[Fot] Weber vs Mikuni

Fri Oct 19 18:21:01 MDT 2018

Thanks for all the great input. I think I'll stay with the SU's for now and
spend the money on Dyno time to see where the issue may be.

mike h

On Fri, Oct 19, 2018 at 7:13 PM fubog1 via Fot <fot at autox.team.net> wrote:

> These are some words of wisdom...
> Glen
> ps- I've found different size holes in the float valves, also grose jets
> are particularly restrictive.
>
> The SU's are so simple minded and easy to work with I'd want to very
> certain that the was a BIG benifit before changing to jetted carbs that
> need a ton of parts of you are going to make use of the capacity of the
> units.
>
>
>
>
> -----Original Message-----
> From: Kas Kastner <kaskastner at gmail.com>
> To: fubog1 <fubog1 at aol.com>
> Cc: Van Mulders Marcel <van.mulders.marcel at telenet.be>; FOT <
> fot at autox.team.net>
> Sent: Fri, Oct 19, 2018 12:32 pm
> Subject: Re: [Fot] Weber vs Mikuni
>
> Lots of times at the higher revs the float bowls of the S.U.'s just run
> out of gas and they need an enlargment of the needle and seat.Many times
> the stock needle and seat j ust does not have enough capacity to flow the
> fuel needed for the much richer needles used and the revvs. The SU's are so
> simple minded and easy to work with I'd want to very certain that the was a
> BIG benifit before changing to jetted carbs that need a ton of parts of you
> are going to make use of the capacity of the units.
>
>  If you do not tune for the day and the weather at that time what is the
> point in having all that adustment. With the SU a couple flats adjustment
> up or down and you are done the hour. Bigger machinery does not mean bigger
> power or even more useful power.
>
> BUT, if you are going for the expensive route, get the msot you can get.
> DCOE 45's are the ticket. Start with a small venturi and work up from
> there. Yes, you neeed to buy  alterate venturies otherwise you have just
> wasted your money.These same carbs were used on the Sebring and Le Mans
> Spitfire coupes 1147 cc engines  and proved 3% more power by tuning. To get
> the benifit you need to work at it.
> *Never be beaten by equipment.*
>
>
> On Fri, Oct 19, 2018 at 9:01 AM fubog1 via Fot <fot at autox.team.net> wrote:
>
> Yes HS4 carbs.
> Glen
>
>
> -----Original Message-----
> From: van.mulders.marcel <van.mulders.marcel at telenet.be>
> To: fubog1 <fubog1 at aol.com>
> Cc: fot <fot at autox.team.net>
> Sent: Thu, Oct 18, 2018 5:48 pm
> Subject: Re: [Fot] Weber vs Mikuni
>
> Glen,
> With 1 1/2s carburettors, I suppose you mean HS4? The SU logic is a little
> weird. 1" + 1/2" = 6/8" so you would think it are HS6s, but when talking
> about HS carburettors, 1 + 1/2 = 1 + 4/8 and they took the 4 to name these
> carbs HS4...
> Marcel
>
> ------------------------------
> *Van: *"fubog1" <fubog1 at aol.com>
> *Aan: *"van mulders marcel" <van.mulders.marcel at telenet.be>, "Mike
> Harmuth" <ofracer at gmail.com>
> *Cc: *"fot" <fot at autox.team.net>
> *Verzonden: *Donderdag 18 oktober 2018 22:39:39
> *Onderwerp: *Re: [Fot] Weber vs Mikuni
>
> Well I won't speculate on the cause, but I doubt that it's the SUs.
> My small crank 1300 w/1 1/2s on a eurospec manifold w/Stahls header, "big"
> valve head, would buzz easily to 9k, still making power, if I let it.
> Normal shift point 7800-8000.
> FWIW...
> Glen
>
>
> -----Original Message-----
> From: van.mulders.marcel--- via Fot <fot at autox.team.net>
> To: Mike Harmuth <ofracer at gmail.com>
> Cc: fot <fot at autox.team.net>
> Sent: Thu, Oct 18, 2018 2:12 pm
> Subject: Re: [Fot] Weber vs Mikuni
>
> -"...hitting a wall at that point..." : is it possible this is rather
> pointing to the camshaft than to the SU's? If it are the carburettors,
> maybe the power would decrease more gradually above 6500 rpm.
> -In general one choke per cylinder is better, and 2 Webers 40 DCOE isn't
> overkill I think
> - what about trying HS6 SU's on your actual manifold?
> At what maximum rpm is your engine still reliable?
> Marcel
>
> ------------------------------
> *Van: *"fot" <fot at autox.team.net>
> *Aan: *"fot" <fot at autox.team.net>
> *Verzonden: *Woensdag 17 oktober 2018 15:49:45
> *Onderwerp: *[Fot] Weber vs Mikuni
>
> I'm looking into switching out my twin HS4s on the 1296 race engine to
> either Weber or Mukinis. I know this has been done for years and I'd like
> to get close the best set up out of the gate.
>
> I don't think the SUs are up to the task of moving enough air with the new
> ported head and Stahl header. I've worked on the SUs and gotten them to
> finally deliver a good AFR , 12.6, at 6500 RPM under load but I seem to hit
> a wall (figuratively) at that point. I suspect that the openings just
> aren't big enough to deliver the mass of air required. (spreadsheet or
> other flow calculator link appreciated)
> Biggest gate I suspect is the intake valve, 1 3/8" head (~35mm) HS4 is
> ~38mm at best.
>
> Recommendations? I've seen all these setups at the track, each with
> pluses, minuses and overkill cause it looks cool.
>
> One weber DCOE 40 or 2? what jets, tubes etc for a starting point? Best
> manifold?
>
> 2 or 4 Mikuni 40? jet size?
>
> thanks
> mike
>
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