I have a 1989 K100RT that has done 60000 miles. I acquired it in January 2016 when it had done only 46000 miles (5 years sitting in a garage unused!). It ran well for about 10,000 miles then started to develop an issue at start up. It would need the 'choke lever' on for a good 10-15 mins of running but once warm would run great. I have replaced the fuel filter, fuel pump seal (old on was perished to bits) and all fuel pipes in the tank and outside. I also replaced the slit crank case breather tube and the coolant temperature sensor but the problem persists. in fact it is much worse now as although the engine starts straight off, after about 15 seconds, the idle drops off even with the 'choke lever' on full and the bike runs really rough with clunking noises from the engine. If I give it some gas and hold at about 1500-2000 rpm, it runs ok but if I try to set off before its warmed up then I have very little power. Once warmed up, the bike runs fine accept some times when i drop the throttle back to stop at a red light for example, the bike will cut out. At other times it idles fine at 1000 rpm. 

My plan was to inspect and clean the injectors and the throttle bodies and all air intakes but wondered how easy it was to do this. Also thought about checking the coils. Again, not sure how to do this so if anyone has any advice, I'd be very grateful. Also, if anyone can think of any potential quick wins before i start digging into the guts, that would be even better.

I am not sure if it will help other than to give you something to do while the brain trust mulls your situation, but have you gone through all the electrical connections, especially the engine wiring harness? 

It can't hurt to clean them all with DeOxit.  Corroded electrical connectors on bikes that have sat for long periods can cause all kinds of strange problems. 

Best to eliminate that potential problem early on.

I would also throw a bottle of Techron Fuel System Cleaner in the tank and run it through the engine over the course of a week.  A good soak with that stuff has cleaned up a lot of junk I had in my injectors.  It made a major improvement in the idling of my K100 that had sat unused for over two years.

Point Seven Five makes a very good point.

When I was doing my K recently it had been running not very well. Pulling off the electrical connection at the throttle position sensor, beside the coil cover at the end of the throttle rail assembly the electrical connections were in poor condition and badly needed cleaning. One clean up later made a phenomenal difference. No disassembly of anything needed, just took the electrical plug out and cleaned it all up. Put it back in and wow. Its got to be a regular maintenance item every few months I think.

Thanks for the initial thoughts. I did try some fuel and injector cleaner in the tank but that didn't seem to do much. However, I have not tried cleaning all the electrical connections so will give that a go before going any further. Ill start with the throttle position sensor! Finger crossed.

In our sort of climate I figure a tank off once a year job and go at all the electrical connections and earths, open them up and clean them all one at a time to avoid any errors or loss of memory reconnections is worth it.

I usually look for a sunny day and park the bike on the patio not too far from the fridge and some good music! It's quite therapeutic and very worth it. Place to lay down the lower fairing panels and bits and pieces, run the fuel low beforehand so not much in the tank when you leave it down. An old car tyre is a great soft bed for the tank.

Thanks Olaf. You paint such a lovely picture I think I'm actually looking forward to the job now! Just need a sunny day at the weekend and all will be well 

I loved Monmouth, regularly travelled the M5 down to Wales. Nice place for an Eccentrics visit!!

Check if there are any leaks on the rubber parts of the intake system, sounds to me like it's getting extra air in there somewhere.

+1 on the rubber bits.  Somehow when I was responding earlier I thought you had already checked them along with the crankcase breather hose.

An easy test for leaks is to shoot a small amount of starting ether near the rubber bits on the intakes.  With a leak, the ether will be sucked in and the engine will speed up momentarily.

92KK 84WW Olaf wrote:I loved Monmouth, regularly travelled the M5 down to Wales. Nice place for an Eccentrics visit!!

I moved to Monmouth about 12 years ago and love it here. I get to commute down the Wye Valley road every day, really nice corners and views. The M4 and M32 into Bristol is less fun though.

Thanks fort he extra pointer RicK G and Point-Seven-Five. I have carried out a visual inspection of the rubber intake parts and can't see any obvious cracks but I will try the Easy Start spray trick to see if that shows up anything. Along with cleaning the electrics, hopefully I will have a better idea of whats going on by the end of the weekend.

I've experienced these symptoms and found that spark plugs needed replacing.
You can test them with a DMM from the terminal nut at the top to the centre electrode they should have VERY low resistance <0.5Ω. I've found they'll operate ok up to a few Ω but anything much higher and they start to fail. Rough running when cold. Long time to warm up. A fair bit of idle throttle to keep her going. And stalling at lights.
Cheers

Holister wrote:I've experienced these symptoms and found that spark plugs needed replacing.
You can test them with a DMM from the terminal nut at the top to the centre electrode they should have VERY low resistance <0.5Ω. I've found they'll operate ok up to a few Ω but anything much higher and they start to fail. Rough running when cold. Long time to warm up. A fair bit of idle throttle to keep her going. And stalling at lights.
Cheers

 Thanks Holister, I replaced the sparks a couple of months back but it made no difference. maybe I need to take a closer look at my HT leads?....

So I spent the weekend going over the bike, starting by cleaning all the connectors. Some were a bit gunked up but most were ok. I then proceeded to  test the resistance in the coils which for the high voltage terminals came out at 9.7 K ohms on each and for the primary coils the voltage was 3.6 ohms on both. This is not quite what is reported in the EFI/Electronic ignition troubleshooting guide on the postal  (12.6 k ohms and 2.6 ohms respectively) but Im assuming that since both coils are the same that they should be ok?

I then tested the resistance across the water temperature sensor ( new one fitted a couple of weeks back) are got  a resistance of 2864 ohms which seemed about right given that the test was done cold at an air temperature of about 15 Celsius. I also tested the old sensor I replaced and got a very similar value (thats £30 I could have saved!)

On testing the airflow meter pins I got some strange readings prior to cleaning all the connectors but after cleaning  got the following: 
pin 7-5: 93 ohms
pin 7-8: 348 ohms
pin 8-5: 368 ohms
pin 8-9: 213 ohms

All these readings fall comfortably in the range in the table provided in the troubleshooting guide so I am happy that these are all good (at leas now that I have cleaned the connectors).

I then had a look at the injectors. I tried cleaning following a you-tube video that suggested connecting a 9v battery across the injector terminals to open the valve then inject carburetor cleaner through. The first couple of times I connected the injector to the battery, I heard a click noise which i assume was the injector valve opening but after that there was no click on re-connection so I am concerned that this may have damaged the injector? I stopped trying to clean them at this point and re-built the bike but as I did not order new O rings and re-used the old ones, I could not get them to seal properly so had to abort and order new O rings. 

Son in conclusion, I have no idea f I have fixed the bike or totally knackered  it by blowing an injector. The O rings are due to arrive today Im keeping my fingers crossed that when i re-build it will all work.

Before I refit fit the injectors, is there any trick or advice for making sure I get a good seam on the o rings?....

Again, thanks for all the advise so far.

Rob, you seem to have looked at everything as you should but I wondered if the fast idle (choke) cable is adjusted correctly and giving the correct amount of lift to the TB's?

Just a thought, good luck.

Your injectors are likely to be okay - difficult to damage them with 9v. IME the best way to reassemble the fuel rail is to fit the injectors to the rail individually as new rings make it a bit of a push'n'grunt job. Make sure the retaining clips are fully home! - otherwise you'll be collecting high-pressure fuel everywhere except where you want it. Also, check and recheck that the engine block injector seats are absolutely clean, otherwise you'll damage or not be able to seat the new o-rings. They push home reasonably easily when you have the fuel rail to lean on. You'll know if they're correctly seated when you come to put the two screws back in the fuel rail as the rubber grommets should just about be brushing against the engine block.

If by some ungodly chance you strip the thread in the fuel rail spigots, there's enough metal there to put in a helicoil or an 8mm tap. It's not a disaster.

Motorbike Mike wrote:Rob, you seem to have looked at everything as you should but I wondered if the fast idle (choke) cable is adjusted correctly and giving the correct amount of lift to the TB's?

Just a thought, good luck.

Mike,

I'm fairly sure that the fast idle is adjusted correctly as its been in the same position from when i got the bike and it worked fine for almost 1000 miles. Some days it seems to run ok at start up and other days it stalls out with the fast idle on. I suspect that because ts worse on damp days that it points to electrics.

Dai wrote:Your injectors are likely to be okay - difficult to damage them with 9v. IME the best way to reassemble the fuel rail is to fit the injectors to the rail individually as new rings make it a bit of a push'n'grunt job. Make sure the retaining clips are fully home! - otherwise you'll be collecting high-pressure fuel everywhere except where you want it. Also, check and recheck that the engine block injector seats are absolutely clean, otherwise you'll damage or not be able to seat the new o-rings. They push home reasonably easily when you have the fuel rail to lean on. You'll know if they're correctly seated when you come to put the two screws back in the fuel rail as the rubber grommets should just about be brushing against the engine block.

If by some ungodly chance you strip the thread in the fuel rail spigots, there's enough metal there to put in a helicoil or an 8mm tap. It's not a disaster.

Thanks for the advice Dia. I will make sure I clean the injector seats before fitting. I read on the forum that coating the o rings in Vaseline also helps so will give that a go.

Vaseline... silicon grease is better as it's totally inert. If you've overhauled a set of brakes recently then use some of the brake grease that's supplied to grease the seals before putting them back in the calipers.

So I managed to fit the o rings tot he injectors this morning and re-insert and thankfully no leaks. I also had a really good check for ant air intake leaks and found nothing as all rubber parts look in really good shape. However, on re-building the bike, I still have the cold start and idle problem . On the positive side, I seem to have gained power when the bike is up and running on the road. 

If anyone has any further ideas on the idle issue then I'd be very keen to hear them.

rob_gordon wrote:I also had a really good check for ant air intake leaks and found nothing as all rubber parts look in really good shape.

Did that check include performing the running check using carb cleaner or propane around the manifolds' rubber bushings?

I am going to go outside the box here and ask about rechecking the inside of the fuel tank.

I am wondering is there something causing a sudden fuel starvation, such as fuel filter losing some pressure [remember the post about some old stock] or an issue with some of the connections on the intake pipe/filter into the fuel pump.

A lot of very important boxes are ticked off and even checking the fuel pump actually works correctly won't pick this up.

Laitch wrote:

rob_gordon wrote:I also had a really good check for ant air intake leaks and found nothing as all rubber parts look in really good shape.

Did that check include performing the running check using carb cleaner or propane around the manifolds' rubber bushings?

 Yes, I tried a number of time but there was no difference in the idle speed.

92KK 84WW Olaf wrote:I am going to go outside the box here and ask about rechecking the inside of the fuel tank.

I am wondering is there something causing a sudden fuel starvation, such as fuel filter losing some pressure [remember the post about some old stock] or an issue with some of the connections on the intake pipe/filter into the fuel pump.

A lot of very important boxes are ticked off and even checking the fuel pump actually works correctly won't pick this up.

I think checking the fuel tank is worth a shot because the old fuel pump rubber housing  was in bits when I replaced it last time round so the tank may have residual debris in it. Ill remove the pump and check the course filter to make sure there are no issues there. Thanks

another option  - Check your oil filler plug sealing "o" ring, is it there and in good condition, the engine can suck air in from there as well?

ungaas wrote:another option  - Check your oil filler plug sealing "o" ring, is it there and in good condition, the engine can suck air in from there as well?

The oil filler plug sealing is all good so no luck there. 

I am now seriously thinking buying a commuter replacement (tiger xcx) so that i can properly work on the RT. At the moment I rely too much on it so have to do any maintenance over the weekend but given that I have failed to find the fault, I suspect I may have to take a good deal more time over it.