My question is , What size secondary rods and hangers would be the best for a Q-jet on a 350 L98? ( I swaped a LG4 out for a L98 and kept the carb)
Also does anyone know what the dia. is for the stock Secondary rods? Ed recomended the CK (.0527")as a replacement, I just wondered how these compared to the stock ones. Thanks JIM

 

No one can really recommend a rod and hanger combo for your specific application, yet they can get you in the ballpark. You should test and tune to find out what combo works best for you. Altitude, climate, driving conditions, etc ... all play a roll in selecting the proper rod and hanger combo.

Yes, those CK rods are a good start with an "F" hanger at worst ("B" being the better one). I don't have my rod decoder with me at the moment, but I am sure someone can look that up, it should be slightly fatter at the tip. The rods are not a constant thinkness, they tapper down. The size given to you is the rod tip, full "rich" mode.

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George P. Lara
1994 Z28 LT1 T56
1984 Z28 High Output
Member: SCCA, SCFB, SC3GFB

 

Thanks MRZ28HO, I did not know where the thickness was measured. I'll playaround a little and see what I come up with. Thanks

 

If your stock rods are the CHs (I think that's the letters- I'm at work right now) then it's got a .0567" tip. If it's got the DPs then they are .0686". Probably the CHs are what you've got- they are the most common. And they're junk for performance.

Now I'm gonna give you the SECRET to making that Qjet haul serious backside from 15 years of experience. IT'S NOT THE TIP DIAMETER YOU SHOULD WORRY ABOUT! Anything in the .0567" range is about perfect for a typical 350. That's the same size as your stock rods, right? So why did I say your stock rods were junk for perfrormance? Becuase of the TAPER on the rod! You are only onto the power tip from about 3500-3800 RPM up. Fat lot of good that does you when you nail it to the floor coming out of the hole. You are working on the TAPER part of the rod at that point. And with a lean taper rod it's gonna feel like you just put your foot down in a bucket of cold oatmeal when you first get on it. That's why the carb is sometimes called the "QuadraBog." It was DESIGNED to have a limp transition into the secondaries.

Now here's the secret- ALL QJET RODS ARE TOO LEAN ON THE TAPER! That's right, ALL of them. THey were designed for EMISSIONS and good fuel economy. ALL Qjets are emissions carbs from day 1. You CAN'T go too rich on the taper no matter what you do- short of just removing the secondary rods entirely and running wide open jets (DON'T do this- it won't work).

So what do you do short of breaking out the lathe and spinning your own rods? You make the best of the stock parts that are available. Get the rods with the richest taper portion available and combine them with the richest hanger available and you are gonna really really like the results.

That happens to be a set of DR rods (same .0567" tip as stock but with the richest possible taper) and a "B" hanger (full-rich).

Combine that with only 1/2 turn of tension on the air valve spring and it'll hit like its got fuel injection from the instant you mash the gas.



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94 Firebird Formula M6- No options but Z rated tires. No mods over $10. 13.5@105.
79 Malibu "beater" w/junkyard 400 SBC, tweaked QJet 4bbl, finally a decent set of heads, a few other tricks. A maddening 13.000001 @ 108 on the motor with little traction. No nitrous runs with the new heads yet.
Grandma's old 78 Malibu (33K miles!) soon to have the powertrain from the 79 put in it.

"One of the last remaining QJet tuners on Planet Earth!"

 

Thanks very much Damon, I printed out your responce. I have a big question for you .
As of now my car is inop because it's running sooooo rich every thing including the plugs was covered with carbon. I changed plugs and a couple clinders had gas in them, I was getting around 3 MPG before she wouldn't run any more. I have no Idea why, my Q jet worked fine on my old 305, I had the carb rebuilt around 2 years ago. All this began when we tranfered every thing over to my 350.
I was running the fuel unfiltered. From what I was told this shouldn't cause any problems (other than dirt). I'm going to put a filter in tommorow to see what it does but I have my doubts this will change any thing. Before she died It would blast black smoke when I gunned it. Waaaay to rich. Do you have any Idea why it's running like this? Thanks in advance JIM

 

Hmmmmm...... sounds like a problem with the primaries. The secondaries don't come into play until past about 2/3 throttle. That is, unless the secondaries aren't closing all the way in which case you will get a very unstable idle and fouled plugs in short order (had this happen recently on a carb where the secondary throttle plate screws had backed out a few turns).

Is this the stock computer controlled QJet from the LG-4? If so, it won't work correctly without a proper signal from the ECM to run the mixture control solenoid. The "default" of the carb in the absence of a correct ECM signal is FULL-RICH- and it'll kill mileage and part throttle performance.

The mixture control solenoid is a 2-wire hookup on the top of the carb, towards the pass. side- a big blue plug. If you have ditched the computer while doing the engine swap you will need to preplace the CC Qjet with a non-CC one along with the Computer Controlled distributor. There is a tech article on this site about how to do that.

 

I'm still running the stock computer and stock LG4 carb. I'm going to play around with the timing some today. Other than that I'll have to take her to a carb shop. I'm getting a code 41 from the ECM . I don't know if there's any to this or not. thanks for the help JIM

 

I'm currently reading David Shelby's book, Camaro Performance. On page 56, he says [concerning the LG4 Q-jet and street performance]: "For most applications, substituting a set of AH metering rods and a G hanger for stock components will suffice. (These are the same rods and hanger used in carburetors that are installed on the ZZ3 engine package)." Any comments about this recommendation?

JamesC

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code 41 indicates a problem that will make your carb run full rich. Check your vacuum hose going to your map sensor and your elect connections at your dist.

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84 350 4bbl sub frames t-tops 4 wheel discs wposi from 88 bird

 

i may be way off base here. I had a bad O2 sensor and mine ran way rich (eyes watering at stoplights and sometimes it'd die on me). i don't remember the trouble code, and i'm at work so my book's not handy (even though i'm at a gm assembly plant, ironic!) but 41 sounds like it might be familiar. Check it out.

 

I think your Right Papa smurf. I found some stuff unplugged on the back of the distributer, and I couldn't find the plug for the ETS (electric spark timming). The plug is in the distributer but the plug that runs near the right hand rocker cover is missing. There is also some vacume lines unplugged and some sort of box ( no clue what is is ) behind the distributor that has 2 vac lines and a electric plug disconnected. I did this car with a friend of mine and before I went out side to start on it he had just about every electric and vac line unplugged and unmarked. I know a good shop that specializes in ignition and carbs. I'll let him unscrew it. If I keep messing with it I'll wind up in a straight jacket!! I'm convinced it's ignition though.