K75 fuel pump noise questions

[mrt6644]

Im a new owner, so bear with me.  Never owned a K anything except the K1200RS.
Ive done several searches but noise is hard to describe.

When I got the bike, it started up immediately, with the cold lever.

After running 1-4 minutes, the fuel pump starts to make a whining noise.
Ive read about the expected noise, but I didn't see this exact condition.
Why would the noise start minutes after starting the bike?
It's super loud (for me).  You can hear it with tank closed and standing 5-10 feet from bike.
How is this normal?  Or isn't it?

Also, the bike doesn't seem to run with cold lever in the off position.

[Laitch]

What is its year of manufacture?

[mrt6644]

1995

[Laitch]

None of what you have described is normal for a Brick in good condition. The fuel pump could be faulty and/or the fuel filter and lines could be clogged.
Is the noise happening when the tank is full or when it is almost empty?
How we handle noise discussions around here is you record the noise on a video, then post the video on YouTube with public access, then publish the link to it here.

[mrt6644]

Thanks.  I will record it and post the link.

[The Mighty Gryphon]

How much fuel is in the tank?  The pump will suck air and make a lot of noise expressing it's displeasure at the low fuel level.

Also, what does the filter screen on the pump look like? 

Last, how old is the fuel filter?  Is it clogged?

[mrt6644]

I added fuel so it is about half tank.  Same noise.
I haven't checked the filter on the pump.
I replaced the fuel filter canister today and no improvement

[mrt6644]

Here are 2 audio files.
The first is when the engine is first started and it doesn't have the loud pump noise.
The 2nd is after running for a bit and then the loud pump noise kicks in

[Laitch]

The "startup" sound is ok to me.

I haven't checked the filter on the pump.
I replaced the fuel filter canister today and no improvement

If the fuel sock or fuel screen on the pump is clogged, that could strain the pump and maybe produce this little howl.
Have you listened to the sound with entire cap assembly removed?
By "fuel canister" do you mean the metal fuel filter on the submerged fuel delivery line from the pump?

[mrt6644]

Yes, I meant the filter submerged in the tank.
This isn't a scientific observation, but it seemed that the bike was better with the new filter, and that the pump noise took longer to come on.

I also have an issue where the bike won't really run well unless the cold start lever is in at least the first position.
I know I should check for the leak in that one hose.

The noise with the cap open is louder.  I will see if I can upload that sound as well.
Thanks for your help.

[sooprvylyn]

I'd pull it and check the pre-strainer to see it's condition.  They frequently break down over time, and then little pieces of that filter can make their way into the pump.  It's possible your pump may be fighting some debris caught in it.  It would also make sense if your efforts in changing the filter improved things a little as that debris from the prefilter may have made its way into your old fuel filter as well, which might increase the whine via turbulence.

It's also possible your pump is simply wearing out, especially if it sat unused for any real length of time allowing seals to dry out.  You can go with a new bosch pump, but they are $$$.  There are quite a few aftermarket pump options out there that are cheaper, and they'll work as well, tho may not last quite as long as a bosch unit. There is also a pump option that is for a camry or taurus or something that works in the k-bikes(you'll need to look up which car its from unless someone here chimes in with the correct model as I cant recall which).

Replace your prestrainer if its deteriorating.

[daveson]

This suggestion is unlikely to be the problem, but I'll suggest it anyway.

The new filter might be blocked.

When you pulled the new filter out of its box, did both ends have a plastic cap on them, or one fallen off? A new filter sitting on a shelf for years can absorb moisture over time, and swell up, especially in high moisture areas. It might be worth checking to see if it's easy to blow through.

[mrt6644]

Thanks for the suggestion.  The new filter seems to be working better than the old one.
But anything is possible.

[daveson]

I spose I should have said the new filter might be partially blocked.

The noise didn't sound loud to me, but my hearing isn't the best. This thread reminds me of something I almost forgot, when I first started riding a brick I thought, there's something wrong, why is the fuel pump so loud? Before the brick, I rode a big, thumping, loud, low revving, cruiser, with drilled out mufflers, it was heaven. On a brick the pump isn't louder, the engine is quieter, with its massive lump of a muffler.

That it seems to be starving of fuel is a problem though.

If you want to try a different pump, just about any might do as a temporary test. One of mine had a Falcon pump because the previous owner drove a Falcon, smaller diameter, didn't fit the holder, just bounced around on the bottom of the tank, he took it interstate and all around the place.

[Laitch]

The new filter seems to be working better than the old one.

Did you lift the pump out of its holder and check its pre-filter, or has the noise stopped?

[frankenduck]

I know I should check for the leak in that one hose.

Are you referring to the crank case breather hose? Yes, that will make it idle poorly.

I'd replace it anyhow on a new-to-me k75.

http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/ccb/ccb.htm

[mrt6644]

Ok.  A couple updates.

I took the pump out and the sock looked ok.  I put the pump back in and ran the bike throughly for nearly an hour, accelerating, idling, etc.  no more pump noise at all.  I’m wondering if the last time the pump was out, it was installed with the sock bent over and maybe wedged in between pump and tank?  Otherwise not sure what happened.  Seems like the sock was previously in a position where it restricted gas?

Now for the acceleration hesitation.  When I rev the throttle, the engine sounds like it chokes for a second and wants to die.  Putting the cold start lever helps a little.  But still that hesitation.
I installed that breather tube (new from Beemerboneyard) and didn’t seem to make a difference.
Is there some throttle position sensor or some other sensor I need to be looking at?
It idles perfectly.  And once I get passed that choke point, it accelerates nicely.

[mrt6644]

I did the following work to the bike today
-changed engine oil and filter
-changed transmission fluid
-changed rear drive fluid
-flushed and replaced front and rear brake fluid
-flushed and replaced coolant
-replaced air filter
-replaced fuel filter (few days ago)
-replaced spark plugs
-replaced breather tube

[The Mighty Gryphon]

The K75 doesn't like to have the throttle snapped open.  The air flow is measured with a barndoor that has a mechanical lag when the throttle is opened quickly.  This causes a rush of air into the cylinders without any fuel resulting in a lean mixture stumble. 

You need to roll the throttle on with the Jetronic control.

Fuel control with the later Motronic is by the throttle butterfly position which eliminates the lag resulting in better engine response when the throttle is opened quickly.

[frankenduck]

Look here: http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/tbleak/tbleak.htm

[mrt6644]

So the hesitation issue seems to have disappeared after cleaning the injectors and replacing the rings.  I also added Chevron fuel system cleaner to the tank.

Anyway the engine runs great.  Pulls strong and no more hesitation