ZONES89RS

iTrader: (2)

Seems the 5.3 is not making much low end power and when i shift, it seems to load up, i played witht he timing, and i wonder if the power valve took a dump, but it idles finne and revs great, but with a load on it, it shifts and then stumbles trying to recover, i will check plugs tomorrow just to see if it looks ultra rich, but with open headers, i cannot smell it leaving allot of unburnt fuel, so i am just gonna keep playing with the carb and what not to get it straight, just want to see any ideas you guys have, the carb is a pro form main body 750, got it used and i am sure it wont hurt to go through it, but it has me wondering if there is a low speed air bleed issue or something.

Orr89RocZ

iTrader: (20)

get a wideband. Or even a narrow band and read the voltage. Verify the air fuel ratio and see where that gets you.

ZONES89RS

iTrader: (2)

Yea, trying to avoid pulling the wide band off the 89.

mw66nova

iTrader: (13)

what's the timing curve setup like? are you using the map sensor? i'd throw a rebuild in the carb just to know it has a fresh build on it, then go from there.

ZONES89RS

iTrader: (2)

Had the timing ramping in slow to 2000, then i tries making it arch in higher, no difference.

Pretty sure a rebuild will help make a better determination, but i would like to try the carb off ther 89 again since i fxed a couple vacuum issues.

mw66nova

iTrader: (13)

what is total timing set at?

ZONES89RS

iTrader: (2)

33* total.


Starting to get pissed at this point, i jetted the carb down just in case from 74/80 to 70/74, still sucked, put the carb off the 89 on it and still did the same thing. So, tomorrow if i get a chance i will try to play with the timing till i see a difference. The MAP is zeroed out. There isnt one but the setting for it i set to zero.

So, i think i will jet it back up and see if i throw even more fuel at it if it helps, i doubt it. Pretty sure it has to be a timing issue. If it had a bigger conveter it would stall above the break up point basically, but i dont. I want ti to roll out when i stab the throttle and it isnt happening. Rolling into it slowly works fine, so that makes me thing it is not the timing.

whitedevilTA

iTrader: (8)

What kind of rear gears does your car have in it?

It could be a timing issue but a 750 seems like it could be a little big for a 5.3 with an auto and lower rear gear. I know your cammed as well but my brothers 91 bird has a 435 flywheel HP (on engine dyno) 350 with a T56 and it's got the identicle carb as you....Holley 750 VS with a proform main body. He runs it with a 70 jet in the front (not sure about rear though) and that carb is perfect for his engine. You don't have a smaller carb you could throw on just for kicks do you?

ZONES89RS

iTrader: (2)

I have a 3.23 rear gear, a taller gear and larger stall would help, but that doesn't mean I dont have an issue some where with it not being able to go WOT and not sputter at the lower end.

I have a 750 VS I threw on but it was out of tune, but my other 750 pro form is dialed in on my 89 and on the 86 ta it still doesn't act right at lower rpm.

mw66nova

iTrader: (13)

sounds like accelerator circuit tuning again like your 89...what's the squirter size, ect?

the lsx's like a larger carb per cubic inch than say a gen I sbc...a 750 is probably really close.

ZONES89RS

iTrader: (2)

That doesnt explain why the carb off the 89 with the 50c pump still does it, this thing is really weird, i am hoping to figure it out, but even the WOT shifts still break up when it drops RPM to the next gear, one mentioned plug gap, so maybe i will open up to .050, i am at .040 right now and that might be too close for the 317 chambers on a 5.3 engine i guess.

mw66nova

iTrader: (13)

a 50cc diaphram isn't going to fix it on it's own. what size are the squirter nozzles?

Orr89RocZ

iTrader: (20)

Curious, how big of a cam and was it degreed in? Sounds like fuel delivery issues with it breaking up and also maybe an ignition related problem, but once you rule those out you could look into advancing the cam alittle more to get abit more low end feel back into the motor.

It also may not like an aggressive ramp in spark advance. Have you tried a lower timing ramp rate?

ZONES89RS

iTrader: (2)

I know, but the issue with iot breaking up under a shift when the rpm drops has absolutly nothing to do with the acc pump, squirter nozzle, ect, that is thew confusing part for me, makes no since, one on tech noted the plug gap could be an issue, i have it at .040, i might try ,050, but i wouldnt imagine it would cause this issue.

It is a Patiot grind, 225/229, .582/.589 lift on a 114 LSA, i set it straight up, i might try bringing the timing in slow, have it in as late as 3000 or so, i had it in by 2000, then droped it to in by 1500 like the 89.

DIGGLER

iTrader: (1)

are you letting off on the shifts or powershifting?

ZONES89RS

iTrader: (2)

This is a TH400 in the 86 Trans am.

xpndbl3

iTrader: (5)

040 is a big gap as it is, personally i'd be looking at plugs for a/f ratio, but if it breaks up during the shifts then that's a high load issue, back the timing down some if the converter is too tight and the rear gears aren't enough. Why are you driving this around open headers anyways?

ZONES89RS

iTrader: (2)

Trying to get it tuned before I get insurance back on itto take it to the exhaust shop, I was thinking about bringing timing in really slow, see if that helps like you mentioned. I checked the plugs and they have a nice, even tint to them, nearly the golden brown color. Think I might get exhaust on it tomorrow.

xpndbl3

iTrader: (5)

timing at the converter stall speed where you're lugging the engine is where it might need to be dialed back a little.

ZONES89RS

iTrader: (2)

How much is a little? I wil expirement, but if i am at 35, i can drop it back to 28 or so, make changes as needed, ect. Gonna try to get exhaust on tomorrow if i can.

Orr89RocZ

iTrader: (20)

pull 2 deg at a time til it clears up, if at all. Does sound like too much timing around the converter stall speed

xpndbl3

iTrader: (5)

we had one car that was 28 total for 400 rpm around the stall speed then right back up to 35 above that and 32 i want to say from 800rpm to the stall speed. Been a while since I played with the laptop numbers for people.

ZONES89RS

iTrader: (2)

Well, that is what I will be trying, hope I just had too nasty of a timing curve.

Orr89RocZ

iTrader: (20)

I'd also wouldnt rule out a lean spot around peak torque since thats where peak airflow demand occurs. Since thats the most load usually, it makes sense it wants less timing there.

LSx motors usually dont like alot of timing anyway.

mw66nova

iTrader: (13)

carb lsx motors DO like timing. i'm running 35* in my car, steve is running similar, as is zone.

xpndbl3

iTrader: (5)

ya mine picked up 3mph from 32 to 34 total

pancherj

I had a similar issue on an old car of mine...maybe you are having the same problem:

heavy car+small cubes+stout cam+slow port velocity+too little stall speed+ not nearly enough gear = poor shift recovery.

What RPM is it dropping to on the shift?

ZONES89RS

iTrader: (2)

I have not paid attention, but shifting at 6500, i will bump it to 7100 pretty soon and hope it will at least fix the issue while already rolling. It does feel it needs a larger conveter, which is weird as this same converter usually stalls higher in other cars i used them in.

I will be going with a 3.73 when money allows, that cam is on the large side for a 5.3 liter.

Orr89RocZ

iTrader: (20)

Yeah the carbs seem to be taking in more timing but like was posted above, somewhere around stall speed and peak torque is usually less timing than at peak hp. You can run 34-35 deg which isnt alot of timing really when some sbc's run 36-38. Around peak torque/stall speed, 28 or so isnt a bad place to try...but on a sbc you'd have all in at 34-36 even below the stall speed. Good chamber altered valve angles generally like abit less timing...but like anything else, you gotta give the motor what it wants.

ZONES89RS

iTrader: (2)

Surely going to find out, would be nice to make it run right today, but watching these kids is holding me back from doing anything, LOL.

DIGGLER

iTrader: (1)

put a dominator on it.

ZONES89RS

iTrader: (2)

LOL, go from bad to worse huh?

Dropped it off at the exhaust shop, and to me, i will keep trying the timing, but it seems it reall needs more converter at least, but this on from Jegs that usuall stalls to 2500 in other car is only foot braking to 1800, so i mihgt be on the lok out for a 35-3800 converter to let it do its job, that and a set of 3.73s would make it work like it is supposed to.

DIGGLER

iTrader: (1)

i donno about the timing... i run 32 degrees normally, and made a few passes with 8-10 degrees of timing pulled for nitrous (but ran on motor).... ran dang near the same. lol
maybe yours is different, though.

ZONES89RS

iTrader: (2)

IDK, there is always the possibility of a cam that was ground wrong.