Backfiring, pop, pop, pop

[TheNose]

Took my "new" '77 GS750 for a test ride after working on it for two weeks and it seems to run fine around the neighborhood. But, when I let off the gas, it backfires lightly. Just a pop, pop, pop. Is this normal? This is my first bike so I don't know what to expect. The muffler is gutted, so it may just be that. (????)

Also, how do you know when the engine is running hot? I don't have a temp gauge on it so I am curious. It's over 100 F here in South Texas and I don't want to ruin it.

Thanks

 

[daveo]

Generally the ole pop pop pop is from an air leak into the exhaust, could be your no baffle, could be at the head, also generally when she gets too hot the valves will start clattering a little more and it may want to ping under load faster. Keep 'er moving, don't sit around in traffic, can you lane split in TX?

 

[TheNose]

pop, pop, pop

pop, pop, pop

Thanks for the help. I'm going to buy mufflers as soon as I get a little extra cash. Hopefully that will help. It's not bad, just enough to make me wonder if it is normal.

No lane splitting here in Texas. My company's home office is in California and everytime a bike comes by when I'm in traffic it scares the h&ll out of me. I've not had the symptoms of getting hot, just was trying to stay ahead of the situation.

 

[Anonymous]

Nose, before you replace those mufflers, there are a few reasons for your pop pop popping. How are your carbs? If I remember correctly your bike has an adjustable Idle mix air screw, turning it in richens the mix and out leans it. (just the opposite of a normal carb adjustment) normally this pop is from to lean of idle mix, try richening it up a bit. a slightly louder pop is more than likely an exhaust leak. check your mufflers, crossover pipe, and header connections at the head.

Matt

 

[Alan Schlosser]

I like the air screw idea also. I had the same thing with my 82 1100L. After a trip to the shop to sync the carb's, they also adjusted the air screws. No more popping when I let off the throttle.

 

[TheNose]

I am in the process of getting new mufflers. The old ones are gutted. When I get the new ones on, I will adjust the carbs as you suggest. Thanks for the help.

Terry

 

[Anonymous]

One other thing to check, see if the rubber boots that hold the carbs to the airbox don't have any leaks in them. If there is air getting through then it will mess up the airflow when you let off the gas and you will get backfiring. I had backfiring on my bike and I found a couple of small air leaks on those boots.