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Old 04-23-2006, 05:57 PM   #1 (permalink)
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Default Question about mixture screws and factory pro settings

I had previously lost one of my mixture screws on my 750 so I got another used carburetor for parting out and took one of its mix screws. Ran ok for a while but since I had a k&n (left the airbox closed) I had to fiddle with them to get it to run alright. Forward about 5 or 600* miles and I've just put in a Factory Pro jet kit + pods. Upon sifting through all the parts in my carbs I find that the spare carbs and mine have different pilot jets (mine being stock 750 parts and the parts carb having 1 step bigger or so). OK so who knows maybe someone changed up my spare carbs. I then realize that since I've been using one mixture screw from each, the one that came from the spare has a larger diameter needle on the mix screw...oops. Since I only have 1 of the originals and both from the spare I take the other spare and use them both so at least I'm being symmetrical (d@mn no wonder synching them was so wacky)

So now who knows the deal with these mixture screws? Is my spare from a 900 even though it was claimed to be 750 or are the mix screws just different across different years? Mainly is there a reason I shouldn't use the larger diameter needle'd mixture screws and get the original ones? Did I damage anything putting the wider ones in my carbs?

Too bad I found this out just after rejetting so I'm still all over the board as far as getting it to run well. And now for the next part of my question...IF there's no quirky sh!t going on with the mixture screws I'm looking for all your setting if you have a factory pro jet kit and pods (and well whatever your exhaust is since it won't matter quite as much as the other 2). Right now I have factory pro:

140 mains
45 pilot
clip #3 (from top)
Mix ~2 out (work in progress)
14mm floats
ru-1750 pods
stock cans

I know BigIain runs quite leaner...I've also noticed that Hiero runs something very similar to what I have, as well as one of the sample installations on Factory Pro's papers that came with my kit. Big Iain you seem to have the most verified settings...way different from the other 2. Big or Hiero or anyone, any comments as to where I should set my baseline? My mix screws gonna set me askew from your settings?

Thanks
David
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Old 04-23-2006, 06:32 PM   #2 (permalink)
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Default Re: Question about mixture screws and factory pro settings

Well I just started it up again and have a bit more info. Mix screws 2 turn out starts fine with choke, but requires a little throttle no matter what once it's started and choke is off.* Otherwise it will idle for maybe 10 seconds before dying. Only the 1st time I started it the carbs were coughing (lean?) as I held the throttle slightly open for warming up. Idle sounds 'soft' don't know how else to describe it...the cylinders don't give a nice pop. Also, the exhaust is a little smokey. Since carbs only coughd the 1st time and from the smoke and soft sounding idle I figured it was running pretty rich and that's how I found that it seems to run about the same (smoke and all) with the mix screws seated all the way in. Do worn needle jets affect idle like this as well? For some reason I though the effect was higher up. Also didn't smoke before the jet kit / swapping the 2nd mix screw.

Bike has ~8300 miles and all these tests are done idling in my garage due to the rain
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Old 04-24-2006, 09:58 AM   #3 (permalink)
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Default Re: Question about mixture screws and factory pro settings

Sorry about the previous rambling, but does anyone have their baseline settings for a similar setup? Anyone know anything about the different sized mixture screws?
Thanks
David
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Old 04-24-2006, 11:09 AM   #4 (permalink)
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Default Re: Question about mixture screws and factory pro settings

I'm not sure about the mixture screws, but I'm a believer in "if it works ok, it is ok". Change the needle jets just to be sure they're ok and cut out a variable in the equation. Factory Pro are very helpful indeed (unlike Dynojet in my experience...) You should find more on the DML on your settings too, but be prepared for a bit of trial and error - identical carb setups on apparently identical machines sometimes produce different results. When it feels about right you could go for a dyno and F/A analysis to check (maybe it could be better...) My 98 M900 runs with 170 mains, Factory Pro needles on highest setting, 42.5 pilots and mixture screws 3.75 turns out - with K&N pod filters and a modified RoadRacing exhaust. It still feels very slightly weak on very small throttle openings, particularly at high revs, but is otherwise pretty good - starts well (choke but no throttle in winter..) and responds quickly. I think that the air filters have a much greater effect on carb settings than exhausts - stock cans flow pretty well. Good luck! [thumbsup]
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Old 04-24-2006, 12:03 PM   #5 (permalink)
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Default Re: Question about mixture screws and factory pro settings

hey whited, I've been gone for the weekend, so I'm just seeing this thread :P

I agree with funkuncut, go ahead and check/replace the needle jets first and see what happens. I don't know the answer on the mixture screws, but seems to me that would have no bearing on the situation as long as you adjusted them correctly and then synched them up. Needle jets definitely do things all over the rev range if they're ovaled.

fwiw, the settings that I ended up with were in an average temp of about 45-55 and it was running a tad rich. I fully expected to have to lean things out a tad with the mixture screws and possibly a notch on the needles when it gets hotter, but as it's high 80's and low 90's at the moment here, the bike actually runs quite well without anything touched.

nothing really changed when I went from cored cans to the desmoworld slip ons either, so i would imagine funkuncut's comment is probably pretty close about the stock exhaust (especially after you core em out a bit)...

After many many small changes, I was still getting not so good running somewhere in the middle rev ranges (+/- a few revs up and down the range). I emailed factory pro directly quite a bit and finally figured out that I needed to set my floats to 15mm. That ended up being the key for me, tuning from there was a cinch
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Old 04-24-2006, 02:45 PM   #6 (permalink)
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Default Re: Question about mixture screws and factory pro settings

Yeah I'll try new needle jets. Just wasn't sure they were worn from the way my stock parts were running fine before pods.

...side note, do 750 intake runners fit 900's? (engine swap will make all this kinda moot, huh ;D)
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Old 04-24-2006, 08:43 PM   #7 (permalink)
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Default Re: Question about mixture screws and factory pro settings

we always fit new needle jets when we do a jet kit, especially with the factory pro ti needles.

i did a 750 this week using the d08 kit. be aware the '97 models (single disc, old style motor) use different jetting to the '98 onwards 750 (from memory anyway). i used bigian's settings - needle on the first notch, 132.5 main. i dropped the pilot to 40 from 42.5 (std) which may be a little lean. new needle jets were the 13240041A part, which is a Y2, same as the 900 as well. 41B is a Y6, pre '98 750 engines. 41E is a Y0 (smallest), cagiva elephant 900.

i think 40 main is a bit small.

the mixture screws were 4 turns out. this gave an idle CO of around 5%, just nice. the idle was a bit high when i first checked it, and it needed the screws 4 1/2 turns out for 5% CO then. once i lowered it i wound the screws in 1/2 a turn.

to check the float levels i have the bike vertical on a rear stand. attach a clear plastic tube to the float bowl drain and loop it up the side of the carb. open the drain and let the fuel level stabilise - you may need to bleed the air out of the tube. ther are two little round bosses on the sides of the carbs - the rh one has a small hollow in it, the lh another little boss. that's the fuel level for the correct float level. it's the easiest way to check it, best done before and after youpull it apart just to be sure. i've never really seen one off.
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Old 04-25-2006, 11:25 AM   #8 (permalink)
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Default Re: Question about mixture screws and factory pro settings

Quote:
Originally Posted by whited3
Yeah I'll try new needle jets. Just wasn't sure they were worn from the way my stock parts were running fine before pods.

...side note, do 750 intake runners fit 900's? (engine swap will make all this kinda moot, huh ;D)
sorry, missed this question, but for sure, carb and IE intake manifolds aren't going to swap, the 750IE and 900IE intake ducts as ducati calls em have different part numbers, so not the same, will it fit, i don't know for sure but I would conservatively say no

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Old 04-25-2006, 01:01 PM   #9 (permalink)
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Default Re: Question about mixture screws and factory pro settings

Was afraid so...ah well maybe I'll keep it fuel injected. Not really topic of this post, but I just bought a 900 FI motor from a 2000 monster that at some point I'll be swapping on to my 98 m750....that is sometime after I pick it up this weekend [thumbsup]

it will be nice to get to the bottom if this carb thing though for the time being. Anyone need a carbed 750 engine??
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