Hello - I need some advice on two items related to my '91 900SS restoration project: 1) Do the CV diaphragms "shrink" when exposed to the air outside of their internal chamber? I ask because it appears as though mine have shrunk at the large top end where they form the o-ring gasket seal up where the cap seats to the carb body. Is there some type of rubber lube that I need to "condition" them with so they are more pliable or do I need to replace them (they have no pin holes or cracks)? 2) Can someone provide me with a PDF manual for these 38MM Mikunis so I make sure I am reassembling everything correctly? I have searched the Internet and cannot locate one but they must exist. I have found low res pages/images that are of poor quality and hard to read especially the arrangement of the washers on the needle/slide/spring and the proper position of the diaphragm white plastic retaining ring (above or below the slide?). I have the bottom end of the carbs completely together with all new o-rings, DynoJet Stage 2 kit and floats each adjusted to 14MM but need some PDFs to help on the upper slide/needle/diaphragm assembly.
MacBulldog, Got some more pictures and photos at home but here is a start. http://litetek.co/docs/LiteTekCarbDiagramDucati.pdf P.S. Nice clean bike. Cheers Gaz.
Thanks Gaz! These pages are the cleanest best detail I have seen yet!!! Do you have the entire manual you can share? Oh, and do you know if the white plastic split locking ring goes inside the top of the diaphragm (in the air chamber side) or does it fit underneath on the slide side of the diaphragm? This is the lock ring that holds the diaphragm to the needle slide that is not shown in these and other pdf diagrams. Thanks so much for the help!!! TWO THUMBS UP!!!
Hello Advikaz - well I am sure yours is running much better than this old Duc! Painfully, this bike has been sitting unloved under a tarp for over 15 years and it is time to get it running again and out on the road. I plan on taking my time and doing the on-frame restoration one step at a time to be sure it is 100% road worthy. I know you know this but for this post (and for others reading) sitting unattended for this long can have terrible side effects (internally and externally) on any machine regardless of how good they may look on the outside. THANKS FOR YOUR REPLY/POST.
Great little project you've got anyway mate. Will keep an eye on this one, I love everything two wheels! Good luck!
MacBulldog, The part diagrame looks to be from another bike, presume the 400. I have a similar parts manual for your year and size of bike. "Start new a conversation" and I will try to send it to you if the file is not too big. The white split ring goes underneath the diaphragm on the slide side. PS These are the same carbs as on Yamaha TDM/TRX850 if you have a local dealer. Cheers Gaz
How far have you stripped the carbs down? If you look hard at the diagram, you will see there is a tiny mesh filter in the petrol inlet tee-piece.... You don't want to get them all back together and on the bike only to find it has a load of cr*p in it..... The other tip which is worth remembering is that the OEM Mikuni parts (jets etc) all have a size number and a little square motif stamped on them..........Dynojet aren't marked....... ...also Dynojet jet sizes are measured differently to OEM Mikuni jets. The little Dynojet washers are for fine adjustment of the main needle......I think they are the equivakent to 1/4 of a notch space..........so the ones that aren't used sometimes get shoved onto the needle on top the circlip...............I'm not sure if that's a good idea. With regard to the float height (opposite to fuel level) how did you measure it? 14mm is an arbitary dimension, because the pilot circuit partly works via the fuel level..........You may find you will have to drop the float height to 12mm or thereabouts, as 14mm makes it run weaker and you will have to wind the pilot screws out to say, 5 turns out.
Great photo of the diaphragm and slide/retainer - exactly where I initially placed it before realizing the diaphragm had shrunk. I lubed the diaphragm with some white lithium grease then let them set for an hour and whipped them down to remove the residue. Then I found an empty container with ends the same size as the groove in the carb body that the diaphragm's o-ring lip fits in and have them stretched to fit. I will upload a pic later once I get back home. Hope this work-around restores the diaphragms shape and I will report back later my results. Thanks for the photo Gaz!
Hello Arquebus - I have the carbs completely reassembled with the exception of the slider top end but will go back through an follow your advice on the T-strainer to make sure it is free of cr*p and the floats reset to 12. Oh, and I was wondering about that DynoJet tiny washer and why it was needed. "Back in the day" (15 years ago) when this Duc was running this Stage-2 kit (150 main) installed - it included the tiny washer on the top of the needle clip and the 2 OEM washers on the bottom - the retainer clip was in the 4th position from the top. This setup made the Duc run so rich at idle it would eventually foul the plugs even with the K&N open air box and Cobra F1R free flow slip-on cans! I hope I can dial the old beast in so the carbs will function properly or I may have to go with a different set like so many others (FCR's?). I will report later on the inline T filter and other adjustments.
As I said, the float height is abitrary.........14mm may be right; so might 13mm be; or even 12mm......my 750 was set at 12.5mm on one carb, and 9mm on the other....... ......it's a case of suck it and see..... ....unless you have access to a dyno on your doorstep.......
Understood, and unfortunately that seems to be the rule rather than the exception with these Makuni carbed Duc's. There is a bike performance shop near me with a dyno and maybe once I get it running I will take to them to do the fine tuning. I have attached two photos 1) one showing the Stage 2 needles, springs, plastic spacers and the 3 washers. 2) my work-around for keeping the diaphragms stretched to their big ends until I get them reinstalled (can ends are exact match of the diaphragms big end o-rings.
Thanks, I picked up a pair of float bowl o-ring gaskets from my local Yahama/Triumph/KTM shop. Good to know the parts that will fit from other brands. I need to locate a list!
Thank for the tips - the fuel T-screen/filter is clean as a whistle and internally it looks almost new. Following the deep cleaning of the carb bodies and all loose parts I blew each passageway and jet I could fine with my high pressure shop compressor multiple times. Glad I did that because I did find some goo still lodged in two places that I removed with a dental pick and then cleaned and blew them out again. I am hoping I have caught all of the "passageways & tunnels" and all seem to be clear. My big next step is obviously the carbs top end and playing with the float levels. Then installing the new cam/timing belts I got from Ca-CycleWorks. I've watched their YouTube installation video several times but any tips on installing the belts is most welcomed. Thanks!
Current Udate on my Progress... I have completed the carb rebuild and have them temporarily installed in the Duc project bike (sure hope these old carbs function properly - keeping my fingers crossed ! I decided to remove the DJ-150 jets and drop down to the DJ-144 to hopefully tone down the over richness of the larger jets that plagued this Duc's performance back in its earlier life. The use of a a pair of hemostat set of fish-hook removal pliers sourced at the local Dick's Sporting Goods ($9.98 U.S.) aided my efforts greatly on the installation of the twist-grip cables (I did not have to remove the the twist-grip or the upper end of the cables). This week (time permitting) I will begin the flushing of the brake and clutch limes and master cylinders and hopefully start the installation of the timing/cam belts; then install the new fuel filter and all new fuel lines and other aged and brittle rubber hoses. I have uploaded some pics of the carbs sitting on the manifolds to update my main newbie original project post. Oh, almost forgot the lube and stretching of the rubber diaphragms on the ends of the food can did the trick and they went right into place with the o-ring matching its groove/seat and my inspection found no apparent pinholes or cracks (manual test of vacuum function seems normal)!
Hello Arquebus - Sorry for the late reply on the way I measured the float levels. I used a digital caliper with the carbs tilted at an angle where the float just started to close the float valve (trying to mirror the same angle if the carbs were mounted on the engine manifolds). I rested the lower point of the calipers on the base of the bowl and the top point of the calipers at the highest point of the float (this I assumed would represent the highest point of fuel level in the bowl when full and starting to close the float valve). I realize this may be the old school method and do welcome any suggestions, advice and/or photos of what has worked for you on these OEM carbs. Much appreciated! -MacBulldog
I have finally gotten the old '91 Ducati 900SS running. I have completely rebuilt the OEM Mikuni carbs; replaced the timing belts; flushed the brake and clutch lines (DOT 5); started and run to full operating temp and then flushed and replaced the oil (20W50) and added a K&N 153 oil filter; removed the OEM open airbox/K&N and replaced the OEM box with K&N RU-2970 twin-pod filter unit; eliminated the redundant fresh air/charcoal canisters/tubes and replaced this set-up with a 3/4" K&N-62-1360 mini filter directlyon the crankcase PVC valve; set-up an external fuel cell to test the engine before installing the gas tank, new filter and fuel lines (great for engine/carb tuning/testing). So far so good on the engine and carbs but now I have noticed that I have a fork tube seeping fork oil and will need to make plans of what to do to rebuild the forks - suggestions welcomed. I need to also look into replacing both tires. Even though the rubber has not touched the ground (always up on wheel stands) they are now over 15 yrs old - so, tire suggestions also welcomed (current: Michelin 120 Front 180 Rear). I am also working with a friend to fabricate a new battery box/coil mounting unit and like what FourRings has done with his 900SS Carby - suggestions also welcomed. My goal is to hopefully have this old beast fully roadworthy by this Spring (funds permitted).
Having low speed idle issues and wonder if this could be a result of using the external fuel tank (gravity feed not fuel pump pressure). Once the engine is fully heated up I can set the idle at about 1200-1300 RPMs and it will idle fine for a minute or two and then speed up to 2000 RPMs w/o me touching the throttle. I can speed the engine all the way up to 3500-6000+ RPMs with no stalling or misfires but deceleration to idle may cause it to stall out - any thoughts or suggested tuning tips? Thanks!
