VTX1300 Sputtering
Pappy
with after-market Cobra exhaust and jet kit installed. It sounds really
good, but when I'm cruising at a constant speed, there seems to be a
sputtering/popping sound.
I'm not a mechanic, but I know how an engine works. What it sounds like to
me is there is ignition happening in the exhaust. The dealer says its fine.
Anyone out there familiar with this?
Thanks in advance.
Albrecht
> I'm new to motorcycles and riding. A month ago I bought a Honda VTX-1300
> with after-market Cobra exhaust and jet kit installed.
Hmmmm. Did the previous owner drill out the EPA anti-tamper plugs so
he could fool around with the idle mixture screws? Look underneath the
carbs, on the side of the float bowls closer to the intake runner.
If you see a slot headed brass screw in a hole there, that's the idle
mixture screw.
Shade tree mechanics don't understand how to adjust the idle mixture,
They think turning the screw open more and more will increase the idle
speed. But it doesn't.
Instead, the idle RPM slows down and the exhaust note becomes dull and
thudding.
If the engine tends to stallfrom being too rich, they turn the master
idle knob up and then they have problems with the engine idling way
too fast because they have managed to uncover the three transition
ports just downstream of the throttle butterfly.
The transition ports are NOT controlled by the idle mixture screws,
they are controlled by the edge of the throttle butterfly.
Adjusting the idle mixture screws is like adjusting the idle mixture
screws on an old two barrel carburetor. Old time car mechanics
remember this.
They would turn the idle mixture screws in until the engine started
running rough, and then they would back the screws out 1/4 of a turn,
rev up the engine twice, and say, "She's a-takin' the gas now, Bubba,"
and shut off the engine and go grab a beer.
> It sounds really good, but when I'm cruising at
> a constant speed, there seems to be a
> sputtering/popping sound.
Well, now, if the sound is sputtering/popping, that is caused by lean
idle mixture. Your carburetors each have an air cutout valve on them
to reduce the amount of
air going to the idle mixture circuits when you are coasting on closed
throttle.
That helps the piffle-piffle-SNAP! a bit, but, if you're getting the
piffle-piffle-SNAP!,
while you're riding with steady throttle, it just may be that the
previous owner set those idle mixture screws a little bit too tight.
> I'm not a mechanic, but I know how an engine works. What it sounds like to
> me is there is ignition happening in the exhaust. The dealer says its fine.
Cruiser riders liked the rumbling sound of a Harley Davidson so much,
Honda built engines with both rods mounted on a single crankpin so the
engine would fire like a Harley. The cylinders fire 1 and 2 and blub
blub and 1 and 2 and blub blub, etc. Some people say
the sound is potato-potato-potato...
During the blub blub period, there is lots of time for excessively
rich mixture to build up in the exhaust system, so Honda, in its EPA-
mandated wisdom, has added an air-injection system to your machine to
help the excess fuel burn in the exhaust system.
Then there is the issue of "single fire" VS "dual fire" ignition
systems.
Carbureted Harleys use a "single fire" system with just one pulser
coil on their signal generator, and that tells the ignitor box to fire
BOTH cylinders at the same time, resulting in the Harley sound, as one
spark plug fires a
*wasted spark* the cylinder that is on the exhaust stroke.
That causes the traditional Harley exhaust rumble.
Harley tried to sue Honda for "stealing" their "trademark" sound.
If you go to www.bikebandit.com oem > honda > 2003 >
vtx1300 > ignition, you will probably see that there is just one
pulser coil to fire both cylinders.
The Older Gentleman
<Snip>
Well, well, you've morphed *again*.
--
BMW K1100LT 750SS CB400F CD250 Z650
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....
Pappy
I bought the bike new, so I don't think the anti-tamper plugs have been
drilled out. Sounds like it may just be a result of the air-injection system
you described.
Thanks again.
"Albrecht" <von.r...@gmail.com> wrote in message
news:1175574196.2...@o5g2000hsb.googlegroups.com...
Albrecht
> Wow, thanks for the detailed explanation.
> I bought the bike new, so I don't think the anti-tamper plugs have been
> drilled out. Sounds like it may just be a result of the air-injection system
> you described.
Well, who installed the exhaust pipe and the jet kit? Did you do it,
or did a shop mechanic install those parts?
When you tweak with the main jets and the exhaust system, something
needs to be done to adjust the idle screws and the only way to get at
them is to drill out the
EPA anti-tamper plugs.
There is a picture of the underside of some Honda carburetors at
www.factorypro.com that shows what the screws look like when the plugs
are drilled out.