Hello All,

I have a 1992 K100 here that owner says hasn’t run in at least 2 years.  When I drained the old gas, it reeked that unforgettable old ethanol stink.  I installed a brand new battery, bike now cranks over just great, but doesn’t fire.  I pulled a spark plug, all new, checked for spark, and there is a good fat blue spark.  I also have installed a new fuel filter.  I’m suspecting I’ll have to clean the entire fuel system, including injectors.  However, is there anything else any of you can suggest could be an issue?  Thank you in advance.

Side stand up?

duck wrote:Side stand up?

You should be hearing the pump prime for a couple of seconds when you turn the key to On if the side stand is up. Here's the relationship—faulty side stand switch function, no fuel.

If the pump is running, try shooting some starting fluid into the air box above the filter when cranking the engine.  If the engine fires, the problem is in the fuel system. 

If not, it could be weak or no spark, or lack of compression because of stuck rings.

No Compression

Beyond that, you need to check for leaks in the fuel tank or sticky injectors.

Dang!  Maybe that’s it, the sidestand is DOWN.  I’ll give that a check.  However, the bike cranks like a champ, just doesn’t fire.

Wirelic wrote:Dang!  Maybe that’s it, the sidestand is DOWN.  I’ll give that a check.  However, the bike cranks like a champ, just doesn’t fire.

That it cranks was made clear in your first post, Wirelic. What it is now is cranky. The side stand could be up but its switch could still be faulty so determine if the fuel pump pumps when the engine is cranking.

This video references one of Point-Seven-five's comments.

Well, duh, I’m so dumb.  I put the sidestand up and the bike fired right up.  Thanks!  Helps to ask an expert.

Wirelic wrote:Well, duh, I’m so dumb.  I put the sidestand up and the bike fired right up.  Thanks!  Helps to ask an expert.

Don't feel so bad.  The guy who works on my bikes is a real knucklehead, but still, somehow, manages to keep them running.

Wirelic wrote:Hello All,

I have a 1992 K100 here that owner says hasn’t run in at least 2 years.  When I drained the old gas, it reeked that unforgettable old ethanol stink.  I installed a brand new battery, bike now cranks over just great, but doesn’t fire.  I pulled a spark plug, all new, checked for spark, and there is a good fat blue spark.  I also have installed a new fuel filter.  I’m suspecting I’ll have to clean the entire fuel system, including injectors.  However, is there anything else any of you can suggest could be an issue?  Thank you in advance.

You dont say what model so we dont know if it is a 2v or 4v enginre. 92 can be either, I have a 92 K100LT but they are 2 v engine.

2v engine does not have sidestand switch and fuel pump does NOT run when you turn on the ignition. Only when you press the start button. You need either neutral light on or pull clutch as there is en electrical switch on the clutch lever on all Ks. 

4v engine fuel pump will prime when you turn on ignition, provided you do above AND have side stand up. There is a switch on it. If you put bike on centre stand with side stand down, turn it on and then retract side stand you should hear the pump [you also need neutral light or clutch pulled for this too].

You may well have gummed up injectors, fuel filter or fuel pump. Check the connections on the fuel pump relay too. If in doubt swap horn and fuel pump relays and try again. Also check the plug into the injection control unit under the seat.

This bike is a 1992 K100 RS.  It cranked, but didn’t fire with sidestand down.  When I followed advise from others here and put the sidestand up, fuel pump activated and bike fired right up.
I do appreciate very much the replies I received here.  Thank you all.  I do yet have to rebuild the rear brake master cylinder, then bled the system and it has ABS.  Any suggestions on doing the bleeding?  As you know, the manuals just say, “take it to a dealer”.

Shitcan the original rear master cylinder and replace it with a ChiCom unit you can get on eBay for under $20.  There are threads here and at MotoBrick.com that explain how to do it.  The job takes about 2 hours and there are many who have successfully done the swap. 

The Commie m/c actually works better than the original.  You can actually trigger the ABS with it, and even stop the bike with just the rear brake, which is something the original never could do.

Bleeding the rear is pretty simple.  The hardest part is putting the reservoir in a spot where you can easily top it up without it spilling brake fluid on the bike. 

Put a hose on the bleeder fitting and let the fluid run into a bottle(I use a gallon jug half full of water to make it harder to knock over).  Do the ABS modulator first, followed by the caliper.  Press and release the pedal s-l-o-w-l-y, the distance from the reservoir to the master cylinder makes the fluid reluctant to flow.  It shouldn't take more than 15 minutes to do the job.

Point-Seven-five wrote:The Commie m/c actually works better than the original.  You can actually trigger the ABS with it, and even stop the bike with just the rear brake, which is something the original never could do.

You can stop any K bike with just the OEM rear brake disc or drum brake. You can also lock up the rear with either brake system or, in the case of an ABS bike, cause the modulator to kick in.

The OEM m/c is still a piece of overpriced sh*t. 

After 30+ years the bore is corroded and the seals are worn so in most cases won't generate the hydraulic pressure to lock up the rear wheel.  Paying $300 for new or $125 to rebuild is the definition of stupid when you can get a perfectly good replacement for $20 from the Commies.