Bogging down once warm

[Dpbeats11]

Once car is warm it seems to want to shut off. I have a carter bbl on a 318 motor. I don’t have a rpm or vacuum gauge. I am going solely off sound. Not familiar with tuning carbs but I need it running somewhat decently it to get it from A to B. Cold starts runs fine, but once warm it slowly starts to shut off until I raise rpms. Shall I adjust air mixture screws when it’s warm or curb idle screw?

Thanks!

 

[69 Sleeper Bee]

Is the choke plate backing off as it should when warm ?

 

[Dpbeats11]

Is the choke plate backing off as it should when warm ?

Yeah it’s opening up just fine

 

[turbine68rt]

If you manually slightly raise the rpm does it seem to run ok? Wouldn't hurt to make sure the idle mixture and curb idle speed are set correctly and go from there.

 

[69 Sleeper Bee]

It could be as simple as raising idle speed.
Has it always been this way ?
Is it running rich when it warms up like raw fuel smell or smoke out of the exhaust

 

[Dpbeats11]

If you manually slightly raise the rpm does it seem to run ok? Wouldn't hurt to make sure the idle mixture and curb idle speed are set correctly and go from there.

Raising rpm does seem okay. Seemed to be bottomed out on curb idle screw. Unless this is the wrong one

 

[Dpbeats11]

It could be as simple as raising idle speed.
Has it always been this way ?
Is it running rich when it warms up like raw fuel smell or smoke out of the exhaust

Just recently this started happening. No adjustments had been made prior to it doing this. Occasionally it does smell like fuel. What is the basically for adjust mixture screws? Turn both screws in until slightly seated then back out 1 full turn?

 

[69 Sleeper Bee]

1 1/2 - 1 3/4 turns to start with I believe.

Yes turn in till lightly seated

 

[69 Sleeper Bee]

That idle adjust screw shouldn’t be that far down.
Unless it’s the wrong screw for that carb I would look into rebuilding the carb.

 

[Ron H]

Ya need an rpm or vac gauge to adjust your carb. RPM gauge nice to give you indication of idle speed setting. Could go further with a timing light to check it. Could run some carb cleaner down its throat. Fundamental equip needed to determine next steps - more ahh - invasive while hoping not..

 

[Dpbeats11]

That idle adjust screw shouldn’t be that far down.
Unless it’s the wrong screw for that carb I would look into rebuilding the carb.

Say the carb was just rebuild and i need to adjust these two screw for the first time, how would i know what they should be at? Should these two screws be adjusted before the idle mixture screws?

 

[Dpbeats11]

Ya need an rpm or vac gauge to adjust your carb. RPM gauge nice to give you indication of idle speed setting. Could go further with a timing light to check it. Could run some carb cleaner down its throat. Fundamental equip needed to determine next steps - more ahh - invasive while hoping not..

do you have any reputable brands for rpm or vac gauges?

 

[pnora]

With the curb idle screw turned in that far and the running condition I would suspect a plugged up carb or bad vacuum leak. With the car running, choke open slightly cover the carb air horn and see if it smooths out and speeds up.

 

[turbine68rt]

Couple things...looking at your setup it appears there's not much difference between the fast idle screw on the high step on the cam and curb idle setting. With the curb idle screw bottomed out like that, the idle speed would probably be excessive. If you're running points, get a dwell/rpm meter and ensure you're within range (around 28-34°) then set timing, as point gap will affect timing. Might want to keep another condenser handy as well. Once you have those set, double check the mixture and rpm settings. Also, the throttle pin shouldn't be that far front in the kickdown rod slot. The kickdown should move with throttle or risk ruining the front clutch under load in 3rd gear. Confirm adjustments with your fsm.

 

[sam dupont]

A vacuum gauge can sometimes help diagnose.

Vac Visual: Quick Guide to Vacuum Gauge Readings - OnAllCylinders

Intake manifold vacuum is a key indicator of engine performance. By measuring vacuum under different engine loads and conditions, you can track down problems within your engine and make the …

www.onallcylinders.com

 

[Dpbeats11]

Couple things...looking at your setup it appears there's not much difference between the fast idle screw on the high step on the cam and curb idle setting. With the curb idle screw bottomed out like that, the idle speed would probably be excessive. If you're running points, get a dwell/rpm meter and ensure you're within range (around 28-34°) then set timing, as point gap will affect timing. Might want to keep another condenser handy as well. Once you have those set, double check the mixture and rpm settings. Also, the throttle pin shouldn't be that far front in the kickdown rod slot. The kickdown should move with throttle or risk ruining the front clutch under load in 3rd gear. Confirm adjustments with your fsm.

What step should the fast idle screw be on when cold/ warm? I have a feeling whoever did tune last just bottomed out curb idle screw and changed the air mixture. This issue just started randomly without even messing with the carb. Cold start would have high rpm’s then even out to steady rpm once warm. Now aoas it just wants to die when warm

 

[69 Sleeper Bee]

Have you tried screwing in the mixture screws to see how many turns they are out now ?
Also did you check the carb mounting bolts to make sure they are tight ?
Still leaning towards carb rebuilding time.

 

[Geoff 2]

If points ign, check that points gap has not closed up. It will eventually as the rubbing block wears.

 

[Ron H]

do you have any reputable brands for rpm or vac gauges?

One I have is Bosch and been fine with it - have a few of these gauges I got over the years, not real expensive and can find them at auto stores. Bosch gauge I have can also read fuel pump pressure.

 

[pnora]

What step should the fast idle screw be on when cold/ warm? I have a feeling whoever did tune last just bottomed out curb idle screw and changed the air mixture. This issue just started randomly without even messing with the carb. Cold start would have high rpm’s then even out to steady rpm once warm. Now aoas it just wants to die when warm

Because it is lean due to being plugged up or a vacuum leak. With the choke on it richens the mixture. Once open your problems start. Did you try the simple test I posted above.