Gee, where to start? It could be either and ignition or fuel problem. I chased the same problem for several weeks before I got it worked out. Could be that your accelerator pump shot in not large enough. This is adjusted by increasing the shooter size and/or the cam that operates the pump. I am not that familiar with Qjet,s; have a Holley myself. The other problem I had was that my vacuum advance canister on the distrubutor had too soft a pull rate and did not back off under heavy acceleration. You can check this by removing and pluging the vacuum line from the advance canister and do a hard acceleration run. If the hesitation is gone, it's the canister, or where you have it hooked up, either ported or manifold vacuum. It could be a number of things, but that's where I would start. Good luck!

 

I just had the same problem last weekend. I put the intial timing at 10 BTDC and shot for 32-36 total advance. No more hesitation. Does it "pop" out of the carb? Backfires?

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1969, X-44, Export Model, Hugger Orange, Std. Int., BC Rear(soon to be a BT 12 bolt), PDB, GMPP 350HO, M22 Supercase, SSM Lift Bars, AirGap, Holley 750, FlowMaster American Thunder Exhaust, FlowTech Headers

 

Nope, no backfires. Just sputters then takes off. Seems weird cause it runs ok after that. Would runnig to rich or lean create something like this. I dont know yet. Havent had a day to just tinker with adjustments. I always get good advice form this board so I like to get alot of opinions. Think I might try playing with the timing first and see what happens. Please keep the suggestions coming thouhg.

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Scott
May we never have to drive a minivan

 

Not sure about rochesters but I seen holleys where the choke opened too far and got right in front of the squirts. The gas just hit the plate and ran down causing it to stall

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69 convertible
LT1 4L60E

 

Check the secondary air valve adjustment.



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Don~ ZZ430DropTophttp://hometown.aol.com/zz430droptop67rs
~~~~and~~~~
70 RS
67 RS/SS Convertible, 70 RS

 

The problem is most likely associated with the carb.....the venerable "Quadra-bog" strikes again! I would say start with re checking the carb and making subtle adjustments. You will most likely find one adjustment, and then it will run like never before......its just finding out which one it will be.

 

"Quadra-bog," I like that. How 'bout "Quadra-junk?" To help Gateruner out, my car was running way too rich as well. This was due to the vacuum leak that I had at the spacer (carb). Corrected the vacuum leak with a Mr. Gasket heat dissapator, re-timed it (10 btdc), adjusted the fuel mixture, checked the vacuum and advance. Now she runs great. Is the car loading up at idle?

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1969, X-44, Export Model, Hugger Orange, Std. Int., BC Rear(soon to be a BT 12 bolt), PDB, GMPP 350HO, M22 Supercase, SSM Lift Bars, AirGap, Holley 750, FlowMaster American Thunder Exhaust, FlowTech Headers

 

Anybody who can tune a Q-jet will tell you that they can run right up with any Holley or Carter...most (but not all!) people who call them Quadra-junk, bog, crap, whatever, usually just don't know how to cure the problem.
Those things can be ported to flow 1100CFM and run on just about any engine. It's nice to run as fast as a Holley could, and get much better fuel miliage, for a heck of a lot cheaper!!

Make sure your accel. pump rod is on the inside hole on the lever.

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1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/

 

Well, money is an object for me and I really dont know alot about carbs so I felt it would be best to replace the carb with what was already on the engine. It doesnt run badly except on really heavy accel. Fine tuning is new to me so I am learning as I go. Just hoping to get some good ideas on where to start. Right now I think I am going to advance the timing just a bit and see what happens. Someone else told me to check the secondary adjustment. It might be opening to soon and creating a lean issue. Also, How do you achieve 34-36 degrees total advance? I just dont see how that happens unless you advance plug wires around the dist. Hmmm

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Scott
May we never have to drive a minivan

 

Is it a bog or a stumble? To fix a stumble, make sure the acc. pump squirts gas as soon as the throttle starts to open. Bend the lever to remove ALL slack to get a better pump shot.

Mark

 

I've had a few Q-jets that leak fuel into the intake, causing the engine to load up at idle, and at shut down. Do you see any black smoke in your rear view when you jump on it? Does it sometimes flood out for no reason when you restart after shut down?

 

I dont see any smoke out the back and I have been looking just because it sat for so long. No flooding either. Cranks right up and runs right into fast idle. As for the bog or stumble, it acts like it is trying to fire,(blublbubbllbilbulbulbblub then zoom). It will basically limp 10-15 yards spitting at you then here we go. Little like a roller coaster huh.

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Scott
May we never have to drive a minivan

 

Scott, those are the classic symptoms of the secondary air valve flopping open.

There is an adjustment.

On passenger side of carb, on the secondary air valve (those flat plates that cover opening) shaft you will see a small screw that a pocket screwdriver will fit into. It is spring loaded.

Below that you will see a small allen head capscrew that is used to lock it. You may need a small mirror to see it at first.

Loosen the capscrew.

Insert small screwdriver, turn clockwise until valve plates just seat. You may have to go back and forth a couple of times...

Continue turning 1 turn, and lockdown allen head.

Test drive.....and please let us know the results.



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Don~ ZZ430DropTophttp://hometown.aol.com/zz430droptop67rs
~~~~and~~~~
70 RS
67 RS/SS Convertible, 70 RS

 

I will try that tonight and will definitly post results in the morning. Sounds simple enough. It always seems like the simple things are what bug you the most. Thanks.

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Scott
May we never have to drive a minivan

 

have you got $15? if so, head to a good book store and buy a book called "Rochester Carburetors" by Doug Roe and published by HP books. read it. learn it. become one with it. use it. tells you everything you ever needed to know- and a lot you didn't- about selecting and tuning your Q-jet.

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1971 Nova(looks like 69 camaro from underneath!)
355sb, vortec heads, HOT cam,T-10 tranny, 3.70 gears 16X8" IROC wheels. 12" Corvette brakes on the way.
see pics here http://community.webshots.com/user/novaderrik

 

my guess is it is worth every penny. I will probably look for one this weekend. I am going to try out soem of these suggestions first and see what happens. I will keep ya posted.

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Scott
May we never have to drive a minivan

 

Ok, adjusted the secondary like the post said. I felt like it might be a little better but not completely correct yet. As I was driving to work this morning in the dark I made an effort to look back at acceleration and I did notice smoke. Couldnt tell if it was black or not. I also, leaned the jets on the carb last night by 1/8 of a turn. CAr felt a little smoother through acceleration but still had some problem on hard accel. I am going to hook it up and recheck the dwell and timing and possible advance it just a bit and see what happens then. Think I will get that book as well. Ill let you know what happens.

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Scott
May we never have to drive a minivan

 

You stated that the car had sat for a while? how old is the gas and have you tried some dry gas additive? just a shot.

------------------
My '68 Camaro
Doug G.
68 Camaro
406 ci.
13.5@102 W/ 2.73POSI.

 

Car sat for 6 years with I am guessing a gallon of gas in it. I drained it when I started re-doing the car about 2 months ago. Ran Berryman through it once. Have changed the fuel filter 2 times now just assuming a bad gas/deposit problem existed. That may still be a problem, I dont know. I was told that I may have to change filter very often for a while in case a lot of deposits in the fuel system release into the fuel. I am using super unleaded from Diamond Shamrock. (ie major company in TX) Had problems with cheap gas long time ago so I try to stay with reputable gas stations.

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Scott
May we never have to drive a minivan

 

Your original post and the post of 10-17 5:59 PM states you adjusted the secondary spring as Don (ZZ430) suggested.

You stated your results were better, but, still there. I can only imagine its a WOT bog. As if the secondaries are opening too soon, as Don stated.

He suggested to turn the adjustment 1 turn clockwise. This is good as you are tightening up the spring tension, making the secondaries open later.

My suggestion is to continue turning clockwise on the spring adjustment, 1/4 turn at a time. I had mine at 1-1/2 tuns, and it helped tremendously. Take tools along and trial-and-error method.

I'll take a Quadra-bog and make it work on most anything, they come 750 cfm rated, Rocehstor made a bi-zillon of them. Super Stockers and Stockers are running them in NHRA class racing as the rules state. Ten seconds on a Quadra-bog, -junk, or whatever.

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Everett "OBJECTS IN THE MIRROR DISAPPEAR UPON RAPID ACCELERATION"

 

I will try that. One thing, I had siad somewhere, think it was here taht I didnt see smoke out of the rear. Well, I was incorrect, when it goes through the sputtering you do see smoke out the rear. Any suggestion or ideas. Does that make it a different issue?

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Scott
73/74 mix. (Its a mutt) 73 350 bored 30 over, Th350 tranny. With the Lord willing, may we never have to drive a MiniVan!

 

Try this thread: http://www.camaros.net/forum/Forum9/HTML/008439.html. My biggest problem was that the vacuum canister was advancing the timing under hard acceleration. There are a whole range of vacuum canisters that start pulling at various amounts of vacuum. A simple test is to take the vac hose off the advance canister and plug it, then run the car and see if it still hesitates.

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68 convertible

 

I had the same problem, I just put in a Newly rebuilt Quadra-Jet , well i should say my recently Fired mechanic installed it, anyway, he failed to connect a vacuum hose, and the electric choke wasnt powered correctly, however, i toop a small hose and stuck a screw in it and that solved my problem, now all i got to figure out is if that vacuum port needs to go somewhere. until then though its running fine., needless to say i paid $175 for the rebuilt carb, and it looks great, im guilty too of using the term Quadra-Bog, that was until i put the new one in, now i couldnt be happier. well thats my 2 cents!

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1984 Chevy Camaro (305)

 

<BLOCKQUOTE>quote:</font><HR>Originally posted by novaderrik:
have you got $15? if so, head to a good book store and buy a book called "Rochester Carburetors" by Doug Roe and published by HP books. read it. learn it. become one with it. use it. tells you everything you ever needed to know- and a lot you didn't- about selecting and tuning your Q-jet.

<HR></BLOCKQUOTE>

I like your post, im eager to learn more about my carb and how to get the most out of it, and what makes it tick, im going to buy it next time im at the parts store (hopefully in an hour) anyway thanks for the post.


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1984 Chevy Camaro (305)

 

I had a sluggish Qjet and found the problem to be the "Power Piston" Spring was compressed too much to enable a proper shot of fuel as I was pressing the accelerator pedal. To get to the assembly, you'll have to pull the top off the carb. May be worth investing $18.00 in the Rochester carb book written by Doug Roe (HP Books). Great information on how one of these jewels work and it's a lot cheaper than a new carb. Stretch the spring about 1/2 inch and polish the brass piston to prevent drag in the carb housing. You'll be amazed at the difference. Here's another website for QJets: http://www.carbs.net/mixtureadj.htm Hope this helps!