ok guys and gals, had to put the lightest springs in my LS5 to get the required 36* at 2700 rpm... went for a test drive and still have hesitation... shuold i try 38* or maybe something else... its much quicker for sure... without the hesitation it'll be downright scary...

 

Your acc pump shot might need some tweeking, what carb you got?

 

what type of distributor do you have? Points? HEI? Electronic?

 

i put a rebuilt 650 q-jet on it from corvette america last summer... as far as the distibutor all i can tell you is its stock with the normal points....other than that, nothing high tech.

 

i put a rebuilt 650 q-jet on it from corvette america last summer... as far as the distibutor all i can tell you is its stock with the normal points....other than that, nothing high tech. i also put a fuel pump on it last fall...

 

Whatsa "conundrum"???
I thought you slipped them on your...well....never mind

Dep

 

71 -
Make sure your vacuum advance control unit is hooked up to a manifold vacuum source and that it's working. You should have a vacuum advance unit stamped "B28" on that setup - check it. Contact me with any questions or if you need info on this.

Once that's correct, if you still have a stumble, check your carb jetting against the carb number and make sure it's right. If you don't have the specs, let me know and I'll give them to you. If the specs are right, richen the carb up 2 jet sizes.

Of course, the Q-Jet is actually 750 cfm (not 650), so all your problems are probably because the carb is too big...

 

my vac advance is connected to port vacuum on the carb... don't know exactly how to hook it to manifold vac, i have one fitting directly on the manifold...should i tee into that line or how do i get manifold vac.. i have all that carb info somewhere lars but if i can't find it, you'll be the first to know... a 750 cfm carb may be too big for a LS5, thats news to me man... i'll try going directly to man. vac and see if that solves the problem and go from there...i appreciate you guys sharing your expertise... this stuff is fun huh?

 

 

I'm kidding - it's a standard joke here on the Forum. The 750 Q-Jet (or any 750 carb) is just great for your LS5.
If the carb is a stock type carb, it should have plenty of manifold vacuum ports on it. A pre-'75 Q-Jet will have a long nipple sticking out of the carb right at the choke pulloff diaphragm on the passenger side - it works great for vacuum advance.

 

I have a part-throttle stumble also. I changed the springs in the secondaries to the heaviest ones, but I think the carb is too big (770 Street Avenger on my 383). As long as I use a little discretion when accelerating at cruisng speed, it's fine. Launches like a bat out of hell off the line though--tough on tires. If you have a auto tranny, maybe your kickdown isn't set right (or not set at all).

 

Just bump your primary shooter size up 2 sizes after verifying your total timing at 36 degrees and a correct vacuum advance control unit.

 

alrighty then, thats where i have the vac advance hooked up, its workin fine..pulls up to 20" on acceleration... looks like bigger jets is the ticket... i'll get # of carb and see if napa has a kit to replace em...will let you know how it goes...thanks ok, i went to a speed shop close by and they didn't handle anything for q-jets. the #'s i got off the carb; 7043202 FS... 3132... need to know edelbrock jets i can interchange with this carb....thanks a whole bunch

 

Your 7043202 Q-Jet is stock jetted with #73 primary jets, #44 primary rods, and "DA" secondary rods. Check and verify that this is the jetting you currently have. If not, set it up to this jetting spec before you start doing any tuning.

Also, verify that your float level is at 3/8". While you have the top off the carb, depress the power piston and observe how deep it goes before it stops: Look at the relationship between the top edge of the brass center cylinder and the very top edge/lip of the plastic retaining collar: When the piston is fully depressed, the brass cylinder top edge should be about .020" above the top lip of the plsatic. If it's flush or below the plastic, you're running too lean from the power piston sitting too deep. Adjust by turning the screw under the steel cap in the baseplate. If it's jammed (most are), you can adjust it by carefully bending the stop lever in the baseplate. Then verify jetting and go from there.

If all checks out okay (correct jets, float level and piston height), increase the jet size 2 sizes. Edelbrock jets are the same as the GM jets. All the Edelbrock and GM part numbers are in my Q-Jet Tuning paper. E-mail me if you need a copy.