Hi, Mike and the usual suspects are:
1. Dirty or clogged air filter.
2. Faulty spark plug.
3. Bad Gas.
4. Improper oil level.
5. Improper chain adjustment and lubrication.
6. Low tire pressure.
7. Dirty or contaminated carburetor needs cleaning and tuning.
8. Broken carburetor spring.
9. Carburetor spring on backwards.
10. Vacuum leak on carburetor or intake boot.
11. Too much slack in the throttle cable
12. Clogged or faulty fuel pump filter or injectors.
13. Faulty pressure regulator.
14. Improper valve adjustment.
15. Slipping clutch.
16. Improper timing.
17. Low compression.
For more information about your issue and valuable "FREE" downloads that you will need for viewing or printing please click on the blue links below. Good luck and have a wonderful day.
https://www.vtxoa.com/threads/intermittent-power-loss.407337/
https://www.vtxcafe.com/threads/trying-to-cut-off-losing-power-high-speeds.55578/
https://www.manualslib.com/manual/722750/Honda-Vtx1300s.html
https://www.partsfish.com/page/oem-parts-for-honda
http://owners.honda.com/assets/ownerlink/model/own_man/powersports/2004/2004_vtx1300c.pdf
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