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Discussion Starter · #1 ·
Just got done with a complete top and bottom end rebuild on my HO. 1400 dollars later, here we sit with it not running worth a damn.

He's built race sleds and what not, and talked to a buddy he races with that has worked on and owned rotax motors all his life. Including owning a 670 for years.

We're going back at it tomorrow morning and its a 40 minute drive for me to get to his place and my sled so getting whatever i can find tonight.

Its bogging really bad right off the bat like to much gas is getting dumped in and sounds like its not getting enough air on the top. Mid range it runs decent. Open it up and back completely off, its like it gets flooded and stalls out.

We're pretty sure its the timing since Rotax motors, your off 1 degree and u can adjust the carbs all day and wont get it right so we're starting there tomorrow.

If anyone has any input or come across this before, feel free to add anything or any know how. Ive had this sled since nov 11th and rode it for my first time early december I wanna say and seized the bearings. Now its been at this guys house for a month- month and half so just want it back.
 

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new fuel, new plugs, check RV timming (if out it should be hard starting) Was the trigger coil moved? if so check timing, clean your carbs.
Did you do any other changes other than the top end job??
 

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Discussion Starter · #3 ·
He did all the work himself. Builds skidoo race sleds and works on them a lot. The crank got rebuilt cuz bearings seaced and pistons were in bad shape so bored the jugs and replaced them.

Plug caps are new from last owner and the wires and coil are brand new since lats guy siliconed the wires into the coil to hold them or something.

I mentioned the fuel cuz it has a container of iso heet in it when it was first giving me trouble and a full tank of premium still. Carbs were fully taken apart and cleaned. Basically everything under the hood that could be checked, cleaned, or needed replacing, did.

It runs like ass when you put the filter box on. runs a bit better with the box on or off without dpm plugged in.

He's waiting till tuesday till he gets the degree tool in to get that checked out.
 

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If your thinking of agjusting the ignition timimg better know someone who has a MPEM programmer or someone who has a laptop with a BUDS interface because that is the only was you can change the ignition timing on that machine (trigger coil is fixed not slotted)
but I am thinking timing might be a problem but im thinking Rotary valve timing might be off
 

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rotor timing is a good place to start
 

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Discussion Starter · #6 ·
Ok good to know that im hearing the same thing on here and doo talk. Hopefully the degree tool will be in tomorrow. He has places we can take my sled if we have too if a comptuer is needed at what not. Thanks for help so far. Hopefully tomorrow night I cant report back and its fixed and running now. If not, i'll be asking for some more help :p

And if it runs, I'll be out in the bay breaking it in since there aent enough snow to ride anywhere yet.
 

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Discussion Starter · #7 ·
Alrighty, its working! He got the degree wheel in and we worked on till 130 last night. It was the complete oppopisate of what one would think. Mag side is completely open when that side is TDC. Measurmments were like 145 open and 71 closed with mag tdc. So if anyone else has rotary problem like this. THATS what you need to know and a degree wheel.
 

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Sounds like a guy who I would trust my engine too!! And he builds race engines but can't time a rotary valve right?? Hope you didn't pay him much!!!
 

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That should have been an easy one, there are marks right on the RV surface of the crank case that will line up with the edge of the rotary valve with the mag cylinder at TDC.
 
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