Ducati.ms - The Ultimate Ducati Forum banner
  • Hey Everyone! Enter your bike HERE to be a part of this months Bike of the Month Challenge!

1 - 20 of 34 Posts

·
Registered
Joined
·
25 Posts
Discussion Starter #1
This one has me completely baffled....

I have just returned from a quick trip. My 900ss was running beautifully for a few hours. We then went up the mountain which is a climb from sea level to 1000m and the bike began missing and surging. It felt like the fuelling was completely out, it kept going but ran badly for the next few hours. When I returned to sea level it came good again. It seemed odd to me so I did it again the next day and the same thing happened. As far as I know a small change like 1000m shouldn’t effect cv carbs at all. Does anyone have any ideas on what might be happening.

Thanks,
 

·
Registered
Joined
·
3,293 Posts
do it again with the spare key in the fuel cap and crack the cap at the top to see if that helps. sounds like something else exaggerating it to me.
 

·
Registered
Joined
·
25 Posts
Discussion Starter #3
Tried the cap - didn’t help. I am thinking the same thing, it’s exaggerating another problem.
 

·
Premium Member
Joined
·
2,496 Posts
Tried the cap - didn’t help. I am thinking the same thing, it’s exaggerating another problem.
Was it cold? It may have been the carbs icing up. Do you have the carb heater kit installed on your bike?

Edit: DOH! Just noticed where you are. :eek: Given the recent temps in Aus lately, I'm surprised you could find some road to ride on that hadn't melted into black puddles...

Maybe clogged breather pipes for the carbs? The ones that run to the small black 'box' on the LH side. A 1000 metre change in altitude shouldn't make any real noticeable difference.
 

·
Registered
Joined
·
7,104 Posts
When you state that a 1000 m change in elevation “ shouldn’t “ affect the tuning. I have found that it does on my Stock Mikuni carbs also. You have probably richenened the mixture to the point that it becomes too rich higher up. Do you have a stock air filter setup ? If so you could remove the lid and see if it helps. Mine runs much better at see level than it does at 500 ft, but not so much that I need to fix it. I can’t really think of what to do other than drop the needles down a notch and try it.
 

·
Registered
1994 900SS CR, 2002 998 Trackbike
Joined
·
303 Posts
1000m is a bit more than 10% change in air density alone. In Australia at current temperatures, the heat will ad another several percent to that figure compared to your "15C sea level" standard

Maybe your bike is running a little rich at sea level to begin with, but overall I also think that this could be caused by the weather and altitude. If you go by the usual formulas, 1000m and hot weather is definitely enough to drop a jet size or two.
 

·
Registered
Joined
·
25 Posts
Discussion Starter #8
When you state that a 1000 m change in elevation “ shouldn’t “ affect the tuning. I have found that it does on my Stock Mikuni carbs also. You have probably richenened the mixture to the point that it becomes too rich higher up. Do you have a stock air filter setup ? If so you could remove the lid and see if it helps. Mine runs much better at see level than it does at 500 ft, but not so much that I need to fix it. I can’t really think of what to do other than drop the needles down a notch and try it.
Thanks that’s sounds like it is worth looking into. The carbs were set up by a mechanic when I bought the bike and I always suspected that it was a bit rich.
 

·
Registered
Joined
·
25 Posts
Discussion Starter #9
1000m is a bit more than 10% change in air density alone. In Australia at current temperatures, the heat will ad another several percent to that figure compared to your "15C sea level" standard

Maybe your bike is running a little rich at sea level to begin with, but overall I also think that this could be caused by the weather and altitude. If you go by the usual formulas, 1000m and hot weather is definitely enough to drop a jet size or two.
The other issue that I have with this is that I’m leaving for Phillip Island to see the superbikes in a month. The planned route is through the mountains to a height of 1,800m. At this rate I don’t think it will be able to do it. I didn’t think I’d need to change jets to do rides like that.
 

·
Registered
1994 900SS CR, 2002 998 Trackbike
Joined
·
303 Posts
The other issue that I have with this is that I’m leaving for Phillip Island to see the superbikes in a month. The planned route is through the mountains to a height of 1,800m. At this rate I don’t think it will be able to do it. I didn’t think I’d need to change jets to do rides like that.
I havent tried with the SS, however I have had an SV650 with very similar CV carbs at nearly 3000 meters many times. It lost at least 1/3 of its power at the top, but it wasn't running bad in a way that it felt like it would die or choke.

If yours is missing and surging to the point where it feels like it won't run if it got worse, then I change my answer and I'll say there is something wrong.

How is it on cold mornings, does it start easy without using the choke function?
 
  • Like
Reactions: RockAZ

·
Registered
Joined
·
25 Posts
Discussion Starter #11
I havent tried with the SS, however I have had an SV650 with very similar CV carbs at nearly 3000 meters many times. It lost at least 1/3 of its power at the top, but it wasn't running bad in a way that it felt like it would die or choke.

If yours is missing and surging to the point where it feels like it won't run if it got worse, then I change my answer and I'll say there is something wrong.

How is it on cold mornings, does it start easy without using the choke function?
It will start without the choke, it won’t idle without it and will need some help for a few minutes but then it settles in ok. I’m going to check the state of the plugs and pull the carbs and check for blockages and anything obvious. If I don’t find anything obvious I’ll get paid help.
 

·
Registered
Joined
·
7,104 Posts
Is your paid help going with you on your next ride to higher elevation ? Some problems that pop up under specific circumstances can be difficult to diagnose correctly when you can’t witness the conditions that bring on the problem.
 
  • Like
Reactions: ducvet

·
Registered
Joined
·
3,548 Posts
All the external fuel lines good? Not collapsing when warm? Fuel filter good? The obvious - air filter clean?
 

·
Premium Member
Joined
·
5,180 Posts
If you get paid help make it a dyno with air /fuel meter.

Starting cold without choke often means rich, but needing the choke (enrichener) to keep running may not be. Either way your complaint was not starting at altitude but running. I would try the next run with no airbox lid just zip tie in the air filter and see if it is better or worse. We don't care if it is good yet just looking for direction of it the added air (leaner) helped or hurt your problem.
 

·
Registered
Joined
·
7,104 Posts
I fine tuned my carbs at sea level and average daily temp around 80f . They are spot on then and the engine will run smoothly almost to idle speed. If you’re bike is a hair rich at sea level, that will exacerbate the problem at higher altitudes. I would try replacing the needles and emulsion tubes with Factory Pro titanium needles and nickel plated emulsion tubes, because when they get worn you can’t tune the carbs properly in the mid range, which I bet is where you’re having issues. Make sure the vacuum slides are lifting together . If they don’t this is going to have an effect on smooth running. Just take the filter element out and start the bike, then slowly open the throttle. If they rise together, try opening it quicker. If they still rise together they’re ok. Since the needles are attached to the vacuum slides they must be synchronized or smoothness suffers.
 

·
Registered
Joined
·
25 Posts
Discussion Starter #16
Is your paid help going with you on your next ride to higher elevation ? Some problems that pop up under specific circumstances can be difficult to diagnose correctly when you can’t witness the conditions that bring on the problem.
That’s a good call. I’ll do what I can before going that route.
 

·
Registered
Joined
·
25 Posts
Discussion Starter #18
If you get paid help make it a dyno with air /fuel meter.

Starting cold without choke often means rich, but needing the choke (enrichener) to keep running may not be. Either way your complaint was not starting at altitude but running. I would try the next run with no airbox lid just zip tie in the air filter and see if it is better or worse. We don't care if it is good yet just looking for direction of it the added air (leaner) helped or hurt your problem.
I’ll give that a go, thanks
 

·
Registered
Joined
·
25 Posts
Discussion Starter #19
I fine tuned my carbs at sea level and average daily temp around 80f . They are spot on then and the engine will run smoothly almost to idle speed. If you’re bike is a hair rich at sea level, that will exacerbate the problem at higher altitudes. I would try replacing the needles and emulsion tubes with Factory Pro titanium needles and nickel plated emulsion tubes, because when they get worn you can’t tune the carbs properly in the mid range, which I bet is where you’re having issues. Make sure the vacuum slides are lifting together . If they don’t this is going to have an effect on smooth running. Just take the filter element out and start the bike, then slowly open the throttle. If they rise together, try opening it quicker. If they still rise together they’re ok. Since the needles are attached to the vacuum slides they must be synchronized or smoothness suffers.
Great advice thanks, I’ll try this as well. Spot on - it’s mid range where the problem comes up (mainly).
 

·
Premium Member
Joined
·
2,496 Posts
When you state that a 1000 m change in elevation “ shouldn’t “ affect the tuning. I have found that it does on my Stock Mikuni carbs also. You have probably richenened the mixture to the point that it becomes too rich higher up. Do you have a stock air filter setup ? If so you could remove the lid and see if it helps. Mine runs much better at see level than it does at 500 ft, but not so much that I need to fix it. I can’t really think of what to do other than drop the needles down a notch and try it.
OK - so I've got Keihins. BUT... I did plenty of rides with the CV carbs where I was at or over 1000m (OK - not for long, there's not that many BIG mountains in NZ) - and as long as it wasn't too cold (no carb heaters = carb icing) had no noticeable problems. Mind you - I can't say that they were 'super-tuned' to a precise performance level. Actually - mostly dead standard for years, until I put a Dynojet kit in them, a few years before I put the FCR's in. Lol - mind you - that lack of tuning is probably what helped, as they would have been a bit lean anyway (from the airbox snorkels being removed within the first few days of ownership), so the altitude would have helped more than hindered.

Yours notices 500 ft of altitude? :eek: I couldn't ride mine like that - I have 500ft high hills in pretty much ANY direction from here. Not mountains - but not flat either.

Heh heh - I know how to fix your problem... >:)



But you already know that solution. ;)
 
1 - 20 of 34 Posts
Top