So I have a friend who dropped off her k75 café conversion. It fires no problem and will idle though it sounds weak compared to my K100 (also a cafe).

The issue is as soon as I touch the throttle it will die.

Having combed through mine with you guys help over the years, I started with the obvious, fuel pump and fuel filter. I figured the fastest way to rule these out would be to swap hers with my tank. I did, same thing. That rules out the fuel pump, filter, and lines inside the tank. There aren’t any vacuum leaks (no cracks in the hose or vacuum caps.

I just pulled the injectors to test them next. 

Does this apply to this situation?

And this?

Start with checking the fuel pressure.
Bad temp sens gives too much fuel.

MikeisonTV wrote:And this?

Getting the sensor off means taking off the radiator. But if you have a spare good one you could plug that in [the connector is accessible] and earth it against the engine block to try it out.

If you think that it idles weakly then pull/inspect the spark plugs.

Is there a way to test the Fuel pressure regulator? Should this dirty throttle body be a concern that would play here? (Green circle)

Can I access the temp sensor by the removed air box as seen here? Not sure what it looks like and realoem.com doesn’t pull up the sensor on a search. Any one have a location of it?

MikeisonTV wrote:Is there a way to test the Fuel pressure regulator? 

Testing the Fuel Pressure Regulator is by seeing if it maintains the pressure it should. Insert a tee piece between the tank outlet and the fuel rail and attach a pressure gauge to the tee side outlet. (You can also do this between the fuel rail and the FPR, but its harder to get at.)

With engine running, it should read about 36psi, with small variations as throttle is opened or closed due to the vacuum line going to the FPR.

If the engine isn't running, when you push the starter button the pump activates and you should see your 36psi. Worst case scenario, you might have to press the starter twice, but if it doesn't get up to 36psi on one press there are questions to be answered. Without a running engine, you won't see the minor variation on throttle change.

Ideally, after the engine is turned off or the pressure has been correct on a starter button press, the pressure should be maintained for a significant time.

Bill

MikeisonTV wrote: I started with the obvious, fuel pump and fuel filter. I figured the fastest way to rule these out would be to swap hers with my tank. I did, same thing. That rules out the fuel pump, filter, and lines inside the tank. There aren’t any vacuum leaks (no cracks in the hose or vacuum caps.

How did swapping your filter and pump into her moto's tank—or swapping your tank with her tank—rule out defective lines in her moto's tank? Did you swap the hoses, too?

Which vacuum hose has no cracks—the fuel pressure regulator vacuum hose or the crankcase z-hose?

That crankcase breather hose does not look correctly seated at the plenum chamber port, does not look like a OE hose

Looks like a crack in the rear of #2 throttle body rubber bushing under/inline with the "518" on plenum box

volador wrote:That crankcase breather hose does not look correctly seated at the plenum chamber port, does not look like a OE hose

Looks like a crack in the rear of #2 throttle body rubber bushing under/inline with the "518" on plenum box?

This!


I found this hose coming off the crankcase that I think is supposed to run to the bottom of the tank. It is screwed closed.

Laitch wrote:

MikeisonTV wrote: I started with the obvious, fuel pump and fuel filter. I figured the fastest way to rule these out would be to swap hers with my tank. I did, same thing. That rules out the fuel pump, filter, and lines inside the tank. There aren’t any vacuum leaks (no cracks in the hose or vacuum caps.

How did swapping your filter and pump into her moto's tank—or swapping your tank with her tank—rule out defective lines in her moto's tank? Did you swap the hoses, too?

Which vacuum hose has no cracks—the fuel pressure regulator vacuum hose or the crankcase z-hose?

I switched my entire tank and outside fuel lines. I thought doing this would isolate the fuel problem as I assumed it was fuel filter, or pump, or line in-between without taking apart 2 systems twice. Just a time saving move on my end.

Don't worry about this. It's fine with a screw in it.  The reason it is there is to vent fumes from the tank to the block.  It's CA emissions crap that keeps ten molecules of gasoline from venting to the atmosphere.

Meant to report that k75 got sorted and “runs better than it ever has!” The owner was so thankful to have her bike smooth and performing. So thank you guys for all the input

MikeisonTV wrote:Meant to report that k75 got sorted and “runs better than it ever has!”

What was the remedy?