Rough Running On 851 SP3...

AndrewS

Hi All

I took the SP3 out for a run yesterday morning, first time it's been started for several weeks. It started first time, as it usually does, and ran fine for 20 miles or so. Then I pulled out onto a main road and accelerated (only up to about 7500 rpm) then backed off. The engine started running what I can only describe as "rough", with the occasional backfire. I managed to get it home, slowly, and when parked in the drive, it idled fine and responded normally to a blip of the throttle. After I turned it off, I opened the fuel cap (don't know why!) and there was a very loud rush of air - no great smell of petrol so I assume the air was going into the tank, i.e. there was quite a vacuum in there.

Any thoughts welcome. I wondered about a blocked/kinked breather, but I'm not sure where it runs; is there any sort of one-way valve?

Thanks

Andrew

Higgins

Hello Andrew,
Here is a the breakdown of my 851 one way valve :
http://ducati-mostro-forum.fr/uploads/member_1393/1555532977.jpg
Just for test you may connect directly the vent hose to the tank (without the valve) try to blow gently in the hose to be sure it is not plugged somewhere. 😉

AndrewS

Higgins wrote

Hello @Higgins

Many thanks for your reply. I haven't had a chance to take the bodywork of the SP3 yet - where does the vent hose run, and whereabouts is the one-way valve located?

Sorry for my ignorance!

Regards

Andrew

sagot

Hi there.
The one way valve should be between the tank and the top triple clamp.
Pull the tank hose and blow directly into the tank nipple, with the fuel cap open.
It wont be fast but you should be able to blow through it into the tank.
The "bump" on the tank is a sort of baffle and they sometimes rust shut!
If its clear then it probably the check valve (one way).
As a test, keep the hose off and go for a ride.

AndrewS

Thanks for the reply. Isn't it the SP4 that has the"bump"?

Andrew

JImmySL

there is a small hole in the actual filler cap (and I mean small) which could be blocked try that, strip it down the cap and give it a good clean, I made the hole a bit larger on mine at the same time

you may find some of the info and comments on my experience handy... http://www.ducati851and888.com/showt...ht=vapour+lock

AndrewS

JImmySL wrotethere is a small hole in the actual filler cap (and I mean small) which could be blocked try that, strip it down the cap and give it a good clean, I made the hole a bit larger on mine at the same time you may find some of the info and comments on my experience handy... http://www.ducati851and888.com/showt...ht=vapour+lock

Many thanks for your reply, I'll try giving the cap a good clean first off. I had a read through the thread you gave the link to, not sure I fancy delving inside the tank... One difference between the problems we had, with my bike when I opened the fuel cap there was a very loud rush of air; hopefully a vent issue then? Still not sure where the vent runs on an SP3 though.

Thanks again.

AndrewS

OK, on the basis that a "picture is worth a thousand words", I just took a photo of the fuel filler on my SP3. Am I correct that the rubber grometty-thing at the top is the vent???

On the assumption that it is, I applied a mild vacuum with a Mityvac (brake bleeder) on the SP3 and on the corresponding place on the 1198S (which looks just the same). On the 1198S I couldn't get any vacuum reading, the pump just drew in air. On the SP3, I could get a vacuum, which slowly decreased, suggesting that there was an obstruction (but not a blockage) somewhere?

Does this help at all???

Thanks.

mikesps

Hi Andrew,

Yes the tank vents up through the cap lock into a small plastic maze which ends at a small hole above the grommet in your picture. This connects to a hose through the tank to one of the outlets next to the fuel outlet and return lines. The other is the drain from the top if the filler.

You could try blowing compressed air through the hose but try not to blow the hose off the fittings in the tank as this activates the auto drain 'feature of this design. There should be hoses from the outlets on the bottom of the tank so check those for blockage too if they are still there.

Mike

AndrewS

mikesps wroteHi Andrew, Yes the tank vents up through the cap lock into a small plastic maze which ends at a small hole above the grommet in your picture. This connects to a hose through the tank to one of the outlets next to the fuel outlet and return lines. The other is the drain from the top if the filler. You could try blowing compressed air through the hose but try not to blow the hose off the fittings in the tank as this activates the auto drain 'feature of this design. There should be hoses from the outlets on the bottom of the tank so check those for blockage too if they are still there. Mike

Hi Mike

Thanks for that, things to check! Funny none of the "workshop manuals" (that I have, anyway) give any detail about tank venting.

Someone suggested that the passages in the tank cap might be blocked - worth a look?

Thanks again.

Andrew

mikesps

You could try blowing through the small hole first.

There is a small spring and a tiny ball bearing which hold the key flap up while you put the key in the lock. It is very easy to lose these as they want to fly out as the lock comes apart but it can be done if you are careful.

Mike

AndrewS

Thanks for the warning - I'll try blowing through it first!

Andrew