Is there a "rule of thumb" to follow when increasing jet size? I've got a bit of stumble/hesitation on acceleration. It has a Q-Jet. Thanks.

Mark

Hope I am not mistaken, but on a Q-Jet, you change metering rods and not actual jets.

I believe the accel pump is on the top of that carb. You maybe able to cure an offline stumble by change where the pin is on the accel rod. I believe up gives you more fuel and down gives you less. Am I right guys??

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Mark

1992 Firebird 355/Six Speed
1991 RS 350 / 700-R4
1987 Toyota Pickup 383 / 500 + HP 10.963 @ 119.95 Slicks / 11.997 @ 114.23 Radials
http://personal.lig.bellsouth.net/~racer383/

First, on a QJ the rods/jets come in matched pairs, 72 jets/42 rods etc.

Yes, if you locate your pump rod to the outside hole in the rod, you might get more pump shot..

BUT,

please be very specific on when/how this bog occurs. It could very possibly be the air door setting. Easy fix.

If the secs open too soon you get a big bog, too late there's no power, still a bog, but a different kind.

Is your bog associated with the transition to the secondaries?

And have you changed the cam to a lower vacuum gnerating one ( ie more duration than stock?)

[This message has been edited by 427L88 (edited 11-02-2000).]

Thanks for the reply guys. It's not a bog. It's more of a stumble for a second and then the engine picks up r.p.m.'s. It happens off idle, just starting out or when changing gears (driving conservatively). If you choke it, the problem goes away. It's not the secondaries. If you romp on it, it runs fine. I'll take a look at the accel. pump.

Mark

Mark,

There is something else to check also. The q jet is known for the metering rods to stick, if they are stuck in the down position you will have a lean condition causing this stumble because there is to little fuel avaliable to make the transition from the idle circit to the primary circit.

To check this, with engine off take a small pocket screw driver and go down the tube that is sticking up by the choke flap. Feel around gently up and down, front to back and see if you can find the top of the metering piston, and if it is not stuck you will find a spring loaded piston there.

If it is stuck, most people pull the carb top to do the fix. I have never seen a tool to do this with so you can make one like I did.

Take the inside part with the handle of an old manuel choke cable, the handle helps use the tool and the steel wire is strong enough to do the job. Leave about 3 inches of the wire, cut it off and bend a small hook on the end.

Use this tool to go down the tube to hook the metering piston to pull it up and unstick it, pull up very gently as not to bend the metering rod rack, use the small screw driver to push it down. Work it up and down using carb cleaner down the tube to flush it off.

Happy Fishing
Larry

Larry, excellent!

Thanks Larry. I'll check it out. Sounds like a job for the spring hook I ripped off from my dad years ago. He worked for Burroughs (became Unisys) as a serviceman for years and had all sorts of tools for those "hard to get" places. Maybe I should patent them as "special" Q-Jet tools and sell them on the net... http://www.camaros.net/forum/biggrin.gif Thanks guys, I'll look into it tomorrow when I get a chance to pull my "baby" out of the garage.

Mark

I would also check the accelerator pump travel. With the throttle closed,slowely press on the acc pump rod for freeplay. There will probably be a little, Bend the lever to remove the play. I have been playing with these Qjets lateley and have found that they are really fun to work with. I went t the bone yard and picked up several I have tried many combinations on the 79 Z28 and finally have one that is very responsive and clean on the lowend, and acts like a 1 to 1 with instant power on the throttle. And to think that I threw these away for years. Galen

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S/B Chevy Lover
67 Camaro street car
10:50's @ 128 on motor w/383 cid
79 Z28 w/383 9.1:1 3.73:1 Restoring stock apearance
13:40's @ 101 stock exh.& intake& Qjet
smog legal
Camaro Lover

Thanks Galen. I know what you mean about people thowing away their Q-Jets years ago. When I was younger, I wouldn't have been caught dead with one. I ended up with this one because somebody decided they wanted my Holley (along with my battery) one dark night. The car actually runs better than it did with the Holley. I remember seeing this guy run this awesome 60 vette at the strip when I was a kid, and freaked out when he popped open the hood and there sat a Q-Jet!

Mark

Thanks for all the input guys. Changing the location of the accel. pump rod seemed to clear up the majority of the problem. It still has a split second hesitation, but I think I can get rid of that with some fine tuning. Everything else you guys suggested checked out fine. Thanks again.

Mark

You need to connect the rod to the INNER hole on the upper accelerator pump arm to get the most fuel.
The accelerator pump cup may be worn or have been attacked by the fuel.
I've seen them where they didn't work at all.

I'd replace the accelerator pump cup seal before doing any permanent mods to the carb.
David

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Check my web page for First Gen Camaro suspension info:
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67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Can Am Vintage Racer

Thanks David. I tried jiggling the throttle (engine running at idle) with the rod in both of the holes and could kind of "re-create" the stumble. It is more responsive with the rod in the outer hole. You're right, the inner hole has a longer "stroke", but the first bit of travel seems to be slack (no fuel delivery). The outer hole takes up this slack so there is instant fuel delivery. Does this mean the pump is going bad on me, or is it normal?

Mark

Hey Mark,

I'll try one other thing, but first of all you must know the Q jet is known as the bend all carb, you know you have to bend all the linkages just right to make it work right.

I am with Dave as far as running the acc linkage on the inside hole. The acc pump well is tapered from the factory, and Dave is probably right in saying you need to replace the rubber cup, but try one other thing first.

Put the linkage on the inside hole, bend the skinny tip of the pump arm down so that it holds the acc pump deeper into the carb. There is most likely some wear in the bore and this will hold the pump just below the worn spot.

Larry

[This message has been edited by lnjstreetrods (edited 11-06-2000).]

Mark, if you were my local buddy, I would pop the top of your QJ off and put 1-2 sizes bigger jets/rods in, a slightly stiffer pwoer piston spring and probably have to tweak your float level. I bet its a freckle low. ( and swap out your accel pump while we're at it.).

With these subtle changes, your QJ would rock.

Digression:

[{You know when I was a kid with time and a little money I tried numerous combinations on my LT1 clone 350. Holley street dominator/.strip dominator Stock QJ and Z28 manis, Holley QJ and even a Carter Thermoquad.

The best combination I had was the Z/28 mani and a QJ on an adapter. I still think that running a spacer above a divided dual plane is a nice touch and that QJ ripped as good if not better than the Holley 750 that came on the Z mani( 750=780 same thing BTW)and the mpg was much better. The Thermoquad was good too becuase it came with all sorts of jets/rods etc and you could really dial it in.

If I could run a fat 800 cfm QJ on my current setup I would.}]

I find the outer holes work best in non rebuilds. I actually drill my own holes ( dont try this at home kids the piece is usually hardened.)

If your plug color seems right, then I;d leave the jets/rods alone and simply change out the power piston spring, freshen the accel pump and reset your float. Setting the float on a QJ require a little bit of feel. If you push the seat end down too hard you will get an incorrect setting.

Are you comfortable pulling the top off this bugger? The only real trick is the dang choke rod. I leave the accel pump arm right in there and do a little twisty thing to get the top off.

Thanks for all the ideas guys. They are greatly appreciated. I have no problem with taking the top off (it's been off a couple times before http://www.camaros.net/forum/biggrin.gif ). I'll mess with the linkage a bit and if that doesn't cure the problem I'll pop the top. I should probably take it apart anyway to check things out. I have just recently gotten the car back on the road after basically sitting in the garage for a few years.

Mark

Anyone know what the float level should be set at right off hand? I'm not sure if my ancient Chiltons has all the carb specs.

[This message has been edited by mbrekke (edited 11-07-2000).]

the trick is to not push down too hard to seat the needle. Just seat it with gentle pressure and the rear of the float ought be 5/16" of an inch below flush with the top of the casting.

Sounds like you might want to dig up a stiffer power piston spring. You can tweak yours, but thats an iffy proposition.

If your plugs are nice and dark tan, dont tweak the jetting, just the power piston. If they look too light, then tweak your primary jetting.

Good luck!

Thanks a bunch. I'll look into it tomorrow. Finally got a day off...

Mark

Hey there 427 L88, I have some of those 800 cfm q-jets here. I get them from Pick a Part off the cads. 78 and 79's. I would think there would be those in the bone yards there too. I use the chevy base plates from the scraped electronic Q-Jets. Only have to drill the hole for the power piston in front. that gets you the right linkage. They work good. Galen

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S/B Chevy Lover
67 Camaro street car
10:50's @ 128 on motor w/383 cid
79 Z28 w/383 9.1:1 3.73:1 Restoring stock apearance
13:40's @ 101 stock exh.& intake& Qjet
smog legal
Camaro Lover

Mark

By the way, the stumble is gone thanks to some bending and tweeking. Thanks to all who had constructive input.

[This message has been edited by mbrekke (edited 11-15-2000).]

[This message has been edited by Al (edited 11-15-2000).]

Thanks for deleting the first part of my message Al. It would have made me look pretty stupid after that guys post was deleted.

Mark