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Discussion Starter · #1 ·
okay, so I picked up my new to me toy: a 2000 m750. current mods are: k&n filters instead of the airbox, dynacoils, and unknown brand high pipes/cans.

the bike runs pretty terrible at low speeds, and if you give it more than 1/2 throttle, it totally bogs & sometimes backfires thru the pipes. Now, at 75-80 MPH, with the throttle just cracked open, it pulls pretty good, up to 95 mph, where my brain told me to let off.

after a good high speed run, the plugs didn't look too bad, but I think the jetting is still too rich.

could it also be that the timing belt(s) could be retarded a tooth or something?

will I hurt the engine (lean it out too much) by installing stock needles/jets with the mods that the bike has, at least to get a good baseline? ...any help will be appreciated...

oh, by the way, I am not too scared of doing the timing belts, etc. at home, even a top-end would probably not be out of my mechanical ability....
 

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I doubt you're off a tooth, that makes a pretty substantial difference, not to mention the noise when the piston and valve meet ;) As for the jetting, I know nothin' about carbs but I'm sure one of the more knowledgeable folks will have something to say.
Nice story about the ride back, btw.
 

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The bike will run terrible with stock jetting too. It will be really lean. If you can't find out what the original owner did, I think it would be best to start over with a new stage 2 kit.
 

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Brandon (can't trick me with your screen name) [cheeky], have you checked the carbs out internally to see if your pilot/main jets are clogged at all?. You didn't state miles, so I wasn't sure if the bike sat around a while w/ bad gas. Varnishing of the carbs also do the same things you're describing. If they are all in clean shape, that's one thing off the checklist anyways. Sounds definitely fuel related. I'm sure others will chime in to help you out further, but that's a good place to start.
MM
 

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I just had another thought. Check to make sure the vent hoses to the diaphragms are not kinked. If the slides don't lift properly the bike will act that way also.
 

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I actually know some history on the bike and I was supposed to get another crack at getting it set right again, but I never got another chance to mess with it :-\

I originally thought there was either a bent valve or timing issue as it ran terrible, you could pretty much out run the thing on foot...

The previous owner is definitely not at fault as this was his first duc and he pretty much thought that's how it was supposed to run :eek: The previous previous owner really didn't take care of the bike and you could tell, keep reading below for some of the big things, but one thing, the PO bought it at a really really cheap price with all the issues known, and he told me he sold it for a bit less than he bought it for and he laid out all the issues he knew of outright, he's a good guy and wouldn't lie about anything as far as I know.

I had the PO do a compression check and he said that both cylinders checked out within a few psi from each other, BUT iirc, that psi was somewhere in the 103psi range... which is low, i would expect somewhere in the 120-130 range

The first things I wanted him to do were compression check and timing check, not bad things to redo now just to make sure, I remember it running at my house like it was just a bit off in timing (yes, it was running that badly), but I'm not sure you would've made it back to cali if it was off, still a good check

When the bike came to see me, it was in worse shape than you've got it now.

We took the carbs completely apart and cleaned them up real good, the jets are all pretty much new as his jetting was completely off from the start, but I only got one or two iterations before he had to go home, so it's still way off, we had the factory pro kit, and I'm sure he gave the leftovers to you

the vent hoses for the diaphragms were definitely one issue that I saw, not only were they open to the elements and SHORT, the little filters weren't on there for sure, that's not that big a deal, but I do know that leaving them open to airflow screws everything up, so I had the PO replace the hoses and route them out of the airflow, I didn't get to see how he did this, but he did tell me that he was able to do that.

the exhaust are some mess of stuff hobbled together from the previous previous owner and the paint could definitely use a complete redo... the PPO really trashed that bike pretty good and the frame fixes were pretty trashed with the welds done in huge globs... might want to take a look at those, as far as I could tell, they looked like they were fine for structure, but damn it was done badly. You already found the shaky headlight, BUT, it wasn't shaking due to loose bolts (one side was definitely loose), but if you look closely at the U-bracket that holds the headlight up, you'll find a broken bracket piece iirc.

I didn't check closely, but I'm sure there are some exhaust leaks in the pipes, so that could be one cause of the popping you're getting too

As you already saw, the chain and sprockets definitely needed attention and it sounds like you took care of that... :-\

hmm, this is all I can remember right now, if you ask more questions, it may jog some more memory...

I think if it were me, I would start looking for some slightly bent valves... that's really my best guess from what I can remember of how the bike ran... but that's pure speculation
 

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I've been having fun with my carby lately and what you probably need to do, seeing as the jets and whatnot have been checked on is go to the next step in your system and take a look at the plugs also.. if the jets were off before it could've fouled them up some... this is pretty easy to do, dont even warm your bike up.. just pop those badboys out and if they're caked in fuzzy black deposits like little catterpillars then just wipe em off with a napkin and some WD40 and you're set :D

if not then I'd consider figuring out what sort of cans you've got and if they're starving the engine.. thats why ducati pipe kits come with a chip to let the injection know whats up...
 

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Discussion Starter · #9 ·
thanks for all the input so far, guys...

Hiero: I do not blame the PO at all...he pretty much laid it all out there for me to see. The hoses going to the diaphragms for the carbs were routed under & then behind the battery, out of airflow pretty well, and I don't think they're kinked at all.

If there are slightly bent valves, a leakdown test should show that, right? I mean, it's either leaking past the valves, or the rings...

Unfortunately, the plugs don't look really bad, the front horizontal cylinder's plug actually was a decent looking light brown, while the vert. cylinder was more carboned up, and (uh-oh) a bit oily :-\

...the few (extremely ugly) welds on the frame I can fix no problem, along with the cobbled together aftermarket exhaust...I'm already planning on cutting off the existing brackets & making some nice tabs, both off of the frame, and exhaust & bolting it up right.
 

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yeah, definitely do the leakdown if you've got the means to do it, that should give you a lot more info

i do remember swapping out some new plugs that I had on hand, the NGK D8EA's and the bike would NOT idle at all and it was actually worse than before, so we put the old ones back in and things went back to what they were... that really confused me, but it's another piece of the puzzle

it sounds like you've got some resources available to you, I'd just cut the whole exhaust off and redo it, that thing really was rough...
 
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