i have a very serious questiion! i have a q-jet and want to get rid of it to use a edlebrock or holley and dont quite have money for a new on. so i checked everywhere fora used one but with no luck so for now i'll keep th q-jet ( for now) i hear everyone here talikg about getting good fuelmilege from theres . but how? i cant get over 6 mpg on the highway! i set the float, re-biult it to spec twice? it wont hold a idle to save its life impossible to start( and keep running chokes fine. so what could be the problem? i've posted numerous quedtions before but no answers! please help i dont know what to do!!

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1989 firebird formula

Mods: converted from T.B.I. to a carburator 305 to a 350. Flowmater exhaust,hedman shortie hedders,202 heads,350 horse cam,bored.40 over, Edlebrock torker2 intake.

Future mods performer rpm air gap intake (polished) and 600 edlebrock carb, comp roller cam, and way better headsa 400 defintely in the works!

 

Well, let's cover some basics first. I assume you're talking about the car described in your signature.

What kind of a q-jet did you use: The kind used on '82-'87 thirdgens (electronic), or an earlier type? Unless you used the ECM, sensors & harness from an electronic model, you should be using an earlier mechanical type. If you used an electronic model without those controls, it is in an enriched "limp home" mode that would result in terrible mileage and poor starting/idle.

What did you use for a distributor: The original TBI distributor, or an earlier vacuum/mechanical advance HEI or something similar? If you used the TBI distributor, you aren't getting any advance above idle, which would result in terrible mileage, and possibly the other problems.

What do you have for a drivetrain? If you're running 4.11's with a TH350 tranny and high stall convertor, that could result in poor mileage. Is your speedometer calibrated for the drivetrain you have? If you have a TH700R4, did you hook up the TCC lockup? It's not the total mileage problem, but without it you're not getting all the mileage you could. Wouldn't affect the other problems, of course.

How much fuel pressure do you have at the carb? I believe you said on another topic that you used a stock mechanical pump - not sure if you kept the TBI pump connected, too. Does the mechanical pump have a return line? If not, then the needle/seat is being over-powered (by the TBI pump) and you're basically flooding the carb, which would result in terrible mileage and poor starting and idle.

For reference, my Camaro with the '86 factory induction and ignition (except for coil & tuneup stuff) and non-functioning TCC gets ~18-19 mpg communting, ~24-26 on the highway; starts easily and idles relatively smoothly. The '57, with the mechanical stuff, gets about 12 mpg commuting and ~14 on the highway; starts easily and idles well.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R. 2.93 limited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, TBD heads, exhaust, paint, etc.).
57 Bel Air, my 1st car. 0.030 over 396, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

 

its a 700r4 stock coverter, vac advance hei, and a non-computer controlled q-jet timing has been set everywhere! ihave it at about 11 degrees btdc(initaltiming ) and i have stock 323 posi rear-end speedo calibrations are correc. tcc locks up manually according to the info in the tech article in this site. ikept thestcok tbi pump but its not working at all (made sure of that one!) has a un-clogged return line(now) and still starts hard.carb was re-biult to specs after specs(instructions with the kit and a fully documented manual)

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1989 firebird formula

Mods: converted from T.B.I. to a carburator 305 to a 350. Flowmater exhaust,hedman shortie hedders,202 heads,350 horse cam,bored.40 over, Edlebrock torker2 intake.

Future mods performer rpm air gap intake (polished) and 600 edlebrock carb, comp roller cam, and way better headsa 400 defintely in the works!

 

One of the biggest problems with older q-jets is a warped airhorn. This is typically either caused by over-tightening the front two mount bolts which go through the cover, or forgetting to remove the two screws under the choke butterfly and prying on the top to get it off. I'm trying to visualize the circuits (and don't have any diagrams in front of me here), but if you have rebuilt it to spec several times, and it runs the same each time, this may be your problem area. Also check for cracks around the passage sealing areas.

The other possibility is the float. If soaked, it will flood the carb even if the "setting" is correct. Have you weighed or replaced the float?

The sweetest q-jet I've seen is the Edelbrock. But, since you can't afford a Holley or Edelbrock Performer, you couldn't afford an Edelbrock Q-jet, either (could buy two of the others for the cost of the q-jet). But, they run great out of the box, and with some tuning, will keep up with either of the others on a street 350.

I just noticed you have a Torker II intake. That really isn't much of a street intake with its single-plane design, but I doubt it is the "cause" of your problem.

Anyone else want to put their oar in the water here?

 

The first thing to check about any Q-Jet is the little spun-in plugs in the bottom of the fuel bowl under the primary jets. They almost always lek; and of sourse there's gasoline on top of them and vacuum on the bottom, so an enormous amount of extra gas can be sucked in at high vacuum (idle & cruise). This will also cause very difficult hot starts, because the fuel bowl will drain into the intake while it sits, then when you try to start it, it will be massively flooded. The cure is to wire-brush, then sand, then lacquer thinner, then epoxy over the plugs. There's 4 of them that you'll see sticking out of the bottom of the bowl if you take off the throttle plate on what looks like 2 towers not far from the front of the casting.

Next question: not all Q-Jets are the same. In fact there are literally hundreds of completely different ones, calibrated for evrything from 69 SS396s to Buick 307s to 70 F*rd Torino 429 SCJ to GMC motorhomes to 305 vans to 74 Vettes to.... you might have something just perfect for some gas-burner dump truck or something. Who knows? What carb # is it? What size primary jets are in it?

The same goes for HEIs. They have an incredible variety of timing curves. Have you tried a curve kit? Does the vacuum advance work? (That would partly explain high fuel use at cruise)

Five7 is right about the intake, it is a complete and total mismatch for a Q-Jet. Put something else on there. I'd suggest an Edelbrock Performer; they're only like $120, a good bit of which you should be able to get by selling the wrong one you've got.

What heads do you have? I assume that when you say "202", you mean that they're supposed to have 2.02" intake valves in them. What cam is that? Is it the 151? If so, that's another thing that will cause poor fuel mileage, and is a mismatch to the rest of the combo. What is the CR? If you don't know that, post the head casting number and the piston shape (flat, dome, dish, etc.) and we can figure it out.


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"So many Mustangs, so little time..."

 

ok where to start ??? the heads have 202 160 vavles.(just what i call 202 heads sorry.) and the hei vac advance works, has a advance kit. i've tried every one fo the springs and combos. i currently have the medium springs in it. i have put one of my friends 600 edlebrocks on there and it runs like a mother. but icant figure out whats wrong with the q-jet?? it a divorce choke q-jet off a 350 engine and i have 72 jets up front with matching rods and a medium horsepower rods on back dont know what the part# is? they're for 300 horsepower or less(that i do know!)as for compresion its like 9.1:1 or so . the float is brand new, no fuel inside also i dont understand what plugs under the jets you guys are talking about? are they the ones that flat head screw in and have a check ball under neath them?how can you tell if you havea warped airhorn????and fianlly its 350 horsepower 327 cam i belive that the original part# specs:

.447 .447
222@50 222@50 (duration)
114lsa hydralic

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1989 firebird formula

Mods: converted from T.B.I. to a carburator 305 to a 350. Flowmater exhaust,hedman shortie hedders,202 heads,350 horse cam,bored.40 over, Edlebrock torker2 intake.

Future mods performer rpm air gap intake (polished) and 600 edlebrock carb, comp roller cam, and way better headsa 400 defintely in the works!

[This message has been edited by burnoutrpm (edited January 19, 2001).]

 

Bingo on the cam, that's the one I thought it might be. It's not my favorite cam, though that's just opinion, I'm no expert on teh subject. There's another post going on right now about a motor that doesn't run right where the guy also has that cam, and some that people say run good with it.
https://www.thirdgen.org/messgboard/...ML/001251.html
https://www.thirdgen.org/messgboard/...ML/004761.html

Anyway, if you take off the carb, take out the 2 rearmost screws through the air horn (the long ones that go into the throttle plate), turn it upside down and take off the thrpttle plate, you'll see the 2 "tower" lokking casting blobs that have the plugs in them. Go look, a pic is worth 100 words. There's no screw or anything. The factory drilled a hole through there in order to drill the internal passages in the castin gabove them, then they use these plugs to seal the holes back up. They're kind of driven in, spun around in the hole, and the casting is staked over on them. Weenie at best.

Another cute little problem that sometimes shows up: remember when you were rebuilding it that the float rode on a little pin that was bent back on itself almost 180°? Well it has to be spread wide enough that when it's in the fuel bowl, it sticks up past the top of the air horn; if it doesn't, it will be able to wander upwards in its slot with the fuel pressure, and just a little movement there translates into a huge rise in the fuel level. Something else to check while you've got it off.

What is the carb #? What is the head casting #? You can put 2.02" valves into almost any casting, that's not really any sort of identification. Are you sure the vacuum advance works? You have verified that if you plug it into a source of continuous vacuum, the timing advances?

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"So many Mustangs, so little time..."
ICON Motorsports

 

Does fuel drip from your boosst venturi
dicharge nozzles at idle? Are your secondary
throttle plates not completely closed at
idle? Is your throttle plate worn at the
primary shaft like it would be from having
a return spring that is too strong? When you
start your engine after it is warmed up, do
you have to hold the gas pedal to the floor
like it is flooded?
These are questions that I ask before I work
on a Quadrajet, although these problems can
occur with most carburetors.

 

thanks everyone for your responses to my question but i solved it! i got a edlebrock 600 and it needs some tuning but other wise a awesome carb thanks again!

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1989 firebird formula

Mods: converted from T.B.I. to a carburator 305 to a 350. Flowmater exhaust,hedman shortie hedders,202 heads,350 horse cam,bored.40 over, Edlebrock torker2 and a 600 edlebrock manual choke.

Future mods performer rpm air gap intake (polished) comp roller cam, and way better headsa 400 defintely in the works!