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  1. #1

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    Tuning After Boysen Reed Install

    Hi Everyone,
    New to this site, more of a snowmobiler than jetskier. This is due to work schedules. Anyway, I have a 1996 SLX780. I bought a set of Pro 30 reeds for it. After installation, the machine ran horrible. I know it's a jetting issue. Plugs are white. I didn't change any jets but did play with the screws but can't get it right. Does anyone have a jetting recommendation for this model that they know works? I can change anything from pop off to the actual jets, I have all spare parts. Or, does everyone use the stock jets? My problem is that I don't have the time to keep taking the carbs off to change things, I live 20 miles from my riding area. I was hoping someone had a setup for 0-3000' altitude that they know works. I tried a search but only found comparison posts, not tuning after the fact. Rest of machine is stock except for the impellor. I apologize if this has been covered, but I couldn't find what I was looking for.


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Welcome to the Hulk

    Do you know what jets are actually in the carbs right now?

    What carb adjustment screw settings are you using?

    Is the engine stock except for the reeds?

    Original fuel lines still installed?

    Did this motor ever run properly for you?

  3. #3

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    Thanks K447, glad to be here.
    Well, after writing this post, I decided to go out and dismantle my carbs, since I am going to do a complete rebuild of them anyway. Upon further review, I found something very interesting. My pilot jets were 72.5, stock is 67.5, mains were 107.5, stock is 110, needle seat was 2.5, stock is 2.0. I have no idea what my pop off is, never thought to check it first. My screws were set to the stock settings, until I played around. I think I went up to 1/2 turn richer on all settings. Now, keep in mind, I bought this brand new! I was there when they uncrated it. There are no other engine mods. Now I don't know what to do, go back to all stock jetting, or go 1 size larger than stock in the mains only and return the rest to stock. I do have all the spare parts to change it to anything I wanted. Thinking that the 67.5 pilot with #80 spring, along with the 2.0 seat will help the semi sluggish low end response. Think the 112.5 main would be too big? As far as running, it always was a little sluggish out of the hole in the first 1/4 stage. Then it would take off and run good up to top speed. I would see 6250-6300 on the tach. I always thought it should be more. Maybe, I never saw the real way it should run. I also added a Nujet impeller. I can say this. since the machine was new, I have never, ever fouled a plug. I change them once a year when I start the season and that's it. I did sync them when I first got it.

  4. #4
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Welcome to the Hulk.

    This should help with the tuning.

    http://www.greenhulk.net/forums/show...-Mikuni-tuning


    What are the last 2 digits on your HIN #?

    It sounds like a different year for jetting, EXCEPT for the 2.5 needles and seats.

    What Nu Jet impeller did you install? That will also affect jetting.

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by xlint89 View Post
    ...What are the last 2 digits on your HIN #?

    It sounds like a different year for jetting, EXCEPT for the 2.5 needles and seats...
    Don't get too hung up on the model year 'official' carb specs. Sometimes Polaris revised carb specs (and other things) during production.

    You may have 1997 specification carburetors in there. Give us the last four digits of the HIN, and we can tell when it was manufactured.

    1996 SL780 had two different initial carb configurations, depending on the engine model number - see attached.

    Also, sometimes there were minor production line screw-ups and engines/carbs (with whatever jetting) for one model could have been installed in a different model hull.

    Have a look at the info in my signature links. There were some Service Bulletins that may apply to your 1996 machine.

    PWC-96-02 Multi Function Display-Erratic RPM / Water Damage
    PWC-96-04 Loose Hand Grips - All 1996 Models
    PWC-96-07 Fuel Valve Restriction May Cause Lean Condition
    PWC-96-10 Leaks At Bilge Plug (Except Hurricane)
    PWC-96-14 Carburetor High/Low Screw Settings
    Attached Files Attached Files

  6. #6

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    Quote Originally Posted by xlint89 View Post
    Welcome to the Hulk.

    This should help with the tuning.

    http://www.greenhulk.net/forums/show...-Mikuni-tuning


    What are the last 2 digits on your HIN #?

    It sounds like a different year for jetting, EXCEPT for the 2.5 needles and seats.

    What Nu Jet impeller did you install? That will also affect jetting.
    Hi and thanks for the "welcome here".
    The last 2 #'s are 96.
    The NuJet is a Destroyer model # PL-A5.0

  7. #7

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    The last 4 #'s are K596.
    I checked the engine #'s and found this: I have an EC780PWE-02 motor. According to the specs you sent over, my jetting was right, except for the needle/seat, but I was using the screw settings for the SLX specs on the bottom. Probably why the thing ran rich when it was running. Why is my motor listed under SL/SLT and not SLX? Now that we know where my jetting is, what would you do about my problem? Think the E-10 gas got to my fuel pump or shut off valve? It went from rich to lean just changing the reeds.

  8. #8
    Canadian Beaver Inspector jkindt's Avatar
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    Quote Originally Posted by topgun View Post
    ...Think the E-10 gas got to my fuel pump or shut off valve? It went from rich to lean just changing the reeds.
    I think the general concensus on the board, and on most marine groups, is to avoid ethanol enriched gasoline at all costs. The ethanol in the gasoline allows any water that may get into your fuel to mix at a chemical level with the fuel making the water separator not function properly. The water molecules may get trapped at the tiny orfices in the carbs causing all types of tuning issues. Not to mention the effects ethanol has on the seals and rubber components in the fuel system. These parts were not designed for ethanol fuels. The other issue with running higher levels of ethanol is that the ratio of fuel to air is different when running ethanol. Back in my 'redneck drag racing' days, we had an engine that we converted to ethanol and we had to change the jets to allow about twice the amount of fuel in order to keep it from running too lean. 10% ethanol is enough to effectively lean out the ratio. The same occurs when converting from oil injection to premix, anything that offsets the amount of gasoline in the fuel will effectively lean out the mix.

    Disclaimer: The opinions provided are based on my best recollection of previous discussions. I have been known to be incorrect lately. Hopefully I can get over the recent 'brain farts' that have been accompanying a recent run of food poisoning that I have been dealing with. If anyone can confirm my opinions, please do so.

    (HERE IS A GOOD POST ABOUT ETHANOL)

  9. #9

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    Quote Originally Posted by jkindt View Post
    I think the general concensus on the board, and on most marine groups, is to avoid ethanol enriched gasoline at all costs. The ethanol in the gasoline allows any water that may get into your fuel to mix at a chemical level with the fuel making the water separator not function properly. The water molecules may get trapped at the tiny orfices in the carbs causing all types of tuning issues. Not to mention the effects ethanol has on the seals and rubber components in the fuel system. These parts were not designed for ethanol fuels. The other issue with running higher levels of ethanol is that the ratio of fuel to air is different when running ethanol. Back in my 'redneck drag racing' days, we had an engine that we converted to ethanol and we had to change the jets to allow about twice the amount of fuel in order to keep it from running too lean. 10% ethanol is enough to effectively lean out the ratio. The same occurs when converting from oil injection to premix, anything that offsets the amount of gasoline in the fuel will effectively lean out the mix.

    Disclaimer: The opinions provided are based on my best recollection of previous discussions. I have been known to be incorrect lately. Hopefully I can get over the recent 'brain farts' that have been accompanying a recent run of food poisoning that I have been dealing with. If anyone can confirm my opinions, please do so.
    I know all too well the effects of E-10. Down here at the Jersey Shore, the marinas have boats stacked up on top of each other waiting to get fuel issues fixed due to the E-10. It is killing all our small engines, outboards, PWC, Atv's, etc. Unfortunatly, your warning has to go by the wayside. E-10 is mandatory in NJ, even at the marinas. It's mandatory in upstate NY where I also ride. I would have to buy racing fuel from our local track to get away from it. My Yamaha outboard has gone through 3 complete carb and fuel system rebuilds plus 1 powerhead due to it.

  10. #10
    Canadian Beaver Inspector jkindt's Avatar
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    Quote Originally Posted by topgun View Post
    ... E-10 is mandatory in NJ, even at the marinas. It's mandatory in upstate NY where I also ride. ...
    Well...I learn something new every day. Why would they make E-10 mandatory??? I suppose you don't have access to av-gas, not that it would be much cheaper than race gas.... I haven't had to deal with ethanol so I am not sure what people are doing about this.

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