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New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: kmart356 ()
Date: January 01, 2019 04:10PM

My Spyder came to me with a Stromberg WW 2bbl downdraft. About nine months ago I replaced the Stromberg with a 38/38 DGV synchronous downdraft and improvements were achieved. The original YH side draft design still held my interest with the side draft simplicity and "clean" installation. I know the SU side draft was a successful conversion if a 2" carb was properly tuned. One of my turbo mentors, suggested I look at the Mikuni smooth bore as it might just provide the additional air flow and response to further enhance the Spyder's performance.

Mikuni HSR45 is pretty dang cool. The 45mm bore is not constricted by a smaller venturi. It is smooth bore with a flat slide throttle plate that opens wide. Yes, the Mikuni carbs are motorcycle carbs, but a vintage racer has been modifying and running the HSR carbs on Volvos, MGs and various other vintage cars that were originally fitted with SU carbs. That was the key to my conversion... I bought an Otto Parts SU carb turbo adapter from Clarks a few years ago and now it has met it's destiny.

Quote from Vintage Performance Developments
Compared to SU carbs, a similarly sized Mikuni HSR will flow 30 - 40% more air. They will provide better throttle response, support more power - especially at higher rpms, and will equal or exceed the SU in fuel economy.

The HSR45 arrived on Christmas Eve and after collecting the remaining gaskets, the installation was my New Years Day project. Everything bolts up nicely. Time ran out for today, so after I re-connect the fuel line all I need to do is find an air filter assembly that will fit. K&N has a big catalog and I am looking there first. Next up will be initial startup and idle adjustments followed by road tests and tuning as required with the jet kit. Should be fun.



SU adapter with a drawn aluminum sleeve to match the turbo (F) intake diameter.



SU adapter mounter to turbo and Mikuni flange bolted on.



HSR45 mounted to rubber flange and linkage connected. The extended throttle shaft and lever arm are part of the modifications done by Vintage Performance Developments (John Parker). You can see the throttle cable bracket still in place... I might remove it or just let it be.



Ken
'62 Spyder Coupe
Florida


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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: 63turbo ()
Date: January 01, 2019 04:35PM

Ken- That thing is so cool! Somebody had to do it! That carb is the most accurate, sensitive, free flowing fuel metering device there is short of EFI, and ought to be a really good match for your turbo. It sure as heck looks trick also. Nice install!

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car



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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: MattNall ()
Date: January 01, 2019 04:53PM

I don't think you'll be disappointed!

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: toms73novass ()
Date: January 01, 2019 04:58PM

Well that didn't take long! smileys with beer

-Tom


63' Monza Spyder Convertable (in process) MY Build Thread
65' Monza MY Build Thread
73' NovaSS 454 Big block
86' BMW 325es
98' Dodge 2500 12v Cummins Diesel with 1200 lb torque!
98' VW Jetta TDI, for daughter
01' Audi Allroad Stage 3 twin turbo

NFCC
Grand Island, NY

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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: Darrin ()
Date: January 01, 2019 05:08PM

Seems like a great option. Nice!

Darrin Hartzler
Bethesda, MD/Catlett, VA

Northern Virginia Corvairs & Group Corvair

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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: jjohnsonjo ()
Date: January 01, 2019 05:09PM

Looks like fun Ken. For many years I have thought about using multiple motorcycle carbs on a plenum manifold with some sort of progressive linkage. My problem is that I have so many other interests that these thoughts often don't materialize. As in tomorrow, I will ski, with my wife and son, not heat the garage and wrench. I will be following your progress, thanks again for the files.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: Chi2 ()
Date: January 01, 2019 06:25PM

Mikunis rock! Been running them on a bunch of XS650s for many years. Good luck Ken!!

Jon
Enrolled in the Culver City Automotive School of Hard Knocks
============================================================
Member of South Coast Corsa
-1964 Greenbrier "The Dog Hauler" Rustoleum Charmer 110hp/4sp/.030 over/Pertronics I/Isky 270 Cam
-1962 Monza Club Coupe "Shaken, not stirred" Tuxedo Black with Red Interior 140hp/4sp/Pertronics I/Clark's 260 Cam

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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: Phil Dally ()
Date: January 01, 2019 06:52PM

Nice and compact...I like it!!!

Is this Amazon listing the right carb?


[www.amazon.com]

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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: kmart356 ()
Date: January 01, 2019 07:56PM

Thanks for the encouragement guys. I’m really looking forward to cranking this up and getting some road testing done. John Parker @ Vintage Performance Developments supplied the modified HSR45 along with a jetting kit and short idle adjustment screw (stock one hangs down). His mods allow the carbs to work in automotive applications.

Phil, the “off the shelf” HSR45 for motorcycle use needs to be modified for automotive engines. I got mine from John Parker. He also sets up the initial jetting according to the engine used. He has tuned a Mikuni on an MG with supercharger so that is the baseline we used for the turbo.
Mikuni HSR @ Vintage Performance Developments

Ken
'62 Spyder Coupe
Florida


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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: Nickshu ()
Date: January 02, 2019 06:40AM

Looks interesting. What is the choke setup?

Nick
_______________________________________________________________________
1964 Monza Spyder Convertible #435 - Rotisserie restored - SOLD ON BRING A TRAILER 4/30/2019 - Check out my restoration thread here: [corvaircenter.com]
Thanks to all the awesome CCF, CF, COG, and CORSA members who helped me with the restoration!
Other fun stuff - Porsche 911 GT3 - Trailered track monster for HPDE and Autocross events.
Northern Colorado, USA

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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: kmart356 ()
Date: January 02, 2019 08:04AM

Nickshu Wrote:
-------------------------------------------------------
> Looks interesting. What is the choke setup?

Nick- All the original controls for the Mikuni are cable actuated. The choke (enrichment) circuit is activated by a choke cable connected where the arrow points in the photo. Not sure yet if I am going to try to connect it for use as my previous carb setups were "sans choke" and our winter is well... not much to speak of most years.



Ken
'62 Spyder Coupe
Florida


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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: MattNall ()
Date: January 02, 2019 08:19AM

I adapted a Rochester Electric choke system to my Weber's "Starter Circuit.."

Works great..

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
..............................110-PG.................................................Webered-Turbo

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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: cnicol ()
Date: January 02, 2019 08:42AM

I've jetted quite a few carburetors but I'm not one of those who can tune "by ear" except to know it's way too lean or way too rich.

My best investment ever was an O2 sensor and AFR gauge I've rigged up with a long cable for temporary installation with the gauge laying on the floor. With the AFR gauge, there's no guesswork; I know exactly what I have and when.

Just my 2-cents not knowing if you're a "by ear" guy or not. Can't wait to hear how the Mikuni works out!smiling bouncing smiley

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
60 Monza coupe (sold, sniff sniff)
66 Sprint Corsa convt - First car! Re-purchased 43 years later
2+2 gnatsuM 5691

+17 Tons of parts

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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Date: January 02, 2019 09:04AM

ITB's no manifold needed.... I dare ya!thumbs up Although at that point its just like using the 3 throat carbs on triported heads.

1961 Corvair 700 Sedan - 3sp - Gasoline Heat - Lowered a bit - Rust in Progress
I live my life 19.5 seconds at a time.


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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: kmart356 ()
Date: January 02, 2019 10:10AM

cnicol Wrote:
-------------------------------------------------------
> My best investment ever was an O2 sensor and AFR gauge …
...
> Just my 2-cents not knowing if you're a "by ear" guy or not. Can't wait to hear how the Mikuni works out!smiling bouncing smiley

Installed last month and have baseline readings from previous carb. thumbs up



Ken
'62 Spyder Coupe
Florida


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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: kmart356 ()
Date: January 02, 2019 03:34PM

Well I jumped on the last few items in order to prepare for 1st start up. The engine started pretty easily and didn't have to pump the accelerator much to get it going. Kept revs up with throttle pedal and warmed it up. No spitting, no hesitations (sitting in workshop) and revs nicely up the curve.

One thing though, these modified HSR carbs have been modified with the 2.3 size needle and seat designed for automotive applications. Fuel pressure needs to be managed down to 2-3psi with baseline target setting at 2.5psi.

The one item that I had not checked off the "to do" list was, yes... Check Fuel Pressure! Measure it at 5psi, so tomorrow is for getting a fuel pressure regulator before any further testing. smoking smiley

Ken
'62 Spyder Coupe
Florida


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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: Phil Dally ()
Date: January 02, 2019 03:49PM

The hunt for the right set up is the best part...Go Ken Go!!!

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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: roger65180 ()
Date: January 02, 2019 04:49PM

I have talked to John about his carbs and can't wait for your results. I have a 2" SU and a mikuni hsr 45 but the hsr is not one of Johns modified ones, I knew that he was changing the inlet size and according to his website he also increased the excelorator pump and that is why you can't just use a motor cycle carb

Roger R
Madison Wi
62 ct pg turbo
65intercooled 180 4sp,autocrosser
62 Rampy

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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: chris ()
Date: January 02, 2019 06:21PM

Pretty cool! Most things I've read about Mikuni carbs have been positive.

'65 Monza 4 door
4 speed
110hp
Gardner, KS

Heart of America Corvair Owners Association

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Re: New Turbo Carb - Mikuni HSR45 smoothbore carburetor
Posted by: triumphcorvair ()
Date: January 02, 2019 07:30PM

I ran four Keihin side draft motorcycle carbs on my 67 Spitfire. Cheaper and easier to tune than dual Webers. This is a screenshot of the type of setup I had. Sold the car on 2015.

Darrell McCracken
Huntsville, Texas

65 140 Monza
71 Triumph Bonneville Bobber

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