#4: Re: KJS Mikuni HS40 can you help ?
Author: eaglebeak, Posted: Sat May 15, 2010
11:07 pm
I rode my '86 XV-700 brand
new off the showroom floor and never got more than 42mpg on its best day.
Perhaps they did a lot of improving during the next 10 years if the 750
was supposed to get 46mpg?
After installing the KJS manifold and
Mikuni HS-40, I typically average 38 to 40mpg riding solo and depending on
terrain and/or headwind; but the bit lower gas mileage is primarily due to
a full mechanical carb with an accelerator pump where the OEM duals were
strictly vacuum operated with no accelerator pump(s). The great increase
gained in hard/quick acceleration from virtually any speed comes at a
price of a bit lower gas mileage and the loss of a few MPH off the top
end.
However, your 26mpg is most definitely an indication of a
problem somewhere, but may not necessarily be a carb or manifold problem.
Checking for a possible vacuum leak is very easy by using a can of
starting spray. Do the test outside in a well ventilated area and only do
it on a warm (not hot) engine that's warmed up only enough to idle without
any choke. Shoot little squirts of starting spray around the manifold
connections to the engine heads and around the carb to manifold boot
(taking care not to spray toward the carb's air intake throat). Any change
you hear in idle speed or engine sound will indicate you've just sprayed a
vacuum leak.
If the leak test shows no leaks, then it's entirely
possible the carb is outfitted with too large a main jet or the metering
pin isn't adjusted at the correct height. If the engine seems to run hard
and good at full throttle with no bogging, misfiring, or evidence of dark
exhaust, the main jet is probably OK. If there's a lot of hesitation or
"dead spots" when going from 1/4 throttle to mid-throttle and/or sluggish
response in the mid to 3/4 throttle range, then you may need to adjust the
metering pin to the next lower position.
If the carb seems to
perform well through all throttle and acceleration ranges, then you may
have an ignition problem or dirty/restricted air cleaner element. Pull
your spark plugs and "read" them to see if they are black and sooty
looking to indicate a rich condition, then let us know what you
find. |