Q-jet tuning

[JJSZABO]

I am weak when it comes to q-jets or carburators in general.  I've read books and the subject is still clear as mud (at best).  I understand the basics.  Now for the question.  When I finish my wiring, I'll be ready to start her for the first time....  When it comes to tuning the 4bbl Q-jet can I use this wide band O2 sensor?


I used it for data logging so my local programmer can tune my chip in my Expedition.   know it can be used on carb applications, but is it really worth it?  I was considering taking the truck to a dyno to adjust it spot on.  If I can use this O2 sensor, it would save me dyno charges.

[Captkaos]

Do you have an O2 connector on the truck?
They aren't that complicated though.  If it has been rebuilt, just run the adjustment screws out 2-2.5 turns, I personally would fill the bowl with gas so it will crank, break everything in and then worry about adjusting it.  I would adjust it with a vacuum gauge and adjust it till you get the highest vacuum reading.
Getting you timing set is probably going to be a bigger pain than the Q-jet.

[JJSZABO]

Thanks Chris - No I was going to weld on an O2 bung in the exhaust.

The Q-jet is a new "rebuilt" one that is supposidly set to manufacturers specs from the company that rebuilt it (I forgot the Co name - I could get it though)  I know which screw is the idle screw, but which one is the air/fuel screw?  I like the idea of using the vacuum method.

Also where are the fuel bowls?  Do I just pour some fuel down the air horns?

Sorry for the stupid questions - I tell you, carburators are "NOT my bag, baby" (Austin Powers).

I would love to put in fuel injection if I had the time and money.  I love fuel injection - for some reason, I can understand all the sensors and tuning.

[Captkaos]

It should be fine if it has been rebuilt. 
The mixture screws are at the front of the carb at the base.
Fuel bowl is a the front of the carb, there is a vent tube infront of the rear air valves, just put the gas in there.

My want to check this article out also.  http://www.73-87.com/7387garage/drivetrain/myqjet.htm
and he list a good book for Q-jets: Doug Roe's Rochester Carburetors

[JJSZABO]

It should be fine if it has been rebuilt. 
The mixture screws are at the front of the carb at the base.
Fuel bowl is a the front of the carb, there is a vent tube infront of the rear air valves, just put the gas in there.

My want to check this article out also.  http://www.73-87.com/7387garage/drivetrain/myqjet.htm
and he list a good book for Q-jets: Doug Roe's Rochester Carburetors

I have Doug Roe's Rochester Carburator book   I might as well be reading the schematics to the space shuttle    I've tried to read it and it just confuses me more.  I just cannot understand carburators.  Wiring, body work, painting, Mechanical, or fuel injection no problem - once someone says carburators, WHAM, brain lock.

Oh well, thanks for the help.  I am sure as I get closer, I'll be asking more questions.

[Captkaos]

hehehe I understand.

[HAULIN IT]

Jeff, I have/use that Innovate unit also. I find it works well. I also have Doug Roe's book, however I feel you should pick up Cliff Ruggles' Q-Jet book, it is newer & has lots of good pictures with arrows, ect. The great thing about Q-Jets is that you can tune them fairly well after a little understanding. I have my unit temporary/perminate in my truck. Going down the road, at cruise it varies just slightly between 14.5-14.8 when I'm at a steady cruise. One thing that you will find (I have discussed this with others also) you will find upon deceleration the carb goes rich. I can't make this go away & couldn't find anyone could either. I have used the Innovate on many different set-ups, Q-Jets,Holley's, tunnel ram set-ups, ect. & have found it to be a good tool, Good Luck & Have Fun, Lorne 

[JJSZABO]

Hey thanks Lorne   I'll try that book.  Thanks for the advice. 

Are you running emission equipment?  EGR etc?

[HAULIN IT]

Jeff, I'm not running any Emission stuff on mine. I just weld an O2 bung in the headpipe & screw in a plug when I'm done in most cases. I also made a 3 bolt collector welded to a  1 1/2" piece of pipe w/ a O2 sensor bung & another 3 bolt collector to insert in the exhaust system & then remove it when done. On a friend's streetrod I got a 8" long piece of 3 1/2" pipe (welded in a bung) with a swedged end to slide over the header & put the turnout back on. If you use your imagination you can check the reading without having a hole left in you pipe. Good Luck, Lorne

[Stewart G Griffin]

i was (still am?) like you as far as Q-jets and carburetors in general.  i read Doug Roe's book and it may as well been writen in Greek or Chinese.  And, i know i'm not that stupid---i can read and understand English quite well.  But i just could not understand any of the concepts.  It was highly frustrating.
   So what i decided to do is get a remanufactured q-jet from Pepboys and sit down at the table with the book and took it apart so i could see what the heck he was talking about and it helped!  Things suddenly started to make sense.  And i could see how the various systems worked.
It was kind of expensive way to learn but:
a) Sometimes you have to pay to play. (actually you could sell the carb when you're done)

b)  You can read about stuff all day long, but i feel the only way to really learn is to do and see.

 Another idea i had was to try to get a Stock or Superstock racer in the area to teach you how to tune one. Put up an ad in Craigslist and pay them shop rates.  Once again, expensive.  But worth every penny.

2) As far as fuel injection, this unit from GMPP captures my attention:  It's several hundred dollars more than the Holley pro-jection unit, but i think it's better.  And i'm not knocking  holley.
http://www.thirdgen.org/techboard/tpi/245843-ramjet-350-p-n.html

But i feel you should still learn carburetors first because it's good to know.  Don't give up;  i didn't know jack about carbs until recently.  Try my ideas and/or keep bugging people on these websites;  There's plenty of other chevy/gm sites----novas ,chevelles etc.

[JJSZABO]

Stewart, thanks for the advice   You make alot of sense.  I have in my hand a rebuild kit for my old M4ME carburetor.  I was going to rebuild it until I started reading Doug Roe's book and got frustrated (and that usually doesn't happen - I am not afraid to fix things myself).  That's why I gave up and bought a rebuilt M4M from National Carburetor. 

I was going to go to Barnes and Noble tonight to buy Cliff Ruggles' Q-Jet book, and sit down with Doug Roe's book and try and rebuild this old carburetor.  I agree, hands on experience is the best teaching tool.  I might as well put 58.00 dollars to good use.  Thanks again - Jeff

[Captkaos]

If you don't get caught up in the technical mumbo jumbo, a q-jet is one of the simplest carbs to rebuild.