408 with a 1050 carb too lean

[Screamin demon72]

Having trouble with the carburetor set up I have. Engine is a 408 with trick flow heads, fully ported trick flow intake. 11.0:1 compression. Cam is a 108 installed at 103, .608 .608 lift, 254 258 duration. 75% race 25% street car. Had a Holley 750dp run 6.84

Put together a 1050 carburetor and I can’t get my WOT to run any richer that 13.8:1. It’s a pro form 1050 annular booster main body, venom 2 metering blocks from pro systems and a billet pro system base plate that has holes drilled in the front and back butterflies. Car felt pretty good with 85 primary jets with a 4.5 power valve and 90 secondaries with a power valve plug but the AFR at WOT read 14.8:1. I then tried going to 94 jets in the back and it was at 13.8:1 afr and I’m wanting to be at 12.2-12.5:1 WOT. went all the way up to 104 jets in the rear and it still read 13.8:1 on the afr. Cruise is a little rich, when I tip into the throttle it goes lean but drops back down.

Has anyone had an issue of bigger jets not making it run any richer? Or should I go back down to a 750 carb? 104 jets seem way over kill and it’s not showing it on the afr gauge.

 

[plymouth4onthefloor]

carb too big cant create enough velovity to pull fuel.
fuel level sinking fuel pump/line to small

 

[66Valiant528]

If you are using an oxygen sensor set up, have you tried resetting your sensor lately?

 

[doug 371]

too big

 

[Screamin demon72]

I have 3/8” fuel line from tank to carb and a high volume Carter mechanical fuel pump. I haven’t tried resetting the oxygen sensor, Iv only have the sensor for about 3 weeks and it’s an auto meter. How do you re set one?

 

[66Valiant528]

Don't know on that brand. I have an Inovative Motorsports I believe. The directions tell me how to do it. Are you running leaded fuel? That's on 02 sensor killer. Find your directions.

 

[Oldmanmopar]

Try installing smaller high speed air bleeds.

 

[92b]

Did you call pro systems yet? They should be able to get you fixed up.

 

[92b]

if you don't have smaller bleeds you can put tag wire in the bleeds for a test. Drawing is on the primary side. Put a little tape on vent tube to hold wire in place.

 

[Oldmanmopar]

Your carb may not have replaceable air bleeds. but they can be removed and threaded to make them changeable

 

[TT5.9mag]

How bout looking at the plugs and verifying what the afr gauge is saying? What do the plugs look like? Then, if your cruise afr was ok with the 85 jets, start tuning the pvcr instead of just throwing jet at it. The carb may not be too big, depending on how much power it makes. But it might be easier to tune with a little more signal from a smaller 4150 style carb. What intake is on it? Is it 4500 flanged?

 

[Newbomb Turk]

It’s not too big.

You need to post ALL the numbers to see what tune up you have.

Calling Patrick at Pro Systems about carb tuning is like calling Aunt Jemima for tech help on a nuclear reactor.

 

[Screamin demon72]

I played around with the air bleeds and got it a little closer. Sadly the metering blocks don’t have pvcr’s but I thought about tapping them for a set screw. Patrick at pro systems helped out quite a bit. My intake is the trick flow track heat that’s completely ported.

I mainly tried this carburetor because I wanted to see how the annular boosters did for throttle response. For now I went back to my other carburetor until I can figure out what’s going on with this carburetor. The plugs are reading lean also.

The 1050 carb felt very responsive and I think it helped some on power, I’ll try some other things you guys mentioned to see if any of them help with the signal to pull the fuel through at WOT

 

[TT5.9mag]

The plugs are reading lean also.

Trust the plugs

 

[Newbomb Turk]

I played around with the air bleeds and got it a little closer. Sadly the metering blocks don’t have pvcr’s but I thought about tapping them for a set screw. Patrick at pro systems helped out quite a bit. My intake is the trick flow track heat that’s completely ported.

I mainly tried this carburetor because I wanted to see how the annular boosters did for throttle response. For now I went back to my other carburetor until I can figure out what’s going on with this carburetor. The plugs are reading lean also.

The 1050 carb felt very responsive and I think it helped some on power, I’ll try some other things you guys mentioned to see if any of them help with the signal to pull the fuel through at WOT

What size main air bleed? It’s hard to figure out if you have an issue if you don’t post the numbers.

If the metering blocks still have the factory drilling that can be an issue.

 

[33IMP]

Your carb may not have replaceable air bleeds. but they can be removed and threaded to make them changeable

View attachment 1716398637

Proform main body sure should have replaceable bleeds!

 

[PRH]

Booster feed holes and/or metering block angle channels may only be about the size of a 100 jet.

 

[Screamin demon72]

My air bleeds are 31 high speed, and 70 idle air. The holes in the metering block may be maxed out too, they look close, but I figured it wouldn’t need a 100 jet anyways. I figured it would be somewhere in the low 90’s for the secondaries

 

[PRH]

I figured it would be somewhere in the low 90’s for the secondaries

I understand, however if there are restrictions downstream of the jets that are similarly sized to the jets, then you’re out of range of the tuning widow for the jets.

Early 3 circuit 4500 carbs had metering block main wells with an area about the size of a 98 jet, and booster feed holes not way bigger than that.
They were often lean and untunable on higher hp applications(if a 98 jet wasn’t sufficient).
I would modify the metering blocks and booster tubes, which would allow me to take out about 10 jet sizes, and still end up richer than it was with the big jets prior to the mods.

My point being, channel sizing downstream of the main jet can be a big player in the jetting requirement.

Mark at Lightening probably has some insight as to whether there’s likely any issues with that for your situation.

 

[Newbomb Turk]

My air bleeds are 31 high speed, and 70 idle air. The holes in the metering block may be maxed out too, they look close, but I figured it wouldn’t need a 100 jet anyways. I figured it would be somewhere in the low 90’s for the secondaries

See post 19.

That’s where I was going. I open up the main wells on every carb I do. I’ve never seen one that wasn’t tapered, even billet blocks.

For a 1050 I start testing at .028 on the MAB and usually end up at .026.

While .031 isn’t massive, it starts the booster sooner (so the fuel curve gets rich sooner at lower rpm) and the .031 will make the fuel curve leaner at WOT.

First things first, I’d check the diameter of the main well like PRH is saying above.

If you still can’t get the fuel curve in shape, reduce the MAB to delay booster start up and cleaning up the rich area where you are still in the middle of the T slot and the booster starts.

That also adds a little fuel at WOT.

Be very aware of using more than two emulsion bleeds. Especially with a good annular booster, you might only need one open to trim the fuel curve up.

More emulsion holes open and bigger holes will make the fuel curve fatter.

Where the bleeds are controls the timing of when the fuel starts moving up the main well to the booster.

I see many carbs with three, four or even all five emulsion bleeds open.

Look through the threads on here about “slugging” and emulsion tuning. It’s very easy to see on the dyno. You can see it in the car IF you data log. If you are just eyeballing an O2 gauge you can’t see it. It happens fast enough the human eye doesn’t catch it.

 

[1MeanA]

My Innovate O2 analyzer requires the user to run the calibration test for the O2 sensor. I assume the Autometer requires the same? It may not be the issue but I would check it out.

 

[PRH]

I’m “assuming”(dangerous, I know) that the same O2 gauge that’s reading lean and shows the 1050 carb to be somewhat unresponsive to jet changes, doesn’t show the same for the 750 carb.

 

[Valman]

JMO, an 830cfm annular discharge DP would run great on that engine.

 

[1MeanA]

I’m “assuming”(dangerous, I know) that the same O2 gauge that’s reading lean and shows the 1050 carb to be somewhat unresponsive to jet changes, doesn’t show the same for the 750 carb.

It should assuming the same O2 sensor

JMO, an 830cfm annular discharge DP would run great on that engine.

There is something to be said for starting with a carb that’s in the ballpark OOTB for the application

 

[PRH]

There is something to be said for starting with a carb that’s in the ballpark OOTB for the application

Absolutely!!

In this case my “opinion” is that a 4150 carb with a Venturi diameter of 1.590” isn’t a real good match for a 408” street/strip combo that likely makes under 600hp.
That carb’s ootb tune would probably be fairly close on something that’s 100”+ bigger, and making 100+ hp more.

I bet a carb with a 1.450” Venturi would have been a better starting point.