I've written here before about various problems with my old (and beloved)
'78 SR500. Lately it's developed an odd habit. If I let it sit for a
few days, it still starts up fine, but dies in about the time it takes to
empty the float bowl - about a 1/2 mile or less. Kicking it over several
times gets it restarted and no more problems stopping and restarting on
that day. If I run it every day, or even every other day, I never see
the problem.

It would seem to be the floats sticking in the up position, being jarred
loose by kicking it with an empty float bowl. But why wouldn't the
vibration (it *is* a thumper, after all) of running jar it loose? Why
only after sitting for a few days?

I use Star Foam every time I fill it up, and when the problem started I
ran some B12 through it. The B12 seemed to help for a week or two, but
then it reverted back to the problem.

Initially the bike had a vacuum petcock, but that was replaced some time
back with a non-vacuum one from an XS650. So no need for solutions
involving that.

Am I mis-diagnosing the problem? Is there something else it could be?

I'm not adverse to replacing the floats and hinge if necessary, but since
it's a PITA to remove/replace the carb I don't want to do that unless I
have to.

--
Intelligence is an experiment that failed - G. B. Shaw

Larry Blanchard <(E-Mail Removed)> wrote:

> I've written here before about various problems with my old (and beloved)
> '78 SR500. Lately it's developed an odd habit. If I let it sit for a
> few days, it still starts up fine, but dies in about the time it takes to
> empty the float bowl - about a 1/2 mile or less. Kicking it over several
> times gets it restarted and no more problems stopping and restarting on
> that day. If I run it every day, or even every other day, I never see
> the problem.
>
> It would seem to be the floats sticking in the up position, being jarred
> loose by kicking it with an empty float bowl. But why wouldn't the
> vibration (it *is* a thumper, after all) of running jar it loose? Why
> only after sitting for a few days?
>
> I use Star Foam every time I fill it up, and when the problem started I
> ran some B12 through it. The B12 seemed to help for a week or two, but
> then it reverted back to the problem.
>
> Initially the bike had a vacuum petcock, but that was replaced some time
> back with a non-vacuum one from an XS650. So no need for solutions
> involving that.
>
> Am I mis-diagnosing the problem? Is there something else it could be?
>
> I'm not adverse to replacing the floats and hinge if necessary, but since
> it's a PITA to remove/replace the carb I don't want to do that unless I
> have to.

That is *really* odd.

I'd be tempted to pull the carb and check the float operation all the
same, since I don't see what else it could be. B12 is a waste of time:
leave that to Krusty and the newbie idiots who believe him when he touts
it as the cure-all from a stuck throttle to herpes.

I'd also lay off the Star Foam - or do you mean Seafoam? If Yamaha
wanted something added to the fuel on every fill-up, they'd have told
you. It's quite possible that whatever it is in the Seafoam/Star Foam is
causing the problem

I'm guessing that the float is sticking. Ordinary running sees it
working fine. Lay it up, and whatever is impeding it has time to set in.

Suggestion: try it without the additive, for a tankful or two. And then
pull the carb and check the float operation.


--
BMW K1100LT Ducati 750SS Kawasaki GPz750 Honda CB400F
Triumph Street Triple Suzuki Freewind, TS250ERx2, GN250.
So many bikes, so little garage space....
chateau dot murray at idnet dot com

The Older Gentleman wrote:
> Larry Blanchard <(E-Mail Removed)> wrote:
>
>> I've written here before about various problems with my old (and beloved)
>> '78 SR500. Lately it's developed an odd habit. If I let it sit for a
>> few days, it still starts up fine, but dies in about the time it takes to
>> empty the float bowl - about a 1/2 mile or less. Kicking it over several
>> times gets it restarted and no more problems stopping and restarting on
>> that day. If I run it every day, or even every other day, I never see
>> the problem.
>>
>> It would seem to be the floats sticking in the up position, being jarred
>> loose by kicking it with an empty float bowl. But why wouldn't the
>> vibration (it *is* a thumper, after all) of running jar it loose? Why
>> only after sitting for a few days?
>>
>> I use Star Foam every time I fill it up, and when the problem started I
>> ran some B12 through it. The B12 seemed to help for a week or two, but
>> then it reverted back to the problem.
>>
>> Initially the bike had a vacuum petcock, but that was replaced some time
>> back with a non-vacuum one from an XS650. So no need for solutions
>> involving that.
>>
>> Am I mis-diagnosing the problem? Is there something else it could be?
>>
>> I'm not adverse to replacing the floats and hinge if necessary, but since
>> it's a PITA to remove/replace the carb I don't want to do that unless I
>> have to.
>
> That is *really* odd.
>
> I'd be tempted to pull the carb and check the float operation all the
> same, since I don't see what else it could be. B12 is a waste of time:
> leave that to Krusty and the newbie idiots who believe him when he touts
> it as the cure-all from a stuck throttle to herpes.

Krustacean has suggested B12 so many times here, that I had to try it.
The non-aerosol liguid, a magnifying lens, and individual fine bristles
pulled from a paint brush worked well in cleaning nearly invisible holes
in jets. B12 was inexpensive too.

> I'd also lay off the Star Foam - or do you mean Seafoam? If Yamaha
> wanted something added to the fuel on every fill-up, they'd have told
> you. It's quite possible that whatever it is in the Seafoam/Star Foam is
> causing the problem
>
> I'm guessing that the float is sticking. Ordinary running sees it
> working fine. Lay it up, and whatever is impeding it has time to set in.

Vibration almost HAS to shake the floats down. They're weighty, and hang
out on a limb.

I'll guess that the little tab on the float assembly that pushes up on
the needle valve plunger isn't *hooked* to the valve, as it should be.
It pushes up, but can't pull back down. Floats go up, plunger goes up.
Floats fall down, valve plunger stays up.

>
> Suggestion: try it without the additive, for a tankful or two. And then
> pull the carb and check the float operation.

Beryl <(E-Mail Removed)> wrote:

> Krustacean has suggested B12 so many times here, that I had to try it.
> The non-aerosol liguid, a magnifying lens, and individual fine bristles
> pulled from a paint brush worked well in cleaning nearly invisible holes
> in jets. B12 was inexpensive too.

Yeah, but he just says to pour it into the tank and let it do its stuff.
Anything more critical than pouring gunk into a tank, and he hasn't a
clue. Anyway, it isn't the issue here.

>
> > I'd also lay off the Star Foam - or do you mean Seafoam? If Yamaha
> > wanted something added to the fuel on every fill-up, they'd have told
> > you. It's quite possible that whatever it is in the Seafoam/Star Foam is
> > causing the problem
> >
> > I'm guessing that the float is sticking. Ordinary running sees it
> > working fine. Lay it up, and whatever is impeding it has time to set in.
>
> Vibration almost HAS to shake the floats down. They're weighty, and hang
> out on a limb.
>
> I'll guess that the little tab on the float assembly that pushes up on
> the needle valve plunger isn't *hooked* to the valve, as it should be.
> It pushes up, but can't pull back down. Floats go up, plunger goes up.
> Floats fall down, valve plunger stays up.

Sounds plausible. I think it's a float problem too. Shouldn't be hard to
fix. Shouldn't be expensive either.


--
BMW K1100LT Ducati 750SS Kawasaki GPz750 Honda CB400F
Triumph Street Triple Suzuki Freewind, TS250ERx2, GN250.
So many bikes, so little garage space....
chateau dot murray at idnet dot com

The Older Gentleman wrote:
> Beryl <(E-Mail Removed)> wrote:
>
>> Krustacean has suggested B12 so many times here, that I had to try it.
>> The non-aerosol liguid, a magnifying lens, and individual fine bristles
>> pulled from a paint brush worked well in cleaning nearly invisible holes
>> in jets. B12 was inexpensive too.
>
> Yeah, but he just says to pour it into the tank and let it do its stuff.
> Anything more critical than pouring gunk into a tank, and he hasn't a
> clue. Anyway, it isn't the issue here.

And Gordon Jennings' carb tuning articles are excellent, as he's
claimed. I recently rediscovered two in my mid-'70s Cycle magazines.
Explicit, detailed knowledge there, like you'd find in technical papers.
Better than what Mikuni was able to offer in their technical manuals.

Beryl <(E-Mail Removed)> wrote:

> And Gordon Jennings' carb tuning articles are excellent, as he's
> claimed.

They are indeed. Very rare, tech journalism of that standard.


--
BMW K1100LT Ducati 750SS Kawasaki GPz750 Honda CB400F
Triumph Street Triple Suzuki Freewind, TS250ERx2, GN250.
So many bikes, so little garage space....
chateau dot murray at idnet dot com

On Sun, 07 Aug 2011 19:34:51 +0100, The Older Gentleman wrote:

> I'm guessing that the float is sticking. Ordinary running sees it
> working fine. Lay it up, and whatever is impeding it has time to set in.

That's pretty much what I'd thought. But I had to ask in case I was
entirely missing something else. That seems to be more common as I get
older :-). Thanks.

--
Intelligence is an experiment that failed - G. B. Shaw

"Larry Blanchard" <(E-Mail Removed)> wrote in message
news:j1p2o9$nhh$(E-Mail Removed)...
> On Sun, 07 Aug 2011 19:34:51 +0100, The Older Gentleman wrote:
>
>> I'm guessing that the float is sticking. Ordinary running sees it
>> working fine. Lay it up, and whatever is impeding it has time to set in.
>
> That's pretty much what I'd thought. But I had to ask in case I was
> entirely missing something else. That seems to be more common as I get
> older :-). Thanks.

Is the float shut off valve *round* in cross section, or is it triangular or
four-cornered?

A round float valve will stick very easily from gum and varnish buildup,
while the other two types are less prone with sticking for that reason.

"The Older Gentleman" <(E-Mail Removed)> wrote in message
news:1k5nhfr.10j6mx11917aiqN%totallydeadmailbox@ya hoo.co.uk...

> Yeah, but he just says to pour it into the tank and let it do its stuff.
> Anything more critical than pouring gunk into a tank, and he hasn't a
> clue. Anyway, it isn't the issue here.

You're as full of **** as a constipated Donald.

I tell newbies to pour 4 ounces of B12 into a full tank of gasoline and
trying to flush out the gum and varnish that way so they can avoid hours of
disassembly and re-assembly work.

If you have a single cylinder Honda with everything exposed and you can
snatch the carb off and strip it down to the essentials in 20 minutes,
that's one thing.

But if you have a plastic wrapped sportbike that has the carbs absolutely
buried underneath tha gas tank and airbox, you're looking at 6 to 8 hours of
work to get at the idle adjustment screws or the float valves and get the
bike back on the road.

In a situation like that, who wouldn't want to *ride* the bike until the B12
cleaned out the gum and varnish?

"The Older Gentleman" <(E-Mail Removed)> wrote in message
news:1k5na4n.1d7buy8l4ocybN%totallydeadmailbox@yah oo.co.uk...

> I'd be tempted to pull the carb and check the float operation all the
> same, since I don't see what else it could be. B12 is a waste of time:
> leave that to Krusty and the newbie idiots who believe him when he touts
> it as the cure-all from a stuck throttle to herpes.

B12 makes an *excellent* martini, too. Stir it gently, don't shake it, as
you don't want to *bruise* the acetone.