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Indy 500 converting EFI to carbs

This is a discussion on Indy 500 converting EFI to carbs within the Polaris forums, part of the Brand Specific Snowmobile Discussion category; I have had some issues with my EFI system on my 92 indy so I'm looking at taking out the whole computer system and putting ...

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Thread: Indy 500 converting EFI to carbs

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    I have had some issues with my EFI system on my 92 indy so I'm looking at taking out the whole computer system and putting in carbs. I'm in need of the carbs, fuel pump, and cable. And how hard is the conversion to do? Also, if the carbs work I will be looking into parting the EFI system. Thanks!

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    Polaris_Parts_MN's Avatar
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    There is also a fitting on the cylinder head that has a hose running to the throttle bodies (cooling rail). Since carbs don't need cooling, put a plug on that fitting. Also, you will have to drill out the hole in the crankcase for the suction line. Vacuum pressure in the motor causes the fuel pump to work on a carbed motor, but EFI doesn't have the hole and fitting because the fuel pump in that system is electric.

    These two things will probably be the hardest part of the conversion.

    My dad converted an EFI motor to carbs and put it in my brother's sled. At first he had a little trouble getting rid of a low end bog. We had both original pipes, but we ended up keeping the EFI pipe attached to the motor even though it isn't for the right chassis so it doesn't fit quite right. EFI 500 and carb 500 use different pipes, different flywheels/stators and different CDIs. Since we kept using all the EFI electrical, I assume that's why the motor ran best with the EFI pipe.

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    RedRocketXCR's Avatar
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    I have everything from a 91 Indy 500 that broke a piston skirt. Got an entire 92 440 without a track or hood and made the engine swap. I'd have to check into shipping to Canada though.

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    Ugly_old_Poo_kid's Avatar
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    You'll find that the 500 carb and efi have different intake port sizes (carb = 38mm, efi = 46mm), this means you'll need different carb mounting flanges. Even if you pull carbs off a carbed 500 motor, they won't fit the bolt holes.

    Then after you bolt the 38 mm bodies onto the 46mm ports, you'll lose your port flow velocity because of the dead-air gaps caused by jumping to a larger port. And you'll have fun tuning the carbs correctly, like mentioned above, because the dead air will allow the fuel particles to fall out and combine instead of staying suspended like they should. You'll actually lose several horsepower in the process.

    The exhaust ports are also larger on the EFI, this is why the efi motors run better with the efi pipes, even after carbing. Switching to a carbed 500 pipe would just lose even more horsepower.

    Fixing the EFI is a much simpler and cheaper idea than switching over to carbs. [thumb] (unless you want to go to 46mm carbs)

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    I would keep the EFI but my chip board is broken when I got it and also someone has messed around with all the wires so the whole thing is messed up. Would the 46mm be to big for that though? As long as I can get it running I will be happy.

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    RMK-KING's Avatar
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    I just did this swap on a customers sled last winter and it worked out great! I used carb boots off a 91/92 indy 650 but they are discontinued now and hard to find. You can also use boots off a 1980 yamaha srx,lots of other yamahas use these same boots and they can still be ordered. You can see where the hole for the fuel pump vacuum line goes on the efi engine,if you have a carbed engine to compare it will be easy to see what needs to be done there. If I remember right I used the carbed 500 pipe and did not have to do any adjustments to the carbs,it never had a single hiccup which surprised me a little after seeing the port difference.

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    Bakernator's Avatar
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    I just did this conversion last year one one of my sleds. I hit a rock and bent the chassis on my 94 EFI and ended up finding a 95 Carb with a basketcase motor that had a bad crank and broken piston. I ended up using the crankcase from the carb motor (as it was easier than drilling the holes), the monoblock cylinder, head, waterpump, and stator from the carbed sled, and the crank and pistons from the EFI on the motor side of things. The head and waterpump off the EFI have extra lines and holes which is why I used the parts from the carbed sled. If I was using the same sled instead of swapping chassis's I would have had to change the wiring harness as well.

    I have a 500 carb Crankcase set for sale in the classifieds if you are interested.

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    How much are you looking for for the carb?

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    Bakernator's Avatar
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    For the crankcase you mean?

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