There's a wide range of jetting kits and carburetor mods available.
But we are just looking at mostly simple do-it-yourself mods that can
be done very cheaply and give you great performance and economy...
without an obnxiously loud bike.
And you know how we feel about loud bikes.
So we start by removing the side covers, the seat, and the fuel tank.
We remove the fuel hose. These grommets here?
You want to take these out before they fall down somewhere.
When you pull the tank off, make sure these rubbers don't fall off.
Once the fuel line is off you'll see this little bit of white plastic,
an annoyingly small fuel filter.
Replace it with a decent-sized fuel filter as per this photo.
This is a critical mod - this breaether for the vacuum carburetor .
If it's dirty or blocked, you're going to
be wearing your carburetor , your bike will stop running.
We recommend servicing this every time service your air filter.
Adding extra foam is not just extra protection, then you never have to service inside one.
You can just pull this out easily.
If you don't modify your dr650 carburetor , leave the snorkel in.
Loosen off these bolts, so we can swing the carburetor around.
Loosen that.
The choke cable is very very fragile.
That's plastic in there, it breaks very easily or strips.
Now we swing the carburetor around, we remove the screws on top.
Many replace these screws because they're garbage.
We lift the top off, there's a spring in there.
Don't lose this o-ring, don't let it go missing.
There's the needle.
This is the slide.
Looking in the top of the carburetor , this is the slide guide.
You can see those holes each side.
When these holes disappear, that's when it's time to replace your slide guide.
It should last 20000km to 30000km.
But if you let this get dirty it'll be way sooner.
If you do taper the needle, you can remove the snorkel.
But don't enlarge this air hole!
You will get increased air intake, but just enough to suit a type of needle...
that's assuming you don't change your main jet.
The problem with the stock needle?
It's too fat down here.
So the bike is too lean off idle.
What a lot of guys do is they drop the needle here
so that they get rid of that 'bog' that happens off idle.
The problem is then it's crap everywhere else for the rest of the rev range.
What we will do is taper the needle to get good fuel air mixture right through the rev range.
So what we do is grind this little bit of plastic so it'll change where it sits.
Now... down in here there's a little shelf. We
grind the plastic on this so the needle sits lower.
It will bypass the shelf and be positioned better.
So this doesn't need to come completely to a point...
but fairly close.
The important thing is just creating a taper here.
Don't take too much off.
You want a shape roughly like this.
And you really want to look after this diaphragm.
If you do make a little hole, the bike is not going to operate properly.
Your carburetor slide won't have a vacuum to work against!
Your throttle will stop working.
Once the engine is running, the vacuum created
is what determines how quickly the slide is going to come up.
We actually drill an extra hole here so that we'll get a better throttle response.
So the quicker this slide comes up, the quicker the fuel comes in...
which is very similar to what a pumper carburetor does.
We will also drill out this second hole.
We'll drill from the side first then straight down.
And enlarge the second hole as well.
So we had just one 2.5mm hole.
Now we have two 3mm holes.
Because we have shaved that bit of plastic and it'll sit further down,
we don't need to make any adjustment of the needle position.
For Australian conditions, year round, this is a good compromise.
Suzuki puts these terrible Philips screws down on the float bowl.
These can strip very easily... they 'burr' very easily.
An important thing..
given how tricky these screws are...
they are not Philips screws!
They are actually JIS screws.
And this is a JIS screwdriver
(Japanese industrial standard).
Now we swing the carburetor around the other way, so we can access this screw.
Again, we're using this tool just to avoid burring the screws.
Always check for water and dirt in the bottom of your float bowl.
We flip this around more to access the main jet.
A 140 main jet if you leave the airbox stock.
But if you're going to a 150 main jet we will cut the airbox.
Main jet coming off.
The main jet is back in.
As mentioned earlier, ensure this o-ring is still in place.
And get a torch just to make sure the needle is definitely sitting off the shelf.
Bingo!
This spring is 112mm long.
We cut it down to 100mm.
Because we've shortened this spring, it means the throttle response will be faster...
similar to a pump a carburetor .
When you throttle off, it also 'backs off' a bit gentler and smoother as well...
a smoother ride all over.
An important thing to watch out for when reinstalling this pipe,
this hose here can drop off.
And we can see it has dropped off.
This hose can also kink and you can get the same issue if it's not on.
It's a hose that you want to check every time you move this carburetor.
We tighten this back up.
Tighten this one back up.
And then tighten the carburetor back up itself.
You probably can't see it with the camera, but there is a notch there and a notch there...
to allow you to line the carburetor correctly.
And now it's time to drill the airbox!
One thing to remember...
these nuts can come out easily if you're not careful.
We usually just put some type of cloth in here prior to cutting.
This is 2 inches, or 51 millimeters.
And one thing we do is we keep this as far away from this breather as possible.
If you go near this breeder you're going to interrupt the airflow...
which we think is the main cause of 'surging'.
Gordon has experimented with smaller holes, bigger holes, different positions....
this is the one that he's found best.
And this size hole works well, regardless of how much further you go with the main jet size.
A very handy thing in dusty conditions?
Put one of these 'Chux Super Wipes' in here without filter oil or any liquid.
Tuck this around properly.
The good thing is when you throttle off the
dust will actually fall off and into the bottom of the airbox.
The dust stays in the bottom.
Canadians love this sort of stuff because they're so lazy lol!
Now this exhaust weld in here sometimes is really messy.
And it always restricts the diameter going into the pipe.
And it creates turbulence.
You'll get a significant power difference simply by grinding this flat.
Now the tricky bit though...
don't grind the whole weld out!
This is what holds these two bits together.
So you probably want to leave about 1mm of weld at a minimum.
You can grind more than this, but this is what's recommended to leave...
just to keep the strength there.
If you really wanted it full performance,
of course, you can grind it smooth on the inside, then add a weld around here.
Even if you haven't modified you bike, the air screw should be one and a half turns out.
Once you do all these mods, it will normally be 1.75 turns out.
This can be plus or minus half a turn, depending on temperature and other factors.
We highly recommend the Suzuki GSXR exhaust for good power gains...
a great sound but far quieter than aftermarket exhausts.
According to dyno charts we've seen these mods all provide
about a 10% improvement across the rev range.
And make a big difference to fuel economy, better starting, and how smoothly it runs at low revs.
Just do this up snugly...
not too tight.
It's a great idea to loctite anything on a DR650 when you're screwing it back up.
Use the caps bolts that come with the GSXR.
Now the muffler is on properly, we tighten all these remaining bolts correctly...
and including the header pipe bolts.
These bolts in particular... you want Loctite.
These vibrate loose easily.
Now we put this on 'prime' after the carburetor has drained...
so it replenishes easily.
An important thing to remember is these little holes here.
They go on little tabs to make sure the side covers stay in securely.
Because the engines running so much better now, we've got to reduce the idle speed.
That's better.
And now we do a test ride.
What we're looking for is a little bit of fluffiness,
a little bit of hesitation, just around quarter throttle.
If so we may need a richer air/fuel mix and change the needle position.