K100 cuts out

[Barrieb]

Morning Guys,

so I went for the 1987 K100LT, but still having problems with initial running.  Here are the symptoms:

Bike fires up on choke and runs for about 5-10 minutes then cuts out dead - you cant restart for about 5-10 minutes after.  just before it cuts out it does sound like it is struggling and idle is not quite smooth, but when it stops its as if it has been turned off.

Today I restarted after about 10 minutes and initially hesitant it did pick up and ran what i would call reasonably up to the point the fan kicked in, so quite warm.

The bike was bought with the previous owner believing it had a Hall Sensor fault and came with a brand new unit - now fitted
I also found a blocked petrol tank breather pipe - I mean completely blocked off, so that was sorted
Airfilter was bad so that was changed
New plugs and usual service, Oil, filter etc

I did check there was a good spark after it stopped running and there was

You can hear the pump running when it should and that sounds ok

Not sure if this is relevant, but battery was initially suspect, but is holding a charge and showing 12.87 volts with the bike not running, but only 11.8 when bike is running? I thought that would be higher not lower??  I'm not happy with the speed at which the battery cranks the engine, this may not be related, but what should the minimum recommended cranking amperage be for a K? as the batteries on offer vary wildly

I cant take it for a test run, until I get an MOT Ticket and tax on it (UK police a not busy at the minute LOL) and I dread the idea of it cutting out while i'm riding.

The engine sounds sweet and the bike is only showing 23K - which matches all the way back to 2000 -however we all know these bikes do not like sitting

oh and i did my first successful water pump rebuild, so good news there and splines are spot on 

My thoughts are fuel, but i have reached limit of my knowledge, grateful for any suggestions.   Love this bike and wanna get her out on the road.

Thanks guys

 

[Laitch]

New plugs and usual service, Oil, filter etc

Does this mean the fuel filter, the oil filter or both?

[Barrieb]

Hi Laitch,

Both

Forgot, I also did the fuel filter and cleaned out the tank of all old fuel, but it was spotless in there.  I didn't take out the pump to check the gauze filter due to the good tank condition, no deposits and all nice and shiny.

could it be the fuel pressure valve or vacuum pipe connecting to the throttle body? 

Bikes been looked after in some ways with new and insulated fuel pipes

[frankenduck]

If you suspect the battery might be getting old then you need to get it load tested.  A voltage of 12.xx V is good but that doesn't tell you how many amps it can put out when starting.

The best way to load test a battery is to take it to an auto parts store and ask them to load test it for you. At least in the US they do it for free because it gets you in the store to buy stuff.

You can also perform a crude load test at home. Go to Step 3 at this link:
https://www.batterystuff.com/blog/how-to-tell-if-your-battery-is-bad.html

If you run the bike up to say 2000 RPM then the alternator should run the voltage up to something in the 14.0-14.2V range.

[Laitch]

I did check there was a good spark after it stopped running and there was

Was that at every spark plug? Was each spark plug wet or dry? When the engine is idling, open the fuel tank cap and see if there's fuel returning to the tank.

[Barrieb]

I did only check plug number 1 and stupidly did not check if it was wet (back to basics for me!)
I've got one of those flaps in my tank (must be a US thing, like i cant turn the bloody lights off! bike was an import from US in 1991 only 2 owners since new)
will look for the post on how to remove, i've never looked in the tank while bike is running, i take it its an obvious constant flow?
The vacuum pipe to the pressure valve does have a bit of cracking, but on sucking to return fuel before removing tank its not taking in air
Battery:
I did that load test and got a reading of 9.6 right on the minimum!
with the bike running at 2000 rpm could only get 13.5 at the battery
Battery is off now and i will get it load tested tomorrow, even though its holding voltage, i think it has sit around discharged (like the bike)
In case i need a battery:
I've seen wildly varying battery CCA EN (cranking Amps)
1. Gel AGM 20Ah  CCA 95A
2. Wet Lead Acid 28Ah  280 CCA
3. Sealed AGM 21Ah 230 CCA
Never had a problem with sealed AGM will 21Ah and 230 CCA do?
What i will do tomorrow:
Load Test Battery
Remove tank Flap
Prep for spark test on each lead
Run Bike till/If cuts out
Confirm fuel is returning to tank
Sparking on all 4
Plugs are wet after cut out
Any thoughts guys?  and thank you

[frankenduck]

Never had a problem with sealed AGM will 21Ah and 230 CCA do?

The Odyssey PC680 (a popular battery in the US) is a 16Ah/170 CCA Sealed AGM and works fine in Ks so I think that'll be fine. (As long as it fits in a K.)

The gas cap flap makes no difference.

If you have the cap off then you can tell if fuel is returning.

My bikes have 50A alternators that put the voltage at 14ish.  13.5 may be fine for the 32A alternator. If the charge warning light in the cluster goes out when the bike is running then you should be fine.

[caveman]

Barried,

Sounds like your on the right track, so I don't have anything to add but good luck.

Duck,

I like your new avitar but it looks like you used $3.16 of lube when most BMW owners use 32 cents worth! I'm somewhere in the middle.

[Barrieb]

Morning Guys,
I got the battery checked and its way down on its expected 300 EN Cranking power, so will get that replaced.  Now the good news!
I set everything up to do the checks - decided to loosed up the petrol cap completely, so i could see in properly.
Bike fired up great as usual and ran for longer this time and only cut out after choke was fully released (it was warm enough)
But this time the bike fired up straight away - so i couldn't do the checks.....argh!
I often use a headtorch when i'm working close up on a bike as it helps focus on specific areas.  Having a look around the area where the vacuum pipe goes to the Pressure valve, I noticed a break in the crankcase breather pipe, moved it slightly and the engine died.  So i proved it by disconnecting the pipe from the Plenum Chamber (think its that) and covered with my finger - bike ran perfect. removed finger and bike ran rough then died.  Tell tale was a very small amount of oil in the area

I'm confident replacing this will fix the problem,  I guess as the pipe warmed from the engine the hole opened up, doesn't fully explain why the bike ran on after fully warm, but lots of different facts could contribute.
New Crankcase Breather Pipe: £15 ($20) happy days!
All the cooling pipes are good, Fuel pipes have already been done, but i will check everything else that might have perished over the last 35 years
Thanks Guys, will post soon
Barrie



 

[frankenduck]

One thing to check for during your shakedown is leaks in the boots between the throttle bodies and the cylinder head. Something not uncommon as these bikes age.

The most obvious symptom is if one or more cylinders won't balance easily when you attempt to sync the TBs.

Another way to check is to use an unlit propane or butane torch to spray gas around the boots with the bike idling. (Using appropriate fire safety precautions of course. Do it outside, no open flames nearby, etc...)  If the idle goes up then you have a leak.