1981 GSX1100 Katana Based Project

[Shin-Ken 1074]

With you on?

Not yet!

The running tally numbers are for dry weight which is fine however, there is no fun with no fuel!

After test rides to check fuel consumption it works out that 13 litres of fuel gives a range of 219.375 km. Using those numbers I can reduce the fuel load from a full tank of 21 litres down to 13 litres and still have enough fuel to have fun for a few hours.

So why do these fuel numbers matter for the project? Less fuel is less weight as well as lowering the centre of gravity and both of those are a good thing to make for fun riding.

The take away from the reduced fuel load is knowing how much fuel I need for a total riding (curb) weight for the Kat and not carry extra fuel that isn't needed.

So as of today the riding total weight of the Kat (without me aboard) is:

199.864 kg

Riding a sub 200 kg 1981 Katana fitted with an EF 1135 engine has transformed my riding experience to a level of enjoyment I didn't fully understand could be possible at the start of this project! The result so far is beyond all my expectations and although this has been a long, expensive and at times a very trying build to find solutions to reducing the weight I can say, hand on heart it has been worth the effort, no doubt what so ever!

I believe there are still some areas that can be modified to reduce the weight further so there will be updates in the future. I am still thinking about installing the Mikuni 38mm flat slide carbs but that is a job for another day.

[Rob S.]

No one has offered an opinion on this, but this may be right up your alley. My '82 11E doesn't have a center stand, so that's good for weight savings. But, if it did have one might not the center of gravity be lower?

Not a huge difference either way, but as someone who's weighing every tenth of a gram, I thought you might have an opinion. I think it's better off without the center stand, as the lowering of C. of G. with it, if any, would be imperceptible.

[Shin-Ken 1074]

No one has offered an opinion on this, but this may be right up your alley. My '82 11E doesn't have a center stand, so that's good for weight savings. But, if it did have one might not the center of gravity be lower?

Not a huge difference either way, but as someone who's weighing every tenth of a gram, I thought you might have an opinion. I think it's better off without the center stand, as the lowering of C. of G. with it, if any, would be imperceptible.

I don't know the weight of an 11E centre stand but a Kat centre stand with bolts, bushes and spring is 2,330 grams so the centre stand is long gone from the build. The centre stand is the lowest bit of hardware (not including wheels) so its effect on the C of G would be minimal compared to having that weight up around the bars, clocks and fuel. Someone here may have the correct answer to the stands effect on C of G but it isn't me.

[Shin-Ken 1074]

Took the Kat out today to test the modified (lighter) seat pad for a two hour ride and so far so good. The new seat pad is smaller in area and 26mm thinner and has lowered the riding position. Although the seat pad is thinner the ride was very comfortable and in fact is more comfortable compared to the previous seat pad with the higher sitting position. I didn't think lowering the sitting position by 26 mm would make such a difference to improving comfort as well as improving handling with the change to the riding position. In this case changing the ride to suit the rider has turned out well even if the reason for the change was to reduce weight with no consideration for improved comfort and handling.

[Shin-Ken 1074]

Now that the Project is a going concern and is performing well, there is now time for some tweeking to shed some grams here and there when any excess weight is identified. There is no bar buzz being generated throughout the rev range so the bar end-weights can go as well as cutting 20mm off the clip-ons to lighten the bars. My guess is around 140-160 grams will bite the dust, will know the answer this weekend after surgery.

[Shin-Ken 1074]

Have removed the bar weights and cut 20 mm off the end of each clip-on.

Barweights 20mm off cut by Max Mutarn, on Flickr


Running tally = 199.724 kg

[Shin-Ken 1074]

Next thing to go on a diet will be the mirrors. Right now the Kat is fitted with genuine Suzi mirrors and being genuine they are a quality part however, that quality includes weight. I found a set of used Barrac mirrors with aluminium stems, compared to the OEM steel stem these should be lighter than what I have now, fingers crossed. Barrac also make these in carbon, lighter but expensive!

The mirrors should arrive in a few weeks with the rest of my parts order.

Barrac Mirrors 1 by Max Mutarn, on Flickr

[Shin-Ken 1074]

My factory mirrors.

Mirror factory by Max Mutarn, on Flickr

[Shin-Ken 1074]

While I am waiting for the mirrors to arrive and see what they weigh, hopefully less than OEM mirrors, I had time to fit the volt meter today. Made the bracket last week and left it over the weekend
for the paint to cure. Adding weight is the opposite to what this build is about however, my electrical adviser strongly suggested that a volt meter is a must have to monitor a lithium battery. In our riding group several lithium batteries have failed with three of them popping the cases and luckily not catching fire. The cause was over-charging and the bikes did not have volt meters fitted so the owners had no way of knowing there was a problem until there was a problem. Found a light weight volt meter that fits under the engine temp gauge and doesn't look too over the top on a vintage Kat. The running tally is jumping up a few grams today.

volt meter 4 by Max Mutarn, on Flickr


volt meter bracket 3 by Max Mutarn, on Flickr


volt meter 5 by Max Mutarn, on Flickr

Running tally = 199.800 kg.

[Shin-Ken 1074]

The mirrors arrived today, 773 grams total for the pair. I was hoping they would be lighter having aluminium stems so this will take a bit of work to make them lighter. If I can get them down to 600 grams that will be just over 30% lighter than the OEM mirrors so that means taking 87 grams off each mirror. Not keen on drilling holes in the stem so it will be changing the profile of the stems to lighten them.

Mirrors before mods.
Mirrors 1 by Max Mutarn, on Flickr

[Shin-Ken 1074]

Update on the mirrors, the stems are cast aluminium and not forged aluminium so drilling or thinning down the stems may weaken them. For now the mirrors will stay as supplied and not be modified however, because they are wider than "Old School" Suzi Kat mirrors I can now see in the mirrors without "Katana Elbow" so that's an improvement and the new mirrors look sporty so two wins.

To align the right mirror with the left mirror I had to make a bracket to position the mirror forward of the mirror mount on the bar.
Mirror 5 by Max Mutarn, on Flickr


Mirror 6jpg by Max Mutarn, on Flickr

[Shin-Ken 1074]

The muffler that had been used for the build decided it didn't want to be on the Team and threw in the towel, the titanium inlet parted company with the can flange. I found a pretty decent used carbon and stainless muffler to replace the damaged titanium unit and installed it today. Sounds good and looks good so all is good!


muffler b1 by Max Mutarn, on Flickr


Muffler b2 by Max Mutarn, on Flickr


Muffler b3 by Max Mutarn, on Flickr

[Shin-Ken 1074]

I scored some used carbon parts on the weekend so a few more grams to be shed once they are installed. Also having a set of machined aluminium mirror mounts made to replace the current set that just look wrong as well as being heavier than they need to be. Pics of carbon parts and mirror mounts will be posted here when they arrive.