Ok, so here I was at a set of lights leading to an onramp to the HWY on my way to work. It’s a 150m straight with a nice smooth turn onto the HWY. As mentioned, I ride this way to work every day and It’s my little bit of ‘fun’ if no cars are around. A HD sportster pulls up next to me as the lights go green. Somehow he gets just enough in front of me to make it into the turn first. Usually this wouldn’t phase me at all, as my ‘racing days’ are over. But this was my little stretch…, yes I know I’m not riding an R1 anymore and I’m happy with my K’s overall performance. BUT somehow this is still bugging me 2 days later.

So, what practical options are there to squeeze a bit more out of my beloved brick?

• ·         K&N air filter?
  
• ·         Different exhaust?
  
• ·         Injectors?
  
• ·         Fuel pump?
  

Yes, I can ‘Ride’ and no I don’t want to turbo charge my bike; just pre-empting some responses.

There is not that much that can be done without getting a bit radical.
A K&N filter will do nothing because the air restriction is at the MAP (air flow meter) sensor.
Exhaust is probably about as good as it gets. Staintune found it very difficult to match the standard pipe let alone make it better but they do sound much better.
Injectors and pump are as good they can be and you wont get any improvement by playing with them alone.

I have never played with a K100 to get more power other than tweaking what is already there but the first port is usually as with any engine a bit of port work and some better cams.

One thing that is often overlooked with the more modern ignition systems is keeping them in good order. Because they throw such a good spark they will work when the coils and earths and plug leads arent at their best. A big improvement can often be had by just making sure the individual components are in good order.

If you really like playing then Mega/micro squirt is the way to go and get rid of a very outdated and obsolete EFI system.  https://www.diyautotune.com/shop/megasquirt-assembled/microsquirt/?osCsid=8458fd523cc226b1d9a5c672b65b0329
I would say at a concervitive estimate the K100 engines would be quite capable of producing 140 to 150 HP if you use a modern engine management system but as always good horsepower doesn't come cheap.
First time I came across the L-Jetronic system was in the late 70s on some Kawasakis

You could advance the timing by 4 degrees if you haven't already...

Or, if yours is an 8 valve, K75 pistons have a higher compression ratio.

Not sure what it gives by way of extra performance or how it affects the power curve.

Unfortunately you can't do much with the ratios to change the gearing, short of changing the final drive to a K100RS and even then the difference is small. You can do the reverse and put K75 final drive which is a lower ratio on a K100 to improve acceleration but again not a huge difference. Even a K75 gearbox doesn't change it a lot.

However I suspect changes like that would take from the nice K100 experience.

Maybe console yourself with the thought that the HD had used one of its 9 lives and will soon be dumping parts on the highway wile you ride past with a smug smile.......

hmm  ill bet you were doing the usual things like changing up at 4 -5 k  
lets be realistic ...the k doesn't start breathing till about 3 k ...so why cut it short ...they love it above 6k
the Harley wont rev far above that figure at all  in fact its run out of torque about then and its on the way down ...yes the harly will kill you for the first 50 meters ...till you get out of 1st gear safely without killing the second gear dogs ....that when it all comes good as the momentum of bike lifts and the torque curve and revs are in your favour without the mass of weight it has to get going from nothing .

typical 1/4 mile times for a lot of Harleys sportsters are in the high 11s  to low 12s ...unless its a vrod design ....those things are like lightning ....but an good condition k100 with rt-lt bevel box gearing  should be a little better than an rs in short tight runs and torque ..  I think I read some where on comparative tests conducted by impartial parties  the k was in the high tens ....

the real stunner  is when the harly runs out of revs ....and we sail past ...upwards of 150 kph

I'm reminded by that dufus jerremy Clarkson ,,,who questioned the 0 to 100 kph of some American muscle car

best he could manage was at least a second or more behind the claimed times ......the advice from the company  was simply ...why change up ?

then he tried their advice ...and bingo ...exceeded their claim ....

a lot of time is lost changing gears and with no real syncromesh box in place  even more applicable on the k

I have ported old gerty ...just removing the sharp and odd curves in the inside and outside radiuses of both inlet and outlet ports ...and yes they are quite sharp angles along the short radius before it hits the valve seat ....with some other mods like 4 hole injectors and slightly higher fuel pressure

seat of the pants judgement as to benefit is minimal at higher revs above 4 k ...but in the 2.5k to 4k region  has more grunt  ..but often find myself being caught up marginally around corners by fellow k riders ...in a lower gear but higher revs ......yes they know the strengths ....but my feeling is I can leave them ..and I have, if I choose to ...not like a k1100 16 valve  with all the better suspension and engine characteristics etc .. but a significant improvement  none the less .

no advanced ignition yet ...and no mods to airfilter ...but a retrograde adjustment to afm to try and maintain fuel,  economy ....if left the same on the afm  definite increase in fuel useage and torgue big time ....infact the snorkel air feed becomes a significant restriction at lower revs ....chuck it !
still looking into advancing velocity through the system at that 2.5 k region  with a dual tuned intake resonance modification in the designing stages ...but the cam profile is restrictive for that torque curve,  being so large in duration ...maybe a tvis enabled cam timing might help at the lower revs  but that's a lot of engineering ....far simpler to go to after market efi control perhaps ?

better check ben kinghams posts about efi etc ....or his website  bskspeedworks, also note he has a lot of gear box issues  first to second at 120 hp

just  some thoughts

 







you just have to get used to the strengths and deficiencies of every bike,  I believe to do justice to your own pride ....

One more important thing. Weight; why belly up to the buffet table for a second go when you're prolly full enough already? The bike, too, can lose a few kilos.

I did wonder about making a weight reduction comment....but my imagination figured on bricks being thrown at me.

The comment on changing up too soon is good. Not long after I got the K100LT I was passing a car on a hill not far from me and wrenched the throttle to overtake. I got a bit of a shock, it happened so fast I closed it again and saw the speedo just dropping off the ton. MPH clocks. But I did let it rev and yes it felt very rev happy.

Shade of Jekyll and Hyde, below 4000rom its nice, torque is good, all nice and smooth. Above its like a different bike, very fast, very responsive and a reminder of the two strokes we all had back before the Ks came out.

I did two things on mine: advanced the timing by four degrees (thanks Rick!) and fitted a set of K1100 throttle bodies. SOTP says it's kicking out four, maybe five more BHP than standard i.e. I felt the difference and standard wisdom has it that the rider's backside can't feel less than a four bhp increase. If it's a K100RS then retrofitting the standard K100 bevel drive will also get you a bit more kick (lower gearing).

Is it worth it? Dunno, but it's fun doing it!

Also, screwing the nuts off it in third gear definately helps. Mine does 60-90mph in minus three seconds. Well, it feels that way!

My red RS, the previous owner, a BMW mechanic who imported the bike from Germany into OZ, had the rev limiter removed. Of course this only makes a diff at high rpm, but combined with K11 TBs, timing advance, a Motad can and keeping her churning, makes the 'red rocket' a potent weapon when urged.

On a lonely NSW road a few years back I closed on 255 kph (indicated) after a flying kilometre or so. Ten grand plus of revs with no significant drop in apparent pull...we do know that it's not necessary to spin the engine this high and it will drop off after a while.

They go alright with a few basic mods.

I looked into all of this when i had the k100rs.
Have a look at this - answers all your questions
http://www.ibmwr.org/ktech/dyno/index.shtml

Best (and cheapest) bang for buck was timing advance by 4 degrees.  The bike sang above 6000 rpm.
http://www.ibmwr.org/ktech/k-bike-ignition-timing.shtml

As others have said, k&n does nothing.  It has been run on a dyno with standard air filter half covered with cling film (saran rap) - no difference to hp.

Different exhausts have been tried - some reduce hp, and none increase it much - and cost a lot.

One other small thing is to improve the ground/earth wire.  Get a big fat wire from the battery to the earth bolt under the tank. This might help the ignition/spark as the electrics aren't doing as much work.

As always thanks for all the tips and info Guys. There are some things that I'll definitely have a closer look at. Trust me weight reduction isn't one. The bike has shed as much weight as it can (Click on the 'Heisenberg' link in my signature) and I'm about 80kg on a 'fat day'.   

Changing up to early has never been a character trait unless my wife in on the back. Dialling back the ego a little is something that may require further investigation.

In addition, I'm now 100% certain that the Sportster had a stage 4 kit on it.

Thanks again.