Re: using volvo remote for "98" 115 omc
Is the shift cable throw correct? Once the outboard is fully in gear, the control can't push/pull the cable any farther. Most control boxes won't allow the throttle to be advanced until the drive is fully in gear. If the Volvo box wants to pull the cable farther than the OMC engine will let it, you will get the result you describe.
On generic remotes, there are different holes in the control's shift and throttle bellcranks to allow for the different throw of different model motors and drives. I don't know what kind of volvo remote you have, so I don't know what this might look like. The Volvo SX sterndrive was based on the OMC cobra. I beleive they were able to use the OMC flush mount control so the setup should be similar. No idea what the DP and AQ series sterndrives were set up for.