Ok guys.. So I'm attempting to tune this thing up so I can get it to the track... But I'm running into a solid wall here.. cant get past a stumble if I throw it down (2500-3k) .. and at idle im luck to pull 8"... So I think I'm going to tear the carb apart and clean it out completely with a good soak and try to start from scratch again... But I'd love some input from all of you.. so heres the setup

5.3 short block
243's shaved .030, w/3* valve job
comp 223/228 @.5 601/617" 112lsa
Vic Jr.
holley 750dp (68p-73s) with a 6.5pv and a blue cam
6010 with all in @34* by 2700
700r4 shift kit (no stall yet)
and 3.23s out back

The only thing I havnt tried yet is a bigger squirter and thats just cuase the speed shop is closed till monday for vacation.. So any thoughts, ideas, long shots at this point I'll chase down... even maybe just to hear a few other similar setups carb settings and maybe tweak from there..
Thanks everyone! I hope to get this thing tuned so I can finish with the spray setup and see what she'll do.. Everyone at the track keeps harassing me, but no one wants to help! So now I just want to show them all up!

 

I could be wrong but if your only pulling 8" of vacuum at idle you need a 3.5 power valve. Also with a cam that aggressive not saying its a huge cam for an LS motor but a 5.3 its quite large you should be running at least a 2800rpm stall without the stall your really gunna have a huge flat spot down low until the motor starts to build power. The stall allows the input shaft to slip alittle so it doesn't put as much strain on the motor until you are into the power band that's why it is highly recommended to run stall converters with large after market cams. I would say match you power valve to your at idle vacuum and that is in gear not in park set the parking brake put some body in the seat to hold the brakes and pull it into reverse or first which is where you have the most load at idle and check your vacuum. Then match your power valve to your actual idle vacuum. Check for vacuum leaks and get yourself a good stall and you will see her come to life. Also check your AFR's general rule of thumb in tuning at least from what I have been taught is get everything right first the F*** with the carb ie: timing which looks good you might could give it two more degrees btw did you degree the cam or just line up the dots and go? Sometimes you can be off on timing by +/- 3 or more degrees without degreeing your cam you truly don't know what your actual timing is. That being said if I had to point fingers at where I would go first I would say Stall and Power valve you get the stall that removes load at idle up to where ever depends on size stall and that changes your power valve size because plenum vacuum changes under load.

 

A stall is deff. in order for it.. just waiting on funds.. I just ordered an afr guage kit should be here on monday... so that should help. And I did install the cam @ +4* so I thought the timing I had in would be ballpark.. Think it could use any more in the lower end? I'm sure there will be a flat spot in there due to the cam/intake combo, but the real issue is the motor runs badly through those rpm, even in park it isnt smooth when I jab it.. the power valve has made the biggest changes as I try different ones.. How should the rear compare to the front? Same size? or go lower rating? I'm hoping between that and a squirter change.. I should be able to at least minimalize it... Also it sounds like I have a vacuum leak in my brake booster... I hate trying to find these leaks!! drives me nuts... Havnt found one yet but 8" seems offly low to me....

 

And the 8" was in park.. thats why it seems so low to me... I almost have to have a leak somewhere I think... Ill have to try and back it up to the wall in R and check it tomorrow but it'll probly be quite low Im guessing... SHould I be running a pcv on this or 2 breathers for the crank?

 

If you feel you have a vacuum leak in the brake booster plug that port off at the carb just to see what your vacuum does. As far as the PCV you need crank case ventilation for the rings to seal properly and reduce blow by, thats why you see some of the hardcore guys running crank case ventilation systems that put bungs in the headers so the exhaust flow creates a vacuum in the case ie a PCV is a smaller version deriving its vacuum from the plentum just under the carb. The carb also needs a good clean Carb signal ie steady vacuum in the case to meter right and with a large cam and single plane intake your going to have fun getting a steady vacuum reading you can play with carb spacers to give you more volume under the carb and smooth out the carb signal. I would be willing to bet your vacuum gauge needle flucuates at idle. Another problem alot of people run into with tuning carbs is trying to set the idle with the idle set screw on the linkage instead of the idle air screw on the metering blocks. As far as jets go your secondaries should be larger than your primaries but again jet size is determined by proper timing and AFRs so I guess what I am saying really is get the rest of your setup right then start tuning the carb. As far as low vacuum and running your power accessories they make a vacuum canister that stores vacuum and makes up the difference at idle to keep you power brakes up to par. Last but not least remember that these motors are not desinged for carbs and a vast majority of the cams out there are not very carb friendly so we are trying to mix technologies that were never meant to work together so these kind of problems ar par for the course. Also can you describe the "stumble" Does it fall flat on its face and then take off like a bat out of hell or does it fall on its face and and never get back up? pull a spark plug see if it is white or black if its ashy white then your lean if its black and maybe even alittle wet then your rich IMHO I would be willing to bet your running rich as with a 5.3 even revving it out to 7000 rpms you should be good with a 650 cfm carb then again some people swear cfm calculators dont work and some swear by them I myself think they are a decent tool but like anything if you put crap in you get crap out. Also you know your 3.23 gears are killing the combination just as bad as the lack of a stall. Just looking at that cam profile your cam looks like it has an RPM range of 2500-6800 rpm on an LS1 on a 5.3 your probaly looking at 3000-7200 so thats another reason for the epic failure basicly until you start to allow the engine to build power thats why you need the stall then the lower rear gear ratio like 3.73 or 4.10's because they help to mask the drop off of power int the bottom end and get you in the meat of the power band quicker. hope this can help you out some alot of this stuff i too learned the hard way with my gen1 sbc i know different motors but principals still apply.

 

I think that you will have some trouble tuning without a stall. Also that gear ins't helping either. My car only pulls about 6 in of vacuum at idle. So 8 may not be that low. Try a 2.5, or 3.5 power valve in the front, and block off the rear. Then set the throttle plates so the fuel transfer slot looks square on the front and the back. Adjust idle with timing, and the four idle screws. Hope this helps

 

Ditto on the power valve, you want half of what our idle vacuum is. Ex... 8 at idle would be a 4 power valve.

Take the carb off and look at the baseplste by the secondary shaft, you will see a small flat head screw going through the baseplate and touching the idle cam deal on the secondary shaft. Now turn that screw in which in turn opens the secondary shaft. You want to open the secondaries enough to square off the transfer slots. After you get this set adjust the primary shaft idle back some if not all of the way closed. Id bet money you have a ton of transfer slot showing on the primaries from using it to set the idle and it is flooding out the motor.

Id set all of the throttle cams, pump cams, squirters,etc back to stock also i dont think that is your problem. Make sure your accel pump linkages are set to where once you barely crack tbe throttle they start moving the arm, there is a clearance spec thst holley gives to use a feeler gauge to set them but i dont remembr what it is off the top of my head and ive always just set them with just a hair of a gap at idle.
I had a built 327 in my nova with a huge cam that only made 7 inches of vac at idle and i ran a pretty much stock 650 double pumper with mechanical secondaries and it ran awesome.

Disconnect your brake booster if you think its leaking.

 

Ya the vacuum bounces alot at idle! probly a good 2* sweep with 9 at the high end.. I've adjusted the Idle mixture screws via vacuum gauge for highest vacuum with the idle set screw set to almost stall the motor.. But it wasnt in drive just in park as I'm by myself up here.. I havnt yet checked the transfer slots underneath. so that will be on the list for today. as far as the secondaries are set is with a block off and 8 jets higher.. Im almost thinking that maybe an issue too.. when I accel smoothly up to full it runs out fairly well, but a quick jab and it falls flat, surges and then comes back.. but it doesnt come back real quick ( going to try higher mains today ) Just to clairify how should I have my vacuum lines set up for this motor.. I only have 2 on currently valve cover w/pcv to brake booster and my heater port to under the carb.. Did I screw that up? I also have a breather line from the other cover to the air cleaner.. And I have a set of 3.73's just havnt had the time to get them in yet... Waiting on the cash for a stall as well, was thinking about a 3k 10" should do nicely w/anti ballooning plate

 

Pull the number one spark plug before you go jetting it richer and see what the plug looks like, like i said before if its black and covered in suit its rich if its ashy white its too lean you want it almost a light golden brown around the electrode. after you check that check your transfer slots should look square not rectangular, also what kind of rockers are you running did you check push rod length just wondering you may have a valve hanging open with the vacuum moving around like that. if you are running factory rockers you may have to long of push rods if your running adjustable rockers you may have a valve or two set too tight. If you know what pinging sounds like ie the clatter from predetenation put a degree of timing into it at a time go drive it once you hit where it starts to clatter under acceleration back the timing down to the last known setting before predetonation and you will know you have as much timing in it as it will handle should help clear up the stumble if its running rich as it sits.

 

Ok now there are 2 things I hadnt yet thought of.. 1st- Im still running the stock length (but new 7.4") pushrods... and as far as increasing the timing I'll take a look at the plugs.. when I first started with this carb it was majorly rich. Looked like a nuclear war zone aftermath.. I've been slowly reducing each time since, have yet to notice any surging at steady state.. surges on the stab though, then if I let off and put it back in itll make its way past the rough patch... Started with a 76 up front now at a 65 primary jet.. Does there need to be a vacuum line from the carb ran specificly to anywhere else?

 

Hate to do this to you but I would be willing to bed if you dumped that single plane intake and ran a 650 or 670 holley you would loose a lot of your stumble. How high are you trying to twist this motor anyways? if your staying below 7000rpm get you a dual plane mill about a 1/4 out of the center divider and put a 1in open spacer on top of it and you will beat that victor jr. throughout your entire RPM range. Don't know if you have seen it but a lot of people have refrenced it before in the past car craft did the dyno comparison between the two intakes and the rpm was killing the victor jr up until something like 6800 rpm which is kinda where the two broke even and the victor started to out shine but for a mostly street driven car you would be surprised the seat of the pants feel you will get with the dual plane and I really do think you are over carbing your setup a 750 vac secondary would probably serve you better as well. but if your dead set on your setup lean it out alittle more throw some more timing in it like I said take the timing alittle at a time til it pings then back it off to the previous setting will help clear up stumble but once you get the stall and gears in it know you will need to tune the carb again. anyways I hope I have been able to help.

 

oh and as far as your vacuum lines you have the map sensor for the ignition that's the small line then you have two larger lines 1 for the pcv and one for the brake booster that should be it.

 

Ya I've thought about changing the intakes.. Problem being for now is funding for it.. Unless I found someone who had one and I could sell mine quick.. itll be a little while before I can do that.. same with carbs although I have a 600 or 650vs over on the shelf at my parents I could try and swap back on... but I have no real idea of the condition of that one, never ran it myself.. Now I went through and changed a few things different sec. metering plate and pv.. almost took out the dead spot, but it wouldnt idle at all... so I changed back to the previous setup exactly.. And now it still wont idle.. runs good above 2k but if i dont keep fluttering the throttle it dies.. Really frusterated at this point. So now since I cant even keep it running i cant check for vacuum leaks or anything... As for my vac lines I had the fat one off the back to the PCV and T with the brake booster.. the single front lower vac just to the trans. the vac on the front metering plate is blocked off...Im pretty sure I may have popped a pv after a back fire.. IFR's make very little change at any setting and my plugs are fouled looking and wet at the base...

 

Yeah definitely clean your plugs. dedicate a single line to your brake booster and the pcv. Why are you running a vacuum line to the 700-r4 to my knowledge they don't require a vacuum line and I have one in the floor of my garage right now not sure if you are running a full manual valve body like I have in my 4l80e now that requires vacuum. also I didn't see you say anything about a map sensor does your ignition box not have provisions for one so that it can act like a vacuum advance for the timing? I know the MSD 6ls requires a map sensor just wondering if you have everything hooked up right. But with the valves wet and fouled your definitely too rich lean both sides out and having the wrong power valve can cause that as well as not having enough initial timing. Without being there its really hard to walk you threw it. Also if for some reason your trans needs a vacuum source the performer has a spot on the number 8 intake runner not sure if the Vic jr does but you can get a car spacer with one in it but I am the kind of guy that likes to dedicate lines so I know I got good vacuum and no leaky as plastic t's.

 

Ya when I get a chance here tomorrow I need to jack the timming up as in the low range there below 2300 its only on its way up to 18* Ill try and set it up to 20 at 800 and see how it does.. along with checking the PV's I originally had a block off in back, now it has a 4.5 so ill change those back and see how it acts.. I'll probly try and give holley a call tomorrw too and see what they can tell me... I'm hoping it's just some dumb mistake I've made or overlooked, But I am emailing a guy about an RPM intake.. any ideas on how the 750 would act on it? The reason for the vac to pcv to brake booster is because the carb only has one large vac tube and one small on the base plate.. how should I seperate those? and sorry not the trans its the heater switch panel.. I'm so frustrated I cant think about it right now everything is getting twisted in my head... Time for a stiff drink!

 

And I dont have a mount set up for the map sensor right now So I just zero'd it out on msd and leave it unplugged for now

 

do me a favor just plumb in the map sensor even if your just letting it hang there by the hose tune it back in and see what it does. Also you can try putting your all in timing to 40 or 45 degrees and see what that does i have seen some people running as much as 50 degrees of timing in the truck motors. The reason I want you to put the map sensor in is it adjust timing in accordance with plenum pressure so you may need more timing in at idle and before 2700 plus i think you need more timing at and above 2700 not sure what head gaskets your running but 243's milled .030 i believe still puts you at a slightly larger combustion chamber than before so you may have lost some compression there then with the .030 mill and your still running stock 7.4 push rods one you may be set too tight on your valves and i bet if you lap the rockers on the valves your not riding in the center valve train geometry needs to be right to ensure good performance and longevity. so long story short clean your plugs and fix your timing curve once thats done start back in on the carb.

 

Picked up new plugs today! I also found my base plate was cracked... guess I tightened it too much... figure that is probly playing a big part.. I put in a new steeper curve as well but cant test yet as I have the carb off a waiting new base plate.. I could plug the map in and run a vac line there to see what it does.. Should I set the map table to the standard 10* across? or just below a certain psi? Not quite sure how that all plays into each other.. My WB should be here tomorrow so hopefully I should be able to get this ball rolling here.. Thanks for all of the help so far, it certainly helps!

 

I would set it to the standard 10* across at first and see what she does yeah a cracked base plate is definitely no good. So funny story I was new to the tuning a carb game and I spent all day chasing poor vacuum one time to turn around and kick myself in the a** I had just put a 200-4r in my el camino in place of the TH350 i had and the 200 doesnt require a vacuum line well I totaly left the damn vacuum hose running down the back of the intake toward the trans well my buddy who had been helping me tucked it upout of the way so I didnt notice it hanging there and when i had checked the intake all i saw was all the hoses where hooked up there so I was like WTF it wouldnt idle for sh*T. Anyways long story short he forgot i didnt pay attention and hponeslty never found it until I finnaly got fed up and pulled the trans thinking maybe the lockup was stuck for the converter and well yeah 1/4 vacuum line going to nowhere slapped me in the face lol.

 

So I found and fixed two issues so far today.. 1-the base plate cracked, most likely leaking. 2- the base plate gasket was the wrong style! with the new proform base and correct gasket, along with a thick anti vib gasket underneath, she Idles like a kitten now.. with a fairly steady 10" in park and about 6" vac in drive while chocked. So now that it idles very smoothly and well its on to kicking that stumble out.. To do so I've got an AFR w/b 02 kit I'm going to try and get installed today... Only new issue is my brake pedal is very stiff, with only One large vac port and 2 timed ones. How should I route the lines for Pcv and brake booster? I'll try the map sensor again, but wont that put an extra 10* in for the entire time since the table runs from 0-16" vac? I just dont want to put too much in it and harm something.. Or am I reading these graphs wrong?