ok guys and gals...im reallllllllllllllllllly frustrated at the moment. for some reason my cc qjet 84 trans am with a bored out 350 (357),performer intake, headers, and 3 inch hooker cat back hesitates at 4000-4500 rpms, then a half second later BURSTS to life and feels stronger then EVER.)still in same gear..1st)..........iv tried everything i can think of...new MSD ignition..spark plugs...fuel filters...fuel line...richen up carb at WOT...fuel pump...REBUILT CARB, and a new computer/chip ....and NONE OF IT HAS FIXED MY PROBLEM!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! i have spent over 500 bucks on this problem alone, and no improvement!! all these parts made my car run better/faster till that RPM...grrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr im soooo pissed right now...........for air delivery i have a dual snorkle with a K&N, and factory cowl induction... WHAT CAN BE CAUSEING THIS??????????PEASE HELP BEFORE I GO INSANE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

Toss the CC qjunk into the trash and put a Holley double pumper on that puppy. Seriously, try to borrow a real carb from someone and try it. Also, does your car have a large cap HEI with mechanical and vacuum advance? If so, make sure the advance is moving freely, and all your timing is in by 3600 rpm.

 

i cant throw another carb on cuase of the computer ****.. and i gotta keep it emissions legal. if i could swap it over..i would. my HEI is all computer controled as well. iv messed with my timing from 6* to 20* and no change in my problem at all...just to add to the list of mods..new th700r4, 2000rpm stall..and yes the TV cable is adjusted properly

 

Whats up?
Could be the dist. or the module in the distributor. Have u checked the fuel pressure at the 4k - 4500rpm range? I dont think its a carb issue.
njdaewoo

 

Does it do it free revving, or only under load? Ignition problem should be there either way. I am tending to lean towards a carb problem. Try putting in a stock air filter and see if it changes at all. By restricting the air somewhat it may give a clue as to what you are dealing with. Some ignition problems can manifest themselves at certain RPM's but since it is all new I think it's a fuel delivery issue. The fact that you get a momentary "bog" then it takes off just sounds like fuel. I have not played with a "rocky" since about 75 or so but I have done much work with motorcycle carbs and it is consistent with what I have seen when they need to be rejetted because of different pipes or high flow air filters. By the way, you can purchase aftermarket carbs that will be acceptable for emission testing. LOL, keep us posted-Dan

 

im pretty sure id doesnt do it while revving, its been a while since i reved that high in park..ill check tonight, also ill check to see if it does it in 2nd gear also,. iv needed the room to beable to do this but im gonig to the track tonight... and as for the emissions legal carbs, i know they exists, but do they make them for the computer control?? i dont have the cash to swap it over to a NON CC system....but then again id probly have it done if i didnt try to track this problem down....i dont have a stock air cleaner to put in there either...ohh i dont know if this helps, but when i open my "cut out"(right after the Y pipe), the problem seems to get worse.

p.s.. i havent checked fuel pressure or fuel to air at any rpm's yet.

 

An easy to overlook possibility here would be the AV flap sticking. The airhorn casting is just garbage AL, over time (and after it's been overtorqued a few times) it can happen that the back side of the casting protrudes just barely into the AV bore enough to stick it.

What that gives you is a strange (and in my case semi-intermittent) problem where when you floor it it takes off pretty good (but its actually riding the primaries) then by the time you get some more RPMs it is just too restricted by the ptimaries and it falls on it'd face. Shortly thereafter it is then possible that the AV finally snaps open and all your power hits you instantly.

My old 85 had that problem. Haunted me for months, but i could never duplicate it with the car off. Then one time i got lucky and it hung up ever so slightly enough for me to notice. File ot the offending metal and get on your way.

Could always be something diferent, but it's worth checking into...

 

that TOTALY went over my head....can you go into more detail?? i know the AV opens good when the car is off, and i have it adjusted to the tech article...also this is my 2nd carb that its done it to..but ill check it when i know exactly what your tlaking about.

 

I agree on the Airvalve problem, i am dealing with it right now. I found two problems. The easy one to see is that the air valve can move left to right on its shaft. if it is all the way towards the drivers side it opens smoothly, if it is towards the passenger side ( mind you all the way is maybe .020") it will stick on the air horn. once you have enough rpm the manifold vacum increases and it POPS open with the resulting kick in the ***.

problem #2 the really annoying one is that there is a roll pin that the secondary rod hanger swings on(the cam lifts one end of the hanger and the other end pivots on the roll pin) in my case this roll pin was too far to one side and if the air valve was slid over in the wrong direction it would open slightly then hit the roll pin. it took 2 taps on a pin punch to move it back.

My advice to you:

slap the air valve closed it should open with out ANY sticking. Apply side pressure to it, does it stick even slightly? go in the other direction and check the same. if it does stick chechthe roll pin, then take it offthe carb and carefuly file down any interference points.

hope that helps!

 

yeah, and the AV shaft itself can bind too

 

i will check that tonight...but here is a interesting little fact i found out lastnight about my "problem"...if i floor it, and then right before i get to 4000....if i back my foot off the pedal 1/2 inch (enough to still make my RPMS rise) it WONT do what iv been describing at all!...but if i put the pedal all the way down, it will do it in 1st, 2nd, and 3rd

 

Another thing to check is the pick up in the distributor. Older ones build up a high resistance. As they get older they get flakey and send a bad signal to the ecm. The hesitation could be the computer switching off its control of the timing and the mechanical taking over. The pickup is under that big rusty brown collar with star shaped block inside it. It is about 7 dollars from an autoparts store and requires you to take the distrubutor out of the car to change it. The computer controlled quardra jet is a good runner if tuned correctly.
With a little work they can flow up to 725 CFM. That is more than what most mild 350s can handle. Good set of heads and an intake would actually bring that thing to life on a 350. And with all the timing setups you can run with that CCd distributor you can really tune the carb in. I have seen a 12 second combo consisting of AFR heads an edlebrock RPM intake and headers. I have no idea what cam he was running, but that was a quick SS monte.

 

my heads have been worked alittle... im just tryin to get it to run good without this hesitation. my motor was built for nitrous, so it crawls all motor. but i will be putin a NX kit on it next spring...that is if i can get this fixed.....is there ANY way to not take the distributor of to change that?? the distributor is a PITA to put back in.

 

its the carb not the distributor, once you clear 4000-4500 it will pull well past redline. I am dealing with the same problem. When you back off the gas and them floor it you are shocking the seconday airvalve loose. You don't feel the kick as much because its opening just about when you let off the gas. A dist rebuild is a good idea but it won't fix this particular problem.

 

i also noticed at the track that it doesnt pull THAT great after the initial problem..RIGHT RIGHT after the hesitation, it pulls hard,, but then i noticed a few more small hesitations that is really killing my top end...enless thats the end of my cam, but my cam is rated to like 6500rpms

is this a common problem with the qjet?? i mean it did it with my first qjet.. then i bought another used one and rebuilt it and its doing the same damn thing.

 

So you have put a totally different carb on there and having the exact same problem. I would think it is highly unlikely the AV is the problem. I mean I realize that is a problem point on Q-jets but to get the exact same problem at the exact same rpm sounds like something else is going on.

You said you fixed the fuel pump problem. What did you do to fix it? Are you able to attach a gage to the fuel system and have it come up from under your hood so you can have a passenger look at it through your windshield while you accellerate under load?

I honestly don't know for sure it is not ignition or computer related but Q-jets have a smaller than average fuel bowl and it sounds like you are running out of steam up top like it's running out of gas. Didn't see what cam you where using so I don't know if your fuel requirements where much more than stock.

 

If it was a fuel supply problem it would not recover, it would lay down and stay that way until he got out of it and let it refill. It would also be more likely to happen in high gears and be fine moving quickly through first.

And it is possible to have 2 qjets with something hanging the AV. It happens all the time. Although it could also be something weird and intermittient in the duzzy.

 

On the subject of Q-jets

MY 84 now with a 383 years ago with an LG4 never reved as good as my brothers 84 HO. his little 305 has seen 7000 rpm. 6500 often and with 120,000 on the clock still zings to redline quickly and smoothly. I thought once my new motor was in place i would see similar operation, but that is not the case. I have had this airvalve problem from the beginning. its only recently that i realized what it is, if i find the time this weekend i'm goiung to pull the carb and clean up the air horn so this can't happen again.

on the subject of fuel delivery, if i'm not mistaken. pretty much every high hp gm car with a carb has been using a 3/8 fuel line and mechanical pump since the 50's. I find it hard to believe that a fuel system tha could feed a bigblock cant feed a small block. I know the q jet has a small float bowl but so many people have raced them this way for so long i don't think this is a problem. I'm going to get this airvalve thing straitened out as soon as i can then i'll report back on how it has worked out.

I might even pin the valve open and see what happens!!

 

yeah im gonna mess with my carb tonight as well, se if i can find what you guys are talkin about...for my fuel..i replaced the stock pump with a Napa OEM mechanical filter (diaphram went out on the old one...had to change oil 4 times in a 2 day period.)..i havent reaplaced any lines going to and from the tank..the only line i replaced was the one going to the carb, and i also put a inline filter on it and got rid of the in carb filter. as for the carb, it has DR rodas and a B hanger. i highly dought im running out of gas...i want to check my fuel pressure...maybe ill try to get a gauge this weekend.

 

i think i fixed my secondary opening problem, it was painfully simple and took about 3 minutes. Here goes:

determine where and which airvalve butterfly is sticking , mine was the passenger side butterfly against the outbored side of the air horn.

loosen the 2 screws that hold it in place, about 2 turns. Slide the butterfly over in the direction opposite where it hits, retighten screws, it will only move a few thousands of an inch. tap the air valve, does it still bind?

mine runs great now, thesecondaries open smoothly and consistantly now

now when i punch it, it will smoke the tires and pull to redline almost faster than i can shift!!!

 

my AV's are fine ...im looking into changing the primary rods, but dont know where to look to buy them...or sizes..anyhelp?

 

as far as a know you can't replace tham on a CCC. don't know why you would want to, mine are stock.

where do you live??

 

i live in illinois. i was lookin into changing them cause i think im running lean at WOT, and thats y im getting this problem.. but if i dont floor it and let my rpms rise then i dont have it... iv already got DR rods and a B hanger, so the secondaries are taken care of...i think. whats richer then the DR's? i was gonna try to richen up the primaires a step or 2... maybe its a bad idea

 

Have you posted anything about htis on the carb board? Someone there will know exactly what to tell you to do! I really sounds like a secondary fuel metering problem to me! By that RPM, I would think the AV would be open already, and you would be experiencing a temporary lean condition. It is possible that you have a fuel delivery problem, and when you back off it the 1/2 inch, it is just enough for it to recover, although I really don't think that is likely, especially since you have changed the pump, although at this point I think I would have put an aftermarket, not OE replacement pump on it.

Good luck.

 

yueah iv been nagging everyone for months about this problem. well i think i found a solution to my problems.........

when i had the engine built, the guy i bought it from gave me a carb.. this carb was sent to the carb shop in cali with my engine specs and all that. it has never been used since the rebuild, has a shelf life of about 2 years. i havent put this on casue its a non-computer controled Qjet....but im lookin into swaping over to non CC soon, as son as i figure out what else it involves besided changeing the carb and distributor, and lockin up the TC. i have heard from many that there mysterious problems went away after they ditched the computer...i hope the same here. so i dont think im gonna throw more money into a area unknown, and just swap it all over.

 

sorry to hear that but i hope it works better for you.

Just so you know, i'm running a stock ccc q jet on my engine. it runs great as of now. I did have to do a lot of tuning to get drivability but i changed no parts other than the rebuild. I'm also of course running the stock computer with a hypertech i bought fotr the original LG4 over 10 years ago.

I'm trying to get to the track but it keeps raining, i'll let you know what it runs. With the G-Tech i got a 5.97 0-60 with the broken posi, and no traction.

 

y must cars be soooo frustrating? all the cash i spent on this one problem..i could have had my paint job done!!

 

i have somewhere between 13 and 17 years of experience doing mechanical/technical work. The one thing i have found is that you need to patient and persistant when it comes to those frustrating problems. Sometimes you just have to walk away from it for a while and one day when your thinking it over the very obvious anwser will just come to you. Why don't you concentrate on some other problem /job you have on the car and give it a couple of days before you spend any more money?

 

im just looking into the non cc swap, thats what im concentrating on at the moment. im not rushing out and buying everything right now...basicly cause i dont have the cash at the moment... maybe ill do more body work.

 

Well, getting rid of the computer isn't all that bad an idea. I typically hate to see the computer system go, but in the case of a carb, the computer doesn't do all that much anyway. It does control the timing though. I would say keep it if there was more out there for tuning the timing curve, but last I checked, the stuff just wasn't out there for the carb ECM's.

In my situation, I would like to keep the carb and cc distributor, and just modify the timing, but due to the lack of stuff for the carb computer system, I'm going to bolt on a TPI.

 

fattie92, does your Q-jet have a working choke pull-off that will
keep your secondary air valves closed until they are needed? Does your carb still have the baffles for the secondary discharge
tubes in it? I would try to lock out the secondaries to see if the
problem occured when driving on the primaries only.

 

ya lost me

 

Well an idea I have always wanted to try is to retro fit the TPS sensor from a CC carb onto a non-CC carb. This way you can still use the computers excellent timing curve, with the much easier to tune standard carb. The problem with that computer is there isn't much out there to modify its tuning. The timing is good, but the enrichment solenoid is lacking somewhat. If you could retrofit the TPS to carter, edlebrock or a holley that would be slick. You would have to mount the old carb solenoid somewhere out of the way and just let it do its own thing.

 

The mixture control solonoid only comes into play while cruising or during small throttle openings. In my case i think if i'm accellerating with any real force i'm already on the secondaries. I don't see any advantage to getting rid of the the mixture control solonoid. it give you the ability for the comp to trim the mixture when you want it to, with no real loss of power. I am amazed with how well my car is running right now. If anything i've had to lean my settings on the idle and primary side since installing the new engine

 

Do you have a MSD 6A or similiar???? I don't know if you are familiar with this but, MSD ignitions come with a disclaimer stating that it is very possible to encounter hesitation with Computer Controlled HEI ignitionsin the box when you buy them. You need to contact MSD and tell them what is up. I had the same problem but in 2nd gear. I scrapped the computer though and now she runs like a top. I know you said that you bought a new ignition, but that really won't solve the problem. It is going to persist whetherit's a new ign. or not. Call MSD and see what they have to say. Hope this helps you out.


A quick alternative would be to disconnect the MSD and run the straight stock HEI. If your prob. dissapears, it's the MSD.

 

i bought the MSD hoping to fix the problem.. but all the MSD did was smooth out the curve a little.

 

I THINK I FIXED IT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! i will know tomorrow for sure! knock on wood,, cross my fingers!!!!!!!!!!!!!! PLEASE DONT BE A FLUKE!!!!

 

sounds electrical like a coil breaking down under load a short that is intermittent. Isyour problem intermitent? Find it hard to believe it is a fuel problem when this occured with 2 different carbs. Ed Maher is right if it was a fuel delivery problem it would never recover. Do you know anyone who has the same ignition setup maybe you can swapout the pickup coil and give it a run. Wouldnt be the first time MSD put a bad coil out there off the shelf.

 

i bought the MSD and upgraded cap coil rotor to all high output crap casue i thought it was my ignition....did it help?? no. the only thing that i havent replaced on the ignition besided the actual disributor is the modual.............but i think i fixed my problem.....but im not sure, i still have to test it some more. so far after 2 runs lastnight it didnt stutter at all........but like i siad, maybe its a fluke.. knock on wood!

 

ITS FIXED ITS FIXED ITS FIXED!!!!!!!!! :lala: :lala: :lala: :lala:
i put in CK rods and got rid of my DR's and put on a K&N 14inch open element instead of my 12 inch K&N dual snorkle... and NO MORE PROBLEMS!!!!!!!!!!!!! thanks for all the help guys!!!!