I have pointed it out more than once, I am not a fan of those single carb setups on Yamaha XV engines, but I am a huge fan of empirical research and when I found out a while ago that there's actually a dyno at a garage near my workshop, this sparked the necessary bit of extra interest to finally get going.
As the Turbo TR1 is for this instance more or less a standard TR1 with stock exhaust the results should be almost universally applicable to XV750SE, TR1, XV1000 and XV1100 models.
Jetting / Setup:
- Pilot: 30
- Main: 185
- Stock needle, 3rd (middle position)
- Air-screw: 1.0 turns out from a soft seat
- K&N Pancake style air filter (63mm inlet diameter), type RC-0850
Additional bits:
- 3x VM38-200 inlet rubbers
- 90 degree throttle cable guide
- 4x M5x16 allen head bolts for the float bowl
Installation:
First was the (somewhat sad) task of de-turbo-ing the Turbo TR1 and swapping the clutch cover for an unmodified one as the old one incorporated the turbo oil-drain port.
Installation of the manifold is fairly straight forward, just bear in mind, you will need 3 VM38-200 inlet rubbers as the stock ones won't work.
In my case I also had to install a stock exhaust again, as for the time being
I had no other exhaust available.
Initially I tried to fit the carb without a 90 degree guide and as should be rather apparent from the picture below this did not yield satisfactory results.
In the end the matter was solved with a custom throttle cable, made at least in part from a left over SR500 cable.
As by now I had the setup on the dyno (even though not on the old Turbo TR1),
but on the Everyday TR1 and ran it against a pair of VM38s and a pair of
TM38s, I can tell you that with a lot of tweaking on can achieve about 2/3 of
the stock max. hp and torque compared to a well dialed in (and not worn out)
Hitachi. Compared to a pair of dual carbs, it's a fairly hopeless affair. The
pair of TM38s yielded almost double the horsepower even though it was limited
by sucking through the frame and (unknown to me at the time) a damaged
throttle cable, which effectively ruined the sync between the carbs at certain
openings and a needle which was too lean.
Further reading:
- Recipe for TM38 carbs
- VM38-9 installation and jetting guide
- AFRs at idle (a deep dive into what the air-screw does)
- An even deeper dive into carb tech
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