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1Back to top Go down   K75 Low power - missing on one cylinder Empty K75 Low power - missing on one cylinder on Wed Jun 24, 2020 3:30 am

MikeyD

MikeyD
active member
active member
Hi all! I offered to help a friend with her K75 so I could ride it as I had never been on one before. I picked it up last year because it wouldn't start. I'll make a separate post about that. After I got it running it had really low power on the test ride. Wide open throttle would only gradually cause acceleration and it barely wanted to exceed 60 mph. Having never ridden one before I wasn't sure what it was supposed to feel like so I didn't know what to attribute the low power to. Thanks to someone on here, I read about using the exhaust temperature as a quick method to check cylinder combustion. I determined the front cylinder was not firing. Below are my notes I took as I tested and made assumptions about the results:

Idled engine and discovered exhaust pipe from #1 (front) cylinder is cold. Assume no combustion on #1 cylinder. Checked resistance values on all three ignition coils - all checked good. Pulled spark plug cap from #1 plug and inserted a spare plug, grounded it on engine, cranked starter. Engine seemed to run as before removing plug wire from #1 spark plug. Repeated same steps for #2 cylinder. Engine barely started and died after a few rough revolutions. Assume no combustion on cylinder #1. Removing #2 plug wire left the engine to run only on #3 and it wouldn't idle.

Tested spark plug wire resistance. Should be about 6,000 ohms. #1 = 1.1 M Ohms (very high resistance), #2 = 350 K Ohms, #3 = 800 K Ohms. All high resistance, though #1 is extremely high. Later attempt resulted in open circuit, no current through #1 plug wire.

Installed 3 new spark plugs. Still runs poorly as before. #1 was black and dry, #2 was black and wet, #3 was black and oily. Though the engine hasn't run enough to warm up, which might result in cleaner plugs.

Replaced all 3 spark plug wires with new wires and it still runs poorly as before. Though #1 plug wire was dead and the other two had high resistance, it wasn't the only thing causing a lack of combustion in #1 cylinder.

Checked resistance across terminals of fuel injectors. Target value = 16 ohms. Each of the 3 installed injectors read 18 ohms. Assume good internal windings for the solenoids. Tested voltage across female terminals of fuel injector wire harness while cranking starter. Each showed voltage, at least 10V. Performed combustion test again as before by pulling spark plug from #1 and #2 cylinders (after installing new spark plug wires) to confirm still no combustion on cylinder #1. Assume fouled injector on #1.

Prior to ordering new injectors I did a quick, cold compression test on cylinders #1 & 2 just to see if compression on #1 is grossly low compared to #2. #1 = 137 psi, #2 = 145 psi. Assume enough compression in cylinder #1 for combustion.

Sanding, preparing tank for patches, patch tank holes with epoxy putty, remove injectors, clean deposits and sediment from fuel rail. Sand and paint epoxy patches on tank, clean injector ports and surrounding intake on cylinder head, install new fuel injectors. As a side note - when I first got the bike the fuel in the tank looked like Italian salad dressing; it was cloudy with different colored chunks. Even if none of that went through the filters, I suspect the fuel that remained in the injectors suffered the same fate after 3 years of not running.

Installed fuel pump into tank, installed tank and fired it up. Engine now runs on all three cylinders. Runs well on test run. It hesitates off idle when cold but that quickly goes away as it warms up. Something to deal with later.

So there was a double whammy on cylinder #1 - the bad plug wire and a bad injector.


__________________________________________________
1985 K100RT (0052390), 1985 K100 (0030066), 2003 K1200GT (ZK01448), 1984 R65, 1984 R80ST, 1974 R90/6, 1976 R90/6, 1997 R850R, 1991 Honda CB250, 1998 Sportster 883
    

Arlina

Arlina
Moderator
Moderator
Also, did you check/replace the fuelfilter?


__________________________________________________
K75 Low power - missing on one cylinder Eu-log10  K1100RS/LT - R1200RT - R1100RS (RIP) - Cagiva SST 350 Ala Verde - K75LT project
    

3Back to top Go down   K75 Low power - missing on one cylinder Empty trouble shooting on Wed Jun 24, 2020 5:25 am

poddy

poddy
active member
active member
Excellent to hear, I'm working on a K100RS myself. Finding the bloke that was at it before me failed.
Finding attention to detail important. loose wiring, repairs done poorly washers & screws missing. Gets a little bit better each time I take a spanner to it. Have fun

    

MikeyD

MikeyD
active member
active member
@Arlina wrote:Also, did you check/replace the fuelfilter?
Yes, Arlina, I had replaced the fuel filter as part of maintenance when I discovered the horrible looking fuel.


__________________________________________________
1985 K100RT (0052390), 1985 K100 (0030066), 2003 K1200GT (ZK01448), 1984 R65, 1984 R80ST, 1974 R90/6, 1976 R90/6, 1997 R850R, 1991 Honda CB250, 1998 Sportster 883
    

MikeyD

MikeyD
active member
active member
@poddy wrote:Excellent to hear, I'm working on a K100RS myself. Finding the bloke that was at it before me failed.
Finding attention to detail important. loose wiring, repairs done poorly washers & screws missing. Gets a little bit better each time I take a spanner to it. Have fun

Right on poddy! Keep at it. You're right about the attention to detail being important. Though there are so many details I find I have to keep notes or I forget what I've looked at, or confuse it with other bikes I've looked at.


__________________________________________________
1985 K100RT (0052390), 1985 K100 (0030066), 2003 K1200GT (ZK01448), 1984 R65, 1984 R80ST, 1974 R90/6, 1976 R90/6, 1997 R850R, 1991 Honda CB250, 1998 Sportster 883
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Have you replaced the infamous crankcase breather "Z" tube?  They have a tendency to crack at the clamps causing lean mixture issues at idle.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
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
    

Two Wheels Better

Two Wheels Better
Moderator
Moderator
Congrats, MikeyD from Juneau, for diagnosing AND fixing a faulty injection valve and errant sparking bolt simultaneously! Your diagnostic methods and noting of directions you went in might help anyone who reads your post. 

Those long cold wet winters landlocked could have a man (or woman) pining for a little less distraction with a mechanical curve ball like that.  What do you have, like fifty miles of roads to ride on round the capitol city of the great state of Alaska? Perhaps another 48 lower visit when/if things clear would open up your horizons!?
Wink


__________________________________________________

Sometimes I lie awake at night, and I ask, "What can I do to keep my life from going by so fast?" Then a voice comes to me that says, "Try slowing down at the corners." 

~Charlie Brown

1970 R60/5, '77 R75/7-R100, '85 K100'87 K75C, '87 K100RS, '93 K11-K12 Big Block, '93 K1100RS, '95 R100-Mystic, '96 K1100RS, '98 K1200RS, '00 K1200RS, '02 K1200RS, '03 K1200GT, '04 R1150R'04 R1150RT, '05 K1200S, '06 K1200R, '07 K1200R, '09 K1300GT & 2013 R1200RT-Polizei  - Beemers owned still or sold.

    

MikeyD

MikeyD
active member
active member
@Point-Seven-five wrote:Have you replaced the infamous crankcase breather "Z" tube?  They have a tendency to crack at the clamps causing lean mixture issues at idle.

Yup, I replaced the crankcase breather early on after I got it to start. It was certainly cracked. The other thing(s) I replaced was the little rubber vacuum caps on the throttle bodies. I think they were causing a lean condition because I heard backfire on deceleration before replacing them but not after.


__________________________________________________
1985 K100RT (0052390), 1985 K100 (0030066), 2003 K1200GT (ZK01448), 1984 R65, 1984 R80ST, 1974 R90/6, 1976 R90/6, 1997 R850R, 1991 Honda CB250, 1998 Sportster 883
    

MikeyD

MikeyD
active member
active member
@Two Wheels Better wrote:Congrats, MikeyD from Juneau, for diagnosing AND fixing a faulty injection valve and errant sparking bolt simultaneously! Your diagnostic methods and noting of directions you went in might help anyone who reads your post. 

Those long cold wet winters landlocked could have a man (or woman) pining for a little less distraction with a mechanical curve ball like that.  What do you have, like fifty miles of roads to ride on round the capitol city of the great state of Alaska? Perhaps another 48 lower visit when/if things clear would open up your horizons!?
Wink
Thanks, Two Wheels Better! And thanks for imparting me with so much of your knowledge on these machines.

Well, we have 50 miles of road, but that's only in one direction. Then there's another 12 south of the bridge. And the island on the other side of the bridge has 36! So many places to go. I'm thinking of taking the week off after the 4th, planning a 28 mile tour (one-way). Maybe I'll do it twice. Since I'm working from home now to avoid the virus I don't get my kicks through commuting so I've resorted to joy riding - not that commuting wasn't joyful.

And yeah, as soon as I get a vaccine I'll head down to spend some time on my way to Colorado for a family reunion. Thinking of bringing the K100RT that is still in bits in the workroom. Though, I can only stop by if you don't have anymore motorcycles to sell, or until I get caught up with the ones I have. mech Green Kangaroo


__________________________________________________
1985 K100RT (0052390), 1985 K100 (0030066), 2003 K1200GT (ZK01448), 1984 R65, 1984 R80ST, 1974 R90/6, 1976 R90/6, 1997 R850R, 1991 Honda CB250, 1998 Sportster 883
    

10Back to top Go down   K75 Low power - missing on one cylinder Empty crankcase breather on Thu Jun 25, 2020 1:41 am

poddy

poddy
active member
active member
Sounds like we are all replacing same pieces. I know the crankcase breather made a big difference with my bike also runs better now with reconditioned fuel injectors.
Blessed down here in Oz, can ride twelve months of the year. Here in Queensland we can normally ride round the rain or wait 5 minutes. Tah Thanks

    

Two Wheels Better

Two Wheels Better
Moderator
Moderator
@MikeyD wrote:
@Two Wheels Better wrote:Congrats, MikeyD from Juneau, for diagnosing AND fixing a faulty injection valve and errant sparking bolt simultaneously! Your diagnostic methods and noting of directions you went in might help anyone who reads your post. 

Those long cold wet winters landlocked could have a man (or woman) pining for a little less distraction with a mechanical curve ball like that.  What do you have, like fifty miles of roads to ride on round the capitol city of the great state of Alaska? Perhaps another 48 lower visit when/if things clear would open up your horizons!?
Wink
Thanks, Two Wheels Better! And thanks for imparting me with so much of your knowledge on these machines.

Well, we have 50 miles of road, but that's only in one direction. Then there's another 12 south of the bridge. And the island on the other side of the bridge has 36! So many places to go. I'm thinking of taking the week off after the 4th, planning a 28 mile tour (one-way). Maybe I'll do it twice. Since I'm working from home now to avoid the virus I don't get my kicks through commuting so I've resorted to joy riding - not that commuting wasn't joyful.

And yeah, as soon as I get a vaccine I'll head down to spend some time on my way to Colorado for a family reunion. Thinking of bringing the K100RT that is still in bits in the workroom. Though, I can only stop by if you don't have anymore motorcycles to sell, or until I get caught up with the ones I have. mech Green Kangaroo
Well, as John Cleese's French waiter character says to Monsieur Creosote in The meaning of Life, "One more wafer thin morsel?" To which M. Creosote replies, "If I eat another thing, I'm going to throw up."
K75 Low power - missing on one cylinder Mcreos10
Good thing this doesn't apply to owning more motorbikes!


__________________________________________________

Sometimes I lie awake at night, and I ask, "What can I do to keep my life from going by so fast?" Then a voice comes to me that says, "Try slowing down at the corners." 

~Charlie Brown

1970 R60/5, '77 R75/7-R100, '85 K100'87 K75C, '87 K100RS, '93 K11-K12 Big Block, '93 K1100RS, '95 R100-Mystic, '96 K1100RS, '98 K1200RS, '00 K1200RS, '02 K1200RS, '03 K1200GT, '04 R1150R'04 R1150RT, '05 K1200S, '06 K1200R, '07 K1200R, '09 K1300GT & 2013 R1200RT-Polizei  - Beemers owned still or sold.

    

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