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Discussion Starter #1
Thoughts on this one, please.

Late last year my 2000 750SSie (24,000 miles) developed an odd FI problem. If you set the idle high enough that the engine would run, then the first time you revved it over about 3000 or so it would "hang up" and not come down again - just "idle" at 3000 rpm. I was able to confirm that it was not caused by the throttle hanging up in any way - both butterflies closing normally.

I messed with it quite a bit trying to solve the problem based on instructions in the factory manual, but eventually came to realize that I just didn't have the tools needed to set up the fuel system properly. So, I took it to a good dealer, and they did a complete setup of the FI, including TPS and all that (actually, they went through the whole procedure twice, since it was so far off - "Sir, someone has really been monkeying with your fuel injection"...Err, really? Hmmmm...). Very expensive.

Anyway, at least the bike is rideable now, but it still has quite a long pause as the revs come down when you pull in the clutch - it still "hangs up" at about 2500 rpm, but only for 2 to 3 seconds or so. I think it is worse when the engine is completely warmed up. Another symptom is that If you open the throttle in neutral, it is impossible to hold a steady engine speed in the 2000 to 3000 rpm range - it will either rev higher than that, or fall down lower.

Any suggestions? I am reluctant to pay another mechanic (or the same one) to look at it again, without any idea about what could be wrong. Otherwise, I am likely to just get a bike that runs exactly the same, and be a couple hundred bucks poorer.

Other info - it has a lightweight flywheel (yoyodyne), but the bike ran well for quite a while after I installed that. Immediately preceeding the problem I did a belt change, but I have checked and rechecked the timing, so I don't think that is the issue. I think the mechanic said he had found a vaccuum leak in one of the rubber TB boots, but had fixed it.
 

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Chilehead
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6,982 Posts
Craked intake manifold.

Get a new one, or fix with rtv and fiberglass tape (the new manifolds took too long to arrive, so I have them as spares).

Tom
 

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Discussion Starter #3
Hey, now I remember - they said they had to make some gaskets for the throttle bodies - not sure where, exactly. Maybe they never did get it all to seal up perfectly? Interesting. I'll see if I can find any manifold leaks. Thanks.

BTW, what is RTV?
 

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I don't believe there is any way they could have done a competent job on your baseline injection set-up if you have a cracked manifold. Part of the job requires syncing the throttle bodies, using dual vaccum guages/manometers The leak would have made it impossible to do this [unless it happened after the job] or I imagine they would have to dramaticly "imbalance" the TB's to get it to read equal. They must not have managed to fix the leak.

Why did they have to "make" gaskets?

RTV is silicone sealant
 

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Chilehead
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Silicone sealer.

I use the Hi-temp range stuff (-75F to 600F), just to be sure. My manifold rubbers had multiple cracks, probably due to age and the fact that I had been removing and re-installing them a few times.

The gasket is an O-ring, nothing special.

Tom
 

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Chilehead
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Yep, no way you can set it up right, which is how I identified that I had a leak in mine. You can sort of get it close, but I definitely had the hanging throttle bit, and running it without the airbox I could see some flames backfire out the sides of the manifolds, so that really made it clear that there were cracks.

Tom
 

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Chilehead
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YellowDuck said:
I think the mechanic said he had found a vaccuum leak in one of the rubber TB boots, but had fixed it.
Just noticed that line while rereading your original post.

Sounds like you still have a leak, as you have exactly the same symptoms I had. I had to repair both last June, been fine since. As I said, I repaired mine with fiberglass-mesh tape (for support) covered with hi-temp range RTV (and then black electrical tape to make it look nice). The new manifolds arrived a couple weeks later, so I'm keeping them in reserve.

Tom
 

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Discussion Starter #8
Thanks, this has been EXTREMELY helpful. I have asked about this problem in several places, and this is the first time I ran across someone who had had similar symptoms.

I will definitely do a thorough search for leaks. I guess if I find one, that might mean that the FI setup I paid for will now be off, due to improper TB balance, as blade 625CT points out. That would still be a small price to pay though if I find the problem and eventually get it running properly again. It is really annoying me as it is now.

The dealer is great though (how often do you hear that about a Ducati shop?), and it wouldn't surprise me if they were willing to help me out when it comes time to readjust things again. In fact, I might even call them and see what they say right now, now that I finally have a decent idea of what might be wrong.

Thanks again. Much appreciated.
 
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