[Fot] Weber vs Mikuni
Tony Drews
tony at tonydrews.com
Sat Oct 20 11:09:46 MDT 2018
Good thought. We had one where the tube to the jet had a little nick in
the end which caused a flap that partially covered the end. Only showed
up under extended load, had a devil of a time finding the issue.
Tony
On 10/20/2018 6:58 AM, Phil Gott via Fot wrote:
> Speaking of holes in float bowls, the exit hole at the bottom that
> feeds the jet can also vary in size. Be sure it’s big enough and the
> hose to the jet is not crimped or restricted in any way. Mike did say
> he got a decent A/F ratio, so. It likely his issue, but it was with my
> TR.
> Phil
>
> Sent from my iPhone
>
> On Oct 19, 2018, at 8:21 PM, Mike Harmuth via Fot <fot at autox.team.net
> <mailto:fot at autox.team.net>> wrote:
>
>> 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
>> <mailto: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
>> <mailto:kaskastner at gmail.com>>
>> To: fubog1 <fubog1 at aol.com <mailto:fubog1 at aol.com>>
>> Cc: Van Mulders Marcel <van.mulders.marcel at telenet.be
>> <mailto:van.mulders.marcel at telenet.be>>; FOT <fot at autox.team.net
>> <mailto: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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>
>
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