Carb help from the experts

[sixty9cobra]

Hi guys been fighting a few issues with my 464 for a while. Had the Victor ported yrs ago and they broke into the push rod tubes I talked about that a few yrs ago. I resolved that by replacing all the tubes etc. SO last week I had enough of the way it ran and did a smoke test. Long story short seemed to be the carb base at the manifold. In the process of diagnosing I had borrowed a Holley hp950. I left it on there so I didn't change more than one thing at a time. I went to a car show on Sunday and the car felt amazing throttle was crisp pulled like it never did before. Idle sounded more radical. Today I put my 850 dbl pumper back on and my butt dyno and my deaf ears says its not the same. The motor was on dyno when i picked it up was supposedly 624 hp with that same 850 on it. Is it typical for these big cu in to want a lot of carb. Also the 950 was 10:1 most of the time on the wide band and the 850 was 12 or 13:1 most places in the rpm range.  I did pull some jet on the 950 but was still pig rich. Its not my carb so I didn't mess to much with it it had 74 primary and 84 secondary


       Thanks in advance
                Harry

[6667fan]

No carb expert but not afraid to tune ‘em for myself and others.
Funny thing about those 950 HP carbs. Some of them, ( all?), don’t flow 950 CFM and could even flow less than your 850. So if that carb is smaller, perhaps that explains the engine feeling more responsive, ( AFR numbers notwithstanding).
10-1 everywhere? I usually try to sort out idle AFR, then cruise and then WOT last. That is going to involve mixture screw adjustment, Hi -Spd and or Lo-Spd air bleed changes and jet changes.
Going to have to get the green light from the 950 owner to go all in on that carb

[jayb]

It might be the difference between a new carb and an old carb.  Carbs will warp, develop internal leaks that affect performance, etc.  The 850 may just need to be gone through.  Also the 850 is a race tuned carb, whereas a 950 (which actually flows more like 800 cfm) is more street oriented.  The A/F numbers don't make sense, the 950 should be blubbering rich at 10:1.  Could your wideband be off Harry?  Maybe needs a new sensor or a good calibration?

[sixty9cobra]

Jay the 950 is rich 10:1 in most spots maybe i was confusing in my explanation. That’s what surprised me that it liked it so much. The car definetly sounded very happy and the seat of the pants agreed. My 850 is like 10 or 15 yrs old i rebuilt it last year changed every gasket. I have no problem buying a new carb just what size and brand. It is also possible that the wide band is off I have no clue how to calibrate it.

[1967 XR7 GT]

You can ask questions here also, I've gotten alot of good info from here:     Racing Fuel Systems   

[cjshaker]

If the reading you're getting is 10:1, the plugs should be telling you if it's actually that rich. If they look good, that would be a good indicator that something in the AFR reading is not kosher.

[sixty9cobra]

i’m not really worried about the wide band at this point more curious as to why it likes the 950s so much more. If it needs a 950 I’ll buy one. I just can’t mess with this one cause it’s not mine.. I have my 850 back on there because I gave him his carburetor back and I got my 12 1/2 -13 to one AFR.

[cjshaker]

My point was that if the plugs looked good at the 10:1 reading, and the engine was running better than it ever had, indicating the wide band is not reading correctly, then that 12.5-13:1 reading may be dangerously lean. Lean can really hurt an engine, and since you can't always hear it if the exhaust is reasonably loud, you don't want to be driving it that way.

[sixty9cobra]

I see your point i’ll pull some plugs tomorrow and see what they look like

[6667fan]

Harry, to calibrate the sensor you have to disconnect & remove it. I would wipe down the snout if it is dirty or sooted. Next it gets reconnected while outside the exhaust. It comes up to temp with the key in the on position. The gauge, ( or separate brain if your system has one), will show a code or letters representing it has calibrated. Turn off key, disconnect, reinstall, reconnect. Don’t turn the key to on again until after sensor is reinstalled and connected.

If that sensor is several years old I would buy a new one and calibrate the new one.
Calibrate the old one before potentially utilizing it as a back up

[My427stang]

I'll take a run at some things for fun

1 - I have seen more crooked metering surfaces than straight, the corners will pull in and allow cross channeling in the middle.  Gaskets fix it temporarily, but as they shrink, it gets worse
2 - An 850 has less venturi effect in the bore, so depending on booster and bleed, could be responding very differently
3 - Accel pumps, cams, and squirters can all be different and I bet they are between that 950 and the 850
4 - There is a ton of tuning in an 850, but if you are far from a normal 850 setup, I'd start over after you address Point 1
5 - Drew recently posted a very crooked carb that was sucking air at the baseplate too
6 - O2 sensors go bad, and usually when you need them

In the end, I'd say if you want to try to work out the 850, machine the metering surfaces, set it all back to factory 4781 configuration, and start tuning again from there.

[Drew Pojedinec]

Not crooked, alignment pins held baseplate off main body.
Actually a fairly common issue.

[blykins]

If it was truly 10:1 A/F ratio, you'd be rolling coal (and washing the oil off the cylinders....)

[My427stang]

Not crooked, alignment pins held baseplate off main body.
Actually a fairly common issue.

Thanks for chiming in.  Something else we all need to watch for

[sixty9cobra]

Today wasn't as humid and only 80 degrees so I pulled a couple of plugs that have been running on my 850. They don't look lean maybe a bit rich nowhere near melting parts. The wideband reads 12.5-13.5:1  I don't have a data logger so that what I see when I look. I found a couple of procedures for calibrating, but I ran out of sweat. I can't explain why I saw 10:1 with the 950 but it definitely felt happier. Someone gave me a 950 so now I have one to play with.