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16 Dec 2020
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Carb and stalling problems..... 5 years 2 months ago #7078

  • Db7gtgrigio
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Hello everyone
I have two irritating problems with my 350 Saturno, which you may recall I have recommissioned after it came to Australia from Japan after a long time idle.
Problem 1 - poor idle and transition. I cant seem to get the idle mixture setting right and there is a terrible hesitation at 3800-4000rpm. If you rev the bike out it is fine but if you hold it at 4000rpm it stutters very badly. Carb has been thoroughly cleaned. all jets and the needle are new and factory spec as per the workshop manual (K54 needle 3rd notch, AB262 nozzle, 128 main, 58 idle, 40 choke). Float is new but 8.5grams not 14grams as 14grams not available and Gowanloch Ducati told me it would make no discernible difference. Float is set as 24mm as per manual. Idle mixture screw is 1.5 turns out but try as I might I cant find a setting that gives a good idle and gets rid of the 3800rpm stumble. Bike runs well all the way to redline and feels good otherwise. When I turn off the fuel the idle speed increases to 2000rpm as the float bowl empties and then dies when fuel exhausted. Any ideals? I'm stumped.
Problem 2 - sometime the bike just dies. It literally just stops with no warning. It did it 3 times yesterday on a 160km ride in 35 degree C heat. Will not re-start. Then after 5-10 minutes it will fire up. Fuel definitely flowing to the float bowl. Feels electrical rather than fuel system as there is no hesitation before it dies.
Would really appreciate your comments on these issues.....its very frustrating.

Carb and stalling problems..... 5 years 2 months ago #7079

  • Kano Nordi
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Hi DB,
Sorry I cant help with standard carb settings (mine has a 600 engine with keihin cr carbs) apart from referring you to the manual, regarding the stopping suddenly and then restarting after some minutes, it maybe the filler cap vent blocked making a vacuum?.
Cheers
John

Carb and stalling problems..... 5 years 2 months ago #7081

  • 72degrees
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Standard slide (throttle valve)? Having said that, mid range stumble on Dellortos is usually more an atomiser/needle issue (well om Morinis it is !) Not sure that the float weight is irrelevant. Have a look at this if you haven't found it already. I would have thought a lighter float might need a lower level:
danskkartingcenter.dk/dellorto_motorcycl...tor_tuning_guide.pdf

The sudden dying when hot sounds possibly the fuel cap vent as Kano Nordi suggests or an electrical problem. Possibly windings insulation breaking down on the CDI system 'charging coil' on the stator. Test the ignition coil resistance (page 17 - 2,1 of the manual = page 116 of the PDF on this site). Or the voltage out of the winding when running. Needs you to carry a multimeter, or try to reproduce the problem when static at home though as it will probably test OK when cold.

I've had this on a GFR and also on other CDI ignition system engines.
"Do not adjust your mind, there is a fault in the reality"
1957 175 Sport
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Carb and stalling problems..... 5 years 2 months ago #7082

  • Joachim
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maybe it's possible to add the missing weight.
At least for a test
Glue something with 5,5g on the float

ciao Joachim
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Carb and stalling problems..... 5 years 2 months ago #7083

  • Db7gtgrigio
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thanks Kano for the vacuum suggestion. I too suspected that but when I open the tank there is no "whoosh" noise which I imagine indicates that the tank is breathing normally. However if you could suggest where the breather hole is I can check it to be 100% certain...

Carb and stalling problems..... 5 years 2 months ago #7084

  • Db7gtgrigio
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Thanks 72 degrees....slide is indeed standard. The workshop manual states 14gr floast bit the one in the bike said 12.5gr and only 8 and 12.5gr are available, so don't know where the 14 gr came from.....Gowanloch Ducati have looked after my bevel 750 for 30 years and they know there stuff so when Mike the owner said he has substituted different float weights with no discernible difference I was inclined to believe them....BUT he also said they always set dellorto floats at 18mm but with the new white floats there is no possible way to change float height as the float arms are plastic.

I will test the components as you suggest but suspect that cold they will all be fine....
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