Ducati Monster Forum

Man, this is ridiculous. I installed a set of factory pro needle jets (they were ovaled) and jet kit 2100 miles ago, and I am now having hiccuping/gasping for air at low rpm, surging and backfiring at midrange rpm; increased choke seemed to help my problems a bit. I popped open the carbs, hoping it was a clogged jet and see that my needle jets are both ovaled out again! The OEM brass jets lasted about 15k miles unless the PO replaced them at some point. My question is why in the world did these go bad so fast? Do the brass OEM jets hold up better than the nickel-plated factory pro ones? Is it caused by using the tapered needle or the use of the jet kit (137.5/42.5/#3 needle clip)? I'm wondering whether I should buy another pair of the factory pro needle jets or OEM, or if i should make some changes to my jetting. By the way I have a '99 M750.

I'll probably get flamed, but if you used the factory pro Ti needles that is the cause.

They are much harder than the jets and cause excessive wear IMO.

The brass OEM jets will do the same thing.

I used a dyno jet kit, which has softer needles, and OEM jets. There's about 13K on them now and it still runs OK, but the jets are no doubt worn.

My question though is if the jets are worn, which would cause a rich condition, why does the choke help? You sure you don't have something else going on at the same time?

Thanks for the input. I might go back to the OEM needles instead, so I'm not having to tear apart the carbs all the time. I'm also confused about the choke helping things. My guess is that it is pushing the RPMs higher and onto the next carb circuit. When I idle higher due to the choke, it runs better, or if I am running at highway speed or under hard acceleration (with choke on or off) it seems to run normally. Accelerating from idle is when i hear the vaccum sound from the airbox mostly and midrange running at a constant speed between 2-3k rpm is where it backfires/pings and has slight surging. I wasn't expecting to see the needle jets ovaled out, I thought might have had a blockage or some goop in the carbs. The jets don't look blocked and look clean to the naked eye. After I get the new needle jets installed, and the carbs cleaned, hopefully all is well. If not then it will be a search for another underlying cause.

You'll probably be disappointed with the stock needles after the kit ones. If you've removed/drilled the airbox lid or the airbox I don't think it will run very well. It will be lean.

On the carbies the choke actually richens things up as opposed to just being a fast idle like on the fi bikes.

How old is the gas? Did you notice any water in the bowls when you ripped them off?

Yes the gas was old, I suspected the gas at first so I siphoned out the gas and put in new gas, added some seafoam, but this didn't really help anything. That's when I thought the next step would be to tear down the carbs for a good cleaning. I didn't notice any water but it could have been mixed in with gasoline. Still not sure if the needle jets are the main cause of my problem, but as ovaled as they already are I'm certainly going to change them while I'm at it. OH yes i remember that the choke is not a fast idle. I'll post an update as to whether the problem persists after putting in the new needle jets and cleaning the carb. I have also wondered if I have some kind of air leak but haven't noticed anything yet. As for using the OEM needles and concern for a lean condition, I wonder if it might help that the needle is in the #3 setting (#4 is stock), or even drop it further to #2. I do have a chopped airbox and megaphone exhaust.

Dropping the needle slightly would negate some of the condition caused by the jet being oval, but not much I don't think and would make things lean when you do get the problem sorted.

When you replace the jets check the needle surface closely. If there are any machine marks or roughness that will exacerbate the tendency for the needles to 'saw' into the jets.

An air leak is another possibility.

Good luck.

My Factory Pro needle jets were stainless and didn't show any wear with the Ti needles, (or DJ needles for that matter). I wore through two sets of stock needle jets in 6000 miles. One was with stock needle jets.

People on this forum have reported oval wear on the needle jets with stock needles if I remember correctly. And as HDP said, you'll be dissappointed with the stock needles.

Have Factory Pro changed the material of the needle jets? My understanding from the importer here in OZ was that they made a stainless jet to avoid the problem of ovaling.

If they still have the stainless needle jets available I would try them. Maybe the DJ needles aren't as harsh. Maybe that could be a combination.

www.factorypro.com/tech/needle_jet_wear.html (http://)
www.factorypro.com/tech/needle1.html (http://)
later..RS

Thanks for the links RS!

Looking at those Factory Pro sites I'd say that you all have no option but to buy 41 FCRs :D