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Backfiring a lot, no acceleration

  • Thread starter Thread starter bmlbytes
  • Start date Start date
B

bmlbytes

Guest
Bike: 1979 GS 550L

Last week I was driving my bike around. I had probably driven it for about 2 hours in the city before I decided to go home. I stopped at a gas station and filled the tank with 91 Octane fuel. The gas here is all 10% ethanol.

So I go about a mile from the gas station and the bike starts to backfire pretty badly. Its an old bike so I didnt think much of it at the minute. I start to enter the interstate. Suddenly my bike wont go above 25 miles per hour. I let off the throttle, and the bike dies. It doesn't start for about an hour. I get it to start and am able to drive it home, at speeds under 25 mph, and in only first and second gear. The whole way home, it is backfiring very badly. Blue flames are coming out of the exhaust.

So its been about a week now. Today I replaced the spark plugs and the air filter. I also oiled the air filter, and topped off the engine oil. I put a half of a can of Sea Foam in the gas tank. The bike still doesn't run any better than it did last week.

Any idea why my bike is backfiring this badly and gets no acceleration?
 
Since the problem started a mile from gas station, that new gas gets no blame since it hadn't hit the carbs yet! However, did you drive in on reserve and gas up and switch it back to on? In other words did you fiddle with petcock at station?
Back in July, you had cleaned carbs ??? so has bike been running OK for two months till last week? You've used Seafoam to it's max, so leave it alone- it's done all it can and don't waste your money on 91 octane!
As mentioned, timing is a good place to start.
 
Thanks for the quick responses guys. By timing I assume you mean ignition timing. I searched the internet, and there are guides that say how to adjust it, but they dont really mention what part on the bike I am supposed to adjust.

I found this very brief guide on how to do it:
The drill is this...With the engine at normal operating temperature and idling, advance the timing slowly. You will hear the engine speed up.Move the timing back and forth, advancing and retarding it till you get the highest engine idling speed. Then back it off (retard it) just a bit. The engine speed slows down just a little. You are still idling, don't touch the throttle.
Click to expand...

The thing is, I dont know how to advance the timing. Can anyone explain this to me?

Much appreciated!
 
If it went bad the minute the new gas hit the carbs, look there. 1 mile after a fill up, that's exactly when a fuel problem will appear. You bought a load of water, or Diesel, or something. Drain the float bowls and see what comes out.
 
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