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Old 28-06-2020, 05:20 PM   #1
Ross090
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M900 Carb Leak

Hi All,

Just fired up my 1993 M900 for the first time since restoring. It jumped into life almost immediately

All is good except I seem to have a fuel leak at the carbs. The only things I did to them when they were off is open one of the black plastic covers, and I also removed two screws to zinc plate the throttle cable mount. I've also replaced all the lines but I cant see that being the problem.

Do these carbs have common areas of leaking? If so, anyone know where I can source some seals/gaskets locally?

Cheers

Last edited by Ross090; 28-06-2020 at 05:25 PM..
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Old 28-06-2020, 05:28 PM   #2
manwithredbike
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Quote:
Originally Posted by Ross090 View Post
Hi All,

Just fired up my 1993 M900 for the first time since restoring. It jumped into life almost immediately

All is good except I seem to have a fuel leak at the carbs. The only things I did to them when they were off is open one of the black plastic covers, and I also removed two screws to zinc plate the throttle cable mount. I've also replaced all the lines but I cant see that being the problem.

Do these carbs have common areas of leaking? If so, anyone know where I can source some seals/gaskets locally?

Cheers
Where's the petrol coming out Ross, is it at the overflow outlets? Could just be the float valve not seating properly after a period of lay up??
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Old 28-06-2020, 05:39 PM   #3
Ross090
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Its quite hard to tell with everything else attached to the bike so I think I will be stripping it down again soon. It appears to be from the left hand carb, but that could be just because its sitting lower when on the sidestand.

It doesnt look like its from the overflow outlets as I have them routed down past the engine, and the tubes were on quite nice and firm there.

Is it possible to test for leaks when they're off the bike and it isnt running or does it need fuel pressure?
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Old 28-06-2020, 07:41 PM   #4
manwithredbike
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Shouldn't be any prob checking them off the bike. The fuel isn't pressurised in the carbs.
It would be useful if you were able to see where it was coming from on the bike though in case it's one of the supply line connections.
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Old 28-06-2020, 09:06 PM   #5
Ross090
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Thank you!

I'll take a good look at things when I remove the airbox, hopefully that'll show me if its lines or carbs.

I've found some gaskets on ebay, but they're pricey and a full kit which isn't really what I want. I'll be calling Ducati tomorrow, but I doubt it's something they stock.

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Old 29-06-2020, 01:21 AM   #6
Sirc
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to answer your question "do these carbs have common areas of leaking?" - apart from the norm concerning needle valve maladies, they do have one other and that is the float chamber drain plug/screw. It uses a very shallow taper as a means of sealing and this means that they need tightening very carefully as it's only too easy to crack the tapered seat of the bowl casting if over-enthusiastic tightening applied. Hopefully your leak is the more common needle valve failing to seal type as a result of standing etc. Careful examination of float bowl interior will usually be visible if taper seat fractured if you need to check.
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Old 29-06-2020, 12:48 PM   #7
Ross090
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Thanks for the info.

I have some seals coming from Ducati, I will be sure to check the casting for any cracks when I have the carbs off the bike again. Hopefully an easy and cheap fix though!
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Old 07-07-2020, 07:34 PM   #8
Ross090
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Looks like it was one of the bowl gaskets afterall
..what a job that was!
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