Hi all, have just taken ownership of a great custom built trike (1996, Gaz's custom shack), doner bike K100RS?? (1984 engine, 1985 frame) numbers to follow. Runs pretty well but would like some more grunt, runs out of steam around 80-85. Hope you all can help me improve on this and any other problems that may arise.

Welcome to the forum.

That's an interesting build you have there, glad to see its got some weight forward too.

The K has a lot of torque when its running right, so a check on things like injectors being clean, throttle bodies balanced, clean air filters can be a help. Check out the section on the home page on what to do if you have just bought a K.

One thing though, the stock exhaust is in fact one of the best and in many cases a change of exhaust actually costs power.

You can tweak the final drive ratio by installing a K75 final drive, but on a standard 84/85K it needs a drive shaft change as well and possibly some other bits.

Having said that not so sure I would fancy 90mph on a trike......80mph limit is printed inside my K for riding with panniers on!

Flash Trike, What rpm does it do at the 80-85 mph, maybe a tweak or two in the final drive.

There's three cheap things you can do to get a bit more grunt out of it:

1. Check and reset the valve clearances (if necessary and it possibly is)
2. Advance the timing by four (4) degrees
3. Swap the throttle bodies for K1100 ones (search the forum).

If (1) needs doing, it will provide the most boost, believe it or not! It can also improve fuel consumption. I also recall RickG saying that it's acceptable to advance the inlet timing by five (5) degrees but I'll let him confirm that.

Is the backend on the trike a hardtail, t-tail or IRS?

Hi guys thanks for the generous comments, as I said its a complete custom from Gaz's custom shack heres some more technical info, the axle is from a releiant robin (diff 3.2:1) as against the bikes (2.8:1) a 15% decrease in speed if you like for same rpm (lower gearing), as the rims and tyres have the same rolling diameter as the bike, then this should help cope with the extra weight and drag, I am not necessarily looking for more speed but the ability to sustain it, on m'way inclines I am wide open to maintain 70-75 mph without changing down (which I haven't tried yet, suicide shift LOL.). I am considering modding a spare standard system in line with caferacer62's post once I clarify which variant he decided was best, along with that I am considering a small air scoop at the leading end of the intake duct as I have no fairngs to accelerate the air for cooling and intake. I think tappets, etc are ok but will be fitting nearly new plug leads as mine are shot as i have a idle misfire some times, is the 4 degree advance to allieviate the retardation used by the rev limiter, many thanks. Yes it is a hardtail currently running 12 psi rear and 18 psi front all car tyres, any advice

caféracer62s  exhaust mod was pretty good sounding ...when fitted up to a chair - rig

cant confirm if there was noticeable improvement in torque though

if your up in the 6 k revs area trying to maintain a 70 mph speed ...I would seriously have a look at why this is so ..this is where those engines shine in a glorious fashion ....mechanically - electronically the spark leads will make a difference at developing good engine torque at higher revs ...also please check the ignition coils ...many have been found to be open circuit on the secondary = high voltage side (but still working ) but surely the ignition process would suffer from losses if this were the case ....probably unnoticeable if this is the only k you have had experience with ..

valve gaps also very important for  good torque

change the spark plugs for new ngk d7ea  (don't forget to find the thimbles that fit to the top of the plugs )

and if possible pull the muffler and observe the colour of the pipes internally ...that could provide a good clue as to the efficiency of your typical riding style   ( you may observe if its running lean on a particular cylinder )

we all want to see a good operating k bike ...in any variation that we can think of

cheers