BMW K bikes (Bricks)

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1Back to top Go down   K75 Maybe fuel/or spark Empty K75 Maybe fuel/or spark Mon Oct 03, 2022 2:32 pm

TimK100

TimK100
active member
active member
Good Day Fellas,
I have a 1988 K75S which has been running terrifically all season. This weekend out for a ride and out of the blue it started losing power a bit. I gave it a little throttle and it really bogged down. Tried to downshift and give it some gas and it was just popping, sputtering, and backfiring. I pulled over and topped off the fuel (it was a little under 1/2 tank) thinking maybe last fill up could have been a little off - even though it was a trusted station). I pulled the plugs to see if they looked fouled or anything unusual, but they seemed ok. When I started it up again it sounded a little off, but ran ok for a mile or two, then started to lose power again and the same popping and bucking. I pulled over and shut it off for about 5 minutes and started again fine for a mile or so, then again same issues. if I pull over and stop it seems to idle fine. It starts up just fine, but I'm not sure where to begin the troubleshooting. You guys have been remarkable with all the tips given for other issues before, and I hope you know how much novice wrenchers like myself appreciate it. Thanks much, Tim

    

2Back to top Go down   K75 Maybe fuel/or spark Empty Re: K75 Maybe fuel/or spark Mon Oct 03, 2022 3:30 pm

Arlina

Arlina
Moderator
Moderator
Tried a new fuelfilter?


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K75 Maybe fuel/or spark Eu-log10  K1100RS/LT - R1200RT - R1100RS (RIP) - Cagiva SST 350 Ala Verde - K75LT project - K75 Schurgers - K75S
    

3Back to top Go down   K75 Maybe fuel/or spark Empty Re: K75 Maybe fuel/or spark Mon Oct 03, 2022 3:39 pm

Bricklayer

Bricklayer
active member
active member
Even after replacing sticky injectors and a bad fuel pressure regulator this exact same issue happened to my 1985 K100RS. I tested my ignition coils (original) and they were bad. My recommendation is based on your bike starting and as soon as it gets a tad warm the issue commences. When I tested the resistance on my coils the resistance would slowly and continously charge.


__________________________________________________
Anthony Mrugacz

https://anthonymrugacz.net

Past Stable of Ponies:
1978 Suzuki TS185
1976 BMW R90/6
1973 Yamaha LT3-MX
1970 BMW R75/5
1970 Suzuki T500

Live Stream Repairs
https://www.youtube.com/@BMWK589
https://anthonymrugacz.net/
    

4Back to top Go down   K75 Maybe fuel/or spark Empty Re: K75 Maybe fuel/or spark Mon Oct 03, 2022 4:11 pm

Laitch

Laitch
Life time member
Life time member
TimK100 wrote:I have a 1988 K75S which has been running terrifically all season.
It doesn't seem like it was running terrifically in June of this year when you posted about a stalling issue, so you must be referring to Fall.  Laughing   You installed a new fuel filter some time in mid-June and maybe cleaned the 4-pin fuel pump plug. You didn't followup that thread with which treatment made it run terrifically after that. Is this the same Brick? How does the stalling now differ from the stalling then?

If the fuel filter was installed correctly; if the tank interior fuel lines are the correct type, in good condition and firmly connected; if the screen pre-filter at the bottom of the fuel pump is not clogged then to consider next would be checking the z-tube connecting the crankcase to the air box, the vacuum caps on two of the throttle bodies and the vacuum hose on the third for slits and cracking; and checking the rubber manifolds of the throttle bodies for leaks.

Checking the coils, as has been suggested already, could be last in the line because unlike the 1985 K100RS coils, the K75 coils have a history of being reliable.


__________________________________________________
1995 K75 81,000 miles
K75 Maybe fuel/or spark Usa-lo10
    

5Back to top Go down   K75 Maybe fuel/or spark Empty Re: K75 Maybe fuel/or spark Tue Oct 04, 2022 7:57 pm

TimK100

TimK100
active member
active member
Thanks for tips, your right Laitch, regrettably I didn't follow up that last thread, which I will. It ended up being a fuel pump issue. I will have to check the rubber parts this week

    

6Back to top Go down   K75 Maybe fuel/or spark Empty Re: K75 Maybe fuel/or spark Sat Oct 08, 2022 12:38 am

TimK100

TimK100
active member
active member
It was a fuel pump issue previously that was resolved in  mid July. I was able to look at the rubber vacuum caps and the 3rd vacuum hose all seemed in good shape. however when I inspected the z-tube it was very cracked at the front elbow. Would this cause that issue? I will have to look into getting a replacement regardless. I am attaching a photo of what it looks like. Thanks againK75 Maybe fuel/or spark Img_2810

    

7Back to top Go down   K75 Maybe fuel/or spark Empty Re: K75 Maybe fuel/or spark Sat Oct 08, 2022 8:22 am

Laitch

Laitch
Life time member
Life time member
TimK100 wrote: when I inspected the z-tube it was very cracked at the front elbow. Would this cause that issue?
It could be contributing to this condition. That's why it was mentioned in post #4.


__________________________________________________
1995 K75 81,000 miles
K75 Maybe fuel/or spark Usa-lo10
    

8Back to top Go down   K75 Maybe fuel/or spark Empty Re: K75 Maybe fuel/or spark Thu Nov 03, 2022 9:01 pm

TimK100

TimK100
active member
active member
I replaced the Z tube, but that didn't seem to have any affect on the issue. I was considering replacing the plugs and wires, because it really seemed like a misfiring type issue.

    

9Back to top Go down   K75 Maybe fuel/or spark Empty Re: K75 Maybe fuel/or spark Thu Nov 03, 2022 10:01 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Did you replace the fuel filter when you replaced the pump? 

There have been problems like yours that were cured by replacing the filter in the tank.  The filter chokes the flow of fuel so that as the engine runs the fuel delivered can't keep up with what is used.  There is enough to sort of run the engine at low rpm, but not enough to generate good running power.


__________________________________________________
Present:
1994 K75RT
1991 K100RS


Past:
1988 K100RS SE
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

10Back to top Go down   K75 Maybe fuel/or spark Empty Re: K75 Maybe fuel/or spark Thu Nov 03, 2022 10:39 pm

duck

duck
Life time member
Life time member
Make sure that the spark plug leads are FIRMLY seated on the spark plugs. What I do is grab the tab on each lead with the factory toolkit pliers and then give the pliers a hearty smack with the other hand to make sure that they are all of the way on. Then I try to wiggle each lead by hand. They should not wiggle.


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

11Back to top Go down   K75 Maybe fuel/or spark Empty Re: K75 Maybe fuel/or spark Sun Nov 20, 2022 3:12 pm

TimK100

TimK100
active member
active member
I did replace the fuel filter earlier in the year when I was having the previous issues. I don't think it would be an issue so soon, but if this sounds like it could be the issue, I wouldn't hesitate to do it again. I believe I have an extra around here somewhere. I have ordered and gotten plugs and wires also, but haven't had a chance to install them yet. Maybe not until next spring, I'll keep you posted, but until then, as always, thanks so much for everybody's input. This forum is invaluable!

    

12Back to top Go down   K75 Maybe fuel/or spark Empty Re: K75 Maybe fuel/or spark Sun Nov 20, 2022 4:04 pm

duck

duck
Life time member
Life time member
Easy to test the fuel filter. Take it out and try to blow through it in the direction of the arrow. You should be able to blow through it fairly easily.


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

13Back to top Go down   K75 Maybe fuel/or spark Empty Re: K75 Maybe fuel/or spark Fri Nov 25, 2022 10:45 am

tinyspuds

tinyspuds
Life time member
Life time member
Not my K but I had similar symptoms this Summer on the Busa. Turned out it was the tank bag causing an airlock. I guess any other cap breather blockage might do the same (esp. with the apparent self healing after a stop or fill-up)


__________________________________________________
1985 BMW K100RT + Hedingham HUB and LL’s. VIN 0028106.
1986 K100RS in boxes. VIN 0141918.
1954 Royal Enfield 350 Bullet. Original.
2000 Hayabusa with Charnwood chair, Wasp forks and EZS wheels.
    

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