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Tuning 750 BLP carbs on a 511 with Indy t ram

General engine tech -- Drag Racing to Circle Track

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mopardave
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Tuning 750 BLP carbs on a 511 with Indy t ram

Post by mopardave »

Street/strip deal. It cruises nice at 14.0afr and idle is 14.-14.5 with a 13.1 wot reading on my wideband. My question is, i have a big flat spot when i flat foot it in 3rd gear at low speed(like to check stall speed). Not as bad in 1st gear, but sometimes noses over a bit. 30IFR, 70IB, 28HB, 70jets with 4.5pv, 31 squirters, have tried 37's and no better. Drives very nice, just need to get the flat spots out before i go to the track. 12.5:1 511 mopar making about 650hp. Carbs have the 1.325 venturi, so small 750's. runs 10 o's with 3400# race weight. Ran flawlessly with a 1100 Dominator.
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Re: Tuning 750 BLP carbs on a 511 with Indy t ram

Post by F-BIRD'88 »

Timing curve is ...? increase main jets to #74.. ignore the afr gauge.

Idle should be best idle not according to a afr gauge.
A cold manifold will want more fuel for best throttle response.
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Re: Tuning 750 BLP carbs on a 511 with Indy t ram

Post by VMC »

Try 6.5 or 8.5 power valves.
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Re: Tuning 750 BLP carbs on a 511 with Indy t ram

Post by ClassAct »

Power valves open too late. You are probably too big on the idle feed restriction. If you don’t have T slot restricters install them. That .028 MAB seems awful small.
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Re: Tuning 750 BLP carbs on a 511 with Indy t ram

Post by Tuner »

You didn't say which pump cams. If they are the common pink cam, they are lazy in the early motion of the throttle shaft and what you describe is a common problem with them (the pink cam). Use Blue cams or turn the pink upside-down and readjust the pump lever angle, bend it if necessary, and spring. Take care that at idle the pump lever is not resting on the mousetrap throttle return spring around the throttle shaft, instead of on the pump cam proper. The slightest motion of the throttle lever from closed idle position should provide a healthy squirt of fuel from the shooter nozzles.

With 511 cu.in. displacement you might (probably would) benefit from 50 cc pumps.

Like the posts above, the PV is too low a number and what is the advance curve? .
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Re: Tuning 750 BLP carbs on a 511 with Indy t ram

Post by mopardave »

Sorry, I got busy. Curve is 30* initial and 36 total all in by 2500. Worked good like this with the dominator as the motor loves timing. Yes, i agree, on pv. I have some 6.5's ordered. Will try that. I tune by ear and then check the AF gauge to confirm. Yes, pink cams in the #1 position. Was gonna try them in the #2 to see, but looks like i need blue cams? Was gonna try .026 HB because the .028 worked well from a .030. If i stretch my gears out while cruising the streets, it goes lean as the rpm goes up, so either bigger on main jet or smaller on HB i thought.
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Re: Tuning 750 BLP carbs on a 511 with Indy t ram

Post by mopardave »

just to be clear. When i stretch the gears out cruising i do it at light throttle and just go thru the gears. The cars runs great, just trying to fill any holes in the fuel curve.
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Re: Tuning 750 BLP carbs on a 511 with Indy t ram

Post by mopardave »

T-slot restrictors are .081.
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Re: Tuning 750 BLP carbs on a 511 with Indy t ram

Post by turbo camino »

Does anybody ever think about how many 'carb problems' would disappear if the pink cams had never been made?
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mopardave
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Re: Tuning 750 BLP carbs on a 511 with Indy t ram

Post by mopardave »

I am surprised to here that as I see pink cams on almost everything.
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Re: Tuning 750 BLP carbs on a 511 with Indy t ram

Post by turbo camino »

I'm surprised they are the default choice too, since they work so poorly on 99% of everything. They are fine if you only go from a dead idle straight to WOT and never anything inbetween. At small throttle movements, though, they deliver next to nothing.
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Re: Tuning 750 BLP carbs on a 511 with Indy t ram

Post by mopardave »

Would putting the pink cams on #2 help at all?
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Re: Tuning 750 BLP carbs on a 511 with Indy t ram

Post by VMC »

White 218 and red 240 cams have proven quite versatile for me.
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Re: Tuning 750 BLP carbs on a 511 with Indy t ram

Post by mopardave »

I installed the 6.5pv and not any better, then upped the jetting 1 size to 71 main jet. The fattened it up a bunch at wot to 12.0afr from 13.1 with 70's. I then replaced the .028HB with a .030HB to lean it back out a bit at wot. Didn't get a chance to check wot, but i did check for flat spots and they and still there. Tomorrow will try IFR's. I have .030ifr with .070IB in it and will try .032ifr tomorrow. Not only is the flat spot at wot, but as i tip the throttle in while cruising 60mph in 3rd gear. I see it on the wideband. When its loaded hard and you open the throttle it shows lean.
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Re: Tuning 750 BLP carbs on a 511 with Indy t ram

Post by F-BIRD'88 »

Up 1 jet size is not enough.. Go +4 from 70 and test. Look for drivability not a AFR gauge reading. ignor the guage..
Also /separate tuning issue/ the idle air bleed size may be a hair too big this the off idle transition drift to lean (idle to off idle) Stop messing with the hsab.

Give it the main jet fuel it wants, first..
The accel pump cam advice is good advice.
Get the main jets right first ...
4 power valves or just 2 primarys.

Readjust the idle for best idle NOT ACCORDING TO THE AFR GUAGE. Primary/secondary idle throttle position (transfter slot exposure) needs to be balanced.


Those that live by a AFR guage will die by a AFR guage.
(give it the fuel jet it wants) The afr guage is at best only a "your too lean" warning device. Start rich ,tune to leaner for best wot power (track mph)
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