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Hey guys, I wanted to share my First time out with the wideband hooked up this morning. Some AFR notes I made:
800rpm Idle 12
At a gentle 2800rpm 60 mph 12.7
When I stab the throttle this is what occurs.
First it stumbles. The stumble immediately goes 16/22 for about three seconds then the car goes steady 9.6 till around 4k where it goes 11.7 and levels to 12.3 until the thing breaks up at 5500 and goes 16/22 like there is a rev limiter kicking in. I am going to hook the laptop up and see if it still has my map loaded. Isn't 55k the default limit?

So much for my brilliant spark plug reading. I said rich all along. I am at the shop building shock brackets all day so I can't hook up the laptop until tonight

newschool72

iTrader: (12)

If it has the lean bog, I would strongly recommend a pump cam change. Its funny that I never hear anyone on here messing with the pump cam, But it has everything to do with the pump shot when you hammer the throttle blades wide open. A pump cam kit is cheap and comes with several cams and a chart showing what each does. Just remember to readjust the acc pump arm before each test dump or you can damage the acc pump .Good luck

89gmcs15

iTrader: (7)

The factory limit is 5500 on the msd box so check that first since its easy. this is what im seeing, your too rich at idle (I have the same issue and am still waiting on the snow to leave to work on it) but that's more of fine tuning and not major. This is where I'm iffy on what I'm going to say next, I'm no expert. It looks to me like your pump shot is too small, then when your engine starts to recover your power valve opens up and starts pouring the fuel in way early. Once the engine starts to recover alittle it slams the limiter. If its not a limiter your hitting I'd check to make sure your carb is staying full, either not enough pump, restriction in the line, your float levels are too low or your jets are being un covered due to no extensions.
These are just theories of mine someone chime inand call me a dumb *** so I quit thinking please haha

3pedals

iTrader: (3)

That's right, pump cams to fix the stumble. you want 1 that has a radical big shot at the instant the throttle moves. I think the black 1 is what I have.
And the take 3-4 jet sizes out of it front, and 2 sizes back( I am assuming you have 70-80 in it now)
And then try it all again, lol

89gmcs15

iTrader: (7)

If he's lean then goes way rich down low isn't it the power valve adding too much fuel too early? It looked like the engine was gettin leaner an leaner the higher it revved, if it were me I'd fix the 5500 rpm limit/stumble and see how much leaner the engine gets up high before I'd change the jets. How high do you plan to spin?

3pedals

iTrader: (3)

Maybe, but not necessarilly, you wont know for sure untill you fix the initial stumble/lean spot. any engine missfire will cause lean readings on the wideband, but a 3 second miss(bog)could be loading up the cylinders with un burned fuel making the wideband show rich when the engine finally recovers.
I only recomended the jet drop because at high rpm he is seeing 12.3, and I think it should be 12.8 -13.0. the engine should not be missing at the higher rpm or it would be pretty obvious something is wrong.
Yes the MSD has 5500 pre programmed as a top rpm limit. Id fix that too, these engines like rpm lol

newschool72

iTrader: (12)

I agree with 3pedels on fixing the lean bog first. That is a huge upset to the fuel metering and the engine it self, so who knows what the wideband is going to read in that few seconds while it tries to recover.
On the jetting ,im a big believer in real numbers at the track ,or to a lesser degree, chassis dyno. No one knows what a particular engine wants as far as a/f until it tells you. One engine may get max power at 12.2,another at 13.1. Just been an observation of mine over the years. Sounds like you are starting to get something to work with now. Keep us posted.

89gmcs15

iTrader: (7)

This makes sense once someone writes it out. In for the results on this one

Pop N Wood

iTrader: (1)

Man, you guys are crazy. The EPA is probably getting warning announcements on his car from space cause it is spewing so much fuel and you are all concentrating on the accel pump shot?

The accel pump is the LAST thing that gets tuned on a carb. Get the AFR's stable with slow and steady state throttle movements first THEN monkey with the accel shot. Right now you aren't even ball park.

Jeff Smith

iTrader: (44)

I ll order autometer wideband @ summit racing..

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It is pouring rain here. I have not taken it for a spin yet, but here is the deal. When my crank sensor was bad a month ago I prematurely sent the 6010 back to MSD for repair. They sent it back, indicating that the box was OK and user settings were left loaded. I never checked and the car has actually been running the default MSD map with their curve and 55k limiter.

As soon as I get some dry pavement I will hammer it a bit while noting AFR with the proper timing curve. I loaded 15 at 0rpm ramped to 35 at 2k straight on from there with a 6600 revhi. The 1 bar MAP is still enabled.

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Hey also, I called Quickfuel and went over the setup. Nice guy there told me to switch the following:
Again I am currently using .074 pri / .084 sec, a 4.5 PV, .033 hs air bleed, .070 idle air bleed.
Quickfuel says go to 72/80 and a .036 hs bleed with the 8.5 PV. This sounds similar to your recs so thanks again for the great help. The squirters will be next to look at afterwards.

The usefulness of the internet sure has expanded beyond spank movies since I got on this site. You all have been very helpful. Thanks folks.

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This thread might go on forever....

I am currently running the following:
Timing is set at 0 rpm-15 degrees, 900 rpm-22 degrees, 2000-31, 6000-33, 6800-32. Min 5/max 35, Rev hi is at 6600, 1 bar MAP Is enabled and goes startup at 12degrees till 8psia and ramps down to zero at 15psia.

My QFT Q750 is setup as follows:
Primary 72
Secondary 80
Air bleeds are primary .036/.073, secondary .036/.073
Primary PV is 8.5 inchHG

Vac at 700 rpm idle is around 16. Gas is pretty fresh. Plugs could probably be switched out, I haven't got to the parts store in a while...

What is happening on the wideband.....
At 650-700 rpm idle cold it reads AFR around 12.7, once hot idle is 11.7.
Gentle around town acceleration is like so.....at around 5% throttle easily driving 14.3, 10% throttle afr is 15. Gas it past 20% throttle and AFR drops to 11.9.
When I get a little heavy footed things change for the worse. At around 2k rpm if I hammer it it might stumble up around 15.5 for a split second then go 10-11 AFR. Any time I go WOT on a roll it will drop to 9.6-10.5 AFR. From a dead stop WOT bogs at 9.0 until the revs get mid to high range and comes back up around 11.5 or so.

You guys have been so helpful. Your feedback is welcomed. I like chasing this problem, it is teaching me quite a bit.

wildcamaro

iTrader: (15)

Def tuned in...I like to see how someone tunes in real time...I just threw my 650 proform on with curve 2 and I've been happy lol, I got a lot to learn as far as carb tuning and this is a great post for that...

3pedals

iTrader: (3)

The 15:1 at 10% throttle is from to low a power valve , put 1 in that is a higher number.-what do you have in it now ? EDIT: read that you have 8.5PV, go to a 10.5
Upon re reading your post it sounds like The stumble from 2000rpm is possibly from too large of pump shot. But dont know till you clarify the next part , below:

The 9.5-10.5:1 ? is that what the wideband reads the whole way through the rev range on a WOT run? If so that is from the main jets, I'd go 4 sizes down front and rear based on those numbers....BUT:
If that 9.5-10.5:1 is only upon initial stab of the throttle, then I suspect too large of shooter in the primary, and I'd ask what the wideband reads the rest of the way through a full run