Carb Tuning guru's!

[Brown_Muscle]

Threw my rebuilt frankenstein 2150 carb (2 pieced together) on the LTD today (5.8L). I'm not new to tuning carbs...however this one's bugging me..I"m also sick so maybe I'm not thinking right.

At idle I can get it to run just fine, however it runs rich. It either runs rich, or it runs rough, I can't get it right it seems. commonly runs about .8 on the o2 sensor

At 2K RPM it runs lean. Now i have a theory that the power valve is incorrect, as the rebuild kit i got came with one that has no markings, and it was not for this intended carb (I assume as I have no ID tag, had to pick the kit out by eye). I asked the company what they sent me...so maybe that's the issue, otherwise I'll have to reject.
The 02 reading is around .1 to .3 and no higher at 2K. It misfires a bit as well.

Any suggestions? The idle running rich is what concerns me the most right now.

[jaywish]

If the idle circuit is clean, the float is good and the float height is correct.

Do you have a tach or a vac gauge ?

[Brown_Muscle]

it is clean, floats good and adjusted.

I had both a tach and vacuum gauge hooked up for tuning. I'm pulling a max of 19in

[marquisman]

Is the needle on the vac gauge nice and steady? Or is there much movement? Its weird that the carb goes from real rich to real lean when you open the throttle. Leveling out from rich when opening the throttle would be easier to diagnose. How did the little round gasket fit on the power valve? Does the original power valve look bad?

[jaywish]

How did you try to tune this carb?

[Brown_Muscle]

So far just idle adjustment screws, experimented with a few vacuum lines as well, but all is as it should be. For the higher RPM's i may try different jets if the power valve doesnt work.

The old one should still work, I'm going to try transplanting that tomorrow to see if it makes a difference...it has size 55 jets in there now..
Vacuum reading is steady, idle depends to wander a little. The round gasket fit fine on the new power valve

[turbo2256b]

Idle circuit is used from idle to commony up to 2500 to 2800 RPM then it transfers into the main curcuit. The power valve shouldnt be cutting in crusing at 2000 RPM unless floored.

[P72Crazy]

Are you running a 2-plane intake such as a factory unit?

[Brown_Muscle]

Using a factory intake that came with the VV carb

[Brown_Muscle]

Idle circuit is used from idle to commony up to 2500 to 2800 RPM then it transfers into the main curcuit. The power valve shouldnt be cutting in crusing at 2000 RPM unless floored.

Are you sure this applies to the 2150? It contradicts what I've been reading about the idle circuit and main jets..

[gadget73]

If its leaning out around 2k, I'd have to wonder if the main jets are too small or maybe the throttle shaft bushings are seriously slopped out and causing an air leak. Power valve wouldn't be related to running lean. Those normally open under low vacuum conditions such as heavy accel. A leaky one might make for a rich mixture though, same with a leaky accel pump check ball. If it won't lean out at idle by adjusting the mix screws, pull them out and have a look. If someone reefed down on them, it will dimple the tapered section and screw things up. If it was run in too hard, the seats might be flared out and it will have a constant internal fuel leak. Internal leaks from a too-high float level or a leaky bowl can cause this too.

[turbo2256b]

Are you sure this applies to the 2150? It contradicts what I've been reading about the idle circuit and main jets..

Its the way most all carbs work at least most automotive ones. You said the carb was cobbled togeather out of 2 of them. Were they off identical engines?
Say one off a 302 might not have the same metering as one off a 351 or another engine. One common misconception is the fuel mixture screw controls the idle mixture. It actually controls the amout of mixture. The mixture is controled by the idle air bleed (witch also controls when the circuit cuts in and out). FUEL IS CONTROLED IN THE IDLE CURCUIT BY THE idle fuuel feed restriction. If any of the metering holes in the emulsion tubes are restricted do to dirt it will through the mixture off. I use gutiar strings to poke through these holes and in the tubes to clean out any blockage. Idle mixture is usally correct if turning the mixture screw in or out a half turn from best idle the RPM drops.
Timing also affects A/F readings. My dually likes 13.8ish idle A/F, cruse at 2000 RPM flat road (difficult to find here) 15 A/F is normmal.

[P72Crazy]

You may have answered your own question. I think I have a 2150 in the basement off a 1975 Grand Torino Elite with 351W. I think it had 59 jets in it. If I get a chance today, I'll take off the air horn and take a peek.

[Brown_Muscle]

Awesome advice, thanks guys! I'll pull the carb and double check that all the idle circuit is clean, human error is definitely a possibility.

The Carb I'm using now has the 1.21 venturi's, which should work with 351's, it has the original jets, the only the transferred over is the throttle shaft and linkage. Both the 2150's have about the same amount of throttle play-although they could both be worn. The #59 jets make more sense than the 55..although I've read a lot of people have #56 in their 1.21's.

[Brown_Muscle]

Ok so I got the 02 sensor to start switching at idle rather than staying constantly rich...at this adjustment it pulls 1 less inch of vaccuum and runs a little rougher...not terrible though. The exhaust smells a lot cleaner as well. Would probably pass emissions as is..but I'm not sure. Still runs real lean in the upper RPM's...debating on which jets to get... .57 or .56. I'm unsure how much of a change the sizes will make