Throttle pickup from idle

 I have a 1996 Honda CBR1000F. I am very happy with it, except for one
little annoyance: When I want to add power after having it completely
closed, it is very difficult to avoid a jerk just as the throttle
opens.

Earlier, it was impossible to avoid the jerk. Since then, I have
replaced the drive chain, adjusted the valves, synched the carbs and
lubed and adjusted the throttle cables and throttle grip. It helped
somewhat, but it is till not right. I have to be extremely careful if
I want to avoid the jerky transition.

Running at a very high gear more or less eliminates the problem, but
that is just masking the symptom, not solving the problem.

The engine runs, as far is I can tell, perfectly otherwise.

This can't be normal? How to I troubleshoot this?
--
RoRo

 


Something sticking slightly in the throttle mechanism ????  Hand grip,
cable, cable connection near carbs, butterfly(s).........it would only take
a tiny bit of sticking.  No (or not enough) slack in the throttle cables?
Too MUCH slack in the cables?  Throttle return spring(s) too strong?
Just some wild guesses.  FWIW.

 Robert Roland wrote:

Hello, RoRo. Are you in Norway?

Motorcycle drive trains have a lot of slop in them. You would have a hard
time
shifting gears if the slots in the freewheeling gears weren't larger than the
dogs on the pinion gears.

So, once you're in a gear, any time you change throttle position, the
motorcycle
will jerk a little bit.

And this jerking is aggravated by the constant vacuum (diaphragm) carburetors
that act like they have a mind of their own. If you change throttle position
the vacuum slide drops and leans up the mixture.

When you open the throttle, the CV carb is also slow to respond to the need
for more gasoline as engine vacuum drops off, especially if the idle circuit
and the acceleration transition ports are gummed up.

There is nothing that responds quite as well as a set of radial flat slide
Keihin carburetors, but that's an expensive solution to the CV carburetor
problem.

Although you've synched the carbs, you still may have a problem with dirty,
gummed up idle ports and passages. CV carburetors are famous for getting all
gummed up and the mechanic$ are eager to get your bike into the $hop and
$ynch your carb$ for you.

But, I recommend that you pour about 4 or 5 ounces of a clear carburetor
cleaner into a full tank of gasoline and then go for a slow ride to clean the
ilde circuits out.

I don't know what is available where you are, but a mixture of xylene,
toulene, acetone and methyl alcohol works very well to clean gum and varnish
out of the jets and passages.

In the USA, I recommend Berryman B12 Chemtool Choke and Carburetor Cleaner in
the liquid form.

If the throttle response is still jerky after cleaning the idle circuit, you
can adjust all the idle mixture screws counterclockwise about 1/4th of a turn.


http://www.bikebandit.com/partsbandit/showschematic.asp?dept_id 5205

 6: SCREW SET is the idle mixture screw.

Don't go too far CCW with those screws, the idle jet is about a #40, which is
fairly large.

If you open the idle mixture screws too far, the idle speed will slow down
and the exhaust sound may become dull and thudding.

The mistake the amateur mechanic makes is in turning the idle speed knob
clockwise,

This uncovers a pattern of three acceleration transition ports which
shouldn't be uncovered at idle. They are NOT controlled by the idle mixture
screws, they are controlled by the bottom edge of the butterfly.

When the amateur mechanic blips the throttle to check for response, the
engine won't idle back down.

So, don't go too far with opening up the idle mixture screws. Just a little
bit to help the throttle response.

--
Message posted via MotorcycleKB.com
http://www.motorcyclekb.com/Uwe/Forums.aspx/tech/200708/1

 On Wed, 08 Aug 2007 17:54:50 GMT, "Albrecht via MotorcycleKB.com"


Yes, I am.


Yes, even cars have plenty of slop. The point is that if the rider (or
driver) is able to take out the slack gently, the jerk will be small,
maybe even not noticeable.


I'll see what I can find. If that does not solve the problem, I'll
take the carbs apart and clean them manually.


It seems I have to remove the carbs to get to them. They seem to be
located on the underside of the carb. Can it be that stupidly made?


I just remembered: The idle speed knob is very sensitive. It is
difficult to get the right idle speed. Even the slightest twist will
be too much one way or the other. Of course, the rubber connection
between the knob and the actual screw does not help.


I will. It may be spring before I get to it, though. Winter is coming,
and we haven't even had a summer yet.

Thanks to you and everyone else for your suggestions.
--
RoRo

 

***************************************
I have one of these for 4-stroke carb adjustment for atvs and
motorcycles:
http://www.motionpro.com/motorcycle/tools/pilot_screw_adjusting_tool/
I've found it to be extremely handy, No more burned fingers, and no
more removing the carbs from atvs, just to adjust the idle fuel screw.
It might help you.

Good Riding and Good Wrenching to You!



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