K75-Long Cold Start

[Eric1514]

Hi all,

Recently, my '87 K75c takes 3-4 secs of cranking before it fires first thing in the morning and after sitting at work for 8-9 hours. If I let it sit for just a few hours, it will fire right up or if I turn it off right after it first starts, it will start right up with almost no cranking. It's just if it sits 8 or more hours. I know 3-4 secs isn't long, but it's longer than it used to be.

Once it's running, it's perfect.

I replaced the plugs to no avail and I've got a fuel filter coming. Anything else I should be looking at?

It is almost as if it needs to build fuel pressure for that 3-4 secs before it fires and that it takes 8 or so hours for that pressure to bleed off. Hence the quick starts within that time frame and the need to crank longer when that time frame is exceeded. I hope it's not the pump. Maybe the battery cranking too slow?

Temp in the morning is around 45F and in the afternoon it's about 80F.

Any thoughts would be greatly appreciated.

TIA,
Eric

[Mar]

How old is your battery? And do you use a Battery Tender or the like if you don't ride the bike for a few days or weeks?

[Eric1514]

It could very well be the battery. It's at least 2 years old and around here, 3 years is a long time for a car battery. Could be a surface charge thing going on.

I'll look closer at that.

Thanks,
Eric

[PGlaves]

I agree it sounds silly but 3 to 4 seconds cranking is unusual for a K75. Even cold they usually fire almost instantly. I agree it sounds like a fuel pressure issue. I would try to verify that. Just stab the starter button which starts the fuel pump for a few seconds, and then the pump shuts off.. Do that a couple of times which should build full pressure at the fuel rail. Then crank the engine. If this changes the starting behavior I would strongly suspect a partially clogged fuel filter.

[Motor31]

On mine for the first start of the day I'd just tap the starter button to pressurize the fuel system, then start the bike. No long grinding sessions with the starter when I did that.

[Bobmws]

If the new filter doesn't solve your problem, it's possible the fuel pressure regulator is slowly allowing pressure to bleed off. You can check it by installing a pressure gauge in the return line coming off the rear of the fuel rail. A cheap pressure gauge attached to a brass 'T' with hose barbs will allow you to measure fuel pressure. I think it should be in the 35-40 psi rangewith the motor running. What you would be looking for is the amount of time it holds the pressure after shutting off the motor.
Also make sure the small vacuum line on the rear throttle body is in good shape, it connects to the fuel pressure regulator and has a control function of some sort, can't remember quite what though.....

[mrich12000]

Injetor leakdown. Time to change..:bolt :thumb :drink :german

[Eric1514]

Startin' to look like a battery problem. Pulled said battery a filled with water. Two cells were lower than they should have been.

Started fine, everytime for two days.

When out to the garage this morning and it was a long crank session, so I took the car. This afternoon when I got home I thought I would try the bump the button method to presurize the fuel system. One bump. Then on the second bump, I got some weird whirring noise, the tach needle swung up and back and the relay clicked, but no crank. The battery reads 10.24 volts without a load.

Now when I turn the key to on, I get a hum, a relay is clicking like mad and the headlight/dashlights blink on and off. I think I fried the starter relay:banghead

Eric

[bmwmick]

Startin' to look like a battery problem. Pulled said battery a filled with water. Two cells were lower than they should have been.

Started fine, everytime for two days.

When out to the garage this morning and it was a long crank session, so I took the car. This afternoon when I got home I thought I would try the bump the button method to presurize the fuel system. One bump. Then on the second bump, I got some weird whirring noise, the tach needle swung up and back and the relay clicked, but no crank. The battery reads 10.24 volts without a load.

Now when I turn the key to on, I get a hum, a relay is clicking like mad and the headlight/dashlights blink on and off. I think I fried the starter relay:banghead

Eric

10.2V is a very dead battery.

[Eric1514]

I just removed the starter relay, popped it open and cleaned up the contacts with some 400 grit paper. Reinstalled.

Hooked the bike up to my car battery and everything works normally.:clap

I'll buy a new battery tomorrow. Living in the desert is hard on those things.

Thanks to all that chimed in. It's always nice to have help when you have problems.

Eric

[Mike Gilbreath]

Noticed you guys covered the usual causes , low battery, low fuel pressure , leaking vaccuum line to pressure regulator but wanted to throw in another cause I ran across. I had a K100 that began to get a little worse about starting everytime I went to start it cold(crank it for us Southerners!)! I checked all the causes you've mentioned and a few more,i.e. hall sensors , injectors, but no change! Then one hot summer day I was riding down a local mountain when the bike suddenly backfired and died! The FI unit had failed! After installing a replacement the bike started like a champ, the unit had been going bad all along!
Also the fuel milage dropped as the FI unit grew worse, again I'm thinking temp sensor, airflow meter, etc ! So if you have a spare FI unit around (which I highly recommend you keep with you!) and you are having problems starting cold and fuel milage is down, try changing the FI unit!