Carb Questions

[vht]

I have a 427 BBC in a Model A I built, it has a tunnel ram with 2 1850, 600 Holleys. The carbs were built by a guy in New Jersey, to be ran on a 2x4 intake. I just now made my first short drive in it, still got some more to do and when you get into the throttle hard it stumbles bad. Here's the thing, this guy eliminated the vacuum secondary assy on both. Now with no acc pumps on the rear, how in the world is this suppose to work? The only thing I know is to buy the vacuum assy and whatever else I need to put them back to the way they were and tune them with a spring kit. I had alky injection for the last several years I drag raced so I may be behind on carb tech but I don't know what the guy was trying to achieve. It starts and idles fine and both carbs look like new. Anyone on here ever seen this?

[rustbucket79]

You could start with bigger shooters and possibly bigger primary jets. I’ve found those carbs can be quite lean on cruise, you might get them to work, or you might be just as well off replacing them with something a bit easier to adjust, like a pair of 500 or 600 Edelbrock’s.

[econo racer]

I would start off by putting the carbs back together as the factory built them. Go from there.

[ClassAct]

I never run those carbs on anything, let alone a TR. Get a better set of carbs, that don't have vacuum secondaries.

[Tuner]

1850s are great tunnel ram carbs. One important detail in making them work well is to plug the lower E-bleed in the primary block, so there is only the one E-bleed and it is at float level. This makes them so they don't get too rich at small throttle opening with a MJ that gives good mid-load, middle of the pedal with vacuum above the PV opening point, the condition of brisk part-throttle acceleration but not full on hard roost. Just using one E-bleed makes them less likely to be loaded up when lifting the throttle in rolling out after a burnout.

This is what to do:
PMJ #67
PVCR .046"
PMAB .031 low position
PIJ .028"
PIAB .063"
Angle channel .140"
P&S booster leg passages .140"
SMJ (drill plate) .076" (original 1850 sec. metering plate #9 is .067")
SIJ (drill plate) .040" ( " ..... " ......... " ..... is .031")
SMAB .028
SIAB .028"
ACPD .035" White 218 cam or if it needs more squirt blue 427 cam
Soft secondary springs, connect secondary vacuum servos with hose between them.
It is worth the effort to drill the curb idle discharge ports in the secondary end of the "snake channel" to mimic the primary CID. This provides "poor man's 4-corner idle" by discharging some curb idle fuel from the primary mixture screws into the secondary bores. At high RPM part-throttle the vacuum servo pulls the secondary open against the closing link. Adjust the secondary closing link so the throttles are open an equal amount at about 1/2 throttle. This will leave some slack in the link when the primary is at idle and the secondary is closed, this is OK, the link is not supposed to completely close the secondary, it is supposed to synchronize the throttles in the near 50% open range so the airflow is similar through P and S at part-throttle.

If you have the skills and drills, drill .026" through to idle well in the little dimple (drill starter) at #7 in middle pic.

[bigfoot584]

Out of curiosity, do these carbs have the choke tower milled off
so you can't see the list number, because what you described I'm
thinking you may have list number 9776 carbs that have no vacuum
secondary pods and a double pump base plate with squirter only in
the primary side, their 450 cfm and sold for tunnel ram use.

View here.

https://www.holley.com/products/fuel_sy ... rts/0-9776

[NormS]

The 1850 carbs have considerably larger venturis than the 9776 carbs. The 9776 carbs can get away with not having a secondary accel pump, because the main circuits tip in so quickly with the small venturi size that those carbs have. But the larger venturi size in the 1850s would require a secondary accel pump if converted to a mechanical linkage to open the secondaries. I agree with the member who suggested converting the carbs back to vacuum secondary configuration.
In a dual quad setup, it is often necessary to modify the vacuum secondary system so the secondaries get to full open position at a reasonable rpm. In stock form, it is common for the secondaries of dual quad 1850s to not get to full open position, even at peak hp rpm.

[tjs44]

Guys,I got these carbs with a pontiac RA V tunnel am intake.They were custom built for the intake.I am a AFB user so I sold them without ever running them.The shop that built them removed to vac pods and made them man secondary's.I think that is the issue with the carbs.What was done internally to them is unknown.I gave the OP the phone number of the builder so maybe he can come up with more info.Tom

[427dart]

There is a carb shop that,if you have the bucks, makes 4160 style double pump Holley carbs in whatever CFM you need.
Around 1200 bucks per carb if you want inline carbs. http://www.compfuelsystems.com/

You need the Vac. Secondary pots back on!

[jmarkaudio]

For $1200 each you can have brand new billet carbs built...

[vht]

These carbs are 1850's, I didn't get a chance to call the guy today to see what was done. Car idles and revs great until you put it under load. I've been finishing up some other stuff on the car and then I'll get insurance on it before I can get it out and try to figure out what's going on.

[vht]

I would think that installing 50 cc pumps would help with the longer duration of fuel or longer squirt.

[NormS]

If the secondaries on these 1850's are set to come in real early in the opening of the primaries, like the 660 center squirter carbs were, then I could see 50cc accel pumps helping the situation. But if the secondaries are set to come in later than that, then I doubt the bigger pumps will help much. What we don't know, is if the calibration of the secondary transition circuits was changed when the carbs were converted to the mechanical opening.
I still think that going back to vacuum operated secondaries is the best bet.