for routine stuff, the thinners were enough, as my carbs were not ugly. Use Berrymans (or the Walmart brand Carb Spray, blue/black can, cheap and wonderful) to hose passages, and the use compressed air. Assemble according to the directions.

Check idle mixture screws are correctly set. After motor is warmed up, shut it off, run both screws in and lightly, lightly seat them. Turn them out 4 revolutions each. Adjust each back in, in 1/8 turn increments, until idle starts to stumble and back out until idle clears. I have put short lengths or w/s washer hose on mine to make them easier to adjust.

Q-jets are excellent carbs, as is evidenced by the long production run they enjoyed. Buy the Doug Roe book, use you factory manual, and take your time. Should be no problem.

Good luck,
Tom

Kalway

Old and worn out?!

My q-jet is probably newer than any of your holleys.

Edelbrock made q-jets until 2004, educate thyself before speaking blasphemy.

Artsvette73

Go to www.corvettefaq.com Look in tuning read the papers by Lars. Got my 77 L48 Quadrajet up and runnung.

...Roger...

Your pump setting is 3" off.

Little Mouse

Holley has been making carbs since 1903 still going strong the
Q-jet lasted 60s to 80s. So if holley was out of business and the
demon was still around you would count it as a holley. All of the
reproduction Cobras are REAL cobras. The fiberglass 32 fords
look and act like a 32 ford are they really henrys 32 ford. Why did
edelbrock stop making there Q-jet there seems to be some market
for them ?? must have been to high in price to compete with all the
rebuilders of Q-jets.

Kalway

Rochester sold everything about the quadrajet to edelbrock and edelbrock reproduced the q-jet exactly the same way as rochester made them. So yes, they are actually q-jets, not a Demon like BG makes.

Little Mouse

Rochestor would not sell out if they had a profitable product they felt they could sell. I'm I correct in thinking Barry Grant worked for
holley had a falling out with them left and built his own version of
the holley seems like I read that somewhere.

Bob Onit

Ok.. here comes a lot of replies

Thanks for the info on the chemical.
It diddnt run any better after it cooled dowm.... IM guessing dirt or crud got inhaled from somewhere.

I have no Idea what you are speaking of.

If you read from the begining of the thread you would have understood that I was trying to build a runner from parts... I still have 2 great running QJ's for this engine

Rochester built carbs for GM
When Fuel Injection took over there was no more need for a carb for any GM car... get it?

I have Doug Roes book and all Lars tuning papers... If I remember correctly, Lars suggested NEVER to Epoxy or JB weld the wells, rather, drill, tap and plug them...I may be mistaken on this one.
As far as glass bead blasting goes, I have 3 Qj's that have been bead blasted and they all run great

1 Is on my 70 El Camino SS LS-6 and the other 2 are set up for my 73 L-48 with no problems at all.

And last but not least...Little Mouse
You have ALOT to say about QJ vs Holley
I have read through many of your STARTED threads and also vieved your profile..

Can you PLEASE tell us all here at this fine CORVETTE forum EXACTLY what year, model Corvette you own and please tell us about any mods you have done on it

Thank you all for the replys
Bob