Not wanting to come off high idle step Rochester 4GC ‘63 Buick

[rodneybeauchamp]

Hi all, I’m having fun learning about automatic choke set up on a Rochester 4GC on a ‘63 Skylark. Have converted back to the automatic choke from a previous owners folly.

 

Have set up carby to specs in the Delco Rochester information (three times now 😀😀😀😀😀) and I thought I had got it correct. 
 

Started easily and had to back off the high idle down to 625 as it was racing about 1100 to 1200 rpm. But it does not want to come off the second step of the fast idle cam unless you manually pull the choke valve plate open.

 

The heat coil on the choke is new and working (tested with her hairdryer 😳😳😳) and is set so there is slight resistance when cold.

 

Does not seem to be any binding of the linkages that operate it all, but frustrating that it doesn’t do as it’s told. Have looked at countless videos and blogs but still not getting it right.

 

Gunna persist on this till I get it right as it should. Initial problem was difficult starting on the manual choke. At least it now starts….. so that part is good. 
 

pictures show where fast idle screw wants to stay and also where the choke vale was until I pushed it home!

Rodney 😀😀😀😀😀😀

 

BTW ignition is good, points with dwell and timing correct.

 

Edited September 23, 2022 by rodneybeauchamp
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[joe_padavano]

If you can pull on the choke plate to move it with the engine warmed up, then the coil is either not adjusted properly or has lost tension. The coil alignment spec in the manual is only a starting point. The coil is intended to be adjusted on the car as needed (and sometimes as appropriate for the season. Move it one notch towards lean and see how it goes. If that doesn't help, get a new choke coil. 

[rocketraider]

Good luck. I fought one on a 64 Olds for several years until I said hell with it and put another carb on it- which worked FLAWLESSLY.

 

The original carb, you could have choke or have it kick off fast idle. But not both. It would do one or the other, but not both. Set to specs, NOS choke coil, set to specs and trimmed again and again till I was tired of it. That chunk of junk went in the trashcan. Did I mention I was tired of it?

 

I am convinced that 4GC are either good or not.

[Oldtech]

There is a bunch of adjustments here. First confirm that with the flap all the way open that the cam goes to the first step. If not, the adjustment is to bend the rod slightly,

Second. Why is the flap not opening all the way? Pull the cover off the choke stove and see if the spring is installed correctly. Some have a loop that goes ON the pin for the choke, some just have a hook that pushes on it.  

Next, Heat to the choke stove. Is it sucking from the carb? is the pipe to the manifold and through it good? As Rocketraider said, you could try a notch or 2 leaner if everything else checks out but my suspicion is that you aren't getting enough heat. 

[carbking]

In addition to the good answers already in the thread:

 

QUOTE: "The heat coil on the choke is new and working (tested with her hairdryer 😳😳😳) and is set so there is slight resistance when cold." END QUOTE

 

Set the choke on a cold engine at an ambient of 65~70 degrees (about 20 degrees) C to JUST TOUCH CLOSED WITH NO TENSION.

 

EDIT: Also, look at the gasket SEALING the choke cover to the choke housing. It must seal.

 

Jon

Edited September 23, 2022 by carbking (see edit history)

[rodneybeauchamp]

OK so big test today. Reset the choke coil as Jon suggested to just lightly close the choke valve with minimal pressure while engine was dead cold. Choke thermostat gasket was still good and appears to seal.

 

Started immediately but had to drop the fast idle back. Put the air cleaner back on and did a short drive around the block. 
 

Interesting because at the fast idle setting suggested by the Rochester instructions the rpm seems way way way  too high which means I have to alter it achieve a 625rpm instead of about 1200rpm that it seems to run at. 🤔🤔🤔
 

So next morning, with a dead cold engine at 7.30am it started on second try after using correct technique, pedal to floor then release but then stalled out. Required a few pumps then started but wanted to stall while in park. Managed to feather it enough to back out the garage with one more stall then it was fine. 
 

At a rest stop for coffee, started fine but again wants to stall, so will have another look tomorrow and perhaps up the fast idle. After going through all the settings carefully to get them right, perhaps a bit disappointed it did not behave.
 

On the good side, now at least it will start …… but doesn’t want to keep running.

 

It hasn’t beaten me yet ….. and it won’t.

Rodney 😀😀😀😀😀😀

Edited September 25, 2022 by rodneybeauchamp
Extra information (see edit history)

[Frank DuVal]

OK, been a while, so open to corrections, but isn't base idle set by the far left screw in the lower picture and the fast idle is set by the screw on the right touching the fast idle cam?

 

Is the hot idle specification 625 (in drive or neutral?)? If so, then the fast idle specification (if there is one) will be higher. It should not be 625 also.

 

When hot (defined as choke open), the fast idle screw should not be touching the fast idle cam.

 

Rare, but I have seen the "welsh" plug in the choke housing leak air (vacuum). Use length of hose to put an ear to it, or use carb cleaner/other flammable substance to see if idle speed picks up.

 

And, is the other end of the choke stove pipe open? i.e. is there a path (not closed by insect nest) from the pipe attached to the choke housing to air?

[rodneybeauchamp]

22 hours ago, Frank DuVal said:

OK, been a while, so open to corrections, but isn't base idle set by the far left screw in the lower picture and the fast idle is set by the screw on the right touching the fast idle cam?

 

Is the hot idle specification 625 (in drive or neutral?)? If so, then the fast idle specification (if there is one) will be higher. It should not be 625 also.

 

When hot (defined as choke open), the fast idle screw should not be touching the fast idle cam.

 

Rare, but I have seen the "welsh" plug in the choke housing leak air (vacuum). Use length of hose to put an ear to it, or use carb cleaner/other flammable substance to see if idle speed picks up.

 

And, is the other end of the choke stove pipe open? i.e. is there a path (not closed by insect nest) from the pipe attached to the choke housing to air?

Correct, base idle screw contacts base of carburettor to adjust idle. Fast idle screw is the other and sits on fast idle cam. 
 

Fast idle spec is 650 rpm in N (assumes N = neutral) and hot idle is 525 in N according to Rochester Products manual but Buick quotes a figure in Drive.

 

Everything else appears OK.
 

One thing that puzzles me is you have to wind the fast idle screw in a fair way to make one adjustment but if left at that setting, fast idle is way too high, 1500rpm or there abouts. This means you then wind it back out to set the correct high idle. Would not this change the previous settings?

 

Will dig a bit more into it today perhaps and see what I find. Possibly I am not setting one of the adjustments correctly.

 

Perseverance will win out eventually 😀😀😀😀😀😀😀😀 

Rodney 😀😀😀😀😀😀

 

 

 

 

[arcticbuicks]

you could just put a electric choke unit off a newer carb,they fit and just one wire to ignition,it wont be original but hidden by air breather and works so much better,ive done it many times,but check coil rotation visibly..... some work in reverse

[carbking]

The fast idle speed of 625 is for a HOT engine.

 

Do not have a cold engine spec, but most V-8's of this era will have a cold (when first started) fast idle of 1500~1800 RPM. As the engine temperature increases, the fast idle cam rotates, and the idle speed comes down automatically.

 

IF the linkages are correct, and the internal vacuum source to the internal choke pull-off is open; then blipping the throttle will cause the fast idle to drop (from the 1500~1800 initial) down somewhat. Blipping the throttle causes the fast idle adjustment screw to lose contact with the fast idle cam, and the vacuum supplied to the choke pull off will rotate the choke shaft slightly, and correspondingly rotate the fast idle cam. When the throttle is allowed to return with no foot pressure, then the fast idle adjustment screw should be on a lower level on the fast idle cam.

 

Setting the fast idle on a cold engine, depending on the ambient, WILL cause stalling when the transmission is engaged in gear.

 

Jon

Edited January 1, 2023 by carbking (see edit history)