1985 K100RS

[MM K100]

Hello Motobrick,
I'm new here, looking for some help.
I just brought this K100 to do some exterior modifications.

A couple weeks ago the bike was starting with no issue and it was running. However, once i drove over 5000rpm the bike started bogging down. added new fuel (octane 93) with a fuel stabilizer.   

Last week I went to try and start the bike and couldn't get it to start. It cranks well but doesn't catch.
I just installed a New Battery and New Spark Plugs.
I also hear the fuel pump humming.

Any advice?
I also tried this video below.  But didn't help.


Thank you
MM
 

[Laitch]

Welcome, MM! Your Brick was starting and running before it refused to run, so that video is unlikely to apply.

The simplest approach would be to disconnect the fuel line where it's attached to the fuel rail, point it into a bucket then crank the engine to determine if fuel comes out of the hose at strong pressure. Be careful that you don't light up the Brick or yourself by splashing fuel or misdirecting the hose out of the bucket. If there's pressure at the rail, refit the hose then crank the engine a few times, remove all the plugs and tell us whether they're wet or dry.

Another simple approach begins with removing the fuel cap assembly: to view the condition of the tank, to determine the condition of the fuel hoses, to verify that the hoses are clamped securely, and to determine the condition of the pre-filter at the bottom of the fuel pump. Replacing the fuel filter should be done if you don't know when it was last replaced regardless of whether fuel was being delivered with sufficient pressure at the rail.

[frankenduck]

Have you checked the fuel filter? If you remove it and try to blow through it in the then air should flow freely. If it is is clogged then replace it with a NAPA 3032 fuel filter.

[The Mighty Gryphon]

+1 on the fuel filter, it isn't unusual for bikes that sit a long time to plug the filter in a short time after being used again. 

If, after you change the filter, the bike still won't start get some starting spray and shoot some into the airbox above the air filter and try starting.  If the engine fires, it says you have a fuel problem.  If it doesn't fire with the spray it means you have no spark.

[MM K100]

Thank you everyone, I will try as recommended above.
Looks like I have plans for the weekend.

Will update after the weekend.

Best,
MM

[MM K100]

Gentlemen,
Here is the update, and wow was I surprised when I opened up the fuel tank to change the fuel filler.

So I’m going to leave my bike builders/ mechanic’s name out of this.
I still can’t believe it but they had left a bunch the green painters tape inside the tank.
After syphoning out all the gas, I removed a bag full of tape. 🤦🏻‍♂️
After that, I removed the old Fuel filter and changed it with the new one as recommended. Added the gas back into the tank.
Cranked the starter… no go.

Moving on, I started to remove the clamp from the fuel line at the rail. As soon as I started to wiggle the fuel line I received a high pressure of fuel spray. (Without cranking the starter) Tighten this fuel line back up as I figured I’m getting fuel to the rail.
As I sit here typing, I’m thinking can I have a blockage at the rail? Perhaps the reason I had so much back pressure?
Cranked the starter again…. No go.

I didn’t know how to get ether into the air box so I tried a quick spray from what I think was the intake.
Gave it a crank along with the choke, and she turned over, started and died. I can’t keep her started.

Let me know what you guys think.
I’m going to try and post some pictures as well.
Thanks in advance for the support.

MM

[MM K100]

Pictures attached

[The Mighty Gryphon]

I suggest that you go back and step by step trace the fuel from the pump to the return to the tank for any blockage.  Break each connection and run the starter to energize the pump.  Confirm fuel flow and move on to the next connection.  Be methodical, who knows what may be hiding in the fuel system.

[Laitch]

Were the plugs wet, or were they dry after cranking?