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  1. #1
    Piston? WHAT Piston?!? JGringo's Avatar
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    What size Gap of the plug is this 780 supposed to be?

    Yea, For a 780 Engine with probably 175 psi in each dome, what is the size gap of the plug (BR8ES right?)? I am having major low end problems and it seems like my rear cylinder is running funny because the plug was charred real bad but the settings of all the carbs were the same.

    Also, I am really unsure about the carbs because appariently they are off of a 785 pro and need dual puls lines, but I have an external fuel pump.

    It bogs really bad if I flutter the throttle and I have to keep it at just the right spot to break plane and then once it reaches high revs it goes great. I can't figure it out. I pulled the carbs and the fuel line routing is all funky and looks really bad.

    I have not pulled the carb intake manifold to check the reeds, but I suppose I will have to do that and check to make sure they are all right on the rear cylinder. Its as if the cylinder isn't getting any fuel!

    Anyone ever had it like this where it has absolutely no low end and dies if you flutter the throttle, but has great high end?


  2. #2
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    175 PSI in cylinders would require high octane fuel, more than 92-93 from the pumps. Most likely you'll need to mix some 110 octane. The two 44 SBN carbs have a fuel pump integrated into them. No need for an external fuel pump. Add another fitting for the second pulse line and following routing instructions for a PRO 785. Open the carbs up and inspect the internals for a blockage, esp. the filters on the back side. And while you're that far into it, inspect the reeds.

  3. #3
    Piston? WHAT Piston?!? JGringo's Avatar
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    Ok, so I don't need an external fuel pump, But what if there is only one outlet for the pulse line? I cannot tee the pulse line because it will make it run funny, and is it possible for the diaphrams inside the 785 pro carbs to be taken out, thus the external pump would be neccessary? The guy said it ran well at one point with the set up it has now, but it looks so messed up that I don't know what to trust...

  4. #4
    Bing-A-Ding-Ding-Ding, Brrrrrap! Brrrrrrrrrap!!! Polaris_Nut#1's Avatar
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    Stock 780's left the factory with BPR8ES spark plugs. The equivalent is a BR9ES not the 8. With 175 psi of compression that goes out the window. Why can't you tee the pulse line? I have never done it, but I'm pretty sure people have done it to run two fuel pumps instead of upgrading to the triple outlet pump on 750's. I don't know anyone that runs carbs without diaphragms. I'd have to see that. How about a picture to make sure you're not getting bad advice?

  5. #5
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    I added a fitting onto the reed spacer for the second fuel pump pulse line. Do not "T" the single line to feed both pumps. It would prob give them both a weak signal. Please post a pic of your set up, we're just guessing until we can see what's really going on.

  6. #6
    Piston? WHAT Piston?!? JGringo's Avatar
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    ok, so turns out your right on the pulse line thing. I tee'd the line and it for sure was not sucking through enough. But I really don't feel like pulling the carbs' 6 bolts and then the manifolds 18+ bolts AHHH.... oh well.... So I am going to put a pulse line outlet on the furthest forward cylinder's reed spacer. Its gonna be a biatch...

  7. #7
    Piston? WHAT Piston?!? JGringo's Avatar
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    Here are some pics before I put it in and tested it. The tee on the pulse line does not work AT ALL... there was no pressure from the suction and no fuel going through the lines...



  8. #8
    Piston? WHAT Piston?!? JGringo's Avatar
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    what size barb fitting did you use to fit in the spacer? There is NO way the 1/4 fuel line barb will fit, it would bust out the side of the walls.

  9. #9
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    WAY my friend!!!! 1/4" fitting from an old fuel pump. Drilled real tight and red loctite. Stock Polaris reed spacer.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  10. #10
    Bing-A-Ding-Ding-Ding, Brrrrrap! Brrrrrrrrrap!!! Polaris_Nut#1's Avatar
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    Damn, something tells me you'll be taking that thing back apart

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