Stumbles when cold

[Flash66]

Hi gang! So don't get me wrong, my car purrs like a kitten. Full tune, clean fuel system and when warmed up to temp everything seems good. But until it's good and hot, giving it throttle, back fires through the intake and takes some padding of the pedal to get it revving. I removed the hot air riser previous to the full tune and my engine bay restoration. Just looking for any advice on this. I confirmed my VSV is working properly and don't have a vacuum advance until the engine is warm. Thanks!!!!

[DMCMW Dave]

Warm up regulator or the vacuum lines to it or the thermal vacuum switch.


Sent from phone

[Flash66]

I think that led me to the problem Dave. I found this hiding under an AC hose wide open. I don't see where to connect it anywhere. Thanks!!


30901

[David T]

I think that led me to the problem Dave. I found this hiding under an AC hose wide open. I don't see where to connect it anywhere. Thanks!!


30901

That is a vent hose and it is there just so water can't get in to the valve. It is only connected on the one end. Your problem is most likely related to the warm-up regulator aka Control Pressure Regulator (that is it in the picture). It's main purpose is to enrich the A/F ratio till the motor warms up so if you are having drivability issues during the warm-up cycle start with it. Check the hoses and wiring and if it is all OK the regulator probably needs to be rebuilt and calibrated.

[Rich]

But until it's good and hot, giving it throttle, back fires through the intake and takes some padding of the pedal to get it revving.

Chiming in with a +1 on Dave's and David's inputs as to likely causes.

Ours started running exactly this way about 5-6yrs ago. In our case it was a vacuum leak between the thermal vac switch and the WUR.

When I replaced the the WUR vacuum hose at the tee behind it (hose was split at the tee barb) the problem vanished.

[hmcelraft]

You probably have the vacuum valve on backwards or one of the vacuum lines installed incorrectly. I'm betting the valve is backwards.

[Flash66]

You probably have the vacuum valve on backwards or one of the vacuum lines installed incorrectly. I'm betting the valve is backwards.

I guess that could be possible. I'll flip it around and see what happens. Thanks everyone!