Author Topic: A question about carbs  (Read 402 times)

Offline 94touring

A question about carbs
« on: December 10, 2017, 02:54:31 PM »
Something I've never given any thought or concern about till now are these little ports on carbs, specifically my hs4s. I'll be running the velocity stacks and afixing a filter to the bell.  However this leaves the ports exposed to suck in dirt.  Dirt is bad.  What are these ports and do I need them?

Offline MPlayle

Re: A question about carbs
« Reply #1 on: December 10, 2017, 03:51:01 PM »
I recall reading somewhere that they are part of the porting for the dashpot piston.  If they get closed off, the piston does not rise/fall as it should and throttle response goes to crap.


Offline 94touring

Re: A question about carbs
« Reply #2 on: December 10, 2017, 03:52:30 PM »
Makes sense. As I blew into it and the piston moved.  Plan B is running a length of silicon hose from the port to the filter.

Offline MPlayle

Re: A question about carbs
« Reply #3 on: December 10, 2017, 04:04:59 PM »
I know most of the filters that have backing plates have corresponding holes in the plate so that those ports are fed by air inside the filter versus outside as the filter full surrounds them.  Why not use one of the very short "stub stacks" you've posted before that fit fully under a filter?


Offline MiniDave

Re: A question about carbs
« Reply #4 on: December 10, 2017, 04:05:22 PM »
I'm mot sure you need to do anything about them, if all it does is goes into the bottom/top side of the piston. I'd check with the stack mfr......will that stack fit inside a cone type K&N filter?
1989 Cooper Racing Green
2009 Clubman S
1969 Jaguar XK-E FHC
2004 Audi Allroad 2.7 TT

Offline 94touring

Re: A question about carbs
« Reply #5 on: December 10, 2017, 04:13:27 PM »
I will look into doing a larger version of my stub stack mod with a huge k and n filter.  Not sure it will fit...

Offline 94touring

Re: A question about carbs
« Reply #6 on: December 10, 2017, 04:22:12 PM »
I may end up modifying the firewall.  I don't mind on this car.

Offline MiniDave

Re: A question about carbs
« Reply #7 on: December 10, 2017, 04:54:08 PM »
Maybe build a box for the air cleaner?
1989 Cooper Racing Green
2009 Clubman S
1969 Jaguar XK-E FHC
2004 Audi Allroad 2.7 TT

Offline MPlayle

Re: A question about carbs
« Reply #8 on: December 10, 2017, 05:23:06 PM »
Will this be a single or dual carb setup?

Offline 94touring

Re: A question about carbs
« Reply #9 on: December 10, 2017, 05:23:39 PM »
So I can get a taller version of that round k&n filter, it's just a matter of space. Plus my intake manifold is maniflow and different lengths and angle.  Now I want to go home and test fit things!
Mike- going with these stacks versus the stubs for max performance.  Went all out on airflow.

Edit: dual

Offline MPlayle

Re: A question about carbs
« Reply #10 on: December 10, 2017, 05:38:55 PM »
How tall are the stacks?  Could you get something like this kit and modify it for a taller filter?  (The kit would give you the mounting back plate for attaching the filter that would put the dashpot ports inside the filtered air.)

https://www.bpnorthwest.com/air-filter-k-n-su-h-series-1-5-carburetor.html


Offline 94touring

Re: A question about carbs
« Reply #11 on: December 10, 2017, 05:47:26 PM »
They're around 3 inches. I can buy the plates and a tall round filter.  The filters I use on my stub stack mod are around 2 inches. I think they have them clear up to 6 or 7 inches.
« Last Edit: December 11, 2017, 10:44:45 AM by 94touring »

Offline 94touring

Re: A question about carbs
« Reply #12 on: December 10, 2017, 05:51:42 PM »
I could always just insert a piece of foam into the ports, provided they're adhered and won't get sucked in. Hmm.

Offline 94touring

Re: A question about carbs
« Reply #13 on: December 11, 2017, 10:43:46 AM »
Ok so foam mushroom filters are too wide at 6.5 inches.  They'd be great on a single carb with one of these stacks though.  The stack height turns out is right around 2.5 inches. On dual filters you are limited to an outside diameter on pancakes to 5.375 inches.  Recommended filter height on the stacks is a minimum of 3.5 inches.  I found a k&n (K&N E-2340) that's 5.375 by 4.25 inches. So there's a solution other than firewall issues I'm sure.
« Last Edit: December 11, 2017, 10:45:34 AM by 94touring »

Offline kcmini

Re: A question about carbs
« Reply #14 on: December 11, 2017, 05:39:44 PM »
itg filters any size you want get a blank plate to match up to carbs

Offline MiniDave

Re: A question about carbs
« Reply #15 on: December 11, 2017, 06:15:26 PM »
That's the kind of thing I was talking about, but that would probably involve even more mods to the firewall.....
1989 Cooper Racing Green
2009 Clubman S
1969 Jaguar XK-E FHC
2004 Audi Allroad 2.7 TT

Offline 94touring

Re: A question about carbs
« Reply #16 on: December 11, 2017, 06:23:29 PM »
Well once I get home and do test fittings we'll see how much room I have. Also looking at these, which are even angled.

Offline John Gervais

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Re: A question about carbs
« Reply #17 on: December 14, 2017, 09:41:43 PM »
Realistically, all you need is filter sock over each velocity stack and a couple of stainless cable ties/cv boot clamps to hold them on.  I believe ITG has 'em.
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Offline 94touring

Re: A question about carbs
« Reply #18 on: December 14, 2017, 10:36:18 PM »
I have those socks but I can't help but think they choke the carbs.  Not a lot of surface area to suck air from with those.  That's my thinking anyways.

Offline BruceK

Re: A question about carbs
« Reply #19 on: December 15, 2017, 07:34:32 AM »
“ not a lot of surface area”  also means not a lot of filtration too, right?
1988 Austin Mini
2002 MINI Cooper S
2007 Triumph Bonneville

Offline 94touring

Re: A question about carbs
« Reply #20 on: December 15, 2017, 08:23:33 AM »
Not really concerned about the filtration aspect, so long as something is blocking dirt.  Airflow on my rx7 was drastically improved when I went from a short stubby filter on the turbo to one twice the size.  So much so that I had to richen the mixture up. I run a wide band so could see the difference.  Perhaps I do some air/fuel ratio comparisons with various filters on these carbs.

Offline 94touring

Re: A question about carbs
« Reply #21 on: January 06, 2018, 04:15:42 PM »
Test fit. They fit!