One of the (few) Achilles heels of our race car, and Volvo Amazons in general, is the carburetor setup. The SU carburetors, sourced from drizzly old England, work well when properly tuned up, but can be somewhat of a bear to actually, you know, “tune up”. Especially now that they are 43 years old and have been lightly charred. Part availability is shrinking, and finding the proper jets and needles (especially for a somewhat hotted-up plant like the one I built for the last race) can be time-consuming and wallet-emptying.
Prior to the last race, my teamate Rob gave me an article about setting up motorcycle carbs to run on vintage European 4 bangers, to replace whatever antediluvian SU/ Zenith/ Guinness carburetors happen to be darkening one’s engine compartment. We went down to the motorcycle chop shop and picked up a set of Mikunis that looked promising- a 4 carb setup for a 1000 cc Yamaha crotch rocket. The bike these carbies came off of would have made somewhere in the 130 to 160 hp range, so they should flow plenty well for our tarted-up B20.
Last weekend, I welded up an intake manifold for them, and last night I hooked them up onto my B20-equipped Volvo (my daily driver) and cranked the engine. After a bit of fiddling, the engine actually idled, and throttle response was quick and strong. The fuel pump on the B20 seems to be providing too much pressure for the Mikunis- I finally got them to run pretty well simply gravity feeding them fuel out of a plastic jug- but a good pressure regulator should solve that problem. Since I was jug-running the engine, I couldn’t take it for a drive, but the engine seemed to crank and run smoother with the Mikunis than it ever had with the SUs. Throttle response was pretty astounding. I could zing the throttle wide open and the engine instantly responded. It even sounded a bit like a motorcycle.
Once I finish rigging up a throttle control and figure out the pressure problem, she should be ready for a test drive. And come race time, it will be a simple matter to transfer the setup over to the LeMons car.
I’ve enclosed some pictures. Try not to drool on your keyboards.
–VCH, Formerly SU, now _Mikuni_ master