Good evening knowledgable people!  So I had a late season run out today on my K100 that has been spot on after my sprag clutch and rear main oil seal(replaced twice!).  Bike started first time after about 6seconds and I held it on the fast idle for 20-30 seconds.  I then set off for my 'Exercise' in these covid times and noticed that every time I slowed down for a junction and then went to accelerate it was like I was riding a bucking bronco for a split second as I put the throttle on, I wondered if it was because I was in too high a gear so started dropping further down the box to third and second but no real difference.  The bike was also when running between 50-80mph and going off the throttle backfiring, the first time I thought I had gone past a farmers field where he was shooting a shotgun!! Ha Ha. 

Then when I came to a total stop the idle droped to about 800rpm as if it was going to cut out but didnt, when I finally pulled over and was getting off I decided to leave it running, as soon as I lent the bike onto its side stand it went to perfect idle and everytime I straighten it up it slows down!!  I am totally confused and wondering if it is someting electrical??  Any pointers welcome.

How much fuel in the tank?  

Is the fuel pump solidly in it's mount?

Is fuel leaking from any of the hose connections in the tank?

Point-Seven-five wrote:How much fuel in the tank?  

Is the fuel pump solidly in it's mount?

Is fuel leaking from any of the hose connections in the tank?

It was 50% full but I stopped and filled up on my way out, did 97miles on it.  No leaking fuel connections and the fuel pump is less than 6months old, yes its solidly in its plastic mount.  It runs great as you wind it on just really strange as you come to a stop and slow down or as I said put it on side stand and speeds up 300rpm ish!

You seem to be describing the symptoms of a vacuum leak. While the engine is idling, check the condition of the throttle body vacuum port caps, the fuel pressure regulator vacuum hose, the vacuum throttle switch hose connecting to cylinder #1 if the previous owner didn't disable that switch, and all the rubber intake manifold bushings by directing propane around them and listening for a change in revs. A change in revs means a leak in that component.

Is the tank connector making good, reliable contact?

Laitch wrote:You seem to be describing the symptoms of a vacuum leak. While the engine is idling, check the condition of the throttle body vacuum port caps, the fuel pressure regulator vacuum hose, the vacuum throttle switch hose connecting to cylinder #1 if the previous owner didn't disable that switch, and all the rubber intake manifold bushings by directing propane around them and listening for a change in revs. A change in revs means a leak in that component.

Thanks i will try the propane tmr morning in case something has moved, I restored this bike in the last 24 months and it has had all new rubber parts/hoses, new vacum caps etc and until today was pretty fine. Mine is a 1983 model and it had that switch that was connected to an electronic circuit enricher or something that was around the back of the inlet rail and I disabled that.

Point-Seven-five wrote:Is the tank connector making good, reliable contact?  

yes I checked all the connections, wobbled it around and no changes.  I will get it on centre stand tmr and go back to basics, will get the propane torch gas and see if it any leaks i am not aware of.

When you lean it the other way is it still good?
When you lean it the other way with the engine off and filler cap assembly removed, you might see water or crap rush over to the right side.

Edit: I got mixed up, I thought you said it ran bad on the side stand and good when upright, but you actually said the opposite.

2 It did actually remind me of the odd block prob. When you changed the pump did you use disposable gloves, and might one have dropped in the tank?

wilbo wrote:

Laitch wrote:You seem to be describing the symptoms of a vacuum leak. While the engine is idling, check the condition of the throttle body vacuum port caps, the fuel pressure regulator vacuum hose, the vacuum throttle switch hose connecting to cylinder #1 if the previous owner didn't disable that switch, and all the rubber intake manifold bushings by directing propane around them and listening for a change in revs. A change in revs means a leak in that component.

Thanks i will try the propane tmr morning in case something has moved, I restored this bike in the last 24 months and it has had all new rubber parts/hoses, new vacum caps etc and until today was pretty fine. Mine is a 1983 model and it had that switch that was connected to an electronic circuit enricher or something that was around the back of the inlet rail and I disabled that.

I also have 83 K100RS and it has that pipe at the front to the vacuum sensor, yes you can disable it by simply removing the vacuum line at the front of No 1 and using a 4th vacuum cap in its place. BUT that sensor does have a massive effect on my 83RS, it advances the ignition timing....... My 84 K100RT has it too and I capped it off but I have tried the 83 RS on and off. 

You also need to really look at the petrol tank plug. It's very very high on the list for an intermittent disconnection and you need to sort the pins to make it a good firm electrical contact.

As a side note I have 3 Ks [83 RS 84RT and 96 K1100] running every day and they take turns. All 3 are suddenly in the last 10 days running a bit crap. Monday last week I got the first issue on the K1100 just assumed it might be some issues as I only had that one 2 weeks. Decided Saturday I might take a look. So Tuesday took the RS out, but it had the same issue. Next day the RT the same too. They all got fuelled up around the weekend before. My money in my case is there is bad petrol about. You guys are sending petrol over to us so you might have similar issues. A friend of mine is a petrol station designer and he has also said that due to petrol stations not turning over stock there are condensation and stale issues and because of falling prices stocks are deliberately run down to the crap.

I am aware that I have a pick up position issue in the RS, it runs out at 14 litres or about 140-150 miles. PO replaced everything in the tank so its good but not correctly fitted. For that reason alone not thinking its water as I had previously drained the tank. Just bad petrol.

83 Ks have the early push to release tank cap, check its ok and check the drain pipe on the left side of it, use a length of pipe cleaner to slowly rod it through. If you are refurbishing brake calipers early K kits for K bikes don't fit 83 calipers even though the calipers look the same, needs the ones off the R bikes.

maybe try cruising at about 40-50 miles an hour and see if it holds a good steady pace , without surging 

that same issue i have seen on more than a few k bikes , replacing the fuel pump solved the issue 

also check the tank electrical connection for any signs of burning the contacts , or simply feel the connector after running the bike for any heat , when the fuel pump gets faulty they can draw heaps of current 

good luck

Check that the both fuel hoses aren't crimped over were they go into the tank. non OEM hoses are more prone to crimping over and high temperatures further exacerbate the problem.
Regards Martin.

92KK 84WW Olaf wrote:
As a side note I have 3 Ks [83 RS 84RT and 96 K1100] running every day and they take turns. All 3 are suddenly in the last 10 days running a bit crap. Monday last week I got the first issue on the K1100 just assumed it might be some issues as I only had that one 2 weeks. Decided Saturday I might take a look. So Tuesday took the RS out, but it had the same issue. Next day the RT the same too. They all got fuelled up around the weekend before. My money in my case is there is bad petrol about. You guys are sending petrol over to us so you might have similar issues. A friend of mine is a petrol station designer and he has also said that due to petrol stations not turning over stock there are condensation and stale issues and because of falling prices stocks are deliberately run down to the crap.
.

Not only do the petrol stations have stale petrol, but this time of year the ones around here are switching from the "summer blend" to the more volatile "winter blend". If sales are slow, there still may be a bunch of the "Summer" stuff in the supply line. That stuff could be causing "drivability" issues as the weather gets a bit cooler and wetter.