: I am looking to make a repair to an older boat and the temperature has cooled
: here lately. I know that bring the temp back up to 70F or so will help the
: epoxy cure faster. But what if I bring it up to 90F? Or even 120F? Will I
: weaken the repair?

The repair won't be "weakened", but the epoxy needs to be able to penetrate the wood, sealing the area with unthickened epoxy first, then making your fill with thickened stuff. You might need more than one "seal" coat to really make a good seal. At 120 degrees farenheight, the stuff you use to seal, might be setting up to a pretty good thickness when you are ready to "fill", so the amount of thickener you use (collidal silica or wood flour or both) should be less than if you thickened immediately on mixing.

: This is on the portage yoke for a 100# boat, so it is important it is strong.
: Which is why I can't risk the epoxy not being fully set before I go.

I don't know your timetable, but if it is on the portage yoke, you could remove it from the boat and do the repair in a location with more ambient temperatures. If time is a factor, try the fast hardeners...MAS has a product they call Rapid Cure...beware, this stuff sets up fast in 70 degree (F) temps...120 degrees (F) won't give you much time to work at all. That is if your not just using left over epoxy. If you are looking for a small repair job, there's plenty of products available that are specifically designed for repairs of this sort, I've seen two syringes packaged together with five minute set times....

Portaging a 100# boat is a big concern if you are very far from civilization...you might consider replacing the yoke with a new one...I've seen 'em in the sporting good stores...or you could just carve a new one out, you could use the "old one" as a template, inclusive of marking your portage "shoulder pads" bolt holes. I know it's out of season for many adventure goods outlets, but they might have one on a shelf in the back left over from summer.

Have a good trip!
Bill Cruz