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 Post subject: Zenith carbs...
PostPosted: Mon Feb 11, 2019 7:55 pm 
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Joined: Mon Oct 15, 2018 3:52 pm
Posts: 57
Car Model: 99
So, the endless tail of getting my impulse-buy 99 continues, but it's almost there! The engine I obtained from flying_dutchman is now up and running, albeit with a Davis Craig EWP.
Initially it was hard to start, required a bit of choke once warmed up to keep running, and also spluttered and wouldn't run well over 2000 rpm.
We took apart the carb this weekend and found that someone has been there before- the disc with drilled holes in had been fitted back to front, so effectively the choke was on when off and off when on! Having tuned the idle based on that, it was well out.
So, with that sorted, it's running a lot happier today.

However- the carb has an interesting feature, in that there's a screw next to the vac hose (see pic) - this doesn't seem to relate to the hose, and merely opens a hole through to the barrel, with a tapered end.
The only place we can find pictures of a Zenith with this is in relation to Volvo's - anyone seen this as standard fitment on a Saab before? Either way, does anyone know what it's for? It currently doesn't want to idle well below around 900rpm, which is in spec according to manuals (for a '77 engine), but would be good to know if we have a carb that's vaguely "right" or not...

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 Post subject: Re: Zenith carbs...
PostPosted: Mon Feb 11, 2019 8:58 pm 
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Joined: Wed May 12, 2004 9:46 pm
Posts: 14903
Location: Mulbarton,Norfolk
Car Model: TTid's only now :-(
Air bypass / bleed screw.

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 Post subject: Re: Zenith carbs...
PostPosted: Tue Feb 12, 2019 1:01 pm 
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Joined: Mon Oct 15, 2018 3:52 pm
Posts: 57
Car Model: 99
Indeed, it just seemed to be (yet another!) way of adding a bit of air into the mix. None of the "setting up" stuff I've found mention this though, and if unscrewed it's rather loose, suggesting it would normally just be done up (closed)?


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 Post subject: Re: Zenith carbs...
PostPosted: Tue Feb 12, 2019 2:16 pm 
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Joined: Wed May 12, 2004 9:53 pm
Posts: 16855
Location: Devon
I don't know for certain as haven't looked it up but is there a chance it is simply a blanking plug in the position where a second vacuum nipple might be installed for some applications?

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 Post subject: Re: Zenith carbs...
PostPosted: Sun Feb 17, 2019 10:10 pm 
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Joined: Fri Jul 07, 2006 10:31 pm
Posts: 66
Location: Northamptonshire.
Your carburettor is suitable.However I have looked at three. Two have the screw, but closed (i.e no threads showing) and an older one has no screw there at all.So I conclude it is closed, as it is not necessary.
Regarding the idle rpm's on the "H" engine I have never been able to get a consistent idle below 900 rpm,although the "B" engine would idle somewhat lower than that.The correct metering needle for year 1977 should be B1DS but I have used a carburettor with Finland spec.with B1BM metering needle ,which seemed to make little difference and both specs.passed through the M.O.T without problems.
John.

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 Post subject: Re: Zenith carbs...
PostPosted: Mon Feb 18, 2019 10:00 am 
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Joined: Mon Oct 15, 2018 3:52 pm
Posts: 57
Car Model: 99
Thanks, that's pretty helpful. No idea what needle is in it right now, but worth knowing what to check


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