Hi PocketHead. What part of California are you planning to start in?

I'm on my own trip right now, but I should be back in San Francisco by the time you start. If you need any logistical help, including a place to crash for a week or two, let me know.

Buying the motorcycle: Unfortunately I don't know the process of buying a motorcycle as a foreign national, but I suspect it can be done. You also need to insure it for the time it will be in the US. You might be able to get some good answers out of the online help agent that some insurance companies (like geico.com) have. Keep in mind that all the rules will change from state-to-state.

If you want to have the pink slip (title) for the vehicle, you usually get it in the mail a week or two after the purchase. This might not be a major issue though, and you can always have a scan sent to you in email and color printed in a major city. I don't believe it's necessary for Central America at least, although I have color copies of mine just in case.

Insurance: Insurance is something that must be done country-by-country. Some countries (eg US, Mexico) require it and some don't. Your US insurance isn't good in Mexico, your Mexico insurance isn't good in Guatemala, etc. In some cases (US) it'll be much cheaper to get insurance only for the short time you will be in the country (and unfortunately you can't register the bike in California without proof of insurance). In some cases (Mexico) it's only a tiny bit more expensive to get insurance for the whole year. I used Baja Bound Mexican Auto Insurance - Travel Safe in Mexico! for Mexican insurance, and will figure out each additional country when I get near the borders.

Heated gear: I left for parts south in December and froze my ass off in the high deserts of Arizona, even with my heated vest and wearing everything I own. Northern Baja was also pretty cold. I've found several occasions to use the heated vest in central Mexico, although I've removed the liner of my jacket. It's much easier to turn the vest on and off than it is to stop and add/remove clothing to suit the current temperature. Also, despite best intentions, you will find yourself occasionally riding at night (ie, you just spent your last two hours of daylight fixing a flat). I'd bring a vest but heated sleeves, socks, gloves etc are overkill.

Immunizations: My doctor only gave me Typhoid, Polio, a Hepatitis A/B booster, and a prescription for Malerone, but I'm not going farther south than Panama on this trip.

Power sockets: I don't think the KLR has a socket (usually BMW-type, I've never seen a bike with a cigarette lighter) stock, but they're easy to add. I hardwired my GPS cradle but charge my other electronics (laptop, phone, cameras) when I sleep in hotels. Haven't had a problem yet. Keep in mind that (like my KTM) the KLR and DRZ alternators are anemic and you have to be a careful with draw... I can't use my heated vest and heated grips at the same time.

Good luck! I will look forward to your trip report

Jeff

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SF to Panama and back
How I Nearly Killed My Friends In Baja