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Re: Lean Spike Coming up on the Brake

Posted: Fri Jun 29, 2012 3:24 pm
by jmarkaudio
If you can post all the info on the carb, size, all metering data including air bleeds, idle jet size, intermediate jets, emulsion bleed size number and position.

Re: Lean Spike Coming up on the Brake

Posted: Fri Jun 29, 2012 3:38 pm
by John_Heard
I have a sheet on it, but I'm not sure it's accurate re:jets/bleeds etc. as I bought this carb used. I'll see if I can verify the info this weekend and post it.

Re: Lean Spike Coming up on the Brake

Posted: Sun Sep 30, 2012 11:52 am
by John_Heard
Sorry to be slow to post this, got to working on some other projects.

I just got done tearing the carb down and everything is the same as this sheet, except the Int Air bleeds are not .060, they are .078, which is a long ways from what the carb had originally. The squirters are also .054, not .052. I don't know why those were changed, but must have been set by the previous owner. Would those larger bleeds on the intermediate be responsible for it going lean like that when coming up on the brake?

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Re: Lean Spike Coming up on the Brake

Posted: Thu Oct 04, 2012 11:48 am
by John_Heard
Talked to Patrick at Pro Systems today, he thought I should try going back to .060's on the intermediate bleeds, he thought it was likely the .078's were likely the reason it was way lean at tip in getting on the chip. So, I've got those in it now, hopefully that and the rebuild will fix that issue.

Re: Lean Spike Coming up on the Brake

Posted: Mon Oct 29, 2012 11:38 am
by John_Heard
Well we tried the .060 intermediates, tip in still lean, went back to .078's, same thing. Didn't really seen any difference with that change.

However I did see a difference in the O2 depending on how I brought it up on the brake on one run. If I brought it up slower, the AFR looks a lot better without spiking way lean. It's sounding like accelerator pump squirters I think?

Re: Lean Spike Coming up on the Brake

Posted: Sun Nov 04, 2012 6:15 am
by silvanova
john, how clean does this Carb run going down the track?

Re: Lean Spike Coming up on the Brake

Posted: Sun Nov 04, 2012 9:20 am
by John_Heard
It's fine down track, nice and flat and pretty even left/right bank about 12.5:1 if the O2's are correct. I haven't calibrated them recently so they may be off some. Just goes lean when you set the brake and bringing the RPM up on the chip. Maybe I need to just change my staging procedure, I'm a bit gun shy after it coughed a few times so I tend to bring it up in RPM a bit before matting it.

Re: Lean Spike Coming up on the Brake

Posted: Sun Nov 04, 2012 10:39 am
by silvanova
just curious. my Carb is a 1200 and its quite a bit leaner and my o2s show way rich. jmark has been helping me lean it out alot. I had 45 squirters in it and he told me to try 35s. so far it's running a lot better just need to head to the track to get some data.

Re: Lean Spike Coming up on the Brake

Posted: Sun Nov 04, 2012 6:28 pm
by 79 Camaro
I always bring mine up to 2000 rpm's before setting the trans brake. Makes sure the carb don't stumble and the trans has some pressure before setting the brake which holds the car better. But I don't have 02 to see all the fancy stuff .

Re: Lean Spike Coming up on the Brake

Posted: Sun Nov 04, 2012 8:31 pm
by John_Heard
That's actually kinda interesting, as I attempt to do that as well, but not quite as high a RPM from what I can see. I did find this when comparing two runs. One run where I had the RPM up higher, it didn't do it. The Arrow shows the pass (blue lines) where it didn't go lean.