Large adjusting screw on a 61 Rochester 4GC

[Bruce Reynolds # 18992]

Gday all,

I have a problem with a 61 Rochester 4GC Carburettor that I am aboutr to install on my 61 390 motor that is in my 60 CDV.

My question is in relation to the large adjustable screw that is in the base of the carburettor, but at the rear and at around 45 degrees off fore and aft.

Could someone please advise me as to what it is for, and the base setting for this screw.   Then, which way is it adjusted.

I have had the carby totally to pieces for reconditioning, and it was set at 4 turns out from seated.

Bruce,
The Tassie Devil(le),
60 CDV

[John Washburn CLC #1067]

Bruce,

The Old Idle air by pass screw problem.

The book recommends that you bring it all the way down then back it off two to three turns.

My experience say three turns, possibly three and a half, due to wear.

Good luck

John Washburn
CLC #1067
Elizabeth, Colorado

[Michael / Denmark CLC#21905]

Bruce,if you have a shop manual,its descripted how to use the air bypass screw in combination with the air/fuel mixture screws to obtain an idle speed of 400 rpm.Mixture screws 1 1/2 turns out-air bypass 2.Put on a rev counter and warm up the engine and put the trans in Drive with the p-brake applied SECURELY!You only have a few minutes to do adjustment before letin`the trans cool of.Use first the air byp. to 400 ,then mix.screw one at a time in or out to highest revs then use the bypass down to 400 again and finish of with the mix.screws, continue til you obtain the smoothest idle.The air bypass should not be to open(Better with 1 than 2 turns out)its to lean and makes noise.
Think i got it right....doing it by the book may be borin`, but work best is my x-perience.;-)
Happy cruuisin` ,Michael

[Michael / Denmark CLC#21905]

OOps,think the idle is 450 rpm,sorry...

[Bruce Reynolds # 18992]

Thanks John,

I am about to fire it up tonight.

Spend most of the day manufacturing the necessary arms and throttle cable mount.

Bruce,
The Tassie Devil(le).
60 CDV

[Bruce Reynolds # 18992]

Thanks Michael,

But, I still have one big problem in that I cannot get to idle at all, unless I screw up the fast idle screw and run it on the choke cam.   The vacuum gauge is all over the place, and the motor was running okay with the Holley before I pulled it off.

Here is what I have so hopefuul someone can assist further.

(1)   61 390 with exhaust cross-over blocked off.
(2)   Positive Crankcase Ventilation.
(3)   No Idle speed-up control.
(4)   Choke there, but not operating.

No amount of adjusting the BIG screw would do anything, but, when I disconnected the PVC and blocked it off, I could get the mixture screws to alter the revs and work properly.

So, is this carburettor supposed to be used with a draft tube ventilation, or are they the same for either ventilation system?

Was I getting too much air via the PCV Valve, and thence, an extremely lean mixture?

If I cant get it to go, the Holley goes back on.   I dont want to as now I have a correctly operating TV rod, which is why I changed in the first place.

Lastly, can I forget the BIG screw, screw it in all the way, and then fabricate a normal idle screw to allow setting the idle, or does the BIG screw meter fuel flow as well as air?

Bruce,
The Tassie Devil(le),
60 CDV

[George]

If you suppose that the carb is for a draft tube. What have you connected the PCV valve to? Are you sure the problem is with the new Carb?

[Bruce Reynolds # 18992]

Thanks to all who replied, but at this stage the Holley has gone back on as I need to make some gasket changes to the Rochester, and some minor modifications.

I now know how to adjust it, and what I did wrong in the initial fitting.

Bruce,
The Tassie Devil(le),
60 CDV (with Holley 650 Vac Sec)