Thank you.

If you are experiencing unexpected behaviour from OpenStreetMap-based routing software which you are using, you will need to raise a support ticket with the software supplier.

Adding a higher speed limit than the real one might reduce the cost of traversing that edge, but to the detriment of other data consumers.

I would also hope that routing software would ignore a 70mph speed limit set on a single carriageway secondary road in the UK, since this is likely to be a legal impossibility.

You may also be a able to find some assistance on the OSM Community Forums.
https://community.openstreetmap.org/