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I have been working on this rhino for months to get it right. Thanks to this forum, I was able to get the help I have needed in most cases and I thank all who participate for your help.

I am down to one last issue and have read posts on this until my eyes cross, and have been replacing and adjusting until I have this thing running like a top, except for one thing, the shotgun blast out the tail upon deceleration.

First off, it's a ‘07 660 Sport, I’m at approx 5000 ft.

I have new:
Fuel pickup, fuel line, fuel filter, out of the box carburetor with a 45 main jet, airbox removed and K&N air filter attached directly to the carb intake. Valves adjusted, new spark plug, Idle set to 1500, carb boot looks good, stock exhaust

One thing I have not checked yet is the header for crack due to the fact that I have to disassemble everything to get to it (roll cage, etc). Trying to eliminate all other possibilities first.

I conducted an experiment today and wanted to share my results in case it may be relevant to my issue...I got up to top speed, decelerated, and pulled out on the choke as I slowed and no backfire. What does that tell you, if anything??
 

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First of all, let me say I'm no expert on these engines. I've read posts on here that say that the choke doesn't reduce airflow like we are accustomed to on most automobile carbs, but does give the engine more fuel. That being said, it sounds like the engine might be running lean. I hope a carb expert will be here to help you soon.
 

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First of all, let me say I'm no expert on these engines. I've read posts on here that say that the choke doesn't reduce airflow like we are accustomed to on most automobile carbs, but does give the engine more fuel. That being said, it sounds like the engine might be running lean. I hope a carb expert will be here to help you soon.
Thanks for the reply, I appreciate any help or words of encouragement.
 

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Maybe there is a trick you can use to determine if there is a cracked exhaust without taking it all apart. I am just brainstorming here, but maybe one of those halloween fog machines stuck in the tailpipe? Or try blocking the tailpipe when running? I have never heard of a lean condition causing a backfire (but there a lot of things I have not heard of)
 

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I have had the same issue off and on for years. My issue is definitely an exhaust leak. The pipe tends to crack right the Y where it goes from 2 pipes to one. I’ve welded the crack closed and it fixes the problem until after a while it develops again. I haven’t figured out a good way to brace it to prevent cracking. I’m no carb expert but have seen dirt bikes pop when they were running lean. You could try and dial in your jetting, but that can be difficult with an exhaust leak.


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