constipated brick (k75)

[kaleb]

Hi brickers!

I feel another learning curve coming on......

So. 100 miles into my 200 mile drive North to my sister's place this afternoon, shortly after refueling (with the more expensive unleaded, as it happens), my '93 k75 became jerky on the throttle. I didn't notice how quickly it came on, but it was definitely after the refueling break that any acceleration over about 60mph became jerky, as though the power was struggling to get out.

Usually in 4th, 3/4 throttle gives 80mph at 6.5k revs and she'll pull hard if I twist a little extra. Usually top speed is a little over 100 (although I don't really go there, of course I've checked).

After a few minutes of unnerving jerkiness the power settled down, but now top speed is 80. Revs max out at 6.5k in fourth, and if I change up to 5th she slows a little and revs don't get past 5.5k. It's like the bike has lost its top 20% of power.

There is a much harsher tone from the engine (must admit I enjoyed it a little after the usual blender sound), perhaps a touch of rattle, and she cut out a couple of times at junctions as I got closer to my destination.

The background is that last month I noticed that, after running the tank nearly empty and then refueling, she started giving an occasional sluggish kind of groan, just once every few hundred miles on acceleration. I wondered if maybe a bit of empty-tank crap had gotten into the injectors but the mechanic who helped me with my first spline lube last week more or less laughed at me about that idea.

So does anybody have any suggestions? I need to ride her home again in a couple of days... Should I assume if she's running then fine to ride to her limits, or should I be limping.......

Thanks in advance!

Kaleb

[Laitch]

Can you give us the maintenance history as good as you can, kaleb, so we don't spin our wheels too much at the beginning?

[bocutter Ed]

I wondered if maybe a bit of empty-tank crap had gotten into the injectors but the mechanic who helped me with my first spline lube last week more or less laughed at me about that idea.

Crap might have plugged your fuel filter.

[WayneDW]

I'm going to agree with Ed. Start with the easy stuff which in this case would be the fuel filter.

[Martin]

I had the same symptoms a few years ago after filling up. In the end I had to empty the fuel tank and blow out the filter ( I  had only just changed it ). Problem solved
Regards Martin.

[kaleb]

Thanks guys. The fuel filter sounds a likely culprit. I've ordered a new one, which I'll learn how to install when I get home.

Laitch, I don't have the service history with me. But, I've just had the bike since August. My maintenance so far has been oil and oil filter change, clutch cable, spline lube and starter motor overhaul... So nothing relevant I think. As memory serves, the fuel filter was on my to-do list because the last owner hadn't done it for a few years.

Fingers crossed I get her home!

Cheers. K

[Elipten]

I always carry a spare fuel filter in the tail of the bike

Sounds like the most likely place to start

[The Mighty Gryphon]

+1 on the fuel filter and carrying a spare even though any metal shell filter with 5/16" barbs from an auto parts place will work.

[TimTyler]

Thanks guys. The fuel filter sounds a likely culprit. I've ordered a new one, which I'll learn how to install when I get home.

Easy job when the fuel level in your tank is low.

[kaleb]

I made it home. In fact, did more like 300 miles with a detour to see a friend.

No new problems, but still the jerkiness each time she warmed up, and still an unnatural cap on power, speed and revs. Oh and definitely a big drop in fuel efficiency. My awareness of that isn't very acute, but it felt like I was running empty almost twice as fast as usual.

I should get the new fuel filter in the next couple of days (although now I have the previous owner's maintenance 'record' (!) to hand, I can see she had a new one installed Summer 2014; by my reckoning about 8000 miles ago).

So I'll try that and update y'all.

Cheers

Kaleb.

[WayneDW]

Check your air filter too.  You might have a mouse nest in there.

[Martin]

You might have got a bad dose of fuel, that's  what caused my problem. It wouldn't hurt to put half a bottle of Techtron in when you next need to fill it up.
Regards Martin

[kaleb]

Hello

I changed my fuel filter this morning.

The tank looked clean inside, except for a few small pieces of brittle, orange brown plasticky sort of bits. I can't decide whether or not they're deposits of some kind or perhaps the remains of a seal or repair somewhere in there.

Anyway, I went for a ride and the problem persists. I put a half tank of fuel in almost immediately because I'd run it down before I changed the filter.

Symptoms:

Jerky on acceleration
fuel pump running constantly
revs maxing out around 7k in 4th

Having ruled out the fuel filter, I understand the next likely issue is the fuel pump itself.

Is that something I could take out and attempt to diagnose/service myself? I am learning as I go here!

I'll also be checking the airfilter, and a certain four-pin electrical connection beneath the right side of the tank which has been suggested.

Oh and I've a bottle of Techron Concentrate Plus on order, thanks Martin.

Cheers all,

K

[kaleb]

Having spent another little while looking and listening I've another symptom to add to the list

engine knocking, every few seconds at idle, more frequent when revving, clear and distinct metallic tapping coming from inside the engine block

[The Mighty Gryphon]

Fuel starvation.  Pull the spark plugs and tell us what they look like.  Better yet, post a good photo of them if you can.

[Laitch]

Is that something I could take out and attempt to diagnose/service myself? I am learning as I go here!

I'll also be checking the airfilter, and a certain four-pin electrical connection beneath the right side of the tank which has been suggested.

You can diagnose problems and replace many of the parts on these bikes with the correct tools, a manual and some reliable assistance.
Check the air filter and connector right now before you do anything else. I wonder why you haven't already. They're about the simplest things you could do.

Then do what Gryph suggests. I also suggest getting a compression tester and a vacuum gauge to get an idea of your bike's combustion chamber conditions. They're simple to use, too, and not costly.

[Martin]

When I got a dose of bad fuel I had to completely drain my tank, sometimes you can see the contamination, sometimes you can't. I had only just  replaced my fuel filter the day before when it was low. When I gently blew out the filter I could find nothing. But when I started the bike up again with new fresh fuel from a different Service Station no problem. It is unlikely but if you had contamination it might have got into your injectors. There are plenty of posts on the net on how to build a cheap injector cleaner, but be careful with vaporized fuel and have a fire extinguisher handy.
 I run probably 1-2 bottles of Techtron a year.
Regards Martin

[The Mighty Gryphon]

Right now I wouldn't be too concerned about the knocking.  If it is doing it at idle, around 1500 to 2500rpm it is probably the anti-backlash spring on the output shaft.  It's annoying, but as far as I can tell, fairly innocuous. 

There are three areas you need to check.  The fuel pump may be going bad, the fuel pressure regulator may be acting up, and there may be air leaks in the rubber bits that carry the air to the cylinders and control crankcase breathing.  Air leaks can cause lean fuel mixtures and lead to all sorts of driveability issues.  Look for cracks in the hoses and bushings.  The bushings above the throttle bodies and the breather hose that goes from the crankcase to the breather box are notorious for causing problems and a lot of riders replace them as preventive maintenance.

[kaleb]

Hi everybody

Thank you all for the help and guidance, and sorry if my naivete has been tiresome!

This problem seems now to be resolved. The spark plugs were pretty sooty around the electrodes, much darker than the healthy 'tan'. Also the electrode gaps, although I didn't have the gauge to measure them, looked all three a little different.

The air filter was pretty full of flies and crud. I hadn't realised (thank you, again, Laitch) just how straightforward it is to check this (confess I hadn't even figured out where it was until last week).

So I've installed a new air filter and three new Bosch spark plugs.

The bike rides good now, perhaps a little better than when I got her in August.

Summary, then:

symptoms:

jerky acceleration, revs maxing out around 7k, top speed of 80 in 4th, fuel pump 'always on', engine knocking


tried:

new fuel filter
checking the 4-pin connection on the righthand underside of the tank


solved by:
either new airfilter
or new spark plugs

(or both! they went in at the same time...)

I'm glad it wasn't something more involved with the fuel system. Although having now gotten my head around *some* of the extremely-basics, perhaps I'll be a bit more ready when the next issue rears its head.

I'm going touring in late April, so there'll be another shout for preliminary/preventative maintenance advice shortly.....


Thank you all again.

Kaleb

[Laitch]

Thanks for the update, Kaleb.  Your positive outcome is probably from a combination of the tasks you completed. It really takes patience and diligence to work through some of this elusive stuff whether you're working alone or have backup. A manual current to your bike's model doesn't hurt either. :giggles 

Ride on! Weather permitting, of course. :2thumbup: I hope you gapped those plugs!

[The Mighty Gryphon]

That's great news, Kaleb!  It's always good to hear of another brick getting in tip top shape.  Enjoy!

cheers,