fuel consumption poor

[jamato]

1987 K75s 125,000km
My fuel consumption has increased to 5.9L / 100km (39mi/gal)

Mechanic tested and found
3rd cylinder with 93% leak down.
2nd cylinder with 35% leak down
1st with 20% leak down

However, bike does not exhibit symptoms of these numbers.  Bike performs well, lots of throttle response, not sluggish at all.  Idles and sounds well.  Mechanic rode the bike after testing it and can`t understand this either.

- All rubber hoses replaced last fall before end of season
- smell of exhaust from the rider position at stoplight (is this normalÉ - I don't remember it before)
- could I have an air leak after the air box causing loss of pressure thus increasing fuel consumption?
- Could an air leak be causing a mis-read of the cylinders or am I in for a costly valve job?

I`m just a rider and do little work on the bike myself so please be patient if my questions are naive. 

All input greatly appreciated

Joe

[WayneDW]

Hi Joe, welcome.  For me the problem is where you wrote " lots of throttle response".  Gets me every time...
(hope someone can give you some real help).

[Scott_]

If it were me I'd do a valve clearance check.
Sounds like you might a a couple a little on the tight side.

[jamato]

Hi Joe, welcome.  For me the problem is where you wrote " lots of throttle response".  Gets me every time...
(hope someone can give you some real help).

Perhaps my "lots of throttle response" is a naive statement.  Let me re-phrase this.  The bike is not sluggish at all.  Doesn't hesitate from a standstill or when accelerating or passing while riding.  Accelerates smoothly, doesn't vibrate, knock, ping, burp or anything.  It sounds as expected and it rides like a well maintained K75s.  I have several friends with K75 bikes and I have tried theirs and they have tried mine.  No difference.  If the valves are needing work based on the leak down report I received, I expect the bike would be running rough based on the loss of pressure.  Is this a correct assumption?

Fuel consumption is the same whether highway or city riding.  I rode 300km from Toronto to Kingston 2 weeks ago (120kmph all the way).  Exactly the mileage I reported of 39mi/gal (5.9L/100km) 

Does this help?

[Motorhobo]

My bike ran Ok  before I checked the clearance and did the valve adjustment. It runs much better now -- the valves clearance was way off. With your leakdown numbers, that mileage and no knowledge of when the last valve adjustment was done I would pull off the cover and do the check now rather than later. A big differential in valve clearance across cylinders and out of spec clearance will eventually result in engine damage.

You can do it yourself even as a n00b -- either you will have to acquire the skills and knowledge eventually, be independently wealthy or get a second job to pay to diagnose and fix all the little things that will eventuAlly fail on a +25 year old MC.

The valve adjustment isn't rocket science. You just need the tool and a $50 to replace the cover seals and the bolt grommets when you're done. There's a greAt video on youtube...

[bocutter Ed]

1987 K75s 125,000km

I`m just a rider and do little work on the bike myself so please be patient if my questions are naive. 

Joe

You are the rider I met outside the Laird & Wicksteed LCBO? Welcome !!

[jamato]

1987 K75s 125,000km

I`m just a rider and do little work on the bike myself so please be patient if my questions are naive. 

Joe

You are the rider I met outside the Laird & Wicksteed LCBO? Welcome !!

I am Ed...thanks for the note. 

Joe

[wmax351]

1987 K75s 125,000km
My fuel consumption has increased to 5.9L / 100km (39mi/gal)

Mechanic tested and found
3rd cylinder with 93% leak down.
2nd cylinder with 35% leak down
1st with 20% leak down

However, bike does not exhibit symptoms of these numbers.  Bike performs well, lots of throttle response, not sluggish at all.  Idles and sounds well.  Mechanic rode the bike after testing it and can`t understand this either.

- All rubber hoses replaced last fall before end of season
- smell of exhaust from the rider position at stoplight (is this normalÉ - I don't remember it before)
- could I have an air leak after the air box causing loss of pressure thus increasing fuel consumption?
- Could an air leak be causing a mis-read of the cylinders or am I in for a costly valve job?

I`m just a rider and do little work on the bike myself so please be patient if my questions are naive. 

All input greatly appreciated

Joe

Sounds like tight valves to me. More particularly, the one with the bad leakdown.

[bocutter Ed]

- could I have an air leak after the air box causing loss of pressure thus increasing fuel consumption?

From my readings, air leaks would cause lean running.

The computer feeds a richer mix when it reads a cold engine.

[Motorhobo]

Chris Harris' valve check vid:



Motomethods valve shim tool usage video:



To get the tool cheap, web search for Kenneth Lively -- he sells it for 18 bucks.

[K75RT Keith]

1987 K75s 125,000km
My fuel consumption has increased to 5.9L / 100km (39mi/gal)

Mechanic tested and found
3rd cylinder with 93% leak down.
2nd cylinder with 35% leak down
1st with 20% leak down

However, bike does not exhibit symptoms of these numbers.  Bike performs well, lots of throttle response, not sluggish at all.  Idles and sounds well.  Mechanic rode the bike after testing it and can`t understand this either.

- All rubber hoses replaced last fall before end of season
- smell of exhaust from the rider position at stoplight (is this normalÉ - I don't remember it before)
- could I have an air leak after the air box causing loss of pressure thus increasing fuel consumption?
- Could an air leak be causing a mis-read of the cylinders or am I in for a costly valve job?

I`m just a rider and do little work on the bike myself so please be patient if my questions are naive. 

All input greatly appreciated

Joe

Sounds like tight valves to me. More particularly, the one with the bad leakdown.

Or the wrench messed up.

Could any of these be possible culprits?   Really cheap gas?  Bad temp sensor?   Bad thermostat?   Gunked up MAF?    FPR starting to go?

[Motorhobo]

IMO such a performance differential between cylinders has to be explained in the ignition chain for individual cylinders, I.e. throttle bodies, valves or coils and you should be checking the things first that could cause the most damage if left unattended. So -- in short,  valve clearance.

Everything I've read on the subject says you should always do a valve clearance check _before_ the leak down test because if a valve isn't seated properly it will result in leak down, ergo the test won't tell you anything about the engine except that you may have valve clearance issues. You have to isolate variables.  Do the the valve adjustment first and you know the valves are good, so the leakdown values pertain to the actual engine i.e. cylinder performance.

Valve clearance out of spec doesn't mean the cylinder isn't firing. It is. So you may not perceive that the engine is running poorly. What will happen, though, is that the valve will eventually burn up leaving you with a non-running brick and few options that don't cost ch1tloads of money.

So even though your poor fuel consumption may have other causes, maybe at this point you should be more concerned about #3 valve. Bad fuel consumption sucks, engine damage sucks a$$.

My $0.02...

[wmax351]

It also depends on how you are riding. High speed kills mileage on a K75. A lot. On my (tired engined) K75, going to Nebraska, I was averaging 34 mpg for a day or two due to 90 mph speeds on the I80.

[rbm]

FWIW, this chart shows my K75 fuel consumption (as plotted by Fuelly) change dramatically since its restoration.

Prior to the restore, I was getting around 41 - 46 MPG with mixed riding.  Ignore the data between October 2012 and May 2014 as this was the period the bike was off the road, being reconstructed.  Since putting the vehicle back on the road, the fuel consumption has gone way down; now its hovering around 50 MPG in mixed riding conditions.  This past weekend, with nearly 100% highway, I recorded 59 MPG.  I hope this isn't an anomaly.

This isn't a stock K75.  I've fitted a K1100 frontend and driveline as well as K1100 throttle bodies and injectors.  These changes probably have a large effect.

[F14CRAZY]

I get around 39-40 mpg but that's with running 80 mph/5500 rpm most of the time

[wmax351]

I get around 39-40 mpg but that's with running 80 mph/5500 rpm most of the time

That's about what I'm getting with the megasquirt on mine: 38 mpg with 80 mph, 6000rpm for commutes. You must be on an adjusted speedometer: that's 72 mph.

FWIW, this chart shows my K75 fuel consumption (as plotted by Fuelly) change dramatically since its restoration.

Prior to the restore, I was getting around 41 - 46 MPG with mixed riding.  Ignore the data between October 2012 and May 2014 as this was the period the bike was off the road, being reconstructed.  Since putting the vehicle back on the road, the fuel consumption has gone way down; now its hovering around 50 MPG in mixed riding conditions.  This past weekend, with nearly 100% highway, I recorded 59 MPG.  I hope this isn't an anomaly.

This isn't a stock K75.  I've fitted a K1100 frontend and driveline as well as K1100 throttle bodies and injectors.  These changes probably have a large effect.

I take it that is UK Gallons?

[rbm]

No, US gallons according to Fuelly. I normally measure in L/100Km but changed the graph to MPG for this post.  In metric, I was averaging 5.5 L/100km but went down to 4 L/100km at the last fuel-up.  That's why it's too soon to declare this as average consumption (possibly only an anomaly).

UPDATE - August 2014 - I think that I can safely say the fuel consumption on my K75 is averaging 4.3 L/100km for 80-90% highway driving and 5.1 L/100km for 50-70% city driving.  I'm using Fuelly to calculate these stats gained over several fillups this year.

[wmax351]

No, US gallons according to Fuelly. I normally measure in L/100Km but changed the graph to MPG for this post.  In metric, I was averaging 5.5 L/100km but went down to 4 L/100km at the last fuel-up.  That's why it's too soon to declare this as average consumption (possibly only an anomaly).

Interesting. When I ran my fuel mileage computers, my fuel mileage would range significantly, depending on the speed. I've gotten MPG into the mid 40's, but that is when riding slowly on secondary roads while following my dad. As the RPM increases and speeds increase, mileage really drops. WOT on the Nevada-bahn drops to about 27 mpg, if I recall.


I'm in process of adding ignition control to the Megasquirt system on my bike. I'm planning to add a bit of part load, higher rpm advance, and lean out the fueling there a bit. I may also add an actual MAF sensor (hot-film type) rather than the Speed Density/Alpha-N mix I'm using now.

[bocutter Ed]

You are the rider I met outside the Laird & Wicksteed LCBO? Welcome !!

I am Ed...thanks for the note. 
Joe

Turns out I had a stuffed fuel filter.
Next up is Mr. Stinky's crank seals.

Was talkin with Mongrel the other day and agreed that a Toronto Fish & Chip meet ...

Any other locals (or not so local) interested in that?

[Motorhobo]

I'd like to meet n greet someone from Detroit who will drive my FD and DS across the border to Bruno's so I don't have to pay the insane intl shipping and insurance. Unfortunately I live 10 hrs from there...meet n greet not practicable.

[bocutter Ed]

Iron Bridge is a lot closer to Saute Ste Marie than Detroit or Toronto (it's almost 7 hour ride). Guy I know was up there plinking with him recently.

[rbm]

When and where are you thinking of the meet and greet?

[wmax351]

I'd like to meet n greet someone from Detroit who will drive my FD and DS across the border to Bruno's so I don't have to pay the insane intl shipping and insurance. Unfortunately I live 10 hrs from there...meet n greet not practicable.

I think it was only 30 bucks or so. "If it fits, it ships"

[bocutter Ed]

When and where are you thinking of the meet and greet?

Any time/day, except Sunday when The Olde Yorke Fish & Chips, 96 Laird Dr, isn't open.