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Discussion Starter #1
Hello to you all,
I'm a new owner of a '03 silver Strom, only 1 week old. I only have 550 kilometers on the bike so far. Today for the first time, it backfired, only once though. I used regular gas (87 octane) from the beginning. What do you think caused this? And does backfiring cause any harm to the engine?
 
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Howboucha Cary!
Congrats on your purchase and welcome to the board. This isn't uncommon. Put a few more miles on it and see if it goes away. There are different opinions on the octane you should use. I use 89-92. Recently my V-Strom started backfiring on deceleration. I have 17K so more than likely I am due for new plugs and an air filter cleaning.

Keep us posted on how it works out for you, and of course if anyone else can help out Cary, please reply.

Brendan
 

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I started running my '03 Strom on the good stuff, 92 octane, and noticed it backfired quite often on decelleration. I dropped down to 89, and it persisted. On the 5th tank of gas I swtich to 87 octane. The bike now has over 15,000km on it and doesn't backfire. I do get the odd fart back up through the airbox, but nothing that seems out of the ordinary for a big twin.
 

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backfires!

Mine has been backfiring since I got it. I have used 87 octane since day one and it still does it. Mine only does it while riding at low RPM's. I have over 11K on the bike and in the last 400 miles it has developed a vibration throughout the RPM range.
I changed plugs last week and will be bringing it to the dealer on the 22nd.

I'll keep the list posted as to what they find.

steve
 
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Discussion Starter #5
When tokenboy posted the "odd fart up through the airbox" that might be caused by the low octane gas. The lower the octane the faster the gas burns and more unstable it is.

This might be the cause of the backfire through the airbox blowing the injector body off the rubber boot posts that I have seen posted a couple of times.

I only ran the first 2 tanks on 87 and have been running 89 since then. I want to avoid the backfire up through the airbox. 89 burns slower than 87 and is more stable and hopefully will be optimum for the stock timing curve.

I'm guessing that the factory set up the timing curve for 89 for the best performance knowing that some people are only going to run premium 91 or higher and that the bike has to be able to run on that as well even if it is not most efficient with that grade. Then they included the knock sensor so that the bike would run on 87 without detonating and are assuming the proccessor is fast enough with the knock sensor to avoid a backfire up through the airbox.

The factories have to engineer the best compromise in these engines to take into account the most likely probabilities of what kinds of fuel people are going to run. Thats why I am betting that the timing curve most closely matches the properties of 89 octane gas. The knock sensor is a safety for the low octane. Thats how they get a bike with 11.3 compression to run on 87 octane gas.

Of course the only way to prove all this is by dyno testing a stock bike with the 4 different grades of gas 87,89,91,and 93. I wish the magazines would include the gas grade they ran when they did the dyno test.

I am actually compromising by running 89 for my own peace of mind. I have had no problems with the 89. My stock bike does surge in first gear at parking lot speeds and surges somewhat in the 2nd gear if you let the rpm fall below 3000 rpm. In 3rd gear and higher at 3000 rpm and above it runs perfect though. I'm learning to compensate my riding style for the first 2 gears.
 
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Discussion Starter #6
backfiring

Some backfiring in the exhaust on deacceleration is normal for big twin as the sudden slow down of the exhaust allows what unburned vapors there are to burn inside the pipe before they can get out. Also if your exhaust pipe connections have loosened up over time this allows fresh air to be sucked into the exhaust on deacceleration and can cause popping, louder backfiring.

I have heard some burbling, slight backfiring in my exhaust since day one on deacceleeration and that is perfectly normal for any big twin and nothing to worry about. Of much more concern would be any backfiring up through the airbox which would indicate to me a timing problem or the wrong gas.
 
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Discussion Starter #7
Both of my '03 Suzukis are high compression fuel injected twins, and I have put about 6000 miles on each of them. They both run fine on 87 octane. They each pop once in a while on decelleration (more of a slight pop than a full fledged backfire), the AN650 does it more often than the DL1000. I have Remus exhaust cannisters on both machines, so you can hear it clearly - gives 'em a little character...

I won't run 89 octane here in the mid-west because it all has that corn alcohol stuff in it. I tried the 92 octane in the V-Strom twice, and each time, it started doing that "fart stall" thing when coming to a stop. As soon as I put 87 octane back in the "fart stall" stopped happening. I'm staying with the 87 octane.
 
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