Is anyone else using the fc40 mobile to drive a whip?

I have my FC40 mounted onto the spare tire bracket of my RAv4. It is connected to a 1/4 CB whip (only 2-3 inches of wire between.) The ground on the FC-40 is directly connected to the ground of the vehicle and all part of the vehicle and bounded together by grounding straps.

Each lead into the radio, antenna control, mike, remote head,and speaker, has an RF choke on that wire.

Works great on 30-6 meter, but will not tune 40m.

If I add 6 feet of wire to the tip of the whip, it will tune 40m NP.

Questions:

1. Anyone have this set up working on 40m?
2. Yaesu's whip for the FC-40 is 8.2 feet long, the CB whip is 9'. Should I trim the whip back to 8.2 feet?
3. Should I ground strap the spare tire itself?
4. Anyway to add 'length' without having a trail 6 feet of wire off the end? A capacitor across the FC-40 terminals? A small coil between the FC-40 and the whip?

Also, 17m will tune, but compared to 30,20,15,12,10 and 6, it seems to have higher (1.7 to 1.9) than the other bands (less than 1.5 all)