Running lean, getting awful mileage; not sure how to fix. 1994 K75

Todd - I've been travelling, so I haven't kept up..

How did that work for you?

Very helpful, I think

This has been a great thread and is helping me with my fairly new to me K75RT. Rather than hijack the thread, I will post a related question/scenario for input from the experts that have encountered a similar situation. In the meantime, I will stay tuned to this thread.

deilenberger said:

Todd - I've been travelling, so I haven't kept up..

How did that work for you?

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Hey Don.

I went ahead and replaced the orings, top and bottom. Unfortunately that did not help at all.

Soooooo, I was FINALLY able to find my can of carb cleaner, as previously recommended, and saw that the vapor was not being sucked into the injector recesses but FROM the recesses under the intake manifolds.

So, I have a set of new intake manifolds on order from Chicago BMW (cost $100 less that my local dealer but I have to wait ~2 weeks). I'll be sure to post up once I get them on.

Seems like I am still having some idling issues. The bike still stalls on me when I let the RPMs drop from highway speeds.

I also noticed that my exhaust is leaking a good bit where the muffler meets the headers. Could that be the cause of any of my symptoms? I'll be getting the gasket on Monday.

Ok so I am STILL having idle issues. I took another look at my bike with the tank off and found the following wire disconnected. I took a look at the manual but couldn't figure out which one it was. It's Brown/Green (or Green/Brown)

Another pic

final pic

From the wiring diagram it looks like brown/green stripe is your oil pressure switch.

Ted said:

From the wiring diagram it looks like brown/green stripe is your oil pressure switch.

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Hmmmm, ok. I didn't see any warning lights on the dash.

Plugging it in didn't fix my issues anyway. I am definitely not getting enough fuel. I would say I could also be getting too much air but I have replaced all the rubber intake bits and test with carb spray and there was no change in idle speed.

My next step is to test fuel pressure.

Can anyone recommend a fuel pressure gauge?

Thanks.

Does anyone have any input to this pressure gauge:

http://www.egauges.com/vdo_ind.asp?Type=Mini_Pressure&Series=Mini_Pressure&PN=153-005

It doesn't say if it's for fuel or not and I don't want to assume that any pressure gauge will work as a fuel pressure gauge.

I don't know about the gauge to which you posted a link. You can find an inexpensive fuel pressure gauge at most auto parts stores, Sears, or off a pro tool truck. Almost all the ones I've seen will require a bit of ingenuity to connect to a BMW. Be warned that most aftermarket gauges will not be damped, so the pressure will appear erratic when the regulator is being affected by vacuum (at idle).

lostboy said:

I don't know about the gauge to which you posted a link. You can find an inexpensive fuel pressure gauge at most auto parts stores, Sears, or off a pro tool truck. Almost all the ones I've seen will require a bit of ingenuity to connect to a BMW. Be warned that most aftermarket gauges will not be damped, so the pressure will appear erratic when the regulator is being affected by vacuum (at idle).

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Thanks.

I ended up buying that one. We'll see how it goes. I just need to find a T fitting that will be compatible with the 1/8" bung off the gauge and the 8mm ID of the fuel injection hose.

I use the T from an Airhead fuel system.

lostboy said:

I use the T from an Airhead fuel system.

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I'm not familiar with Airhead models. Can you give me more specifics? A part number would be great too.

Do you have one mounted on your K? I would love to see some pics on where and how it's mounted. I still have to figure that part out.

toddlamp said:

Does anyone have any input to this pressure gauge:

http://www.egauges.com/vdo_ind.asp?Type=Mini_Pressure&Series=Mini_Pressure&PN=153-005

It doesn't say if it's for fuel or not and I don't want to assume that any pressure gauge will work as a fuel pressure gauge.

Click to expand...

Todd,

You need a guage that will go over 100lbs.. If there is a problem with the regulator, you could see pressures above 100psi. Normal reading is between 35 and 40 psi.

Get a cheap 160psi water pressure gauge from your local hardware store. Preferably with 1/4" threads.

Go to your car parts store (or hardware store) and get a BRASS 5/16" barbed T, a 1/4"
NPT x 5/16" barbed nipple, and a 1/4"NPT BRASS coupling. Also pickup 1' of Fuel injection fuel line and 4 hose clamps to fit the hose.


Remove the fuel line from the right hand side of the fuel rail, connect 1" of fuel line to the rail, then the tee, then reconnect the fuel line to the tee. Connect the gauge to the tee with the remaining hose. As previously stated, the pressure will rapidly fluctuate maybe 15psi because the gauge is not dampened. Not a real problem as you are only trying to see if it's in the ballpark. If the regulator has failed, it will be way off. If you're really concerned by the fluctuations, you can take a pair of pliers or vice-grips and slowly squeeze down on the hose to the gauge until the fluctuations are minimized.

This is for diagnostic purposes ONLY. You do not want to be doing a lot of riding with a cheap gauge hooked to your bike. Around the block is OK (but you would probably want to use more hose between the T and the gauge so you can strap the gauge on the dash pad.

Great info from Lee.. and a bit more commentary from me:

Removing the vacuum line from the rear-most throttle body and capping the port it connected to (the line goes to the FPR) will eliminate almost all the pulsing of fuel pressure.

The pressure will (from memory) rise a bit at idle - to around 40PSI. This shows the fuel pump is working, and the FPR is working. If you rev the engine with the vacuum line disconnected, fuel pressure should remain about the same pressure. This shows the fuel filter isn't plugged and the pump has adequate capacity.

Thank you both for the added info.

If the vacuum line can be disconnected what is it there for? I thought it was there to "turn on" the FPR so that it was only open when the bike was running.

toddlamp said:

If the vacuum line can be disconnected what is it there for? I thought it was there to "turn on" the FPR so that it was only open when the bike was running.

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It slightly enriches the mixture under hard acceleration(when the vacuum drops) and slightly leans it out at cruise and idle (when vacuum is high).

The latest part number for the T is: 13111254083. The original P/N-used since 1970: 13111336900.

Received my fuel pressure gauge the other day. Still waiting to get the proper hose fittings to get it installed.

I am still having issues, however it seems like I am no longer running lean at idle. If I set the choke and hit the starter button I get an RPM increase. I'm starting to wonder if the FI computer is off.

Assuming that my fuel pressure is correct, what's the next step?