The Tech Zone => Mods & Maintenance => Topic started by: HotPursuit on July 06, 2019, 05:40:14 pm

Title: Trying to extend fuel range
Post by: HotPursuit on July 06, 2019, 05:40:14 pm
I done multi-day trips on the Magna before, because it was the only bike I had, but the bike, as it's currently configured (15T main sprocket instead of 16T stock) barely gets over 100 miles on a tank.  I'm consistently having to switch to the reserve tank at 80 miles.  When it comes time to replace the chain and sprockets again, I'm going back to the stock gearing, but even when I was running the stock gearing before, I still didn't get more than 130 miles on the tank even with that gearing...  Going up to a 17T I think is too tall and going to bog the engine down too much.  Playing around with gearing calculators seem to confirm this.  When I had the bike on the stock 16T, I felt the gears were a good match to the power curve of the engine.  Going down to the 15T with the last chain replacement was more of an experiment than anything, I definitely did not get the extra scoot that I expected for the loss of fuel economy sustained.

I'm also debating having a fabricator enlarge/widen the gas tank to as close to 5 gallons as possible (or maybe fabricate a new tank entirely?), bringing the tank size closer to the Interceptor's, of which I get between 180-200 miles per tank.  I understand also that fuel injection is more efficient than carburetor engines, but I'd really like to be able to take the length of trips on the Magna that I've been able to on the Interceptor.  I've had too many close calls of running out of gas in the middle of nowhere on the Magna, and I'd rather not use my luggage rack space to carry a fuel can if I can help it.

Ultimate goal is to get the Magna to reach around 150 miles on a tank.

Thoughts?  Anyone else have any other ideas?

Title: Re: Trying to extend fuel range
Post by: Blue is Best on July 06, 2019, 09:37:36 pm
Gas tank size? Is the bike tuned up sharply? I know you are in the high desert and if you really don't get to sea level you can rejet the carburetor. Every 1,500 higher feet go down one jet size. Seems like the bike should get 42 to 50 MPG when cruising.

Title: Re: Trying to extend fuel range
Post by: HotPursuit on July 07, 2019, 06:10:56 pm
With the stock jets (102s I think) and stock gearing, I used to average about 35-40mpg.  The previous owner put straight pipes on it.  I replaced the stock air filter with a K&N filter with the regularly scheduled oil change, which only exacerbated the infamous "lull" just before 5k rpms.  At that point I had larger jets (108s) installed to match the intake and exhaust for most elevations, based on the carbjetkit recomendation.  I've ran it through the Rockies and San Diego without issue.

Surprisingly, I didn't lose any noticable amount of fuel economy from the jets (but it did help the torque curve flatten out).  I did have to switch from 87 octane to 89.  When I changed the gearing, that knocked my mileage down to about 30mpg.

I've read in Magna specific forums that 17T front sprockets help with highway fuel economy, but can't find a whole lot about how that gearing affects the bike in more technical roads.  With the 16T, I found myself downshifting to pull out of corners fairly often, whereas the 15T I almost never have to downshift.  After checking rpm/speeds on a calculator 17T seems to put the bike a little too low in the power band  than I think I'd be comfortable with, especially on the freeway.  I might just need experiment with the 17T just to see how it feels, the extra downshifting might be worth the potential fuel economy.

I've seen guys attach marine fuel tanks as well to their luggage racks, and install/modify the petcock so they essentially have a main tank, aux tank, and reserve, and easily pushes the bike up to 6 gallons of fuel, but then I'm back to using luggage space for fuel.  That's how I came around to the idea of enlarging the main tank.

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Title: Re: Trying to extend fuel range
Post by: zer0netgain on July 07, 2019, 09:04:24 pm
Any chance of finding a larger capacity tank compatible with your bike?

Title: Re: Re: Trying to extend fuel range
Post by: HotPursuit on July 08, 2019, 03:13:53 am
Any chance of finding a larger capacity tank compatible with your bike?
Closest I've seen is someone who cut the mounting base from a Magna's tank and had it welded onto either a Shadow's or an Interstate's tank.  The dimensions work for steering clearance, but the Magna doesn't seem to share the same frame as any of Honda's other cruisers.

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