carburated Ducati 900ss starving for fuel at 5000 rpm -FIXED- !!!

[Rough Edge racing]

 Randy, I have a complete set of carbs from a 900 Monster. I not saying they are better than yours, but I'll sell them for a reasonable price if you want spare parts....
  I bought a new set on Ebay a few years ago...$360 because they were for a 750...Just change the jets and it's identical to the 900 carb...

[Tom]

I had to reread your original post.  What have you done to make sure of the same flow of air in both carbs?  In other words what have you done to synchronize the carbs? and their flow of air at idle & at higher rpm's?

[MedicAndy]

I don't know anything about Ducati's, but I had a fuel starvation issue with my 1996 Suzuki GSXR1100. It turned out that the fuel tank's petcock on the GSXR1100 is activated (opens or closes) by the vacuum drawn on the petcock as the engine rpm's increase. The last owner of my bike, after installing a racing carb set, removed the vacuum line and plugged the petcocks vacuum port since the new carburetor set didn't have a vacuum port, which kept the petcock maybe 1/4 - 1/2 way open at all times. My bikes engine would bark down at random, sometimes when riding faster, and other times at very low speeds, or it sometimes wouldn't start at all.   

I removed the factory vacuum operated petcock and replaced it with a free flowing racing petcock, which fixed all of my bikes issues. I would also check to see on how much fuel is actually making it through the petcock (if it is a free-flow).  Maybe your petcock needs to be rebuild?

Make sure that your petcock's fuel tank filter is clean.




Make sure that if you have a vacuum port, it is actually hooked up to something, unlike mine, which was plugged......




This was my fix. I installed a free-flow racing petcock

[Rough Edge racing]

 What Andy says above,^^^^^^ most or all Ducati's of 90's had a vacuum operated petcock...I have heard complaints about them....Mine was ok but I replaced it with a manual petcock..

[randy yocum]

But remember from my original post when I apply full choke at 5000rpm the bike takes off like rocket and will continue on till I roll the throttle off and release the choke.To me there is no problem with fuel delivery to the float bowls.I will try shimming both needles in the slides tomorrow,well see what happens.Now Rough Edge Racing said he uses a size 150mm main jet in his carbs and they work great.I checked and my carbs have the stock 140mm  jets,maybe I need those larger jets?

[Tusayan]

A ‘97 900SS has a manual petcock.  After you get the carb problems figured out and are riding the bike, to prevent future problems it’ll be a pretty good idea to shut off the petcock and drain the float bowls when the bike will be sitting for more than a couple of weeks.  The drain screws are easily accessible on a half fairing bike, one with a screwdriver and the other with an 8-mm or 5/16 inch open end.  Drain hoses from each carb route the fuel to an area adjacent to the side stand.

[SmithSwede]

Rough Edge---I agree with you.  If you engage the "choke" and the bike runs fine for an extended period of time, then I think that proves fuel delivery to the float bowls is adequate.   The choke circuit is just adding extra fuel which the engine obviously needs, and it is getting it from the float bowls.  Therefore the main jet could also supply that missing fuel, but for some problem. 

Personally, I still suspect the slides aren't raising up all the way, and/or there is some kind of vacuum leak.   

[oldbike54]

Rough Edge---I agree with you.  If you engage the "choke" and the bike runs fine for an extended period of time, then I think that proves fuel delivery to the float bowls is adequate.   The choke circuit is just adding extra fuel which the engine obviously needs, and it is getting it from the float bowls.  Therefore the main jet could also supply that missing fuel, but for some problem. 

Personally, I still suspect the slides aren't raising up all the way, and/or there is some kind of vacuum leak.

 Yes , the added fuel is masking a lean condition , probably caused by an intake leak . If the main jets are stock size , and the motorbike is otherwise stock , it should at least run clean to redline . Going up one size on the main might make it run a little better , but you are still simply masking the underlying problem .

 Dusty

[nc43bsa]

Don't assume that just because the jets, etc., are the correct numbers that they ARE correct.

I chased a vicious off-idle richness on my MilleGT for a long time because the atomizers (needle jets for you Amal guys) had been drilled out.

Right numbers, wrong size.

This particular example obviously doesn't apply in the OP's case, because his situation is an apparent leanness at WOT, but the principle still applies.

[randy yocum]

I tried my idea of shimming the slide needle up ,but had disappointing results,the original setup is one .5mm washer I added a 1mm washer to that at first seemed to make no difference,then added another 1mm washer for a total of 2.5mm and the bike acted poorly at 3000 rpm and didn't help my original problem at all at 5000rpm.I switched back to the one .5mm washer,so I'm back to square one.Everyone talks about an intake leak,I tried everything I can think of to find it,The propane bottle trick as the engine is running,and I tried spraying ether with a long straw to direct the spray in different areas of the carbs to see it the engine would speed up at idle if I found the leak,No luck.I have a question about those vent hoses that come off the carburetors ,there are 3 of them why are they there?I mean if were talking vacuum leaks seems like if they are open vents to the atmosphere ,that  could be a possibility for air leaks. I wish I had an extra set of known good carbs to try, is there  a good place  to buy parts for these carburetors?I might try larger main jets next.

[jpv7]

I tried my idea of shimming the slide needle up ,but had disappointing results,the original setup is one .5mm washer I added a 1mm washer to that at first seemed to make no difference,then added another 1mm washer for a total of 2.5mm and the bike acted poorly at 3000 rpm and didn't help my original problem at all at 5000rpm.I switched back to the one .5mm washer,so I'm back to square one.Everyone talks about an intake leak,I tried everything I can think of to find it,The propane bottle trick as the engine is running,and I tried spraying ether with a long straw to direct the spray in different areas of the carbs to see it the engine would speed up at idle if I found the leak,No luck.I have a question about those vent hoses that come off the carburetors ,there are 3 of them why are they there?I mean if were talking vacuum leaks seems like if they are open vents to the atmosphere ,that  could be a possibility for air leaks. I wish I had an extra set of known good carbs to try, is there  a good place  to buy parts for these carburetors?I might try larger main jets next.

Does the bike have the charcoal canister in place, or has it been removed?  Both our '97s came with them.  We removed them, but I can't remember the plumbing, sorry.  But it is worthwhile to verify.

[mcmuck]

Hi There! try removing the K&N filter and installing an original Flat slide carbs react poorly if there isn't enough "draw" in the airbox. A GSXR suzuki with the airbox lid removed will not come off idle it will just backfire from the lean condition created. Ducati engineers spent a lot of time balancing the air intake to the carbs, the K&N may be causing issues. As previously stated if you can add fuel with the enrichner / choke circuit and it doesn't starve it isn't a fuel delivery issue. Shimming the Needles will only change the mixture at one point on the needles taper, CV carb slides are only fully open at high vacuum at roll on they drop to maintain constant airspeed in the venturi and return to approx mid way once the air speed has stabilized (hence the name constant velocity) The wearing needle jet is fairly common Dyna Jet needles cause the same condition they are harder than the jet so the jet becomes the sacrificial part. If you can't or won't replace the K&N a quick and dirty test is to tape off the air inlet 30% and see if things improve. As with all testing make some careful notes of "everything" you do lots of odd problems drag on because of details missed in the early stages of trouble shooting. FWIW

[LowRyter]

The easiest thing it get a Factory jet kit.  Various jets, washers and rings will be there to rebuild and dial-in the carbs.  Those kits used to be $100.

[Rough Edge racing]

  These things will run with aftermarket airfilters... This is my 96 Monster 900....This engine runs flawlessly from idle to over 8000 rpm. There is no hesitation or flatspots.. The engine runs cleany for a Ducati at low rpm and you can cruise through town at 2500 rpm in third gear with almost no  lope...about 42 MPG...
   The hose in the middle of the air filters is the common carb vent...Around the battery you can see a steel/rubber line, there is one on each side from the carb vacuum chamber vents to the rear of the battery, dead air space...Performance Pro needle and nickle plated needle jets, stock #40 pilot jet, #150 main jet. most important, the float is set to 14mm on the rectangular shaped float half...5/16 fuel line with manual petcock,, stock vacuum fuel pump....

       

[randy yocum]

Thanks again everyone for your kind assistance in try to resolve my problem.To answer the last few questions,there is no charcoal canister on the bike it was removed by a previous owner.
   That's an interesting notion about getting to much air flowing to the carburetors ,Here's a picture of my air box as you can see a opened space with a K+N filter verses what  I assume is a normal stock, air box with much of the area is closed off except for those snorkels,I took this picture off of the internet.I will definitely try duck taping a good portion of the air box off to see if it makes a difference.I've got nothing to lose.

[jpv7]

Randy, at the time the instructions I remember from Factory Pro were to remove the snorkels only from the lid of the box with the K&N.  But I recall others having the lid removal set up without having issues.  Its worth a try, but I doubt that taping a portion off will make a difference.

[Two Checks]

Too much air to the carbs? The engine will only take in as much as it can volumetrically handle.
Its the air/fuel mixture that has to be correct. An engine cannot take in too much air.
This sounds like a main jet that is too small.
My Cal III when I got it would not pull red line WFO. Pulled the main jet it was a 130. Bumped it to a 142 and it pulled like the UP Big Boy. Looking at the plugs I think a 145 would be better.


A few years later it stopped pulling high rpm. It acted as if it hit a rev limiter. Doing a normal tune up I pulled the stock air filter to clean it. It was like a rock. Replaced it and really put a whopping on my friends with the Road Star and Low Rider Sport that had been worked on.
I could pull ahead of em before the work. They swore I did something to the engine.
I think a bigger main will cure it.

[randy yocum]

Hallelujah It's fixed!!!just got back from a 40 mile ride ,2 lane ,twisties and interstate,Wow! what a difference,it runs beautiful. Thankyou,Thankyou  To one and all, who helped me figure this crazy problem out .
  Today mcmuck provided the final piece to this puzzle I needed, with his posting,here is part of it;  Posted by: mcmuck
« on: Today at 08:53:31 AM » Insert Quote
(Hi There! try removing the K&N filter and installing an original Flat slide carbs react poorly if there isn't enough "draw" in the airbox. A GSXR suzuki with the airbox lid removed will not come off idle it will just backfire from the lean condition created.)
   My bike didn't have a cover over the air cleaner at all when I got it,I suppose I thought they all came that way.But after reading his post I researched the innerweb and found out different, they did in stock mode use those covers ,so  I copied the design of an original cover for a 900ss ,took me all of 10 minutes to make.The bike runs flawlessly right through the rpm range.It's scary fast,no hick ups anywhere.Blows right up to red line with no problem.(To be honest I have lost some of that wonderful low end grunt,It gets there, but not as quickly as before.(probably needs a little more air, ha ha )I know I can live with that trade off.Man was that a bugger to figure out,I knew there wasn't a fuel delivery problem,and the carbs were squeaky clean,the ignition system checked out fine,I had the carbs adjusted and balanced to perfection,they were in specs as far as jetting and all,I just couldn't figure it out,but now its all good.
I do have a couple questions though ,
  1) someone who knows, needs to explain how this is possible,shrinking down the intake volume of air can help an engine run better?
  2)does anyone have a Ducati 900 air box cover with snorkels ,that is unmolested they will sell me ,I doubt my card board version will hold up for very long.
What a great resources this forum is.Thanks again Randy


random face generator
 

[RinkRat II]

      Congrats on solving the problem. WG is the best!
         Maybe this will work.........https://www.ebay.com/itm/Ducati-750ss-900ss-Airbox/322561888159?hash=item4b1a2fcf9f:g:xOUAAOSwnK9ZScf5

        Paul B

[SmithSwede]

Glad you got it fixed.   And I love your home brew air filter cover.   Guzzi content !

[Rough Edge racing]

 This is interesting , my bike and the OP's bike with the same engine  I believe,mine has the V2 stamped heads .His needs the stock airbox to get it running sharp...My runs sharp with no air box..  Something to think about...

[Tusayan]

Randy, at the time the instructions I remember from Factory Pro were to remove the snorkels only from the lid of the box with the K&N.  But I recall others having the lid removal set up without having issues.  Its worth a try, but I doubt that taping a portion off will make a difference.

In my experience jetting another ‘97 SS-CR, identical to this one, removing the snorkels has a noticeable leaning effect and removing the airbox lid has a big jetting effect.  If the bike isn’t jetted to suit, it won’t run well.

[twinswin]

It’s too bad that there is not a Ducati website that is comparable to WildGuzzi.    I’ve looked but haven’t found one. 

Which is a backhanded way of saying how wonderful this forum is.

Really? Ducati.MS not a good forum IYO?

There's a ton of technical threads there and a good number of really tech savvy contributors covering all types of issues for all types of Ducatis.

I'm surprised you have that opinion of Ducati web sites and don't know how you could have reached it quite frankly. 

[randy yocum]

I don't know where that is coming from,I never once said anything bad about any Ducati site..This Ducati 900ss is new to me and I know of a couple guys in the Wild goose club that own them,That's the reason I'm asking Guzzi guys about Ducati's ,they are fluent in Italian.

[LowRyter]

wow

[jpv7]

Hallelujah It's fixed!!!just got back from a 40 mile ride ,2 lane ,twisties and interstate,Wow! what a difference,it runs beautiful. Thankyou,Thankyou  To one and all, who helped me figure this crazy problem out .
  Today mcmuck provided the final piece to this puzzle I needed, with his posting,here is part of it;  Posted by: mcmuck
« on: Today at 08:53:31 AM » Insert Quote
(Hi There! try removing the K&N filter and installing an original Flat slide carbs react poorly if there isn't enough "draw" in the airbox. A GSXR suzuki with the airbox lid removed will not come off idle it will just backfire from the lean condition created.)
   My bike didn't have a cover over the air cleaner at all when I got it,I suppose I assumed they all came like that.But after reading his post I researched the innerweb and found out different they did make those covers so  I copied the design off an original cover for a 900ss ,took me all of 10 minutes to make.The bike runs flawlessly right through the rpm range.It's scary fast,no hick ups anywhere.Blows right up to red line with no problem.(To be honest I have lost some of that wonderful low end grunt,It gets there, but not as quickly.(probably needs a little more air, ha ha )I know I can live with that trade off.Man was that a bugger to figure out,I knew there wasn't a fuel delivery problem,and the carbs were squeaky clean,the ignition system checked out fine,I had the carbs adjusted and balanced to perfection,they were in specs as far as jetting and all,I just couldn't figure it out,but now its all good.
I do have a couple questions though ,
  1) someone who knows, needs to explain how this is possible,shrinking down the intake volume of air can help an engine run better?
  2)does anyone have a Ducati 900 air box cover with snorkels ,that is unmolested they will sell me ,I doubt my card board version will hold up for very long.
What a great resources this forum is.Thanks again Randy


random face generator
 

So I see that you have stock mufflers, but one route you could take is to go with the Dynojet Stage 2 jet kit 7201 for $120.  This kit is intended to be used with the open air box.  But then you would need to get proper mufflers so you can hear this beast sing...which is mandatory in my opinion...

[oldbike54]

 An airbox is effectively a slightly pressurized chamber that provides stable and consistent airflow to the carbs . Modern motorbikes are tuned to run with the airbox in place , what you have done is put it back to factory spec .

 I might need more caffeine , hopefully this makes some sense Randy 

 Dusty

[Two Checks]

What you basically did was enriched the a/f mixture. Same as when you applied the choke.

[Rusnak_322]

I would look to getting bigger jets and a exhaust to unleash more power. I have had 4 ducati's, including a 2 valve air cooled bike with carbs and all have had either Ducati Performance open airbox lid that came with the full termi system or a aftermarket jet kit and instructions to drill a bunch of holes in the factory airbox lid. All ran great - no issues revving out.


looks like this but not carbon -

[Tom]

Randy.....fiberglas s your cardboard lid and spray paint it black.  Glass matting, resin & activator w/black paint has to be less than the used Ebay one.  Guzzi content.