I've got a 1985 8 valve K100RT.
It's just started misfiring on the over-run. The effect is that I'll close the throttle, coast or brake. When I open the throttle again the engine runs on three for a bit and then kicks in. I've just done the obvious and pulled all the plug caps. Number 1 had a white powdery deposit inside. I've not had a chance to run it since - could I have fixed it or is there something else I should be checking while I've got the toolbox open?

If you have an ohms readable multimetre, check the resistance of each HT lead and compare their readings. 5K ohms is the usual (if OEM) resistance but see if any are well off that mark. It's a place to start.

Just want to add to the info allready given by GITH about the 5K ohm resistor at the plug cap, that it also is a 1K ohm resistor at the coil end.

As an aside, check that you have the little screw on caps on top of your spark plugs, I had a white powder in my lead caps because there were no screw on caps on the plugs. Running was awful.
RT

Might also be worth checking the TPS (Throttle Position Sensor) it may have been disconnected by PO - do a forum search for Throttle Position Sensor

RT wrote:As an aside, check that you have the little screw on caps on top of your spark plugs, I had a white powder in my lead caps because there were no screw on caps on the plugs. Running was awful.
RT

hard to tell from the information given ...but "rt" is spot on ...the ngk and some other brands dont come with furules installed these days ....champion and a few others do ....but you shouldnt see the white powder in the connection to the plugs or the actuall connection points (coils and plug tops) they should be clean and shiney ....if not ...make it so .

hope you find the issue and enjoy the ride ...cheers !

charlie99 wrote: they should be clean and shiney ....if not ...make it so .

This is how they should look like:

aye inge ...good pic !

You can't fool me Inge, that has to be a brand new one.
Otherwise mine still are shameful.
RT

I bet your toothbrush tasted horrible after that,Inge.

Paul.

+

+1

Thanks for the ideas guys. I cleaned the plug caps and plug tops and it made no difference. Since the problem occurs when I close the throttle, I'm now looking at the fuel injection and the throttle position sensor.
As an aside, aren't HT leads a ridiculous price? I looked at a well-know parts supplier and they are quoting £18 each for second-hand leads. Has anyone tried making their own - using parts from say, Vehicle Wiring Products? (See http://www.vehicle-wiring-products.eu/VWP-onlinestore/htterminals/htterminals.php)

tps ...yes ...but also check for vacuume leaks paul ...rubber hats over take offs ...throttle body rubbers , plenum to crankcase ...etc ...dont forget the oil filler is screwed up and sealed

funny Paul I had the same view on them being over priced... £30 each from the main suppliers...

this place have got them for far less... RAM HT Leads

€41.75 each ......or is that for a set?

88

Poor running and backfire on trailing throttle is something my 1985 K100RS just began to do. I've traced the problem (I think) to intake leaks, but I'm mystified at what to do about them. I'd just recently replaced the rubber bits between the TB and plenum chamber. To do that, I coated the parts to be joined with silicon grease and after much cursing and tool throwing, everything went together. 1,500 miles later, there's leaking again. So, what's the solution?
I've never heard that it's necessary to glue the rubber connectors to the TB and plenum. Should I? When I fitted the new rubber connectors, I examined them to see if there was a top and a bottom -- could find no indication of that. At present the hose clamps are as tight as I can make them, visually, all the pieces seem to mate as closely as is physically possible, yet the idle speed jumps up when I spray electronics cleaner around the connectors! What else can I do to make the intake trace leak-free?
Anyone have a clue?

Hi, I think the rubber parts that connect the plenum to the bodies have two diameters I believe there are two sizes of clamps as well.

Top clamp: 50mm, bottom clamp: 48,5mm.

I dont know if you could put the rubber parts on up side down or not , but when I did mine, I did not even consider there was a difference till I orderd the parts.

88KE wrote:€41.75 each ......or is that for a set?

88

I think/hope it's a set.... not been brave enough to phone them up yet!!!

"€41.75 each ......or is that for a set?"

It's a set. I purchased a set of those leads and they are excellent. Not a problem at all.

owwww would that mean if I buy a set I won't be expected to clean up my old ones?!

Swapped out the plug leads for a better but second-hand set and it runs like a charm.

Of the original set, the leads for cylinders 1 and 3 showed no continuity at all on my meter. That would be why it was mis-firing, then.

Thanks for all the suggestions.

I just love happy endings

On my K100 I used the non restive Blue silicone leads and resistive plugs which still did the same job but heaps cheaper NGK DR7EA instead of D7EA