Terrible MPG

[1968CHEVYC10]

My q-jet is running pretty rich on my 350 in my 68 lwb 3OTT, And I'm getting pretty bad gas mileage probably around 5mpg, is there anyway I can tune etc the carb to get it to run leaner and get better mpg?

[GruntMoanCough]

Could be a number of things, fuel well plugs, float, etc. Probably needs a going over. Have you changed anything on your engine lately that could effect the Q-jet from working properly?

[1968CHEVYC10]

Haven't really touched the carb, had the truck a year now and just got it on the road last week, I do have problems with it bogging down when I hit the secondaries. So basically it just needs a rebuild?

[oldblue1968chevy]

too bad your not closer!

dad gave me a book for the 70's

'how to tune your car'

has step by step pictured(black/white) how to rebuild your q jet lol) its GREAT!

[ERASER5]

What is your diff gears?

5MPG is pretty low. A rebuild kit can help. I would look at the lead plugs in the bottom of the middle section. Those tend to leak, and I can assure you, they can devastate MPG. Mine did.

[1968CHEVYC10]

Originally Posted by oldblue1968chevy

too bad your not closer!

dad gave me a book for the 70's

'how to tune your car'

has step by step pictured(black/white) how to rebuild your q jet lol) its GREAT!

Yeah I found a book on amazon all about rebuilding q-jets, probably need to order that pretty soon.

[1968CHEVYC10]

Originally Posted by ERASER5

What is your diff gears?

5MPG is pretty low. A rebuild kit can help. I would look at the lead plugs in the bottom of the middle section. Those tend to leak, and I can assure you, they can devastate MPG. Mine did.

3.73, what are the lead plugs?

[Notrodder]

Rebuild could only help and it is a fairly simple task. The kit doesn't come with a float or throttle bushings, which you may or may not need. You can see if the float floats when you have the top off of the carb and an auto parts store most likely has one in stock.

To determine if you need throttle bushings, check the amount of play (judgement call) in the primary shaft. It takes some tooling skill to bush these and the kit is fairly expensive, so it may be best to have it done by someone with the kit and experience with it.

[GruntMoanCough]

Originally Posted by 1968CHEVYC10

I do have problems with it bogging down when I hit the secondaries. So basically it just needs a rebuild?

Probably dumping too much fuel when you get into the secondaries. I would think that an overhaul is in order.

Originally Posted by 1968CHEVYC10

Yeah I found a book on amazon all about rebuilding q-jets, probably need to order that pretty soon.

Doug Roe's Rochester Carburetors is an excellant book, I highly recommend it.

Here's an article from another site, if you want to have a look..... http://www.circletrack.com/techartic...ech/index.html

[GASoline71]

Originally Posted by Notrodder

To determine if you need throttle bushings, check the amount of play (judgement call) in the primary shaft. It takes some tooling skill to bush these and the kit is fairly expensive, so it may be best to have it done by someone with the kit and experience with it.

This is a very common overlooked problem with the Q-jets. Good post.

Gary

[VetteVet]

I really like this one.
http://www.lbfun.com/warehouse/tech_...ng%20Paper.pdf

[Sinister]

Here's a pretty good link for Quadrajets: http://www.florida4x4.com/tech/quadrajet/

[cdowns]

have you checked for leaks? the rubber connector hose under the cab leaks when dry rotted

[Lee H]

Get your hands on a good book. I would recommend Cliff Ruggles book. Get a good kit and a new float. Follow the instructions for a stock rebuild paying careful attention to cleaning, the float level, and secondary wind up spring adjustments. Make sure you get an accelerator pump that is ethanol resistant, most kits have the old school pumps that swell up when they come in contact with ethanol causing the dreaded bog and almost stall out when you floor it. Don't worry to much about the lead plugs or the shaft bushings, I've only seen a few that were bad enough to cause problems. To check the plugs, remove the carb, take the top off and put a small sharpie mark about 1/2 way up the bowl, put in some gas almost to the mark, and then check the level the next morning. Stay away from the modification tricks. Unless your have a race engine you'll never now the difference. Good luck and let us know how this comes out.

[1968CHEVYC10]

Hey thanks for all the help yall, since this is my DD I'm thinkin' about buying a used q-jet and rebuilding it? Are there certain year ranges/models that were better than others?

[Beachcomber]

I changed to hei and get better milage.
Your timing could be backed off too.

[Notrodder]

Originally Posted by 1968CHEVYC10

Are there certain year ranges/models that were better than others?

According to the link that 'GruntMoanCough' posted for you, there are.

[Longhorn Man]

have you actually confirmed the 5 MPG thing? You need to know what you have before you try to improve it.

[capev86]

the q-jet is the best bang for the buck on a vintage daily driver.

good throttle response and economy due to the small primaries and great power when those huge secondaries open up. it just makes sense from an engineering standpoint when you compare them to square bore carbs. only carb i would reach for when i decided to ditch the 2bbl on my 72 burb c20.

only thing better would be a tbi setup using the throttle body from a 454 tbi and hogging out the small block intake to match. i hear that will give you 700cfm (close to the q-jet's 750).

good idea to replace the float while you have the carb apart....it could fail soon enough due to age.

[Ronnny]

One of the best qjets is the one that came on your truck. These were the years before emissions. I like a 2 bbl rodchester but the fours will get better mpg ifin you keep your foot out of it. a good one is and will be one of the best carbs you can have. If you still got points one of the best things you can do is get a hei dist. from a newer sbc in the 70' or 80s and will see a night and day difference.