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Good morning to all, thank you for providing this incredible forum to discuss our machines. I recently bought a 1988 K75S, from a person who had attempted to repair some wiring on it. He had no real mechanical experience (self admitted).
That being aid, the starter was seized and the key switch was smashed. I replaced the key switch, and the starter. The machine now cranks beautifully, all lights, horn etc. function. However the machine fails to start. After some poking around I found that the cooling fan was hotwired with household lamp wiring.
I got my cyber hands a nice flow chart for diagnostics. While cranking, no action at the fuel pump, no spark. There is power at the coils. I do have power up to the fuel pump relay. I have cleaned and verified ground connection at battery to transmission housing.
Any help would be greatly appreciated. I do have some fairly specific wiring questions for anybody who can possibly help out. There may be other wiring issues created by previous owner I have not found yet. I do not want to just throw parts at it, and waste money, however, I am also not opposed to replacing things that need it.
Again, thank you for such a great site.
 

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There's no sidestand switch on the '8K75S as I recall. It uses a cable set up that prevent pulling the clutch in if the sidestand is down. Later Ks do have a sidestand switch and its failure does create those same symptoms.

I'm having similar problems with an '88 K75S I picked up "As-IS" for a friend. It will crank and almost wants to run but never quite gets under it's own power. At best I had it running on two cylinders for about 30 seconds.

I have a well running '87 K75Cs as a parts donor for diagnostic purposes. I did all the usually checks on the K75S--plugs/coils/ignition, fuel deliver/injectors, loose connections at the ECM and Fuel injection module, all with no joy. Then I started swapping parts, fuel tank, injectors, Mass air flow sensor, coils/wires still with no joy.

I'm running out of places to look and now thinking the Throttle Position/Hall Effect Sensor is the culprit. If I've read correctly, it directly impacts what the ignition firing and indirectly effects the fuel flow (fuel pump wont run unless the sensor shows he engine is running.

The sensor is a pain to get at on the K75S--lots of bodywork to pull off, so I haven't looked at it yet. I did read on another forum that often the sensors themselves don't fail, but the connecting wires do from acumulated grease and engine heat. There are numerous on-line sources available for information checking/replacing the sensor. They are not cheap if you want to replace it with a new one.

I'm not sure when I'll have a chance to dig back into the K75S. When I do I'll update the thread and hope you keep us posted on your progress.
 

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OP stated there is power to the fuel pump relay. He did not say the fuel pump ran, which it should, for two seconds or so when you bump the start switch, regardless whether the bike starts. Repeated bumps and two-second runs (about four or five) of the pump will activate the pressure relief valve on the pump, which makes a different, louder, "angrier" buzzing noise.

FUEL, AIR, and SPARK are required to run any internal combustion engine. Verify that you have all three at the proper time and place.

FUEL: does the pump run? Does it provide fuel to the fuel rail? If it runs, you can assume pro tem that the pressure is adequate.

AIR: no mouse house in the intake or exhaust, not it the airbox either. This one is pretty simple.

SPARK: remove a spark plug, ground it securely, and crank the bike. There should be a blue spark, not yellow or absent.

The rewiring of the fan may have little to do with the problem, or it may be symptomatic of the problem, in that if the fan wiring was buggered, what else did the PO do?

'Scuse me if this sounds like I'm talking down, but the basics have to be checked AND reported to have been checked. That way we get, in part, a feel for the level of knowledge, competency and determination of the man with the problem.
 

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Honolulu said:
OP stated there is power to the fuel pump relay. He did not say the fuel pump ran, which it should, for two seconds or so when you bump the start switch, regardless whether the bike starts. Repeated bumps and two-second runs (about four or five) of the pump will activate the pressure relief valve on the pump, which makes a different, louder, "angrier" buzzing noise.

FUEL, AIR, and SPARK are required to run any internal combustion engine. Verify that you have all three at the proper time and place.

FUEL: does the pump run? Does it provide fuel to the fuel rail? If it runs, you can assume pro tem that the pressure is adequate.

AIR: no mouse house in the intake or exhaust, not it the airbox either. This one is pretty simple.

SPARK: remove a spark plug, ground it securely, and crank the bike. There should be a blue spark, not yellow or absent.

The rewiring of the fan may have little to do with the problem, or it may be symptomatic of the problem, in that if the fan wiring was buggered, what else did the PO do?

'Scuse me if this sounds like I'm talking down, but the basics have to be checked AND reported to have been checked. That way we get, in part, a feel for the level of knowledge, competency and determination of the man with the problem.
And don't forget some compression!

Good advice when it comes to a crank no-start situation. What's missing from the suck-squeeze-bang-blow formula?
 

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So it cranks but won't start, and no spark. I assuming when you say no spark that is on all cylinders. No spark on one cylinder could point to a single bad coil, wire or spark plug. No spark on all three cylinders suggests no signal from the Hall Effect Sensor.

I'd go through and check all the connections first--Hall sensor, EFI module, ground to the coils, etc. etc.

I got the K75S I had started today. It also cranked and would sputter but would not start. I had spark and fuel, or so I thought. After checking connections, coils, wires, swapping a good MAF in, etc, etc, I finally swapped in a spare fuel pressure regulator. That was the ticket--I sputtered to life and now cranks right up and sounds great!

The bike still needs so cleaning and work but I found it for a friend so that will be his new mistress to care for.

Kontoboy.
 
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