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Discussion Starter · #1 ·
Ive had this pcv and auto tune for around 2 months and cant seem to get it right no matter what the bike was poping on decell bad got that taken care of now its doing it on acell not sure if its rich or lean anyone know
 

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Woverby
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Here is a partial reponse that was posted previously by someone else on the forum:

A Back-fire or backfire is an explosion produced by a running internal combustion engine that occurs in the intake or exhaust system rather than inside the combustion chamber. The same term is used when unburned fuel or hydrocarbons are ignited somewhere in the exhaust system. A visible flame may momentarily shoot out of the exhaust pipe. Either condition causes an objectionable popping noise, together with possible loss of power and forward motion. A backfire is a separate phenomenon from the fire produced by Top Fuel dragsters.

Also, an explosion in the inlet manifold, carburetor/throttle body, or air cleaner of an internal combustion engine can occur when the intake valves are not shut prior to fuel combustion.

The term was derived from experiences with early unreliable firearms or ammunition, in which the explosive force was directed out the breech instead of the muzzle. From this came the use of the word "backfire" as a verb to indicate something that produces an unintended, unexpected, and undesired result.

Explanation

Backfire in an automobile engine typically results from various malfunctions related to the air to fuel ratio. Backfiring can occur in carbureted engines that are running lean where the air-fuel mixture has insufficient fuel and whenever the timing is too advanced. As the engine runs leaner or if there is less time for the fuel to burn in the combustion chamber, there is a tendency for incomplete combustion. The condition that causes this is a misfire. The result of a misfire or incomplete combustion is that unburned fuel or flammable hydrocarbons are delivered to the exhaust manifold where it may ignite unpredictably. Another backfire situation occurs when the engine is running rich (with excess fuel) and there is incomplete combustion during the Otto cycle, with similar results.

When starting an engine, timing that is too advanced will fire the spark plug before the intake valve is closed. The flame front will travel back in to the intake manifold, igniting all of that air and fuel as well. The resulting explosion then travels out of the carburetor and air cleaner. A common air filter will allow the gases to escape, but will block the flame front. On many small marine engines, no air filter is used, but a screen is placed over the intake of the carburetor as a flame arrestor to prevent these flames from escaping the intake, and potentially igniting fuel, or fuel vapors in the enclosed sump or bilge of the boat and causing a fire or explosion. Improperly adjusted carburetors that create a lean condition during acceleration can cause the air fuel mixture to burn so slowly, that combustion is still taking place during the exhaust stroke, and even when the intake valve opens. The flame front can then travel up the intake and cause a backfire. In this situation it is conceivable that there is a backfire occurring in the intake manifold and exhaust manifold simultaneously.

Causes

Exhaust system backfires occur in engines that have an emission system malfunction, like an air injection system diverter valve problem, an exhaust leak, or when the catalytic converter has been removed. In some high-performance vehicles, when a driver shifts up and lets off the accelerator, the engine has a moment of running rich. This causes an incomplete burn which causes the fumes to explode in the exhaust system along with an audible clacking sound. However this condition is a result of working smog equipment, and is unlikely to cause any damage.

A fuel injected engine may backfire if an intake leak is present (causing the engine to run lean), or a fuel injection component such as an air-flow sensor is defective.
Common causes of backfires are:
• Poor or unregulated engine timing is often a cause of intake backfires, but can also be responsible for exhaust backfires
• Improper wiring in the ignition can also lead to timing issues and backfires
• Low fuel pressure, clogged fuel filters, and weak fuel pumps could cause a severe lean air-to-fuel ratio during fuel injection
• Missing or damaged catalytic converter can result in backfires out the tailpipe
 

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Ive had this pcv and auto tune for around 2 months and cant seem to get it right no matter what the bike was poping on decell bad got that taken care of now its doing it on acell not sure if its rich or lean anyone know
Any black smoke on accel? If not you are most likely a little lean, but if it has been recent change and with the temps you have had locally, PA, then I am going to bet rich and or a bad tank of fuel. Change where you are getting your fuel from for a tank or two and see if you have any improvement.

When you fixed the decel pop you did only work the 0% column, correct? If you made manual changes in other columns it will take a while for the AT to retune.

What is your setup, bike exhaust, intake, etc?

If running with the AT try one of the latest maps I have posted. These will start out a little rich as I did most of the tuning when the temps were in the 20's and 30's. Then give the AT time to work in and it should run rather well. Even open up your AT to 25 or 30 percent to help tune quicker.
 

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Discussion Starter · #4 ·
ok not sure if theres any black smoke yes i just did the 0 column in the fuel table and my bike has a cfr and k&n topless from what i can see not sure if theres any motor work done
 

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ok not sure if theres any black smoke yes i just did the 0 column in the fuel table and my bike has a cfr and k&n topless from what i can see not sure if theres any motor work done
Well if the only changes made were to the 0% and the bike had not had the accel problem prior...I will lean towards some bad fuel. I had a similiar experience here and after getting thru that tank and then some good fuel (a station that has the 3 seperate hose pumps) I am back to running fine.

If anyone has the true educated answer as to how much of the cheap stuff you get before you get the premium that you are paying for, I want to hear it. I look at an open pump here in Ak and it looks like I would get at least a quart or more of low octane fuel before the good stuff makes it. So if only dropping 2 to 3 gallons in at a time it would not take long to lower your octane. My theory anyway.

I know back there in Pa some of the Citgo stations use to have the 104 racing fuel on the pump(take a can as you cannot pump it into a street vehicle) and most of the Shell stations have 93 on a 3 hose pump.
 

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Discussion Starter · #6 ·
yeah thats a good theroy on the gas that could be the problem ill let you know when i go fill up agian
 

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If you are still running the pipe that's in your avatar, it would seem you wheel and/or part of the swingarm would be blacked up if you were running fairly rich. Mine doesn't pop under accel, but rather when the throttle is steady. I've been slowly fixing it in certain cells, and the more I fix it, the less black soot there is on my swingarm.
 

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Woverby
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Do you lean or enrichen the cells to reduce or eliminate the steady popping?
 

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I tried both. Enriching the cells seems to make it worse and stumble. I have been leaning them out slowly, and it seems to be working.
 

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Woverby
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Interesting. Thanks for the info.
 
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