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post #11 of 14 (permalink) Old 02-21-2011, 11:43 PM
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Like you mentioned the obvious things are the first to check.
Spark is fine but you didn't mention the spark plug condition. With those kind of miles you may be looking at the injector fuel assembly or the fuel regulator or the ECU.
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post #12 of 14 (permalink) Old 02-25-2011, 07:00 AM Thread Starter
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I received the rebuild kit today and installed it got the same deal so i took it back apart and i noticed the needle jet was in upside down :x I dont know if that would make a difference but i turned it around and turned the pilot air screw out to 3.5 turns and it is getting better... The spot that it used to stumble at has gotten alot smaller but i still have backfiring. Now it may just be the main is too small?? The stock main is only a 150 and with the big bore kit k&N filter and web cams I would prob need to rejet? I should have a stage 1 and 3 Jet kit here on Saturday.... tomorrow if Im lucky.
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post #13 of 14 (permalink) Old 02-26-2011, 07:19 AM
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It is normal for many high performance exhaust systems to moderately backfire or pop when the throttle is closed from mid-to-high rpm. In fact, one should expect a well-tuned high performance engine to "pop" and "crackle" when the throttle is closed at high rpm. The popping is a result of the air/fuel mixture becoming very lean when the throttle is closed and the engine is rotating well above idle speed. It is also necessary that the exhaust system have rather open mufflers for this to occur.

Why This (normally) Happens:

1) When the throttle valve is in the idle position, fuel does not flow out of the main system (needle, needle jet, main jet). Fuel is only delivered to the engine by the pilot (idle) system.

2) The combined effect of the closed throttle and elevated engine rpm is to create a fairly strong vacuum in the intake manifold. This vacuum, in turn, causes a high air flow rate through the small gap formed by the throttle valve and carburetor throat.

3) Under these conditions the pilot (idle) system cannot deliver enough fuel to create a normal, combustible air/fuel ratio. The mixture becomes too lean to burn reliably in the combustion chamber. It gets sent into the exhaust system unburned and collects there.

4) When the odd firing of the lean mixture does occur, it is sent, still burning, into the exhaust system where it sometimes ignites the raw mixture that has collected ---- the exhaust then pops or backfires

Other possible causes:

Air Leaks:

Any source of fresh air into the exhaust system can create or worsen the conditions that bring about exhaust popping. The most common entry point is the junction of the header pipes and mufflers. Even a small air leak can dramatically increase the intensity or likelihood of exhaust system popping. A high temperature silicone sealant, as can be found in many auto parts stores, may be used to seal the pipe/muffler junction.

Lean Carburetion:


While exhaust system popping may be considered normal, it is certainly made worse by an overly lean idle circuit. Be sure that your carburetor's pilot jet is the correct size and that the idle air mixture screw is correctly adjusted before looking for other causes of popping. The procedure for adjusting the pilot circuit is covered in the Tuning Manual.

Ignition: If exhaust system popping is very loud, irregular and accompanied by loss of power, then you should suspect that the ignition system is not performing as it should. If, for some reason, the ignition sometimes fires at the wrong time, then exhaust popping can become very energetic (loud). Look for failing high tension leads (plug wires), failing ignition coil(s) and especially switches or connectors as possible causes.
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post #14 of 14 (permalink) Old 02-27-2011, 02:46 AM Thread Starter
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ok I got it running good... your gonna laugh at me but the needle jet was upside down lol yea go figure i changed it back to the 180 main and the jet needle that must have come with the jet kit that was in the carb before I got it now i just need to change the pilot jet because it spits and dies if i hit it hard off idle.. Oh and I had the carb boot upside down which tilted the carb up.... wow how stupid was that. the only reason i figured that out was because when i went to put the top engine mount back on it wouldnt fit because it hit the top of the carb. Well thanks for all your help!!! Oh and I took it for a small ride this afternoon and it is impressive!! I had a 2005 Polaris Predator 500 but this one with the 600cc Big Bore kit is just way way stronger....
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