Technical Insights
by Elden Carl
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11/01/10

KLR650 / DR650 "Carbonmakers"

Every time I turn the WR250R key to the on position and hear the fuel pump pressuring
the injection system I get the "willies". Why? Because, to paraphrase Kevin Cameron
"Motorcycle fuel injection systems are very reliable, but if one fails, be ready for a long
walk".

Fuel injection systems are far more complex and expensive than carburetors and usually
can't be repaired in the field the way some carburetors can.
What's NEW!
Top Gun Motorcycles
employing a UNI or K&N air filter), don't increase wind drag (big square boxes and high
windshields etc.) and gear for the overall load on the engine. For example, on our
biannual Big Bear two day 425 mile mountain run, Pauline and I, two-up and geared
15/45, get approximately 47 mpg despite traversing elevations from sea level to over
8,000 feet on mostly two lane mountain roads. Although our gross load is approximately
750 pounds, we keep our wind drag low with roundish soft bags riding close to the frame
on Happy Trails racks, Kawasaki tank bag and no wind shield. Our 15/45 gearing keeps
us in the most efficient and thus most economical part of the power band, smack dab in
the middle between pumping losses and friction losses. Do it right and you not only save
money, but avoid adding unnecessary pollutants to our rapidly degrading atmospheric
environment.

Ride smart - Ride safe.
Elden enjoying some of those
million miles, this time in Baja.
With proper set-up and care, your
carbureted MSM can take you
almost anywhere.
(Big Bear Lake, CA - 6,750')
With approximately a million miles on
motorcycles since 1955, I've suffered only
one fuel supply failure which occurred at
Ojos Negros, Baja about a year ago. Rod
Morris and I came out of the dirt and went
directly to the Pemex Station to air up the
tires for pavement. When I attempted to
restart the engine of my DR650 it turned
over fine but wouldn't fire. To make a long
story short, a tiny fuel filter located inside
the fuel intake pipe of the carburetor had
filled with particles preventing fuel flow.
Wow, I didn't even know it was there.
The fix was easy:

  1. Remove the tiny factory fuel filter,
    throw it away, and refrain from ever
    installing a replacement copy.
  2. Install a larger, transparent in-line
filter between the petcock and carburetor.
Fast forward. Mike Henshaw called me the other day to discuss a KLR650 problem.  Mike
wondered if his difficulty might be fuel supply related. His first mistake was to attempt to
get the answer from cyberspace.  

The "experts" on the Internet suggested that if his problem was fuel supply related, it
could be:

  • The vacuum tube running between the petcock and the upper front of the
    carburetor may have collapsed.
  • The fuel could be boiling and bubbling inside the fuel line between the carburetor
    and the petcock.

Both of these theories are pure bull ----.

In the first instance, there is sufficient vacuum in the vacuum hose to move the thin
neoprene diaphragm allowing the fuel to flow, but not enough to collapse the hose (could
it be kinked?).

As I wrote back in the nineties in "Dual Sport News", you should rebuild a KLR650 petcock
from time to time because with age, the neoprene diaphragm may crack and leak air
causing at least partial interference with the fuel supply.

The only way to insure that you get all of the fuel possible all of the time is to convert the
petcock to manual only. The downside is that you have to remember to manually turn it off
when the engine is not running.

In the second instance, assuming all is well with your vacuum petcock, fuel flows down hill
in a gravity feed system. If the petcock and fuel line have no obstructions, the fuel
continues to fill the float bowl with the float and float valve controlling the fuel level and
ultimately joining the closed diaphragm in shutting the fuel off when the engine stops
running. It's close to a fool-proof system and even better if you make it manual and keep
your filters clean. Remember, you must do the job of the diaphragm by shutting the fuel
off and on as needed.

I'm enjoying the fuel injected WR250R, but when it comes to traveling to far-away places
I'll trust in gravity fed and carbureted fuel systems.

Being a maintenance freak, I periodically clean and rebuild my carburetors replacing all
neoprene parts. If inspection reveals a defect I also replace the float needle and or float,
being sure that the float level is set properly.

The KLR650 has always been a sloppily assembled motorcycle from the factory
(especially since it moved to Thailand). It didn't surprise me when long time expert
multisurface motorcyclist Ron Jensen complained about his new KLR650 running roughly
back in the late 90's. Ron, like most top riders, is very sensitive to how his equipment is
functioning; I was not shocked to receive a specific answer when I asked him to describe
his problem. He related, "Between the speed of 60 and 75 MPH, I have a constant lean
surge that is driving me crazy." I believe the KLR650 to be one of the best carbureted
motorcycles ever to come out of Japan (ask any hog pilot riding a late model Harley
equipped with a similar Keihin fuel supplier). Consequently, I immediately suspected the
float setting. After removing the carbonmaker, as Alan Dietor, my Tecate 500 Enduro
leader used to call it; I broke out my very accurate 1975 model Honda float level gauge
and promptly discovered that the float had been set 4.5mm lean by the factory. After
carefully adjusting the float level to its proper setting and reinstalling the float bowl, I
reassembled all the components and readied Ron's scooter for a test run.  As Ron
jumped onto his KLR650 and took off for the freeway I crossed the trigger finger and
principal signal finger of my left hand. One should always try to keep his
throttle/brake/gun hand unencumbered whenever possible. About 10 minutes later Mr.
Jensen returned and upon removing his helmet displayed a big, near jaw-breaking grin.  
Problem solved!

The moral of the story is that if your motorcycle is in stock configuration and is carbureting
poorly at idle, check the pilot air screw. If it stumbles and surges in the midrange, it's best
to check the float level. If you still have poor running, it's time for tear down, cleaning, and
high pressure air.
Properly set, I've never had a better stock
carbureted motorcycle than the KLR650.  
Even when Ron Jensen led Pauline Read,
Robert Buchanan, and me over Schofield,
Cinnamon (in the rain), Engineer, and Ophir
Passes in Colorado in the mid 90's, the
KLR650's lost some power but ran smoothly.
Other motorcyclists were having trouble
starting and running at 11,000+ feet - but
not the 4 of us on KLR650's.

If you want a better carbureted motorcycle
than the Keihin equipped KLR650 you have
to go to fuel injection. If you want your
KLR650 (or any MSM) to operate in the
most economical zone, leave the intake and
exhaust tracts near stock (except for