Here's some background:
'96 M900 with 35,00 miles, D&D, K&N, Dynojet.
Had some recent rough running, rich cylinder issues and assumed it was probably worn needle jets.
Got new ones and a Factory Pro Ti kit which I installed without issues (145 main, 42.5 pilot, 3 turns out, middle clip position, set float height to 14mm). Started up and idled great, but have the same off-idle cut out issues. Partial throttle is very rough and it seems to be fouling the rear cylinder plug. Full throttle pretty good, but a little "off", like the cylinders are unbalanced.
Worked on it 13 hours today and have still not gotten anywhere -- I am seriously doubting my mechanical skills at this point. I feel like I may be missing something obvious here, so any help would be appreciated.
Symptoms:
Idles great, low throttle rough / missing cyclinder, mid and full throttle OK.
Can't seem to sync the carbs with gauge - As I adjust second carb vacuum down to match first, bike will die -- not idle.
Am getting a wet plug on the rear after the missing and roughness.
Strong spark -- jumped more than a 1/4 inch when I slipped off the bolt I was grounding to.
As I type this I am thinking this looks like a float valve problem. I had the carbs apart several times today and the float valves and seats look perfect. Is there any way to test these parts?
Any other possibilities?
Thanks,
Are you sure the slide is lifting on the vertical cylinder carb?
What are your idle mixture screw settings?
Stock is supposed to be 3.5 turns out, but I found that 4.0 turns out worked better on both the 1996 and 1997 M900's that I owned.
What is your float height?
When I opened up the carburetors on my 1997 M900, the height was 9mm. Factory Pro suggested 14mm, and that clearly worked better. That's actually a lower level for the gasoline in the float bowl. It was such a big change that I called Factory Pro to make sure.
On my '95 M900, I just rebuilt the stock fuel pump b/c it was leaking externally. During the rebuild, I noticed fuel on the *vacuum* side of the pump. Soooo.... The pump was leaking into the vertical manifold.
Perhaps yours is too?!?
(BTW- I just found this last night and haven't finished the job yet so I don't know for sure that the rebuild kit (Winderosa) is a good one or not.)
<mild thread-jack>
I couldn't find a float height spec. Are you sure it's 14mm? Measured from where to where?
</mild thread-jack>
BTW, my fuel mileage was down to 32-35mpg before this. I didn't think about the pump leaking internally, so I just ordered up a pair of brand-new floats (which include the needles/seats) and installed them last night.
Thanks for the replies.
One odd thing I noticed besides the uneven vacuum sync issue is that when I screwed the mixture screw for the rear cylinder in all the way, the motor would still idle on both cylinders. It seemed to be making no difference. The front cylinder would die once I got close to seating the screw.
I had the carbs on the bench so I raised the floats to 15mm. I filled a tall hose with fuel to the carbs and let it sit for 20 minutes. No leaks, so float valves should be OK, right?
I also pulled the vacuum hose off the fuel pump and opened the petcock. No fuel out the vaccuum hose, but I'm not sure it would leak much if it was a small tear.
I'm not understanding why it is idling so well -- around 800 - 900 RPM no problems.
I may look into electrical -- coils and plug wires next.
Thanks again. Keep the suggestions coming, and I'll keep you posted.
Quote from: CX500 on August 25, 2009, 11:08:55 AMOne odd thing I noticed besides the uneven vacuum sync issue is that when I screwed the mixture screw for the rear cylinder in all the way, the motor would still idle on both cylinders. It seemed to be making no difference. The front cylinder would die once I got close to seating the screw.
It's possible to break an idle mixture screw.
From what you've described, it sounds like the one screw might be broken off in the minimum fuel position. And no, I don't know how to remove a broken idle mixture screw.
Quote from: Duck-Stew on August 25, 2009, 09:27:46 AM
On my '95 M900, I just rebuilt the stock fuel pump b/c it was leaking externally. During the rebuild, I noticed fuel on the *vacuum* side of the pump. Soooo.... The pump was leaking into the vertical manifold.
Perhaps yours is too?!?
(BTW- I just found this last night and haven't finished the job yet so I don't know for sure that the rebuild kit (Winderosa) is a good one or not.)
<mild thread-jack>
I couldn't find a float height spec. Are you sure it's 14mm? Measured from where to where?
</mild thread-jack>
Do NOT by the Winderosa kit. The diaphragms fail big time. I saw one Monster with that rebuild kit suffer hydrostatic lock in a couple of cranks. I hear Polaris uses the same pump and has kits available or you could try this:
http://www.ca-cycleworks.com/shop/catalog/ducati/fuel.html (http://www.ca-cycleworks.com/shop/catalog/ducati/fuel.html)
Scroll down.
It turned out to be that d*$# fuel pump causing my problems. Actually my needle jets were worn too.
The diaphragm in the pump just had the beginning of a small slit, which didn't seem to affect the bike at idle.
These were the WINDEROSA repair diaphragms with about two seasons on them, so no, they DO NOT LAST!! I have heard that people who use these replacements just change them once a year, since they don't last. Not sure how that cost works out over a new one.
So, if you use the Winderosa repair kits, then they should be the first thing you check for any weird fuel issues. Yes, I'm talking to you, Duck-Stew.
Thanks again, some of your suggestions were right-on!
Quote from: CX500 on August 28, 2009, 05:35:04 AM
So, if you use the Winderosa repair kits, then they should be the first thing you check for any weird fuel issues. Yes, I'm talking to you, Duck-Stew.
I know now! Thanks guys!!! [thumbsup]
Quote from: CX500 on August 28, 2009, 05:35:04 AM
It turned out to be that d*$# fuel pump causing my problems. Actually my needle jets were worn too.
The diaphragm in the pump just had the beginning of a small slit, which didn't seem to affect the bike at idle.
These were the WINDEROSA repair diaphragms with about two seasons on them, so no, they DO NOT LAST!! I have heard that people who use these replacements just change them once a year, since they don't last. Not sure how that cost works out over a new one.
So, if you use the Winderosa repair kits, then they should be the first thing you check for any weird fuel issues. Yes, I'm talking to you, Duck-Stew.
Thanks again, some of your suggestions were right-on!
Correct me if I am wrong but it really should not affect the idle. If the vacuum is pulled from the manifold then it is lowest at idle and is probably almost nothing so the bike is really more gravity fed. As you open the throttle vacuum at the manifold would increase stretching the diaphragm and opening the tear more causing raw fuel to enter the manifold through the wrong side of the pump. Seems like it makes sense.
I don't think the amount of vacuum affects the function of the fuel pump. I believe it's the pulse of the intake that works the diaphragm back and forth. The fuel pressure to the carbs probably doesn't change much with RPM. (??)
I am sure you are right about higher RPMs stretching the split further open. That doesn't explain why full throttle worked OK, but I never claimed my jetting was right to begin with.
MarcuSS
Well, WOT means max air too. So the extra fuel that comes in was probably not enough to adversly affect performace at full throttle but at part throttle it would be.
Quote from: needtorque on August 28, 2009, 10:34:43 AM
Correct me if I am wrong but it really should not affect the idle. If the vacuum is pulled from the manifold then it is lowest at idle and is probably almost nothing so the bike is really more gravity fed. As you open the throttle vacuum at the manifold would increase stretching the diaphragm and opening the tear more causing raw fuel to enter the manifold through the wrong side of the pump. Seems like it makes sense.
Except that you have the part about vacuum backwards. It's lowest at WOT and highest at idle.