Morris Minor Owners Club

Any hints as to what might cause 1098 running on an hif38 with 12G940 head to begin to run fast when engine warms up - 1200-1500rpm. The throttle adjusting screw is fully wound out.
The engine has been running well for quite a while since trouble shooting the initial problems.
Could it be a timing problem?

I would check the ignition timing.

Has your butterfly got a small valve on it?
These can leak air and cause idle problems and are best soldered closed.
I had this years ago on a Marina.
They are used to reduce emissions on over run.
Don’t forget to check your dashpot oil.
Regards John.

Thanks for the suggestions - timing etc not been changed, checked for air leaks and lean running device but it was still blocked off. It turned out to be the effect of the recent daily temperatures as it happened far less on evening runs causing the acc cable casing to expand and lengthen proportionately more than the cable itself thus pulling the cable as though accelerator was being depressed slightly.
Solution to lengthen cable adjustment and fit stronger return spring.