Hello all,had my 85 k100 a month or so,bought with a running fault,had to replace the air flow meter,that cured it,been running about on it,last used it around a week ago,it was fine when I put it away,took it out yesterday,did around 50 miles,when on the 'A' roads/motorway at speeds of 50/60/70mph+,everything ok,but when I got on the 'B' roads,slowing for bends etc,it started to feel as though I was in the wrong gear,prior to yesterday it would pull away smoothly from 30mph in top gear,it just felt lumpy and lurching,could it be a mixture problem?Cant understand why it didnt do it before!! Any ideas anyone? Would be most grateful,cheers,Colin.

Sounds like a petrol problem... I feel quite well that the bike becomes very lazy with the 92E, whereas with 98E it's like a fire...

30 mph is too slow speed for top gear.

Turn the gears up with engine running not less than 3000 rpm and you'll feel your bike better.

I do the following:
I gear - 0-20 mph
II gear - 20-35 mph
III gear - 35-45 mph
IV gear - 45-60 mph
V gear - 60->

I concur with Vudis regarding 98 Octane as that is what it was designed to run on and you will also need a lead substitute I believe.
3000 revs is also about spot on as that translates to about 80 k's on my bike where it pulls like a train.

So could definitely be a fuel problem either bad fuel or a clogged filter etc. It could also be something totally new like a vacuum leak and also ignition faults also show up when the engine is under load.
Fuel problem is quite easy in that get a fresh tank with no ethanol and from a reputable garage and go from there.

Thanks guys,understand where your coming from re speed and gears,but up to yesterday it was fine with my style of riding,They are quite torquey after all,have been told it could be throttle position sensor??This would result in the symptoms ive got,juddering and lurching,anyone know how to test it????

Oh, besides I heard that k100s, with VIN up to >25000 need leaded fuel. Not sure if it's true. But if it's true, you should look for a lead substitute. In Lithuania I saw Wynn's additive for older vehicles, where one of main components is Potassium instead of lead.

But for me it sounds like either a clogged filter or bad fuel. But at first try Tesco or Shell 99 RON fuel (or at least BP Ultimate) and see if it made a difference. If it not - change your fuel filter first.

As I said, my k100rt becomes very lazy with 92E fuel and it changes radically with 98E... Like a shift from Cessna to Tu-144

If you are going to use a lead substitute, try Castrol Valvemaster Plus. It comes in a nice handy 250 ml "squeeze up" bottle that you can carry on the bike. It also gives an octane boost to the petrol. We used to use it in the old Hillman Avenger rally car and never had a problem with it. One bottle will do 250 liters of petrol.

normanmarina wrote:Thanks guys,understand where your coming from re speed and gears,but up to yesterday it was fine with my style of riding,They are quite torquey after all,have been told it could be throttle position sensor??This would result in the symptoms ive got,juddering and lurching,anyone know how to test it????

The motor only works well above 2500-3000 rpm because the torque curve just kicks in. I can only use 3rd or 4th gear to cruise around the build up areas and need to be in the 3rd to pull away with any urgency.

As for the TPS, yes, it will cause lurching as you suggested. To test, simply unplug it. It will cause no harm. As your system is L-Jetronic the TPS is used only to switch the injectors off at low speeds and/or enrich the mixture at full throttle. As your style does not include full throttle often, the only effect you will have is a smoother bike at low speeds.

Try it and see.

Thanks guys,you are a good bunch,refreshed the tank with higher grade go juice+lead replacement,fine!!!!!!Thanks,Colin.

Btw, do the 1984 k100s have fuel injection?

All K-bikes have fuel injection.

Avenger GT wrote:All K-bikes have fuel injection.

Though I wait for someone to graft a pair of Weber 48IDA carbs onto a K-100. With velocity stacks facing to the sky! Would look awesome... and could probably be made to work.

BadjerJim wrote:

Avenger GT wrote:All K-bikes have fuel injection.

Though I wait for someone to graft a pair of Weber 48IDA carbs onto a K-100. With velocity stacks facing to the sky! Would look awesome... and could probably be made to work.

I asked that question once and sparked off a long discussion about pros and cons of FI and Carb systems. I must say now that I ride a 1975 Goldwing and a K100 I tend to lean towards FI.

Cabs are simple, but hard to control and hard to tune and synchronise. FI is technically more complex, practically simple and when going well (not hard to do) FI is fantastic and great when the weather is cold and things are hard to start. Shorter warmup makes things a pleasure ...

However, I hate to have the pump stop or pressure drop... it is dead duck
With carbs at least you can limp home.

Low revs will ruin the cylinder coating ... keep your revs up matey.
Ajays