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Next: Bimbling on the SL125
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External
Since: Aug 25, 2007
Posts: 12
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(Msg. 1) Posted: Mon Aug 27, 2007 9:37 pm
Post subject: It Runs!
Archived from groups: uk>rec>motorcycles>classic (more info?)
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The CB 750 sprang in to life this avo. Thanks to all who offered advice.
I took the carbs off and cleaned them again. I'm not sure this had much
effect.
The CB750 has a vacuum operated fuel valve in series with the manual
fuel tap. It only allows fuel through when the engine is running. If you
can't start the engine owing to a lack of fuel - you're stuffed.
OK, that wasn't the main problem but it sure didn't help. Hmm. Thinking
about it, the vacuum device stopped a whole tank of fuel from
evaporating out of the float chambers... So, perhaps a double edged sword.
Slight leak from the sump plug. Tightened it slightly - felt ominous.
I'll be thoroughly F'd O if it's stripped.
So I'll stick it all back together tomorrow night, get an MOT and it'll
be the eighties all over again.
Cheers,
Nick |
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External
Since: Jul 09, 2007
Posts: 17
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(Msg. 2) Posted: Tue Aug 28, 2007 5:43 am
Post subject: Re: It Runs! [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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On 28 Aug, 14:30, Nick Wilson wrote:
> Grimly Curmudgeon wrote:
> > We were somewhere around Barstow, on the edge of the desert, when the
> > drugs began to take hold. I remember Nick Wilson
> > saying something like:
>
> >> The CB750 has a vacuum operated fuel valve in series with the manual
> >> fuel tap. It only allows fuel through when the engine is running. If you
> >> can't start the engine owing to a lack of fuel - you're stuffed.
>
> > That's what the Prime position is for, though.
>
> Yeah. I've heard of bike with a "prime" position but mine has "res",
> "off" and "on".
Then it's an ordinary gravity tap.
>
> The vacuum valve is physically separate from the manual tap and it has
> no controls of its own.
>
> But there is clearly something I'm missing - unless cranking it is
> supposed to create enough vacuum to fill the float chambers??
>
No, that's not how it works. The float chambers will only fill if fuel
from them is being sucked into the engine. It's like a lavatory
cistern: the float does exactly the same job as a ballcock. |
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External
Since: Jul 09, 2007
Posts: 17
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(Msg. 3) Posted: Tue Aug 28, 2007 7:12 am
Post subject: Re: It Runs! [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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On 28 Aug, 14:59, Mark Olson wrote:
> Nick Wilson wrote:
> > Grimly Curmudgeon wrote:
>
> >> We were somewhere around Barstow, on the edge of the desert, when the
> >> drugs began to take hold. I remember Nick Wilson
> >> saying something like:
>
> >>> The CB750 has a vacuum operated fuel valve in series with the manual
> >>> fuel tap. It only allows fuel through when the engine is running. If
> >>> you can't start the engine owing to a lack of fuel - you're stuffed.
> >> That's what the Prime position is for, though.
> > Yeah. I've heard of bike with a "prime" position but mine has "res",
> > "off" and "on".
>
> > The vacuum valve is physically separate from the manual tap and it has
> > no controls of its own.
>
> Same setup as my 1981 CB900C. Not one of Mr. Honda's finest designs.
>
Ah, I misread that. So there's a manual tap connected through a vacuum
tap. How bizarre is that? >> Stay informed about: It Runs! |
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External
Since: Jan 04, 2007
Posts: 847
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(Msg. 4) Posted: Tue Aug 28, 2007 1:01 pm
Post subject: Re: It Runs! [Login to view extended thread Info.]
Imported from groups: per prev. post (more info?)
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External
Since: Aug 25, 2007
Posts: 12
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(Msg. 5) Posted: Tue Aug 28, 2007 1:30 pm
Post subject: Re: It Runs! [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Grimly Curmudgeon wrote:
> We were somewhere around Barstow, on the edge of the desert, when the
> drugs began to take hold. I remember Nick Wilson
> saying something like:
>
>> The CB750 has a vacuum operated fuel valve in series with the manual
>> fuel tap. It only allows fuel through when the engine is running. If you
>> can't start the engine owing to a lack of fuel - you're stuffed.
>
> That's what the Prime position is for, though.
Yeah. I've heard of bike with a "prime" position but mine has "res",
"off" and "on".
The vacuum valve is physically separate from the manual tap and it has
no controls of its own.
But there is clearly something I'm missing - unless cranking it is
supposed to create enough vacuum to fill the float chambers??
Cheers,
Nick >> Stay informed about: It Runs! |
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External
Since: Jan 13, 2007
Posts: 51
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(Msg. 6) Posted: Tue Aug 28, 2007 8:23 pm
Post subject: Re: It Runs! [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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On or around Tue, 28 Aug 2007 07:12:20 -0700,
TOG@Toil,chateau.murray@btinternet.com,
enlightened us thusly:
>On 28 Aug, 14:59, Mark Olson wrote:
>> Nick Wilson wrote:
>> > Grimly Curmudgeon wrote:
>>
>> >> We were somewhere around Barstow, on the edge of the desert, when the
>> >> drugs began to take hold. I remember Nick Wilson
>> >> saying something like:
>>
>> >>> The CB750 has a vacuum operated fuel valve in series with the manual
>> >>> fuel tap. It only allows fuel through when the engine is running. If
>> >>> you can't start the engine owing to a lack of fuel - you're stuffed.
>> >> That's what the Prime position is for, though.
>> > Yeah. I've heard of bike with a "prime" position but mine has "res",
>> > "off" and "on".
>>
>> > The vacuum valve is physically separate from the manual tap and it has
>> > no controls of its own.
>>
>> Same setup as my 1981 CB900C. Not one of Mr. Honda's finest designs.
>>
>
>Ah, I misread that. So there's a manual tap connected through a vacuum
>tap. How bizarre is that?
if it was mine I'd remove the vacuum one.
--
Austin Shackles. www.ddol-las.net my opinions are just that
Travel The Galaxy! Meet Fascinating Life Forms...
------------------------------------------------\
>> http://www.schlockmercenary.com/ << \ ...and Kill them.
a webcartoon by Howard Tayler; I like it, maybe you will too! >> Stay informed about: It Runs! |
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External
Since: Aug 25, 2007
Posts: 12
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(Msg. 7) Posted: Tue Aug 28, 2007 9:23 pm
Post subject: Re: It Runs! [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Austin Shackles wrote:
>
> if it was mine I'd remove the vacuum one.
Very tempting. But I'm too lazy to turn the manual one off when I leave
the bike for ten years. :->
Cheers
Nick >> Stay informed about: It Runs! |
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External
Since: Mar 19, 2006
Posts: 208
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(Msg. 8) Posted: Tue Aug 28, 2007 9:23 pm
Post subject: Re: It Runs! [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Nick Wilson wrote:
> Austin Shackles wrote:
>>
>> if it was mine I'd remove the vacuum one.
>
> Very tempting. But I'm too lazy to turn the manual one off when I leave
> the bike for ten years. :->
It works fine 99% of the time. The other 1% is an inconvenience, but
it's not worth taking the chance of a hydro-locked cylinder if you
have a leaky float valve and you forget to turn off the tap.
--
'01 SV650S '99 EX250-F13 '98 ZG1000-A13
OMF #7 >> Stay informed about: It Runs! |
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External
Since: Aug 25, 2007
Posts: 12
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(Msg. 9) Posted: Wed Aug 29, 2007 6:52 am
Post subject: Re: It Runs! [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Mark Olson wrote:
> It works fine 99% of the time. The other 1% is an inconvenience, but
> it's not worth taking the chance of a hydro-locked cylinder if you
> have a leaky float valve and you forget to turn off the tap.
On this bike a leaky float valve results in a pool of fuel on the floor
as it runs out of the overflow pipe. I guess if the overflow was blocked
it might find its way into the cylinder.
I think the vacuum valve saved my bacon while the bike was sitting. I
prevented the whole tank of fuel from evaporating through the carbs.
Cheers,
Nick >> Stay informed about: It Runs! |
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