Posted by Scott Seely on July 21, 2008, 9:09 pm
I have cleaned both carb bowls and all the jets. Fuel filter is OK and
fuel pump is pushing fuel thru gas lines. Plugs look OK. Air cleaner
is off, so there is no air blockage. Rubber carb intake boots are tight.
Why won't this bike rev up and run right at higher rpms??? Any ideas?
Posted by Ed Cregger on July 21, 2008, 9:36 pm
>I have cleaned both carb bowls and all the jets. Fuel filter is OK and
>fuel pump is pushing fuel thru gas lines. Plugs look OK. Air cleaner is
>off, so there is no air blockage. Rubber carb intake boots are tight. Why
>won't this bike rev up and run right at higher rpms??? Any ideas?
------------
Weak spark.
Ed Cregger
Posted by Scott Seely on July 22, 2008, 3:12 pm
Ed Cregger wrote:
>
>>I have cleaned both carb bowls and all the jets. Fuel filter is OK and
>>fuel pump is pushing fuel thru gas lines. Plugs look OK. Air cleaner is
>>off, so there is no air blockage. Rubber carb intake boots are tight. Why
>>won't this bike rev up and run right at higher rpms??? Any ideas?
>
>
> ------------
>
> Weak spark.
>
> Ed Cregger
>
>
I am thinking Ed Cregger may be onto something (weak spark) because I
did blow out all the ports in the carbs and the bowls and jets were
pretty clean to begin with... Here's another clue: this bike has 2
plugs per cylinder. When I pull one plug lead on the FRONT cylinder the
idle speed does not change at all, but if I pull a rear plug lead the
idle drops and runs rougher... Even though my plugs look good, maybe I
will get new ones anyway...
Posted by . on July 22, 2008, 4:27 pm
> I am thinking Ed Cregger may be onto something (weak spark) because I
> did blow out all the ports in the carbs and the bowls and jets were
> pretty clean to begin with... �Here's another clue: �this bike has 2
> plugs per cylinder. �When I pull one plug lead on the FRONT cylinder the
> idle speed does not change at all, but if I pull a rear plug lead the
> idle drops and runs rougher... �Even though my plugs look good, maybe I
> will get new ones anyway...
It's your money. I have changed spark plugs needlessly more than once.
Then I saved the perfectly good "old" plugs for spares when news ones
didn't cure the lean idle mixture problem...
Japanese motorcycles are designed with small, lower voltage ignition
coils that will fire more easily at higher RPM.
This low voltage means that the spark will not jump a larger gap, so
the
spark plugs are gapped tighter.
The tight gap means that there is less change for burnable fuel/air
mixture to be in the gap when the plug fires.
The EPA already requires the carburetors' idle circuits to be adjusted
very lean.
When the carbs get dirty inside, the mixture gets even leaner, the low
voltage spark cannot ignite it, and owners change plugs, imagining
there is something somehow *wrong* with the plug.
Posted by The Older Gentleman on July 23, 2008, 2:30 am
> Japanese motorcycles are designed with small, lower voltage ignition
> coils that will fire more easily at higher RPM.
>
> This low voltage means that the spark will not jump a larger gap, so
> the
> spark plugs are gapped tighter.
As I've used exactly the same type of plug in Japanese bikes and bikes
made in other countries, without any recommendation to change the plug
gaps, I think this is nonsense, but I'm quite happy to be shown proof in
the form of (say) a NGK B8HS[1] plug gap spec for two different
manufacturers.
[1] Used in two completely different marques I've owned. One Jap, one
German.
--
BMW K1100LT Ducati 750SS Yamaha XT600E Honda CB400F MZ TS250/1
chateau dot murray at idnet dot com
"What you're proposing to do will involve a lot of time
and hassle for no tangible benefit."
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>fuel pump is pushing fuel thru gas lines. Plugs look OK. Air cleaner is
>off, so there is no air blockage. Rubber carb intake boots are tight. Why
>won't this bike rev up and run right at higher rpms??? Any ideas?