Bigbore kit for xs1100?

[TADracer]

What He Said

So as a power-adder, a big-bore really won't add much power (a few HP) unless you also improve the breathing, and things like a professional ported head and aftermarket cams are definitely not lo-buck. Very careful tuning is the best path to power on a budget, with particular attention paid to ignition timing, both initial timing and the timing curve.

I reiterate what Crazy Steve said above. Remember that the things you add/change alter the balance of a fine machine from the factory. Add a header, you change the balance....add pods, you change the balance, and so on and so on. Most external mods change the power curve to higher RPMs where you will never use them on the street/highway, making for most of the common complaints like 'my motor bogs until 4,000' or there is a big flat spot in lower RPMs'. You will get the most 'bang for the buck' doing smaller tuning things. I have been tinkering with my XS since 1980 and the three biggest 'bangs for the bucks' I have done to my 79 Special are slotted cam sprockets, mild head porting and a carb swap.

If you have a bit of shop capability, a drill press, degree wheel, dial indicator and TDC locator you can slot your sprockets and tune your stock cams to help bring the power band back to a more useable range. Most of the effect will be gained adjusting the intake cam and the exhaust has little effect.

Concerning the head, if you have a die grinder and a few stones/burrs along with an accurate burette you can port XS1100 heads yourself on a workbench. The runners are somewhat restrictive and in the intake runner there is a large ramp cast in just in front of the intake valve that can be smoothed and shaped for better flow. The exhaust runner is very small and can be widened out a lot. Give your valves a 30 degree back grind and that will have the effect of opening up the seats a lot. This can be done with a drill press and a small grinder jigged up on the drill press table. Use the 'quarter rule', that is if you remove more than the amount of metal from a runner that exceeds the size of a quarter then you probably took out too much. Port match your intake runners to the manifolds and open the exhaust runner to a diameter that is about 1/8" smaller than the exhaust gasket. Even your runner volumes using a burette and some tinted rubbing alcohol but, leave the combustion chambers alone! You can feel the difference in performance but remember, whatever you do here is not reversible.

Swap your carbs for some from a 1999-2002 Kawasaki ZRX-1200. Pretty much a plug and play deal. Do a search on this site and you will find out a lot about this.

Will all this give you 10% more horses? Nope. Will you feel the difference in performance? Yes you will. What these three changes can yield (providing you are willing to do the tuning dog and pony show once a year) is a machine with better than average performance that holds a good tune for a long time and has power that can be dialed in to come on at 2,500 RPM instead of the usual 3,500 RPM, no stumbles or flat spots and can get over 40 MPG.

Works for me!

[James England]

Personally, I like to put green Dyna ignition coils on bikes too.....

[mrbsyammy]

I reiterate what Crazy Steve said above. Remember that the things you add/change alter the balance of a fine machine from the factory. Add a header, you change the balance....add pods, you change the balance, and so on and so on. Most external mods change the power curve to higher RPMs where you will never use them on the street/highway, making for most of the common complaints like 'my motor bogs until 4,000' or there is a big flat spot in lower RPMs'. You will get the most 'bang for the buck' doing smaller tuning things. I have been tinkering with my XS since 1980 and the three biggest 'bangs for the bucks' I have done to my 79 Special are slotted cam sprockets, mild head porting and a carb swap.

If you have a bit of shop capability, a drill press, degree wheel, dial indicator and TDC locator you can slot your sprockets and tune your stock cams to help bring the power band back to a more useable range. Most of the effect will be gained adjusting the intake cam and the exhaust has little effect.

Concerning the head, if you have a die grinder and a few stones/burrs along with an accurate burette you can port XS1100 heads yourself on a workbench. The runners are somewhat restrictive and in the intake runner there is a large ramp cast in just in front of the intake valve that can be smoothed and shaped for better flow. The exhaust runner is very small and can be widened out a lot. Give your valves a 30 degree back grind and that will have the effect of opening up the seats a lot. This can be done with a drill press and a small grinder jigged up on the drill press table. Use the 'quarter rule', that is if you remove more than the amount of metal from a runner that exceeds the size of a quarter then you probably took out too much. Port match your intake runners to the manifolds and open the exhaust runner to a diameter that is about 1/8" smaller than the exhaust gasket. Even your runner volumes using a burette and some tinted rubbing alcohol but, leave the combustion chambers alone! You can feel the difference in performance but remember, whatever you do here is not reversible.

Swap your carbs for some from a 1999-2002 Kawasaki ZRX-1200. Pretty much a plug and play deal. Do a search on this site and you will find out a lot about this.

Will all this give you 10% more horses? Nope. Will you feel the difference in performance? Yes you will. What these three changes can yield (providing you are willing to do the tuning dog and pony show once a year) is a machine with better than average performance that holds a good tune for a long time and has power that can be dialed in to come on at 2,500 RPM instead of the usual 3,500 RPM, no stumbles or flat spots and can get over 40 MPG.

Works for me!

Lots of great info, I have built many performance engine car wise so will that equipment work on cycles? I have everything you mentioned but for car engines? And as I stated I do have an extra xs1100 engine short of carbs so that's my Ginny pig per say. I have well over 10,000 cycle parts here but mostly Honda so that sucks..lol Oh! I forgot I also have an 80 xs1100 bike too so I'll leave mine pretty much alone except for minor things and would it be the best to use the 79 xs engine instead of the 80 or wouldn't that make that much difference? 79 is better correct? Hell I have little to no money in the 80 and the 79 engine was free so even IF I make a catastrophic mistake I won't be loosing a lot of money and if I don't have what I'll need for any type of machine I have a friend that has about any machine you can think of and would enjoy helping me for cheap. So again this has to be more labor then money on this project. I'm going out and replace the head gasket on the 79xs so any little things I could do like whats the best timing on a pretty much stock engine short of 4 into 1 exhaust K and N filter that's it.?
Till then and Thanks again Mr.Bill