Afternoon all, As per my thread in the Newbie's section, two weeks ago I bought a '93 900SL which I finally got on the road yesterday. I have a bit of an issue where there's no power above 6k, as if the slides are only opening half way but they're not, they're fine. I've done many searches both on here and Google but haven't come up with a definitive answer. As far as I'm aware it's a stock motor with a pair of cans, although one of the baffle tubes has snapped and has moved by about 10mm but not enough to cause this issue (new tubes on order). It has stock ignition with Electrex coils and good leads, new DCPR8E plugs and Champion non-resistor plug caps, and FCR41 carbs jetted as they came from Sudco, fitted with blue bellmouths and a single Ramair filter which I've also removed to test but other than making it a little crisper the issue is still very-much there. I've checked the fuel pump and tank breather, both are fine. One thought is that maybe the cam timing is out a tooth, where this morning I ordered a pair of belts from Exige so I'll check that once the belts arrive. The tickover is a little lumpy but I've ordered some 52 pilots (down from 60) - I've got it as good as I can on the fuel and air screws. The mid-range up to around 6k is good, there's just nothing after that. It will rev out if you're willing to wait and not going uphill, and it feels the same in every gear. I assume it's advancing ok as the mid-range is good, but I've loaned my strobe to a mate so I need to get that back and I'll check the ignition timing. It looks to be charging ok and the battery is good. Any suggestions as to anything I'm missing? There's nothing to the bike so I'm drawing a blank!
Worth having a look at the dyno recently posted, as these things dont make top end power and fall off quite a lot once peak is made. If it’s new to you, have you flushed new fuel through? Have you ridden one before to make a comparison? My experience of those old air cooled is they are a bot breathless over 8k
Much to comment on but WLTTE. I guess you have examined spark plugs to check how it's running, I would try a plug-cut at around 6K for starters.
Thanks for the rapid responses! I have never owned a Ducati, though have had a couple of water cooled 4v vees (KTM 950 Adventure, Cagiva Raptor) but certainly didn't expect a 2v air-cooled vee to be anything like those. Looking at the curve in the link above that actually ties up quite well with how mine feels, so maybe it's just me after all? Sat next to it in the garage is a sorted 1100 Katana and Z1000J.... I know the SL is running a bit rich, but up until yesterday if only been tinkering in the garage so I'll go and do a plug chop once the new pilots arrive. It currently has a 37t rear sprocket but I have a 39t which should make it more lively. Hmmm.... 944.... ST2 cams..... Hmmmmm...
It's probably due a new one but the flow at the carbs is good. The fuel was fresh yesterday too. Sorry, I forgot to mention that.
Agree as above @Billywiztheelder check the fuel filter, i had major issues with my 900ss ie and it was the fuel filter being dated 2001 same one it was born with and crap in the fuel tank!
If removing the filter made it crisper then it sounds like it's running too rich (MAIN JETS) at the top end to me. Steve R
It's on 155s as the carbs came with which most people seem to find to be about right. I'll try it again once the weather improves....
Sorry, the pilots are 60s, not 55s. I was getting confused with the 155 mains. That, and a bit of a hangover.... But, the pilots won't affect the top-end of course.
Most companies when supplying carbs fit them with "Ball Park" jetting set on the safe side as in too rich. After that you're meant to sort out the jetting to spot on for your machine. Steve R
I’m not familiar with the carby bikes but if the fuel filter is in the tank the fuel filler is an absolute b’stard to get out and back in again. Plenty of patience required. https://www.ducatiforum.co.uk/threa...tank-seal-refitment.32516/page-2#post-1638380
Yep, it's in the tank... I need to take the filler out anyway as the surround has been fitted 180° out. The bike had a hideous carbon filler cap when I bought it but the original cap was in the box of bits. But, the elephant is upside down! Thanks for the link, I've ordered a new o-ring.
Valve clearances / timing and mechanical setup notwithstanding, correct jetting and breathing is a corrective help, and I found that on my SL and 900SS the biggest gain came from headers. Really quite a remarkable difference in urgency and power kept coming higher into the rev range. My ‘91 900SS had modified 851 Termi headers and cans and my ‘94 SL MkIII had Sil Motor headers and cans. I’d say that the fit / finish was nicer on the SM system but the power was more pronounced with the Termi, but Baines had been at my bike under a previous owner so I’m not ruling other mods out on that one.
Were these headers Spaghetti type systems as in equal length headers with 2 balance pipes between them, doing away with the 4 way joint on the standard headers? Steve R
Have to say the first step is to check that all the mechanical bits are OK, valve timing, ignition timing, fuel filter, air filter, throttle balance and adjustment, compression figures adequate and within limits, spark plugs and ignition supplying good reliable spark. Until you have all these in place you cannot effectively fault find or tune your fueling as they will all have an effect on the demands of the motor.
That’s right Steve, I was pretty impressed with the gains. And if it was purely psychological then I was still pretty impressed. Bum dyno was happy anyway.
Thanks everyone for your input, and I agree with all comments. Carbs are balanced and clean, and I have all remaining service items on order. My request for help was mainly to make sure that there wasn't a specific item I'd overlooked but I think it's maybe a sum of the whole and also just me! I'll update my Newbie thread once I have it as good as I can, and we might have a little trip to see the dyno man across town once it's mechanically right.
