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Discussion Starter #1
I have an 06 660 that I bought with an intake backfire. I rebuilt the top end with all new except for a cam. After all the work and retaining 3 or 4 times I have still not fixed the backfire. I have tried changing jets and haven't had any luck. Engine had 920 hrs prior to rebuild. I am starting to think maybe my issue could be with the old cam being worn throwing off the valve timing? Anybody think that could be a possibility?
 

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well you don't give any symptoms or how it runs or when it backfires, but if you are at a point to think it cam timing I would double and triple check the cam chain timing and make sure it is correct or not stretched
 

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And if you have custom exhaust it will require LOTS bigger jets, not just a couple sizes .... I have a fairly quiet Can Am Maverick muffler and had to put like a 162.5 jet to stop the backfire.


ALSO, very important ... check your air filter and box and all the intake hoses going to the carb .... not sealing will cause trouble and a dirty filter will to.
 

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Discussion Starter #4
So it has a brand new timing chain and new vavles. I have checked my timing several times. When I get it started and let it idle, it will cough out the carb. When I rev it up it seems to be alright as far as high rpms go but when it idles back down it will backfire again and sometimes blow the carb off the intake. I have used starting fluid and sprayed down all the intake area to check for vacum leaks and didn't find anything. It has an electric fuel pump and I just installed some clear line so I can see how the fuel pumps and it seems to be alright. When I pull the plug it is white which as everyone know means lean so I am guessing it's a jetting issue. I have went to my local shop to get some jets to try and they tell me they dont sell individual jets and I have to buy a carb to get different size jets which I know isn't true. Do any of you know where I can buy some jets to try out?
 

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First thing I notice is the blowing the carb off. This carb is the same gravity flow unit that was used on grizzlies. If this is a normal fuel pump and you do not have a pressure reducer you are pushing way too much fuel into the carb and maybe loading it up so that when it backfires you get those results. Fix fuel pressure first.
Have you set the cam marks per service manual? I can't see these pics and not reading manual but IIRC there are two marks and they have to be right or the timingof the valve opening will be off a few degrees. The manual id=s a free download somewhere on this forum.
 

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Discussion Starter #7
I have the service manual and have set the Mark's correctly. Manual says to set the cam gear with the 3 dots so that 2 of the marks are parallel with the top of the head and the 3rd is straight up with the lobes on the cam facing down. I haven't thought much about the fuel pressure but I'll see about finding a pressure regulator and turning it down.
 

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I am going from an old memory but I found some jets for a Rhino at a motorcycle shop a few years back. I cannot remember the manufacturer of the carb, but found a motorcycle shop that had a box of jets in the available sizes. Think it was $2 per jet or so.
 
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