Done a bit of searching on this, but can't find any real answers. My '97 Formula 50LC (Morini Engine) has the standard Dellorto PHVA-12 Carb. It always ran well with the original Exhaust, pulled fairly strongly up to an indicated 55mph (yeah, I know!), the thing is, the last 1/4 of throttle travel did nothing, i.e. once up to speed, you could roll off the throttle by approx a quarter of the total travel, and it didn't affect the speed. Is that normal? Does it point to the Carb being a bit on the small side? Would a slightly larger Model work on a 50, as in actually giving a bit more performance, or is the restriction elsewhere (Inlet manifold, Reed Block, Porting, Exhaust Port size, etc)? Just fitted a new Exhaust (due to the original rusting through), and am in the process of playing with roller weights. I've gone from 5.4g down to 4.7g which feels about right. Tested it earlier, similar to before, straight up to 50-ish cleanly, stopped to turn round after less than half a mile to come home, struggled to get to 30mph! I'm guessing the choke was making it run OK, but then ran too weak when the choke closed. Now looking at re-jetting (which I was expecting to have to do anyway), current main is a #54 Looking at Jet kits, but not sure where to start size-wise. Needle clip is on middle slot. Thanks.
You should upjet about 10% for a new exhaust....54+5=59 Try a 60 if too rich and you will know from your exhaust fumes or oil drip from the end drop it down to a 58. For a new air filter add another 5 and drop down if too rich. You may need to uprate your clutch springs and torque spring. Then find the correct roller weights. How did you get on?
Thanks Indy. Got it close, can't remember which Jet I stuck in there now, I'm on Holiday so can't check either! It pulls away OK, not as strongly as before but it's close. Seems a bit 'flat' after that but, but gets to the same top speed or thereabouts, just not quite as quickly. I think I need to fit slightly stronger Clutch Springs (or lighten the Shoes). What's the gen with the Torque Spring, do I go stronger/weaker for better acceleration? I just picked up another Italian two-wheeled toy that's taking up most of my spare time now . . .
OMG...I know that drive shaft and those twin cylinders. What a beauty. Is this the Guzzi? Did they license from BMW? Ah torque springs... they hold the clutch in for longer before engaging. I think it goes Black, white, blue, red. Black standard, white adds 1500 rpm, blue 2000 rpm and red 2500 or 3000 rpm. Something like that anyway usually you can not change the torque spring without changing the clutch springs to match. I stick to standard as I am mainly riding in town. e.g ATM my clutch engages at 3500 rpm by changing to white it will engage at 5000 rpm. I am not into wheelies as yet.
