improve my honda c70(passport) mpgs

[nickeastwood]

in a month i will be riding my 1981 honda passport from nyc to columbia sc. I was interested if anyone had some tips on how to improve some mpgs on this weird little bike. So far i have replaced all bearings, and went for a lower viscosity oil. I live in nyc so i'm not interested in changing the gearing due to traffic or any type of fairings because those will probably get broken from parking in the street as well. So far it looks like my only options will be skinny over inflated tires. anyone have some quick tips for me?

[Grant-53]

A tune up is always a good idea before a long trip. There may not be time for a valve job and head planing. A inexpensive front fairing such as one made from coroplast or sheet aluminum could be fashioned to come off the bike easily for storage inside. The same could apply to a tool box or duffle behind the rider. Start with tire inflation 10% higher than rated to see how the bike handles. Comfort and safety are paramount. Some riders put a piece of duct tape across the bottom of their visor to act as a sun shield when the visor is up. Only light, rounded luggage on the front rack such as a sleeping bag. Consider using the bike route option on the computer mapquest program.

[bschloop]

If you are carying luggage on your road trip. A tail case will be better than panniers. You could even build an aero trunk without too much trouble. Just start your trunk the same width as your body, and taper it toward the rear. At the least this will allow you to carry your stuff without hurting your mileage. Tires are going to make little difference on the open road, as a bike suffers from such horrendous aero, but they may help in the city at lower speed.

[theicecreamman]

Lessee, ceramic wheel bearings, Microblue coat the chain, blow the engine apart and Microblue everything, add a set of Total Seal Gapless rings, ceramic coat the piston, combustion chamber, exhaust system, freer flowing muffler and air filter. Ride carefully.

[Superfuelgero]

Gearing will help too. Choose a sprocket that will keep the engine in its sweet spot for the desired speed. Other than this (and the recommendations already made), that's a long ride, look into a throttle lock, comfortable riding gear and a seat cover.

[nickeastwood]

Sounds light higher compression may be the only way to be able to get my gearing taller. Right now the bike is geared about as tall as it could possibly pull. I don't see how a less restrictive exhaust and filter would help. I'm used to working on small two stroke bikes so this is all fairly new to me. Also I have adjusted the valves cleaned and gapped points and set valves. It's running as good as it possibly can at the moment

[renault_megane_dci]

What's preventing your engine from pulling taller gearing is your aero.
But at a C70 speed, is it already that paramount ?

I don't know about NY but I can't think of a well integrated fairing being broken just for fun in a civilized country ...
Obviously not the same for cardboard and duct tape attempt ...

I'm all for engine tuning but to be honest there is not much efficiency hidden in a motorbike engine ...
Front fairing is your best bet money wise.

You need to offer least resistance to air and position is important.
Think racing moppeds.

[Ironside]

I don't see how a less restrictive exhaust and filter would help.

Take my advice, dont mess with non standard air filters and exhausts, unless you have access to a wideband AFR meter it will never run properly. Honda knows best.

I agree with Grant-53 re. tuneup, it might help to advance the timing by 2deg (a no cost option and worth a try), and a small screen at an acute angle can add as much as 5mph to your top speed.

I don't think you will see much better than 100 miles per US gallon without some radical changes.

[renault_megane_dci]

One can use the calculator to try and find some improvement for a given speed.
I didn't spend time on it but I fear you might find yourself in a configuration where is is not fast enough to see gains from aero improvement given the weight penalty

[renault_megane_dci]

Did my homework out of curiosity.

Reducing Cd from 0.9 to 0.45 in the calculator brings a 83 mpg @ 40 mph vehicle to 151 mpg at the same speed.
I didn't change anything else and focused on a low speed.