Ducati popping on deceleration

Shaun @ Tru6 · 03-19-2009, 03:25 AM

took the bike out yesterday, 95 Supersport with a 98 SS/FE longblock that we put in last fall, left the original carbs in the bike.

it is running very strong, but have a lot popping on deceleration, figure it's running lean.

looking for help on carb adjustment or if I need to re-jet it.

good excuse to post a pic.

Chocaholic · 03-19-2009, 03:43 AM

Either lean or rich. A quick dyno run or two will tell you which (with AFR). Rejet accordingly. A shop with a dyno should only charge you $30 or $40 for a couple of pulls.

masraum · 03-19-2009, 04:19 AM

I thought the cause of popping on decel was because there is unburnt fuel in the exhaust or an exhaust leak.

jwasbury · 03-19-2009, 04:34 AM

Exhaust leak will definitely make for popping on decel...had the same thing happen on my 1995 M900. I had the headers off and reused the exhaust gaskets. It immediately began popping on decel. New gasket fixed it up fine. Are you running stock CV carbs? The diaphragms can dry up, crack, split and leak air which will make you go lean too.

Shaun @ Tru6 · 03-19-2009, 04:40 AM

Thanks guys. I think it may be the exhaust gaskets based on recalling how the motor install went.

CV carbs? Not sure. It's a bit of a mystery bike and I'm assuming it has the original 95 carbs on it.

will call local dealer today and inquire about new gaskets.

one thing is for sure, this bike brings such a smile to my face every time I get on it. can't wait to really get comfortable on it. think I need to take the intermediate course soon.

Flatbutt1 · 03-19-2009, 05:34 AM

Quote:

Originally Posted by jwasbury

...... The diaphragms can dry up, crack, split and leak air which will make you go lean too.

+1.... intake manifold leaks can do this as well

HHI944 · 03-19-2009, 05:48 AM

Before ya pay a shop 30-40, check your plugs. Better, buy two new ones, put em in, suspend the ass end about 6 inches up and take it up to redline and back down 3-4 times in your garage then check the plugs. White=lean Black=rich You want a light brown ideally.

nostatic · nostatic's Garage

"they all do that..."

Well, actually it depends on how much popping you're talking about, but every Ducati I've had will do some popping and burbling off throttle.

Shaun @ Tru6 · 03-19-2009, 05:53 AM

Quote:

Originally Posted by nostatic

"they all do that..."

Well, actually it depends on how much popping you're talking about, but every Ducati I've had will do some popping and burbling off throttle.

Todd, this popping is new. There was some popping on decel with the original motor, but it sounded proper. This sounds like something is wrong.

plugs are new. will pull them later today.

Jeff Higgins · 03-19-2009, 06:29 AM

Mine pops and crackles on the decell all the time, but only above 6,000 rpm or so. I kinda like it...

Anyway, these guys pretty well nailed it. Just make sure you have airtight inlet and exhaust tracts as a starting point; fixing air leaks in either is virtually "free". I always like to start cheap and work towards expensive...

Shaun @ Tru6 · 03-19-2009, 06:43 AM

I could live with it, I was more concerned about running lean than anything.

gaskets are $3.15, need to get a pair of gloves anyway, so good excuse to run over.

thanks everyone!

Jared at Pelican Parts · 03-19-2009, 07:57 AM

You have a leak somewhere, or your jetting is off. A quick test, is it easier to induce when you blip the throttle quick or when you gradually let off.

HardDrive · 03-19-2009, 08:18 AM

While it is not mechanically correct, I rather like a few pops off the throttle.

Gratuitous photo

Shaun @ Tru6 · 03-19-2009, 08:20 AM

Quote:

Originally Posted by Jared Fenton

You have a leak somewhere, or your jetting is off. A quick test, is it easier to induce when you blip the throttle quick or when you gradually let off.

I honestly don't recall now. I know it happens when I run hard on the highway accelerating and then ease off on the throttle.

Here's another data point:

I'm on the highway, get off, roll up to a stop light, clutch in, throttle off. It idles at 3K. Heavy blip of the throttle and it comes back down.

Raining today so I can't test.

Hugh R · 03-19-2009, 08:51 AM

Popping on decel is usually a rich condition. The fuel is above the upper explosive limit and comes down into the explosive range as it enters the exhaust and expands and mixes with air.

jwasbury · 03-19-2009, 09:17 AM

Quote:

Originally Posted by Shaun 84 Targa

CV carbs? Not sure. It's a bit of a mystery bike and I'm assuming it has the original 95 carbs on it.

Stock carbs should be the same as on my 1995 Monster. They are Mikunis and CV stands for "Constant Velocity" With CV carbs, your thottle input simply opens the intake butterflys, and the slides in the carbs are opened by vacuum. Sooo, if the diaphragm is compromised, the slides will not open up correctly. Its fairly common for people to bolt in Flat Slide Carbs (Keihin FCRs, I believe) as a good performance upgrade. I'm not sure if those are "CV" or not, no experience.

Anyhow, when the diaphragm went bad on my bike, it idled poorly and popped, backfired through the intake as well as exhaust and was particularly fussy at part throttle. It actually ran fairly well at larger throttle openings.

The exhaust leak at the header gasket manifested as a lot of backfiring on decel only...otherwise it ran perfectly.

Hope this helps.

varmint · 03-19-2009, 09:20 AM

smell the exhaust. should tell you if it's that rich.

Grog · 03-19-2009, 09:25 AM

Popping on deceleration is a lean idle condition. With the throttle closed you are on the idle circuit. Each carb will have a needle valve you can adjust. A lead plug could cover the valve or screw head, that EPA made manufactures install plugs to keep you from being able to make your machine run right. That being said, if you are idling at 3000 rpm when you release the throttle I would say that could be your problem, fix that before you worry about the popping. High idle could be like some have mentioned, a vacuum leak, sticky choke, sticky throttle, sticky throttle cable, look on the intake side for the leaks. If it were a head gasket I would think you could hear it blowing on the compression stroke. Also if water-cooled loss of coolant due to a bad head gasket. Check the Ducati forums.

Hope this helps,
Steve

ramonesfreak · ramonesfreak's Garage

ever since swapping my can for a D&D can, i get wonderful pops on decel and i LOVE it. :-) sorry i cant be more help...but maybe youll learn to enjoy the sound?

greglepore · 03-19-2009, 12:07 PM

The throttle is likely binding cable or bad return spring, not related unless its trying to keep butterfly open on decel, if it is, it could cause your issue.