Engine missing at high speeds

"Zebee Johnstone" <zebee DeleteThis @zip.com.au> wrote in message
news:slrnc6uq4t.9qh.zebee@zeus.zipworld.com.au...
 > In aus.motorcycles on Sun, 4 Apr 2004 09:33:56 +0800
 > John Smith <loopback@localhost> wrote:
  > > float levels but that hasn't helped either. Fuel flow seems to be OK;
I've
  > > opened the carburettor drain while the fuel tap is on to see that fuel
is
  > > flowing through the system.
 >
 > Air filter properly clean?
 >
 > Battery definitely topped up and reasonably new? If it has points, are
 > they properly timed and adjusted?
 >
 > Zebee

Yeah, the air filter is pretty clean and the battery is brand new. I've also
just done the timing but it's easy enough to check again so I'll have
another look at it. I would have thought though that the timing would only
effect high revs, I can rev it to about 8000RPM in first and second gear and
it doesn't miss a beat. Yet at 100kmph and 5000RPM it starts missing - a bit
like what happens when it's time to switch to reserve.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Engine missing at high speeds 

John Smith <loopback@localhost> wrote:

 > The Clymer suggests that the main jet might be too large but in order to
 > test it I'd have to spend money

 > There's got to be something else that I can try...

Try new spark plugs. Apparently they're cheap.

Gary<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Engine missing at high speeds 

 > Yeah, the air filter is pretty clean and the battery is brand new. I've also
 > just done the timing but it's easy enough to check again so I'll have
 > another look at it. I would have thought though that the timing would only
 > effect high revs, I can rev it to about 8000RPM in first and second gear and
 > it doesn't miss a beat. Yet at 100kmph and 5000RPM it starts missing - a bit
 > like what happens when it's time to switch to reserve.

HT leads/coils breaking down under high load?

Poor fuel flow causing starvation at high revs?<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Engine missing at high speeds 

I've also seen a bad stator cause this...


"John Smith" <loopback@localhost> wrote in message
news:406f6610$0$16598$5a62ac22@freenews.iinet.net.au...
 > I'm hoping that one of you mechanics out there can give me some tips. I've
 > got an old CB750 that runs well at anything up to 80kmph but anything over
 > and the engine starts missing on one or more cylinders.
 >
 > I've just adjusted the needle position in an attempt to rectify it and the
 > spark plugs are now a nice tan colour, instead of black so that's done
 > something useful but hasn't fixed the engine missing. I've also adjusted
the
 > float levels but that hasn't helped either. Fuel flow seems to be OK; I've
 > opened the carburettor drain while the fuel tap is on to see that fuel is
 > flowing through the system.
 >
 > The Clymer suggests that the main jet might be too large but in order to
 > test it I'd have to spend money
 >
 > There's got to be something else that I can try...
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Engine missing at high speeds 

John Smith wrote:
 > I'm hoping that one of you mechanics out there can give me some tips. I've
 > got an old CB750 that runs well at anything up to 80kmph but anything over
 > and the engine starts missing...

"Engine located below petrol tank after a brief search..."

 > ... on one or more cylinders.
 >
 > I've just adjusted the needle position in an attempt to rectify it and the
 > spark plugs are now a nice tan colour, instead of black so that's done
 > something useful but hasn't fixed the engine missing. I've also adjusted the
 > float levels but that hasn't helped either. Fuel flow seems to be OK; I've
 > opened the carburettor drain while the fuel tap is on to see that fuel is
 > flowing through the system.
 >
 > The Clymer suggests that the main jet might be too large but in order to
 > test it I'd have to spend money
 >
 > There's got to be something else that I can try...

Is it a CDI ignition? On a CX500 (and most other CDI equipped Hondas
of that era) there are 2 coils on the stator that drive the ignition -
one for under 5000rpm and one for over. The high-rpm one tends to
burn out, and the symptom is pretty much exactly what you describe.
Does it misfire and generally refuse to run over that rpm in the lower
gears too?


BTH<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Engine missing at high speeds 

"John Smith" <loopback@localhost> wrote in message
news:406f7b0d$0$16581$5a62ac22@freenews.iinet.net.au...
 > "Zebee Johnstone" <zebee DeleteThis @zip.com.au> wrote in message
 > news:slrnc6uq4t.9qh.zebee@zeus.zipworld.com.au...
  > > In aus.motorcycles on Sun, 4 Apr 2004 09:33:56 +0800
  > > John Smith <loopback@localhost> wrote:
   > > > float levels but that hasn't helped either. Fuel flow seems to be OK;
 > I've
   > > > opened the carburettor drain while the fuel tap is on to see that fuel
 > is
   > > > flowing through the system.
  > >
  > > Air filter properly clean?
  > >
  > > Battery definitely topped up and reasonably new? If it has points, are
  > > they properly timed and adjusted?
  > >
  > > Zebee
 >
 > Yeah, the air filter is pretty clean and the battery is brand new. I've
also
 > just done the timing but it's easy enough to check again so I'll have
 > another look at it. I would have thought though that the timing would only
 > effect high revs, I can rev it to about 8000RPM in first and second gear
and
 > it doesn't miss a beat. Yet at 100kmph and 5000RPM it starts missing - a
bit
 > like what happens when it's time to switch to reserve.
 >
 >

Maybe a kink in a fuel line? If it's not rev-related but road-speed
related, perhaps something is flexing in the wind-blast.

--
conehead
try one of these wild-man pills, sir<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Engine missing at high speeds 

have you had the jets out and cleaned them and all the carb passage ways
with compressed air ??

how old are the plugs ???

are u positive that the float levels are correct ???

"John Smith" <loopback@localhost> wrote in message
news:406f6610$0$16598$5a62ac22@freenews.iinet.net.au...
 > I'm hoping that one of you mechanics out there can give me some tips. I've
 > got an old CB750 that runs well at anything up to 80kmph but anything over
 > and the engine starts missing on one or more cylinders.
 >
 > I've just adjusted the needle position in an attempt to rectify it and the
 > spark plugs are now a nice tan colour, instead of black so that's done
 > something useful but hasn't fixed the engine missing. I've also adjusted
the
 > float levels but that hasn't helped either. Fuel flow seems to be OK; I've
 > opened the carburettor drain while the fuel tap is on to see that fuel is
 > flowing through the system.
 >
 > The Clymer suggests that the main jet might be too large but in order to
 > test it I'd have to spend money
 >
 > There's got to be something else that I can try...
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Engine missing at high speeds 

"Johnnie5" <ducatiau DeleteThis @hotmail.com> wrote in message
news:c4ol32$2hf$1@lust.ihug.co.nz...
 > have you had the jets out and cleaned them and all the carb passage ways
 > with compressed air ??
 >
 > how old are the plugs ???
 >
 > are u positive that the float levels are correct ???
 >
 >
I'm pretty positive that the float levels incorrect actually The spark
plugs are pretty new though and the carb is pretty clean. I haven't sprayed
compressed air through the jets but I've had them out and had a look at
them. The float level is something that I can experiment with - I tried
ringing The Honda Shop to see if they could tell me the correct setting but
they don't have information for bikes that old. The Clymer has some settings
but the diagram looks nothing like what my carbs look like.

How accurate does the level have to be? Could I just put clear hose on the
drain and measure the level that way - say to fill 3/4 of the float bowl?<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Engine missing at high speeds 

"John Smith" <loopback@localhost> wrote in message
news:406fe889$0$16586$5a62ac22@freenews.iinet.net.au...
 > "Johnnie5" <ducatiau.RemoveThis@hotmail.com> wrote in message
 > news:c4ol32$2hf$1@lust.ihug.co.nz...
  > > have you had the jets out and cleaned them and all the carb passage ways
  > > with compressed air ??
  > >
  > > how old are the plugs ???
  > >
  > > are u positive that the float levels are correct ???
  > >
  > >
 > I'm pretty positive that the float levels incorrect actually The spark
 > plugs are pretty new though and the carb is pretty clean. I haven't
sprayed
 > compressed air through the jets but I've had them out and had a look at
 > them. The float level is something that I can experiment with - I tried
 > ringing The Honda Shop to see if they could tell me the correct setting
but
 > they don't have information for bikes that old. The Clymer has some
settings
 > but the diagram looks nothing like what my carbs look like.

i would be changing the plugs as a matter of course

i would also pull the carbs and pulling out all jets

pressure pack carb clean and compressed air all passages and jets
(this is most carb probs )

 >
 > How accurate does the level have to be? Could I just put clear hose on the
 > drain and measure the level that way - say to fill 3/4 of the float bowl?
 >
 >

float level is usually measured with a special tool 12547*98120/8200 costing
$5679.00

some carbs u can use the hose method , just depends

also check needle and seats are in good condition and operating correctly ,
u can check this
by blowing down the fuel line and operating the float up and down to make
sure it seals

also some carbs have filters under the seat or somewhere in the line to
each carb, check for these
as they might be blocked enough to allow only a little fuel through wo when
a large amount of fuel is
required the fuel in the carbs runs low so get the probs you are having<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Engine missing at high speeds 

John Smith wrote:
 > I'm hoping that one of you mechanics out there can give me some tips. I've
 > got an old CB750 that runs well at anything up to 80kmph but anything over
 > and the engine starts missing on one or more cylinders.
 >
 > I've just adjusted the needle position in an attempt to rectify it and the
 > spark plugs are now a nice tan colour, instead of black so that's done
 > something useful but hasn't fixed the engine missing. I've also adjusted
the
 > float levels but that hasn't helped either. Fuel flow seems to be OK; I've
 > opened the carburettor drain while the fuel tap is on to see that fuel is
 > flowing through the system.
 >
 > The Clymer suggests that the main jet might be too large but in order to
 > test it I'd have to spend money
 >
 > There's got to be something else that I can try...

Are you sure it's not fuel related. Ie a high frequency (ie RPM) noise or
something from the CDI? (Do they run a CDI?). Could have something going on,
perhaps the pickups are a bit dodgey. Perhaps test the CDI to see if there
are any faults. You can usually do this with the multimeter and a Haynes
manual or workshop manual.

Cam
'03 954<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Engine missing at high speeds 

BT Humble wrote:
 > John Smith wrote:
  >> I'm hoping that one of you mechanics out there can give me some tips.
I've
  >> got an old CB750 that runs well at anything up to 80kmph but anything
over
  >> and the engine starts missing...
 >
 > "Engine located below petrol tank after a brief search..."
 >
  >> ... on one or more cylinders.
  >>
  >> I've just adjusted the needle position in an attempt to rectify it and
the
  >> spark plugs are now a nice tan colour, instead of black so that's done
  >> something useful but hasn't fixed the engine missing. I've also adjusted
the
  >> float levels but that hasn't helped either. Fuel flow seems to be OK;
I've
  >> opened the carburettor drain while the fuel tap is on to see that fuel is
  >> flowing through the system.
  >>
  >> The Clymer suggests that the main jet might be too large but in order to
  >> test it I'd have to spend money
  >>
  >> There's got to be something else that I can try...
 >
 > Is it a CDI ignition? On a CX500 (and most other CDI equipped Hondas
 > of that era) there are 2 coils on the stator that drive the ignition -
 > one for under 5000rpm and one for over. The high-rpm one tends to
 > burn out, and the symptom is pretty much exactly what you describe.
 > Does it misfire and generally refuse to run over that rpm in the lower
 > gears too?
 >
 >
 > BTH

That's interesting, you learn something new every day eh? Will remember that
for future splutters n fuck ups on old Hondas.

Cam
'03 954 (And if anything goes wrong it'l shit itself)<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Engine missing at high speeds 

In article <70800dae.0404041512.1c5a130f RemoveThis @posting.google.com>,
za2bb RemoveThis @optusnet.com.au (BT Humble) wrote:

 > John Smith wrote:
  > > I'm hoping that one of you mechanics out there can give me some tips. I've
  > > got an old CB750 that runs well at anything up to 80kmph but anything over
  > > and the engine starts missing...
 >
 > "Engine located below petrol tank after a brief search..."

I'm glad _somebody_ mad that joke

big
--
"A magazine here has a bunch of bonobo's in the zoo and a bunch of
market analysts from major banks picking stocks weekly. So far the
bonobo's are turning in a profit and the analysts lose money. The
banks haven't made the logical step yet." - Lieven Marchand in SDM<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Engine missing at high speeds 

BigIain wrote:
 > za2bb RemoveThis @optusnet.com.au (BT Humble) wrote:
 >
  > > John Smith wrote:
   > > > I'm hoping that one of you mechanics out there can give me some tips. I've
   > > > got an old CB750 that runs well at anything up to 80kmph but anything over
   > > > and the engine starts missing...
  > >
  > > "Engine located below petrol tank after a brief search..."
 >
 > I'm glad _somebody_ mad that joke
 >
 > big

Why's that Big? Were you afrad that if you had to tel it you'd maek a
typo and buger it up?


BTH<!-- ~MESSAGE_AFTER~ -->
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