Throttle Butterflies on Solex 40 PII Twin Shaft Carburettors

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Rene Santos
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Throttle Butterflies on Solex 40 PII Twin Shaft Carburettors

#1 Post by Rene Santos »

Gentlemen,
I am in the process of rebuilding my S 90 carbs fitted with twin shaft 40 PII carbs. Part of the rebuild is to convert to single shaft. I will be re-machining the carb bodies since there are score marks on all the bores. My question is relating to the butterflies. Should the butterflies at any time come in contact with the bores of the carburettor? Obviously with mine they have hence the scoring. But if the throttle shaft bushes are new and the shimming of the shaft is correct, is it normal for these carbs to fully shut closed in the rest position? Thank you
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Martin Benade
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Re: Throttle Butterflies on Solex 40 PII Twin Shaft Carburettors

#2 Post by Martin Benade »

They should touch at least when the idle stop screws are backed out. Do you have a source of larger throttle plates to match your re-bore? Making your own with the correct angle on the edges is not that simple.
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Re: Throttle Butterflies on Solex 40 PII Twin Shaft Carburettors

#3 Post by Tim Berardelli »

Partsklassic has oversize "butterflies" . Rene, don't know your history or skill level, however this process requires some very exacting KSA's ( knowledge , skills and ability)-like the guy says on the radio, " just a thought, not a sermon"

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Re: Throttle Butterflies on Solex 40 PII Twin Shaft Carburettors

#4 Post by Rene Santos »

Hi Martin,
Great thats what I had assumed. What do you see are the challenges in making the throttle plates? Thanks for your response.
Rene
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Re: Throttle Butterflies on Solex 40 PII Twin Shaft Carburettors

#5 Post by Rene Santos »

Tim Berardelli wrote: Fri Jan 17, 2020 6:45 pm Partsklassic has oversize "butterflies" . Rene, don't know your history or skill level, however this process requires some very exacting KSA's ( knowledge , skills and ability)-like the guy says on the radio, " just a thought, not a sermon"
Thanks Tim, My brother has the machine tools, lathe milling machine. Have already made the jigs to machine the throttle valves. Will manufacture the shafts (single) too and replace the bushes with a modification to the design to increase the longevity. Should work, he's good. PhD in maths trained in engineering.
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Harlan Halsey
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Re: Throttle Butterflies on Solex 40 PII Twin Shaft Carburettors

#6 Post by Harlan Halsey »

There is one of those terrific cartoon format articles on butterfly making in the Registry magazine a few years back.

The usual problem with high mileage Solexes is the wear of the shaft bushing, primarily on the lever end. The worn bushing leaks air which makes the idle setting impossible. Ideally you should line ream all four bearings exactly on the original center, install new bushings, and ream to shaft clearance size. Then clean up the body and install larger butterflies. All four butterflies should seal, but of course when adjusted, they don't touch. Harry Beeker used to do an excellent job of this machining, and he also converted 40s to 44s. Unfortunately I don't think he's in business anymore. A properly rebuilt Solex runs beautifully.

Sometimes you can get away with only replacing the lever end bushing, if the wear is not too bad otherwise.

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Re: Throttle Butterflies on Solex 40 PII Twin Shaft Carburettors

#7 Post by Thomas Sottile »

CarbRescue Jim Kaufman and his wife do a good job

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Re: Throttle Butterflies on Solex 40 PII Twin Shaft Carburettors

#8 Post by Martin Benade »

I am pretty sure they don’t have bushings originally. The learning curve is such that the third set you rebuild might turn out really well. You should at least buy the shafts and plates, boring the bodies correctly will keep you busy enough.
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Rene Santos
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Re: Throttle Butterflies on Solex 40 PII Twin Shaft Carburettors

#9 Post by Rene Santos »

Harlan Halsey wrote: Sun Jan 26, 2020 4:15 am There is one of those terrific cartoon format articles on butterfly making in the Registry magazine a few years back.

The usual problem with high mileage Solexes is the wear of the shaft bushing, primarily on the lever end. The worn bushing leaks air which makes the idle setting impossible. Ideally you should line ream all four bearings exactly on the original center, install new bushings, and ream to shaft clearance size. Then clean up the body and install larger butterflies. All four butterflies should seal, but of course when adjusted, they don't touch. Harry Beeker used to do an excellent job of this machining, and he also converted 40s to 44s. Unfortunately I don't think he's in business anymore. A properly rebuilt Solex runs beautifully.

Sometimes you can get away with only replacing the lever end bushing, if the wear is not too bad otherwise.
Harlan, Thanks for this feedback. Yes the carbs Im rebuilding has play on the shaft bushings as you mention. Interesting point, the numbers of both carbs are 70338 and 70339 ( I mention this since reading lots on the forum about the issue of carb numbers). If I understand you correctly, Harlan, when the throttle stop screw is fully out the throttle valves will seal the bore totally then when adjusted correctly they dont!
Regards
Rene
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Re: Throttle Butterflies on Solex 40 PII Twin Shaft Carburettors

#10 Post by Rene Santos »

Thomas Sottile wrote: Sun Jan 26, 2020 2:04 pm CarbRescue Jim Kaufman and his wife do a good job
Hi Thomas, Yes they have been extremely helpful in my research on the issues fo how to fix these carbs.
Rene Santos
356B S90 Coupe
991 Turbo S
Harley Davidson CVO Street Glide
Location UK

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