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Old 07-01-2013, 11:08 AM
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help with tune

Hey guys, so went to the track last night,
Truck ran good, went a best of 12.98 @ 117
Zero hook on radials, walking it past the 60ft
Consistant 13 teens most of the night, MPH ranged from 115-118 as a high
Guys there with traction running mid 11's at the same MPH.
Its running fine in every way except at idle.
Its not "rich" but shows very poor combustion, it smokes and its not black, its just unburned fuel.
A little bit when your on it, but lots at idle.
383
Vortec heads (mild porting)
Performer rpm cam.
488/520, 234/244@0.50
Air gap rpm intake
Quick fuel 650 dp
Stock jetting, 4.5pv
Long tubes.
Msd dist HEI style with external blaster 2 coil
Msg 6a box
Summit wires.
Holley blue pump
Holley reg
Fuel pressure at 5psi
Floats at bottom of sight glass.
4 corner idle, all screws roughly 1 turn out.

That's all I can think of. Any suggestions?
Edit, timing is 24* initial, 34* total, all in by 2800rpm
Vacuum advance is limited to 10* using a manifold source.
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Old 07-01-2013, 11:29 AM
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So you're seeing 34 degrees w/the vacuum advance connected? Are you getting that eye watering deal at idle, or no?

Are the boosters dripping any raw fuel at idle? Are those air bleeds replaceable?
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Old 07-01-2013, 11:35 AM
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Quote:
Originally Posted by cobalt327 View Post
So you're seeing 34 degrees w/the vacuum advance connected? Are you getting that eye watering deal at idle, or no?

Are the boosters dripping any raw fuel at idle? Are those air bleeds replaceable?
No, 34* is with vacuum disconnected. Nope, no dripping at idle, and yes, the bleeds ate replaceble, I believe they are 70/70 and 28/28 but will have to double check. I do have some 35's kicking around that I thought about swapping out the 28's for
Oh and yes, badly eye watering at idle
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Old 07-01-2013, 11:53 AM
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we can call you 12 second Dave for now? after the carb is leaned out,you really need to work on the hook. We have guys here running 12.1s at 102.
my 1980 Z-28 ran 11.9s @ 110
what was the weight of the truck with you in it?
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Old 07-01-2013, 12:25 PM
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Originally Posted by vinniekq2 View Post
we can call you 12 second Dave for now? after the carb is leaned out,you really need to work on the hook. We have guys here running 12.1s at 102.
my 1980 Z-28 ran 11.9s @ 110
what was the weight of the truck with you in it?
Lol, if you saw the night you would be calling me a moron before anything else, I made like 5 runs in the low 14's, sideways like an idiot, then ran a few 13.50's, my buddy jumped in it and ran 13.20 first pass, then 13.1, then the 12......my best way 13.56.
Its a stock rear with a mini spool, if it hooks, it will break.
Truck was scaled at just over 3050# or some where around there. I'm 300#, my buddy is 170 soaking wet.
He figures with traction, it should go 11.20's .....that seems real optimistic given the combo.
The MPH seemed high, as it did for a bunch of other cars too, hell even the silly g-tec was only showing 114mph.
Either way, it was kinda dumb and I won't be back until I can get a rear end under it and some traction. We both almost wrecked it on the 2-3 shift when it spun and jumped sideways. So for now just trying to get the idle cleaned up cause its real embarrassing sounding as good as it does, but smoking like a chimney.
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Old 07-01-2013, 12:29 PM
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Just pulled the Carb now, the primary transfer slots seem a little over exposed but hardly. You can't open the secondary as they are much further up in the bore and to expose even a sliver of them hangs the front of the butterflies open a bunch.
I can open the idle bleeds up from the 70's using a drill bit, I have one that's just a shade bigger then the 70 but isnthks really going to change much?
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Old 07-01-2013, 12:45 PM
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Sorry Vinnie, your were right, I was optimistic, 113-115 as a high. Consistant 2.4-2.6 60ft.....so embarassimg.....lol
My best was a 13.65, not 56
Oops
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Old 07-01-2013, 12:46 PM
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A diff and slicks will get you heaps closer.Try short shifting 1-2 if the truck breaks loose
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Old 07-01-2013, 01:00 PM
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Originally Posted by vinniekq2 View Post
A diff and slicks will get you heaps closer.Try short shifting 1-2 if the truck breaks loose
Best run with Chris driving
2.21 60ft
8.56 8th
10.9 thousand
12.98 @ 115.2mph 1/4
Through the lights at just over 5000rpm
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Old 07-01-2013, 02:06 PM
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Carbs back on now, hand honed the idle bleeds a touch, installed new 4.5 pv just because I had one.
Transfer slots primary are at a perfect square, rears are still closed as they were when I got the Carb. Floats are just above the bottom of the sight glass.
Reset mixture screws, highest vacuum is 15 in park, idle screws app 3/4 to 1 turn out from seated.
Still the same, smokes at idle, waters your eyes, wife hates me.
Next?
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Old 07-01-2013, 02:40 PM
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Forgive my attempt at humor but what if you put some sparkplugs in the tailpipes LOL

Are you sure you're only pushing 5 psi for fuel pressure? Id see if you could bum another carb from someone; see if the problem changes. Have you pulled your sparkplugs and inspected them? Are they the correct plugs for your application. I don't think any one thing is going to CURE this, but lots of little things can attribute to it
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Old 07-01-2013, 02:48 PM
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Forgive my attempt at humor but what if you put some sparkplugs in the tailpipes LOL

Are you sure you're only pushing 5 psi for fuel pressure? Id see if you could bum another carb from someone; see if the problem changes. Have you pulled your sparkplugs and inspected them? Are they the correct plugs for your application. I don't think any one thing is going to CURE this, but lots of little things can attribute to it
Lol, it was a decent attempt.
Plugs are rs12yc, gapped at .45
I was chasing fuel pressure issues, I drained the fluid from the guage, then set it for 6.5 as per qf recomandations.
Then had to reset float levels because they dropped very low after the fp change.
The Carb is a quick fuel HR650, its 4 days old.
1 tank of fuel through it.
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Old 07-01-2013, 05:01 PM
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Opened up the secondaries, closed up the primary a bit more, set idle off secondary while running, still same issue, started truck in gear, almost drove through the house, wife hates me, timing shows 24 at idle, nut now something is sticking, it was dead nuts on 34 total by 2800, now it keeps climbing, by 3000 its 40, by 4000 its 50*.
Going to have to pull dist, sucks one a friggen S10...but this wouldn't have affected my idle regardless so still have no clue what's up there.
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Old 07-01-2013, 05:02 PM
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If your running a higher compression like 10 to1 or over try reducing spark plug gap to .035" it may help give a hotter spark! higher compression raises resistance for the spark to jump the gap and creates a voltage drop at the electrode! Just a suggestion I don't know your compression but as compression is increased I reduce the gap at my plugs!

That may not be your problem but it could be a contributing factor, resistor plugs and high resistance per foot plug wires reduce voltage efficiency TOO (to protect homes and vehicles from radio and TV interference) LOL! Who cares about your neighbors TV or RADIO reception and you can gain 10 to 15 HP

Jester
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Old 07-01-2013, 05:21 PM
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Originally Posted by painted jester View Post
If your running a higher compression like 10 to1 or over try reducing spark plug gap to .035" it may help give a hotter spark! higher compression raises resistance for the spark to jump the gap and creates a voltage drop at the electrode! Just a suggestion I don't know your compression but as compression is increased I reduce the gap at my plugs!

That may not be your problem but it could be a contributing factor, resistor plugs and high resistance per foot plug wires reduce voltage efficiency TOO (to protect homes and vehicles from radio and TV interference) LOL! Who cares about your neighbors TV or RADIO reception and you can gain 10 to 15 HP

Jester
I have only one neighbour that's close, and he isn't exactly a fan of my shenanigans, so I'm not really worried about his reception lol.
Comp is 10.1, the thing is this isn't always this bad, long periods idling make it worse, after a really hard run its not bad at all, then sitting idling for a bit it gets bad again.
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