First time out on my carby 900ss today and it's also struggling much over 5000rpm. My airbox is missing the trumpets as shown below so that's what I'm blaming. I've posted in the wanted section so if anybody has a set please let me know. @Coose I wonder if you have the same problem?
Once everything is spot on mechanically, get it to the dyno and get a fuel/air run to sort out the jetting. My monies still on it running too rich at the top end, from 1/2 or 3/4 throttle to wide open. Steve R
Better breathing for the motor and a washable filter that will probably last the lifetime of your bike. The induction will also sound awesome. Steve R
No, not been on the dyno yet but I will once I've been through the mechanical bits. Although, for the price of them I may go down a size or two on the mains as a test beforehand. At least then it'll give a definite direction.
Looking at where you are, I’d have a word with someone like Ray Dudding from DOCGB and see if you’ve any local people up there that know their onions with those carbs, or get down to Italia in Lincoln as Phil there will have them singing, he’s done a few SL / 900SS with FCRs.
Cheers, we have a couple of decent dyno folk here who know their onions when it comes to carbs, although I'll be keeping a close eye. I raced in the Yorkshire hillclimb championship for many years, with a lot of the time on a v-twin TZ250 so trust me, I understand the principles of jetting!
My 97 M900 was terrible when I first brought it, not revving out, really uneven power curve, etc etc. It has an SS spec engine with V2 heads. I sorted it out by putting most of the 'performance mods' carried out by previous owners back to standard, but what made the biggest difference was going back to an airbox from the twin K&Ns, and re-instating the breather boxes. A pair of decent coils and changing the standard ingitor boxes for an Ignitech system then improved it even more. Nasher.
A bit of progress. Having this morning been woken at 5:30 by arthritis and my bladder I got to thinking, and also Googling. There's soooo much info and so many dyno curves out there for 2v motors and FCRs it's unbelievable! But, one thing that came up a couple of times was float heights. Some people have dropped them as low as 12mm, so I thought that as mine seems to be generally rich I'd have a look. I'd set them to bang-on 9mm, so I dropped them to 10mm. Massive improvement. Once the new pilots arrive I may try them at 11mm to see if it makes any difference, but once the mechanical bits are sorted I'll still have a trip to the dyno.
Hi Sev, Many years ago now when I 1st started playing with/tuning my 851, John Hackett told me that if I wanted to start making real power I needed a set of 50mm headers. At that time almost unobtainable... Whilst shopping for parts for another Ducati I stumbled across a rather crude (but later to be found out very effective) F1 Thunderball Racing full 50mm Spaghetti system with lightweight thin walled S/Steel headers/all the pipe work and 50mm carbon cans. These systems were originally supplied by Gio Ca Moto the fore runner of Ducati Performance before they tied themselves to Termi'. In a fairly mild state of tune my 851/916cc motor kicked out 128 rwbhp and 76.8 ftlbs of torque using this system. More than a standard 996SPS at lower revs despite using less capacity, heavier crank/rods, lower comp', no plenum chamber HUGE airbox and smaller inlet valves. It pulls up tree stumps from as low as 2.5K rpm. Despite what the science might say I think Mr Hackett was right on the ball with his advice. My 884cc '79 900SS Bevel is kicking out more power than most of the 900SS Bandies, using equal/tuned length 46mm Id headers without any balance pipes into megaphones and then tapering down to 50mm Id outlets, it also peaks at 7,800rpm but can rev on quite happily. Steve R
Looks like it also sorts out the lack of ground clearance, in the area between wheel and engine, that I used to experience with my stock 900SS pipes...
Thanks for that, an interesting bit of reading which bolsters my findings today. It's still struggling to rev right out so I think I will try my float heights at 11mm, and maybe consider chucking some 150 mains at it. It definitely smells less rich, splutters up to 3k when cold (as you'd expect with FCRs) and feels a lot crisper. I was about to try it without the filter but the rain strikes again... Thanks again to all for your input.
