Mikuni HSR45 carbs

zed660

Forum User
After reading up on the Mikuni HSR45 Flat slide carbies and seeing their application, primarily in the US, on various make and model cars, I decided to give them a try as a replacement for my triple Weber 45's. It wasn't that I was unhappy with the Webers, I just wanted to try something different and the Mikunis had less restriction in the bore and flowed better.
I purchased the carbs from the Australian Mikuni dealer (Mikunioz) in Queensland and then set about adapting them. As I wanted to mount the Mikunis similar to the Webers, my first job was to pair the carbs by having a shaft made that would join each pair so they worked in unison and I could utilise the original throttle linkeage in case I wanted to revert back to the Webers. After a clever machinist made and fitted the three shafts for me I set about mounting the carbs on the Weber manifold using the spigot mountings. A problem I found was that the bowl of the number four carb fowled one of the extractor pipes and wouldn't fit securely. What I needed was an extension piece that would move the carbs out enough to clear the exhaust. I looked far and wide and eventually came upon Alfaholics in the UK who made alloy extensions for Alfa Romeos. They came in two lengths and I found that the longer size was perfect and the ID suited a 45mm carb. I refitted the Mikunis and sorted out the linkeage to give me full throttle. A mate loaned me an AFR guage and I spent time sorting out the jetting and tuning, which was pretty straight forward being a motorcycle carb. I did try quite a number of jets and as my motor is just over 3.0l I ended up running jetting close to what would suit a 500cc motorbike engine. Eventually I got it where I wanted and the car has been going very well with very good throttle response a gain in mid range torque and better economy than the Webers. All in all a worthwhile exercise and a project I thoroughly enjoyed doing.
 

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