Re: XS400 carb swap from later modelOn Mar 5, 9:38=C2=A0am, "." <Rhiann...@gmail . com > wrote:
> On Mar 5, 5:14=EF=BF=BDam, MisterWhite <84fi...@gmail . com > wrote:
>
> > Thanks a ton. You really know your stuff. I sort of figured the same
> > thing about the CDI
>
> Your Yamaha wouldnot have a real CDI, which means "capacitor discharge
> ignition", but ignorant mechanics and parts counter dorks have gotten
> into the habit of calling transistor ignition modules "CDI" and we're
> stuck with it.
>
> Ignition modules work, or they don't work, there is no in-between
> operation where they sort of work occasionally.
>
> The 80 XS400 had 135 mains, and the
>
> > same idle jet save the crossdrilled holes. The 82 carbs have 125 mains
> > as you said. The carb bodies APPEAR identical Mikunis #s and all, save
> > the drain screw is different in the 82 model & it had no rubber plugs,
> > and has plastic floats.BS34SS 34mm's.
> > I am going to tear back into them, I assumed I had everything clear
> > but I will take another look and clean again.
>
> Getting all the branches of the idle mixture circuit requires spraying
> Berryman B12 or GumOut or STP carb cleaner through the idle jet and
> the pilot air jet and having a good stream of carb cleaner squirt out
> through the single idle mixture port that is controlled by the idle
> mixture screw and the three acceleration transistion ports down stream
> of the throttle butterfly.
>
> The pilot air jet is sometimes in the carburetor intake, and is
> sometimes underneath the rubber vacuum diaphragm.
>
> > With the pod filters and straight pipes, and assuming that the 80
> > model originally had 135s, should I use the 125 mains on the carbs, go
> > with the 135s, or maybe 140s? Thank you again, I am confident I am
> > close.
>
> I can't imagine how an engine that small can use #135 main jets. I
> can't use #135's on a GS1100 with pistons that are larger than your
> XS400 pistons. I use #125's in my large bore bikes.
>
> Now, if you were running wide-open throttle around Daytona, you'd need
> to waste a lot of fuel to keep that air-cooled motor cool but I doubt
> that you will ever ride full throttle for more than a mile.
>
> There is a way to tell whether your mixture is marginally lean. When
> an engine pings, it deposits little black specks on the nose of the
> spark plug that look like pepper. That tells you that you are as lean
> as you can safely go on the total jetting.
>
> The next step after pinging is aluminum throw-off. When the total
> mixture is seriously lean, =C2=A0the top of the piston starts melting and
> you see little silvery aluminum balls on the spark plug.
>
> Tuners used to tell you to look for a light tan color on your spark
> plug nose to indicate proper mixture, but that was back in the days of
> leaded gasoline.
>
> Nowadays, unleaded gasoline leaves a sooty black ring about 1/16th to
> 1/8th inch wide deep inside the spark plug where the hot insulator
> meets the cooler steel body
> and that's why you see race tuners peering down inside the plug with a
> magnifying flashlight.
>
> With the advent of 10% ethanol gasoline, an engine that is jetted lean
> from the factory will run even leaner, because ethanol carries some of
> the oxygen needed to burn it.
>
> If you read the "carburetor tuning guides" that tell you to start
> jetting by selecting the main jet that allows the engine to run best
> at full throttle, you may get the impression that the main jet and the
> idle jet work only at different throttle settings, but this is not
> true at all.
>
> The engine sucks more and more fuel through the main jet as you open
> the throttle more, but it sucks fuel through the idle jets until the
> butterflies are wide open.
>
> It's just that the engine sucks less and less fuel through the idle
> jets as you open the throttle more. But that's why I say that you need
> to work on your total jetting and get
> your idle mixture set for optimum throttle response as you crack the
> butterflies open.
Will do. I will let you know what happens. I am not sure why it has
135s, I thought that was kindof large as well. Possible that someone
put them in there, but it had stock everything and only had 4000 miles
on her when she went down (for 20 years in my cousins barn).
Hopefully, with a little luck, I will be able to run her this spring.
I appreciate all of your information and experience!!! I have a
GS850G, BTW, I love that bike more than any other. Any good way to get
the rear end to stop sliding? Seems like everytime I hit a hard corner
or brake it hard, it wants to come around. Just being shafty I guess.