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  1. #1

    Carb setting suggestions, SL 750

    So I'm going to install the 780 carbs I got from Beerdart onto my 95 SL 750 this weekend. He set them up with 110 mains, 67.5, and 18 psi pop off. They also have ocean pro f/a's.

    I've read through most of the carb tuning on here and have a basic idea, but it's a lot to take in. I've got a massive stack of paper to bring with me that I'll have to sort through once it's up and running (assuming there is an issue with how it runs). Boyseen pro reeds are the only other mod that may have any effect on the setup. I'm sure this is a common setup people have run, and am hoping to get some feed back on where to start with the h/s and l/s screws, and where other people have ended up.

    I see stock is 1/2 turn on the l/s screws, and 1m, 1/2c and 3/4m for the h/s screws. Should I expect to be at about these settings, or maybe just start here.

    thanks
    Eric


  2. #2
    Bing-A-Ding-Ding-Ding, Brrrrrap! Brrrrrrrrrap!!! Polaris_Nut#1's Avatar
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    I'd start there. It should be pretty close. 750's have 90 mains but with the air cleaners you need the bigger mains. It might be on the fat side but that's a safe way to start.

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Stock setting goes out the window with mods. Are you running premix or oil injection still? So far my 750 with premix, V Force II reeds with spacers, Vortex F/A's and the PSI dry pipe are currently using 85 lows (might be a tad big with slight blubber) set around 3/8-1/2 turn. And 120 mains in CEN and PTO. With the MAG using a 122.5 main. I'm still fine tuning, but this is an example of how much bigger than stock you may need.

  4. #4
    what is the stock jetting and pop off pressure? I'm thought I read that stock lows are 70. So do I really want smaller lows?

    I'm still running oil injection. I plan to pull it out and block it off this winter.

  5. #5
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Stock 750 is 75 low, and 90 mains. Pop off is like 18 psi. Keep the 75's for now. It's better to have too much fuel and lean out accordingly, than to start lean and burn a hole in the piston.

  6. #6
    Got the carbs assembled and installed today, with the new reeds. I ended up installing the 75 lows to start with. I played around with it for a while, and couldnt really get rid of a bottom end hesitation. I'm pretty sure it was bog from being too fat. I had the l/s screws every where from 1/4 to 1-1/2 out, and it was the best around 3/4 to 1 turn out. This seemed to produce the highest idle, but after a 10 second shut down, it wont start right back up and idle clean without touching the throttle. I spent 45 minutes with it tied to a dock giving it wot blips. Not sure if I need a smaller l/s jet here, or different pop off pressure. I didnt have time to change the jets or springs, and I also dont know what spring is what pressure, nor do I have a guage.

    I also noticed that when you let off the throttle to a stop, it would idle around 1300-1400 for about 20 seconds, then drop down to 900-1000. Maybe this is an indicaton of where my adjustments are off?

    Max rpm is about 6250, 49-50 mph on the speedo. I put the h/s screws at stock settings, 1m, 1/2c, and 3/4p, and really only tried in and out about 1/8 turn from those settings with minimal change. What should this thing turn for rpm? Also, what's with those dumb caps slid over the top of the h/s screws?

    thanks. hope someone can help.

    Eric

  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Post #7 is the Mikuni manual, it may help with spring pressures and needle/seats. http://www.greenhulk.net/forums/showthread.php?t=15433 The hesitation you have, is it a fall on it's face (lean), or blubbers? (rich) Max RPM will change depending what size impeller you have. 64-6500 RPM I believe. The limiter caps on the screws are removable, just pull them off. They are from the factory to prevent people from changing the settings too far out.

  8. #8
    cheatin' piston popper addicted's Avatar
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    Quote Originally Posted by Larsonator View Post
    I also noticed that when you let off the throttle to a stop, it would idle around 1300-1400 for about 20 seconds, then drop down to 900-1000. Maybe this is an indicaton of where my adjustments are off?


    Eric

    Pull your flame arrestors off and look down the throats while it's idling. If you see gas dripping from the booster, bullseye, whatever you want to call it, either your needles and seats are leaking, or your popoff is too low. the dropping idle is a telltale sign. Also the fact that you need to give it gas to get it started means that theer is too much gas in the motor or carbs, and it needs a breath of fresh air.

  9. #9
    after playing around with the l/s screw, I'm pretty sure it's a blubber from being rich. With the l/s screws turned way in, it seemed to fall on it's face more.

    I'll read up in the mikuni manual. I'd like to have a good plan of things to try next weekend, as it's probably coming out of the water on Labor Day. So we're thinking I'll probably need a higher pop off pressure? I dont 100% understand where the low speed jet and pop off pressure overlap. I was thinking that if the 75 l/s jet was too big, I would of seen improvement as I leaned the screws out, but it only fell on it's face.

    Beerdart set up the extended pump setup I have with a stock 750 impeller. I'm not sure what's on the machine now, and I remember the guy telling my parents he put some sort of "performance" impeller on it when they bought it 10 years ago. I wont worry about the max rpm until I can verify impeller size, I guess. I did used to show 52 mph on the speedo when it was only a couple years old, for whatever that's worth. Not like this is a high speed machine, anyways.

  10. #10
    I just put 780 carbs on my 750 and finally got it running after tracking down a bad stator wire. #105 mains and #75 lows, with ocean pro F/A's only. Started at stock settings, M-1, C-1/2, P-3/4. Never got any hesitation or blubber, leaned it out a tiny bit and it's running at 6400 so far with just a little adjustment. You've got those boyesen reeds, but maybe it'll help you. I can sit idling for 10 seconds or a couple minutes and hit full throttle and she goes like stink without hesitation.

    BTW, disregarding the subtle differences between similar motors, I think it would be cool to have a thread listing your mods, jetting, screw settings, and the resulting performance. Might give a good baseline for those with similar mods, eh? Someone's bound to have a mod combination similar to you and already done the hard work!

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