Turbo Tech: The Mikuni HSR45 carburetor

[kmart356]

Executive Summary: There is an alternative to the YH carb as well as performance upgrades such as the Weber sidedraft. The Mikuni HSR45 has proven itself to be adaptable to the Corvair turbo.

The engine in the '62 Spyder came to me equipped with the venerable Stromberg WW conversion. A custom offset adapter was added to allow the installation of an air filter.
.
.

Stromberg WW.JPG (35.07 KiB) Viewed 137 times

.
That was eventually replaced by a 38mm DGV downdraft on the same offset adapter which improved idle, throttle response and improved breathing for a bit more boost.
.
.

38DGV .jpg (24.25 KiB) Viewed 137 times

.
Continuing the quest for ease of tuning as well as improved breathing (ie, more boost), the "Mikuni HSR45 conversion" was made. I contacted John Parker to discuss how the HSR45 might work with the Corvair turbo. The plan used a sleeved SU adapter with Mikuni mounting flange and a short K&N air filter.
.
.

SU Manifold - Turbo.jpg (25.02 KiB) Viewed 137 times

.

Mikuni.jpg (27.05 KiB) Viewed 137 times

.
John Parker @ Vintage Performance Developments has put together a nice "Mikuni kit" for the Corvair based on the work we did on my conversion. It includes the modified Mikuni HSR45, fabricated mounting adapter and oan ptional air filter assembly. See photo.
.
.

.
That black nipple on right side is for choke cable if you decide to add one. Choke not needed in Florida.
The vacuum fitting, I plugged mine. That black tube is the float bowl vent and should be routed to a safe location in case of overflow.
Some guys used the stock air cleaner assembly with hose connection to Mikuni intake side instead of that K&N. K&N is non-restrictive.
.
You will need an extended linkage arm on turbo shaft and just slide it over to position. Add a downlink and use the stock throttle return spring.
.
.

K-N-1 and Throttle linkage.jpg (36.85 KiB) Viewed 137 times

.
Fuel pressure needs to be down around 2.5psi so i used the 30-804 fuel pressure regulator. I do not have a return fuel line to the fuel tank, never had one.
.
.

IMG_4251.JPG (21.86 KiB) Viewed 137 times

.
John has a good write up on his website for initial tuning. Mikuni Carb Installation and Tuning Instructions.

Disclaimer: I am not affiliated with VPD and don't get any benefits from posting this information.

[Nashfan]

Just the ease in which fueling is adjusted with these carbs is almost worth the price by itself!!

[toms73novass]

If I did not do blow thru on my turbo, this is what I would have done.