Yamaha XS650 backfire - Page 3

 Dave wrote:

I recently bought a 1984 VF500F that wouldn't run unless I had the enrichener
lever turned all the way on.  I tried B-12, Yamaha Carb Cleaner, etc.  I took
the mixture screws out and sprayed B-12 through the passageway.  Nothing really
helped except removing the carbs and poking a soft copper wire strand (really
fine and really soft) through the pilot jets.  2 of the 4 pilot jets were
completely blocked, the other two partially blocked.  When those little jets
are fully blocked, no fuel system cleaners are likely to do anything because
none of it actually flows through the jet.  If the jets are only partially
plugged then you have a chance of cleaning them out chemically.

You are dealing with an engine that has carbs that are relatively easy to
remove & replace, plus there are only two of them.  Stop putting it off and
pull the carbs.  Only take apart one at a time, take your time, do not, I repeat
do not adjust the floats unless you are *sure* they are misadjusted, just remove
all the jets, the idle mixture screws, and run a shitload of spray carb cleaner
through everything.  Especially make sure the idle circuit, idle mixture port,
and the transition ports all are totally unblocked.

Avoid getting carb cleaner on the diaphragms, it generally
won't really hurt anything but until they dry out they will swell up a lot and
you'll have a hell of a time getting them to fit.  Also make sure you don't
lose the little washer, spring, and tiny O-ring on the mixture screws.  I like
to work with an old towel on top of my workbench to catch little parts and keep
them from skittering off into oblivion.  Sometimes there are tiny O-rings between
the diaphragm covers and the top of the carbs, keep a sharp eye out when you're
taking that apart too.

If you don't have an official Yamaha manual, try and get your hands on one, if
you can't or aren't willing to pay for one, at least get a Clymer or Haynes
manual or google for a diagram that shows where all the little passages in the
carbs go.  Despite what I said about not touching the floats, you definitely
need to check the float height before putting the carbs back together.  It's
really nice to be able to check the actual fuel level with the carbs assembled
but getting the float level correct is good enough 99% of the time.

Good luck.

 

Deep down I already knew this.  I'll try to fit it in on the weekend.  It's
just such a pain in the you know where to adjust and balance them.  I've got
to take it out for some highway rides and start the painful guess 'n check
process of re-jetting for my new exhaust, so the carbs will be coming off
anyways, one more time won't kill me.


I've got the manual, it's available online for free.  Thanks for your
advice.

Dave

 

Steer clear of Dynojet kits. Dynojet is trying to enhance their bank
account by keeping speed secrets *secret*.

I recommend going to www.factorypro.com and studying what they have to
say about jetting CV carburetors. The owner of Factory Pro is *not*
trying to keep secrets, he's telling how to rejet a carburetor using
stock Mikuni or Keihin parts.

Your carbs are probably made by Hitachi, but Mikuni main jets should
fit just fine.

The problem with re-jetting is that most home mechanics do not
understand how the size #'s relate to orifice area.

Since I've explained this concept dozens of times in this NG, I won't
go into it again, but you can google up "round jet" and find the
information.

 

Nonsense

Mikuni, actually.

You really are preaching from a position of ignorance here.


--
BMW K1100LT  Ducati 750SS  Honda CB400F & XBR500  Triumph Street Triple
Suzuki TS250ER
If you don't know what you're doing, don't do it. And RTFM.
chateau dot murray at idnet dot com

 

Listen to this man. He speaks the truth. Lots of people put their faith
in all these magic potions and cures, but ultimately, fixing something
properly is the only sure way.


--
BMW K1100LT  Ducati 750SS  Honda CB400F & XBR500  Triumph Street Triple
Suzuki TS250ER
If you don't know what you're doing, don't do it. And RTFM.
chateau dot murray at idnet dot com