4K-C engine stalling while down shifting, need help!

[Silent Icecream]

Car starts as well as an older carby starts, then idles fine. When I drive it for over 5 - 10 minutes while slowing down and down shiftin when the revs get too low it stalls about 50% of the time. I’m trying to diagnose this problem. It idles great after I start it again. Drives fine, no misfires. 
 

Anyone got any ideas? I’d love any! 

[altezzaclub]

Manual gearbox?

Does it start with not touching the throttle?

Maybe wear in the butterfly shaft, there must be a difference between having the throttle off when the motor is off and having the throttle coming off as you lift off for gear changes.

Maybe the clutch is dragging so when in neutral the idle does no work, but when in gear the drag kills the motor.

The simplest would be to add a little idle throttle or timing advance and lift the idle speed a couple of hundred rpm.

 

[Banjo]

Did this start to happen, all of a sudden; where before it was working perfectly ?  Or is it something, that has been getting gradually worst over time ?

Altezzaclub's suggestion is the most likely; caused by the clutch cable inside the outer sheath, needing a good clean. Take the clutch cable out completely, & hang it up in a vice, by the outer sheath, at one end. Add light oil down the cable whilst moving it up & down, by hand.  Put as much oil in as you can; & leave it hang overnight. Once it is free, oil it generously, & reinstall. 

Even if it doesn't fix your problem, it a good thing to do to your Rolla, every couple of years.  There is a couple of guys on this forum, over the years, who have put in hydraulically actived clutch operation, but it involves a lot of mods.

Cheers Banjo

[Silent Icecream]

On 4/26/2025 at 8:15 PM, altezzaclub said:

Manual gearbox?

Does it start with not touching the throttle?

Maybe wear in the butterfly shaft, there must be a difference between having the throttle off when the motor is off and having the throttle coming off as you lift off for gear changes.

Maybe the clutch is dragging so when in neutral the idle does no work, but when in gear the drag kills the motor.

The simplest would be to add a little idle throttle or timing advance and lift the idle speed a couple of hundred rpm.

 

Yes it is a manual gearbox, it doesn't start without some throttle.

I never considered the clutch being part of the issue! Thank you for your response.

[Silent Icecream]

On 4/26/2025 at 10:17 PM, Banjo said:

Did this start to happen, all of a sudden; where before it was working perfectly ?  Or is it something, that has been getting gradually worst over time ?

Altezzaclub's suggestion is the most likely; caused by the clutch cable inside the outer sheath, needing a good clean. Take the clutch cable out completely, & hang it up in a vice, by the outer sheath, at one end. Add light oil down the cable whilst moving it up & down, by hand.  Put as much oil in as you can; & leave it hang overnight. Once it is free, oil it generously, & reinstall. 

Even if it doesn't fix your problem, it a good thing to do to your Rolla, every couple of years.  There is a couple of guys on this forum, over the years, who have put in hydraulically actived clutch operation, but it involves a lot of mods.

Cheers Banjo

This is something that has gradually become more of a situation over time. I am interested in giving this clutch cable some love! Thank you so much for your response.

[Banjo]

Quote

This is something that has gradually become more of a situation over time.

That's a very; very good sign, it is the clutch. You'll know instantly, once you get the full cable assembly out, & try to move the inner cable back & forth, whilst holding the outer sheath, in the other hand. I've seen them so tight, that you had to squirt WD40 down them, & wriggle the inner back & forth, before it would free up. Trick is, once You get it free up; to add copious amounts of light oil down inside the sheath, until it is free & offers no resistance.

Cheers Banjo