[Fot] Weber vs Mikuni

Fri Oct 19 10:51:57 MDT 2018

 These are some words of wisdom...Glenps- 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?
thanksmike

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