87 K75 Dying in traffic

[Nothsaw]

'87 K75 here. Having some serious seeming misfiring often leading to the bike dying in the middle of busy traffic. Seems to have no issue at idle or when revved in neutral. Only while in gear and rolling. Twisting the throttle gives no response or rarely gives somewhat of a rev. Before I start just throwing parts at it I figured I'd ask if anyone knows some troubleshooting tricks to tell weather the issue is fuel air or spark related. Thanks in advance from a motobrick noob.

[Laitch]

First off, bring us up-to-date on that cranking issue you had back in this post and what solved it. Post its resolution—or lack of one—back in that thread. Following up on threads helps others who are looking for solutions. Ghosting doesn't. 

The simplest cause of your current problem would be a clogged fuel filter, a clogged fuel pump screen or damage fuel pump filter sock, and/or loose fuel lines within the tank. There are a multitude of other electrical or electronic sources for this condition—a corroded or loose four-pin fuel pump connection, loose spark plug and coil connections, a loose Jetronic plug connection, and others.

[Nothsaw]

Thanks Laitch. Forgot about my old post due to unrealated life issues. Going to attempt to remove the fuel pump and take a look at it over the weekend.

[The Mighty Gryphon]

+1 on what Laitch has said.  When was the last time the bike was serviced(oil change, plugs, filters, etc.).  Besides fuel, which is the first thing I would consider, how old are your spark plugs?  I ask because opening the throttle under load will increase the compression pressure in the cylinder.  An old plug will have trouble firing under pressure where it will fire fine at idle or in neutral.

If you can't remember when the plugs were new, spend a few bucks and replace them.  If you get NGK D7EA plugs, get some terminal nuts for the top.  You need them to get a reliable connection from the BMW plug wire.  If you don't have any nuts, you can usually get three of them at almost any repair shop, especially one that works on small engines(lawnmowers).

While you're at the auto parts store, get a new fuel filter.  The NAPA gold 3032 is a very good one. 
Then remove the filler cap, and before you replace the filter run the engine and watch to see if there is fuel spraying out of any of the connections.  Some dripping from the roof of the tank is okay, it's just the fuel returning from the regulator.  Is the inside of the tank nice and clean?  Is there a bunch of black goo all over the place?

After you check the connections install the new fuel filter.  Don't use the fuel line that comes with the new filter, it's not rated for use in the tank and will dissolve.  Use the old stuff and make sure the clamps are snug.  Then run the engine again and check for fuel line leaks before you replace the filler cap.

When you've done that stuff, get back and let us know if things are still not right.

[The Mighty Gryphon]

While what you describe doesn't necessarily point to it, the four pin tank connector is notorious for causing the engine to break up and die at embarrassing times.  You might want to take a few minutes to clean the contacts and make sure it is making a good connection.

[Laitch]

Going to attempt to remove the fuel pump and take a look at it over the weekend.

Do the simplest things first—inspecting and cleaning the four-pin fuel pump electrical connector at the right-side of the frame and the Jetronic plug. Check fuel flow into a bucket at the fuel rail when the starter button is pressed. Try not to ignite the moto by misdirection of the fuel stream.    Is there a strong, consistent stream of fuel? No? Remove the fuel filter. If you can't blow through it, it's probably clogged. The fuel pump should be firmly mounted. If it's rattling around in its holder, it can bottom out and reduce flow. Fuel lines need to be tightly clamped.

If there's still a problem then start removing components for inspection. Be methodical. Don't jump to conclusions. That's for us to do. 

[Nothsaw]

These are all great suggestions! Order new sparkplugs, needed to be done anyway. Will do some investigating and return results here.

[Nothsaw]

Actually just ran out to check the 4 pin connector. looks okay but there is a 2 pin connector that runs along side the 4 pin that has some pretty serious corrosion. Don't know if that connector is related in any way.

[The Mighty Gryphon]

It's probably for the speedometer sensor or the rear brake switch.  Neither has anything to do with your current problems.

[Laitch]

The two-pin is related in that if your motorcycle is moving, it will send a flow of electrons up the instrument cluster to let you know, if you're unable to feel the breeze. What "looks good" with the four-pin connector?

You've got a few other items to check. When you're finished with them, let us know what's up.

[Chaos]

Another possibility is water pooled in the bottom of the tank, it could stay put idling but get sloshed around when riding, and get picked up by the pump.  I had issues like that and a can or two of HEET took care of it.