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post #21 of 56 (permalink) Old Jun 25th, 2019, 3:33 pm Thread Starter
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Originally Posted by RockAZ View Post
My stock carb bike is exactly this, so if you sort it out by all means share!

Edit: to get to this relatively satisfactory performance I went back to the stock airbox lid, put Db killer's in the exhaust on their 2nd quietest setting and fiddled excessively with the needle height and idle enrichment settings. All new needles on a zero mile NIB carb. Now after 1,200 miles on two sets of plugs with perfect looking burning I've accepted the low rpm performance although it does rush through the 2-3krpm's very quickly with a Nichols flywheel and a 41 tooth rear!

Could be a co-incidence but in the last week I've replaced the throttle cables and for a while the "surging, unevenness" at steady throttle was worse until I loosened the return throttle cable. Now while I can still hear and feel the steady throttle roughness below 5k, I can no longer see the variation in the tach. Slightly too tight throttle return cable amplified the unsteady issue.
OK I am using the stock airbox top not modified w/ K&N filter, & Carbon Tech exhaust, Factory pro stage 1 jet kit everything else is bone stock---I am using 130 main jet, Slide needles 2nd position from the top & 37.5 pilot jets that is the set up as of now( had 40 pilots-too much), I tried moving the slide needles to the top position this did not work so put them back air screws 3 turns out-if I go in it gets worse-3-4 turns out works. I am still getting a little stumble off idle under load. I am thinking of trying the 127.5 main jets that I have and see what I get-the stumble is not real bad and goes completely away over 4K rpm. It should take me about 1 hour to change the main jets and get it back together. It's a lot better but not exactly where I want it-- though it is now rideable

1991 Ducati 900ss-Euro, 1991 Ducati 907ie. 1978 Yamaha SR500, 1979 Yamaha RD400 Daytona Special, 1973 Truimph X-75, 1975 Triumph T-160, 1976 Triumph T140, BMW's too many to list
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post #22 of 56 (permalink) Old Jun 26th, 2019, 7:17 pm
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Nice job on a period correct early 900 carby.

Keep in mind those are fuel screws not air screws so the further in you put them you are leaning it out. Early 900's used 40 pilots but the carbs may not be original but later similar looking carbs that did come with 37.5's. Bottom line it will tell you which it prefers and if the heads were ported then it will want less fuel so if the carbs are right but has ported heads that might account for the smaller pilots working better.

Odd looking reaction rod on the rear brake I do not remember seeing that design before. back in the day they were mostly stock or carbon fiber tubing.
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post #23 of 56 (permalink) Old Jun 26th, 2019, 7:51 pm
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My bike had only a few upgrades on it when I bought it - carbon fiber rear hugger, clutch cover and Remus pipes, rear view mirrors all from the Corse catalog, Goodrich brake lines on the front brakes and oil lines. The original seat was included but that is a Corbin. This has the original early model black brake and mounting position on the rear, original stickers. NOS body panels with a darker windscreen added. I'm the first owner, those are manufacturers plates.


1991 900SS
1995 900SS SP #746

Last edited by RockAZ; Jun 26th, 2019 at 7:57 pm.
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post #24 of 56 (permalink) Old Jun 26th, 2019, 7:52 pm Thread Starter
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Rode her home tonight for the first time it is very close to perfect running, This was a European sold bike not a N.A. bike, I think the numbers on the carbs were a little different but I dont have the book here at home to look, I have the fuel/ air screws out right now 3 turns with the 37.5 pilots, the mains right now are 130 and pulls great up to redline. I had a spare airbox lid (the one that was originally on the bike was modified) with the intact original lid I could not clean the running up where I was happy, So I tried removing the snorkles this was too much air way too lean cleaned up all of the stumbling but under hard throttle when I close it it would still stay at higher RPM --then it would finally start to slow down way too lean--so I then tried the original lid that was modified-( with the original snorkles) picture a triangle cut between the snorkles,-this cleaned everything up almost-It is night & day better -tomorrow I may play with the fuel screws a bit more just to see if I can dial it in better but she is very close
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1991 Ducati 900ss-Euro, 1991 Ducati 907ie. 1978 Yamaha SR500, 1979 Yamaha RD400 Daytona Special, 1973 Truimph X-75, 1975 Triumph T-160, 1976 Triumph T140, BMW's too many to list
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post #25 of 56 (permalink) Old Jun 26th, 2019, 7:56 pm Thread Starter
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and the reaction rod yes I have not seen one like that before -who knows with Renato being the original owner --it's not like he had a problem getting or having parts made lol
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1991 Ducati 900ss-Euro, 1991 Ducati 907ie. 1978 Yamaha SR500, 1979 Yamaha RD400 Daytona Special, 1973 Truimph X-75, 1975 Triumph T-160, 1976 Triumph T140, BMW's too many to list
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post #26 of 56 (permalink) Old Jun 26th, 2019, 8:02 pm
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"picture a triangle cut between the snorkles"? Pic pretty please?

1991 900SS
1995 900SS SP #746
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post #27 of 56 (permalink) Old Jun 26th, 2019, 8:05 pm Thread Starter
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I'll have to do that tomorrow but I'll post a pic tomorrow
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1991 Ducati 900ss-Euro, 1991 Ducati 907ie. 1978 Yamaha SR500, 1979 Yamaha RD400 Daytona Special, 1973 Truimph X-75, 1975 Triumph T-160, 1976 Triumph T140, BMW's too many to list
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post #28 of 56 (permalink) Old Jun 27th, 2019, 7:05 am Thread Starter
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OK here are pictures of the modified airbox top, The triangle cutout was there when I got the bike-I drilled the 4 extra round holes--the last picture is a rubber plug that I can use to block off any of the round holes if I find it's too lean. the plug is a BMW part --it's the timing plug for any BMW twin from 1952-1995
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1991 Ducati 900ss-Euro, 1991 Ducati 907ie. 1978 Yamaha SR500, 1979 Yamaha RD400 Daytona Special, 1973 Truimph X-75, 1975 Triumph T-160, 1976 Triumph T140, BMW's too many to list
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post #29 of 56 (permalink) Old Jun 27th, 2019, 7:14 am
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Interesting,...

1991 900SS
1995 900SS SP #746
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post #30 of 56 (permalink) Old Jun 27th, 2019, 9:00 am
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I think that hanging idle has more to do with ignition advance and idle setting and less to do with jetting.
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