Lousey gas milage

[Tom H]

Over the last couple of months mys son's KDX has started getting really cruddy gas milage. It runs fine, has good power,doesn't foul plugs. It just sucks up gas. Currently he uses a tank in about 35 miles of hard desert riding. It used to go 60 easily.
One would suspect the air cleaner. We clean it regularly by washing with gas, followed by hot soap water, hot clean water, dried, and oiled with Bell Ray filter oil. We just cleaned the filter yesterday, and he only made it 35 miles on a full tank in a cross country race today.
The top end was rebuilt maybe 6 months ago, and it hasn't got that many miles on the new piston & rings. That shouldn't be it.
Any ideas?

 

[jaguar]

Either the float valve isn't sealing completely
or the float height when the valve seals is too high
or the float bowl seal isn't sealing and gas is leaking out
or the fuel petcock is leaking gas
or the fuel line is leaking gas

 

[David Trustrum]

Or he is syphoning gas out to pour into the family car so you don’t notice he has been ‘borrowing’ it to go see his girlfriend late at night.

Wondered why it had started to smoke a little?. . .
;)

 

[Tom H]

It doesn't leak gas. Wouldn't it run really rich if the float was malfunctioning? Come to think of it, the family wagon is smoking a but...

 

[GreenPeace]

Maybe a combination of the family wagon option and sniffing with a couple of friends!!!!

 

[Canadian Dave]

Any big changes in air temp etc lately? Could the jetting be too rich now?

David

 

[McRider]

That is a radical change in gas mileage and it is really poor for a KDX. I would re-route the float bowl overflow tube to somewhere that it is obvious if gas is pouring out of it (like on top of the engine case). This would indicate a worn or stuck float needle. It may have some grit keeping it from sealing, but in this case it should leak fuel even when it is not running (as long as the petcock was on). Another possibility is a clogged exhaust or muffler, since that has the same effect as a clogged air filter. In my experience, about 60 miles of hard running is normal on a tank, which is what your son used to get.

 

[Tom H]

When he first starts it, smoke does come out of the joint between the pipe and silencer 'til he turns off the choke. I have never checked the silencer and spark arrestor to see if they are clogged. Sounds worth checking, and I'll check the float level & re-route the overflow to where I would notice a leaky float valve too while I am at it.
It has been cool weather while I have noticed this (from 30 to 50F). I have not had this problem in previous winters.
Thanks for the ideas guys

 

[Tom H]

Mc Rider, I suspect you were right about a clogged silencer. When I got the silencer off, it was obvious that something was wrong. It weighed like 5 lbs! I tore it apart (which was a nightmare) and it was just full of carbon. The little turbine shaped gizmo in the middle of it was clogged solid. I have it soaking in parts cleaner now overnight & will put it back together in a few days.
Although I haven't proven that this will cure the lousey gas milage yet. Let's assume that it will. It obviously is not a good thing to have a constipated exhuast system. I could understand how it could cause all sorts of problems, like keeping the bike from even running. But lousey gas milage isn't one of the things I'd intuitively suspect as a symptom of a clogged silencer.
Can anyone explain why a clogged silencer would cause lousey gas milage?

 

[David Trustrum]

Lose of power meaning throttle opened wider longer to compensate? Also may have made jetting too rich for such a restriction.

Hope it sorts your problem out fully, but you know these things come in 3s.

 

[canyncarvr]

A different take on the matter.

Nothing is wrong with the kdx. What has changed is your kid.

Based on observations of my riding buddy's kid riding over the past short number of months. He gets worse 'mileage' than he did. Has to! He doesn't ride the same, either. (little snot has taken to actually having the gall to pass people these days!! Oh...he's not so little anymore, either!! ...still a snot ;) I have proof!!)

I got 26 miles on a tank in the sand on the coast. Bike was in perfect condition, jetted perfectly.

I could suck a tank of gas in 35 miles easy. I'd be lucky to get that far!!

You said 'hard desert riding'.

 

[McRider]

Tom H,

Like I said in my first post, a clogged exhaust is like a clogged air filter, which you suspected yourself. Either one reduces the flow of air through the engine, reducing its efficiency and power. Consequently, like the previous poster said, you have to use more throttle to get the same amount of work done, using more gas.

 

[nectar]

Also check your reeds for separation from the cage as that to would cause poor gas milage.

 

[mrowe]

High,
My son's '89 kdk200 is exactly the same (and i have heard about this problem with quite a few KDX's), but never heard of anybody solving it.

We checked absolutely everything and couldn't find anything obviously wrong.
This bike starts easily every time, runs really well and shows no symptoms of incorrect fuel/air mixture etc. It just uses heaps of fuel.

I know that this doesn't solve your problem, but you aren't alone.

Does anybody know how to get directly in touch with somebody at Kawasaki who might be able to help. (i'm sure that they know about this problem.

Unfortunately, our solution to this problem was to take heaps more fuel with us when we go riding.

Good luck.

 

[canyncarvr]

What does, '..shows no symptoms of incorrect fuel/air mixture..' mean?

If it (or the bike that started this thread) has not been REjetted, they are too rich.

Tom H's situation was a change in range, though. Not that it had 'always been this way.' In his case, though, it's easy to get 'only' 35 miles on a tank in wide open spaces if you're on it all the time. That's well within what could be considered 'normal'. My bike goes from the 26 I mentioned to close to 100! It all depends.

 

[jaguar]

You said it doesn't leak gas.
Are you sure?
Look at the petcock, float bowl, and cases under the carb to see if they are wet when stopping for a rest. Maybe something only leaks while riding.
You didn't change the jetting, so unless the air filter is clogged up then gas is leaking out.

 

[HOTRODKY428]

OK YOU HAVE A LOT OF MECHANICAL INFO TO CHECK OUT. IF EVERYTHING CHECKS OUT, ONE THOUGHT IS THAT WHEN YOU REBUILT THE TOP END, YOU SOLVED AN AIR LEAK.ANOUTHER POSSIBILITY THE INCREASED VACCUM MAY HAVE DISLODGED SOME DIRT IN THE CARB THAT WAS PARTIALLY CLOGGED....I WOULD SAY ITS A COMBINATION OF SMALL THINGS....GEARING CHANGE?? SON PLAYING WITH A SCREWDRIVER?? IF IT WAS A USED BIKE IT MAY HAVE BEEN JETTED TO FIX A MECHANICAL PROBLEM.