85 K100 ...all of a sudden backfiring and stalling when HOT! Still not fixed!

[Atabeach]

Ok was running absolutely perfect, yesterday...she always backfired under deceleration but now on low rpm throttle. Starts right up, soon as the temps get up backfiring & stalling on low RPM.  OK soooo I used the propane trick to check for leaks at the throttle bodies...no noticeable increase in RPM. Pressed the starter button, verrrry slight decrease in RPM. The fuel pump is new , Z hose new...checked for leaks in and around air box... next Im going to take out plugs and see how they look. any usual suspects Im missing? TIA

HALL SENSOR...
 

[Laitch]

Verify that the battery positive clamp, the battery ground clamp and the battery ground cable attachment on the transmission are tight.

Click this link to the opening post of the Service Manual section here. Click on the link to Vogel's troubleshooting guide at the bottom of the opening post. Perform the tests of the throttle switch and the coolant temperature sensor explained on pp. 25–29. Let us know the results.

[Atabeach]

Thanks Laitch, So I checked the Grounds and Positive terminals and then spent about an hour reviewing Vogels detailed post. Very informative, thanks.
1) The post referenced non start issue regarding throttle switch. Page 7/8 I did not see how to test it. For historical purposes the bike is an 85 and …backfires. Maybe It should be changed. Please advise.
2) I did not see how to test coolant temperature sensor either. Please let me know the ohm value or how to test the unit ….
 I did discover an oil leak coming from the bottom of the air box ( photo 1) 
 Thanks again.

[Laitch]

Thanks Laitch, So I checked the Grounds and Positive terminals and then spent about an hour reviewing Vogels detailed post. Very informative, thanks.
1) The post referenced non start issue regarding throttle switch. Page 7/8 I did not see how to test it. For historical purposes the bike is an 85 and …backfires. Maybe It should be changed.

The photo of the air box in your post is of the intake air system on an 4-valve engine, not a 2-valve engine as should be in an '85 K100. The 2-valve air box that connects to the throttle bodies is pictured below. What's going on, Florida Man? 

[Atabeach]

Ok soooo no internal hose, Check!
Can i assume since the fan clicked on the coolant sensor is good?...or is there a different sensor?
In Vogles post he stated that the hall sensor seemed to act up when heated...we are in Florida.

[Laitch]

Ok soooo no internal hose, Check!

Check? None of that assembly belongs on a 2-valve K100 Brick so what's a photo of it doing in a thread about the performance of a 2V Brick engine? I don't know what you've got going down there in the steamy sub-tropics. Will you offer a comprehensible explanation? My next dose of coffee isn't until after 8am tomorrow.
 

[Atabeach]

The photo was posted in error, I will attempt to remove it.

[Laitch]

I did discover an oil leak coming from the bottom of the air box   
IMG_7491.jpeg (53.38 kB . 768x576 - viewed 115 times)

Is this a photo of one of your Brick's throttle bodies? If it is, what is the blue linear object in it?

[Atabeach]

Throttle body nearest to Z hose ...Blue object is pointer to the area of oil leak...

[Laitch]

The 2V air box has throttle body intake pipes molded into it as can be seen in previous post #3. There are no joints in the box’s construction to leak; it would need to be cracked. Leaking is unlikely because crankcase blow-by is received into the air box from the z-tube then mixed with air being drawn from the box through the throttle bodies. Oil shouldn’t be "flowing" anywhere in the air box to create a leak. Oil should be in blow-by vapor that enters the throttle bodies to then be ignited in the cylinders. It’s possible that the z-tube is leaking where it is attached causing some oil vapor to condense on the outside of the air box instead of all oil vapor entering the throttle bodies. If the intake rubber hoses were leaking, that would have been evident in your propane test.

Closer inspection is needed.

[Atabeach]

Further inspection revealed some oil at the top of Z hose so that is probably where the oil is coming from….obviously not the reason for the bike running poorly.
The post by Vogel specifically mentioned running rough when bike is hot would point to the Hall sensor. I tried to remove it from the bike to test it but the 5 pin connector crumpled miserably in my hand. I need to change it anyway so hopefully that was the issue.

[Atabeach]

Verify that the battery positive clamp, the battery ground clamp and the battery ground cable attachment on the transmission are tight.

Click this link to the opening post of the Service Manual section here. Click on the link to Vogel's troubleshooting guide at the bottom of the opening post. Perform the tests of the throttle switch and the coolant temperature sensor explained on pp. 25–29. Let us know the results.

  It was the Hall sensor. Vogel had it right...when the bike fails when HOT....

[Laitch]

 

[Edward]

Honeywell S7C - 2AV54 a discontinued parts from long long ago. Try Chen Yang CYHME56 Hall Vane Sensor. High temp leads may have to be added. Current price 1-10 $5.00.

https://www.chenyang-gmbh.com/en/hall-effect-vane-sensor-cyhme56c-output-npn-oc-power-supply-4.5-v-24-v-dc-alternative-for-2av54-2av16a-2av51a-2av56-honeywell.html

[Atabeach]

Gentlemen…the issue is not resolved. Ok a few rides and the bike fairly warm no problems…Then a nice decent ride…the problem still exists. Backfiring , only runs at 3500 rpm. What are the odds of another bad hall sensor?

[Laitch]

Test the coolant temperature sensor as was recommended in Reply #1. It's a simple test. 

The multimeter is set to Ω. The ignition switch is Off. The ground lead touches contact #1 of the fuel injection plug, the positive probe contacts pin #10. There's a photo of the plug with the contacts numbered in Vogel's a few pages after the Hall Sensor section. At ambient temperature the multimeter should read approximately 2.5KΩ.

If the values are close to that number, start the engine and point a thin stream of propane at the joint of the z-tube with the air box as shown in your photo of the oil leak. If the revs change during spraying, that's one problem uncovered. If okay, move on.

[daveson]

Here's a way to test the hall sensors without removing them.

This short video only shows the test results for one output, the test should be done for both, the brown wire and the orange wire.

https://youtube.com/shorts/P3X0zvDY6Vw?si=V3UK2QuetQEQQroF

If your brick is the earlier model of 1985, the coils aren't the best. You could use a timing gun to check for a good signal from the coils to the spark plugs, or even look at them for cracks. In your troubleshooting guide, there are also tests for the coils.

[Atabeach]

Thanks Davison, At this point I will in this order
1) test temperature sensor & propane around z tube , thanks Laitch!
2) test coils ( I think I have spares from box of stuff )
3) remove the used hall sensor I bought and bench test

Thanks, I’ll post the results
Meanwhile in the garage… another barn find

[Laitch]

Meanwhile in the garage… another barn find

That's one of the rare BMW unicycles. Great find!