Sebring Daily Rider

[Nick]

In the highly unlikely event that anyone out there is actually riding a Ducati 350 Sebring for daily transportation or is considering doing so, here are a few words on the dramatic performance and rideablity improvements a 26mm Mikuni VM (round slide) make to this model. This particular carb was one of two on a beat-up old 650 Triumph Bonneville 'Desert Sled' that found its way to me. Since half a 650 is almost a 350 I mounted it on the Sebring as is and it worked perfectl. I simply used a piece of radiator hose to mount it to the stock manifold, opened up to 26mm.

1. Significant power boost: Seat of the pants tells me 2~3 more HP and, with the longer intake tract, much more torque. It pulls strongly all the way up the rpm range. The stock 24mm mixer is totally inadequate. A 28mm would probably also work well, but the 28mm VM has a larger body, and there isn't much space there.  

2. Easy starting: The Mikuni enrichener (it's not a 'choke') is very effective. Prior to starting I depress the enrichener, kick the engine through twice using the compression release, then close the enrichener. One kick and the bike literarily leaps into life, as if impatient to be running. This is no doubt due to the better air/fuel mixing of the Mikuni. Stock points ignition has worked flawlessly for many years. 

3. Steady idle which is easy to adjust with the idle screw. Jets, slides and other parts easily obtained. 

All of which unleashes (!) the Sebring's true potential, making it much more fun to ride.

[themoudie]

Aye Nick,

Sounds a good conversion and I'm pleased to read the wee beastie is regularly used. Others have used Mikunis on 250/350/450 models and typing "mikuni" into the "Search" window, top right of the screen will show other examples. The Chinese options have also been used, with some success.

Good health, Bill

[Duccout]

Hi Nick,

When you get a chance, could you lost the jetting specs that your Mikuni uses? The jetting set-up for Mikunis is very difficult to get right, and I gave up on my Mikuni for that reason, so any info helps others in the future.


Cheers,

Colin

[Nick]

Slide: 2.5
Needle: 5F3 - Clip in bottom groove
Pilot jet: 20
Main jet: 100

Edit: Forgot to look at the needle jet (aka 'spray bar') will add later. Regarding those who have 'trouble' jetting Mikuni carbs, it's important to remember that 2-strokes use different needle jets than 4-strokes. Thus, if the Mikuni was originally fitted to a 2-stroke you need to change the needle and needle jet. Further, any Mikuni jetting for a 350cc~400cc 4-stroke is going to be pretty close.

Never had any trouble with the radiator hose/hose clamp mounting, but it would be best to fab a slightly curved manifold for improved distance from the fuel tank, one that would also allow use of the stock Mikuni manifold. Also, rather than having the throttle cable exit vertically from the carb, use one of the curved pieces of tubing that Mikuni or other makers use to route the cable horizontally from the carb.
I've also added a bit of rubber under the rear of the tank to raise it slightly.

Edit 2: Amal concentric carbs also work well and are much easier to mount. However, as with the Mikuni, if the carb was originally fitted to a 2-stroke, make sure it has a 4-stroke needle and needle jet. The jetting from a Triumph 500 should be very close for a 250 Ducati.