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Bad surging and popping noise

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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Hi, I have a 1977 GS750 that is being a pain. I've had the bike for a few years and it?s ran fine, until that last few weeks. It became hard to start and when riding it would not hold a constant rpm, it bounced around a few hundred rpm's. It acted like it was out of fuel, as if it needed to be switched to reserve but it had a full take of fuel.

So, I cleaned the carbs. I bought an O-ring kit from someone on this forum and soaked the carbs in Barrymans cleaner. I set the bottom screws back to the settings they were at and the side screws to 1.5 turns out. The carbs don't leak at all but the bike still doesn't run right. I haven't sync'd the carbs on the bike but I did on the bench. I also pulled all 4 plugs and noticed they were all a powered black color.

The bike still runs bad. At all rpm's it stutters really bad and makes popping sounds. It does this when accelerating, decelerating, steady rpm, different gears, everywhere.

Any tips would be great.
Thanks
Brent
 
did you purchase new intake boots? they could have cracked or got a leak which will cause those symptoms....
 
Yep,could be an air leak, but you also have to sync the carb's, bench syncing is not close enough.
 
spray some wd40 on the front of the intake boots and see if your rpm rises this sounds like the typical intake boots are old weak adn leaking :wink:
 
I forgot to say that I replaced the O-rings between the engine and the boots. The boots themselves were still flexable and not cracked.

I just went out and warmed up the bike and at idle sprayed WD40 all over all 4 intake boots and nothing happened. So it doesn't look like they're leaking.

Would a carb sync really fix this engine from running so rough? Or are there other things i can try?

Thanks
Brent
 
Did your maintenance work fix the original problem(s) or is the bike doing the same thing? You said it's still not running right.
Assuming you did all work correctly, your dark plugs, depending on throttle position, could be because you adjusted the pilot fuel screws (underneath) wrong and the side air screws may need fine tuning too.
The pilot fuel screws are VERY precision and even small changes will effect mixture. Turning them out, richens the mixture. You may have set them a bit further out than they were. Where are they set now? Stock intake/exhaust? The two float bowl vent lines clear?
The side air screws must be set using the highest rpm method. Setting them to 1 1/2 is generally close, but they should be set exactly. Adjust these and test before making any pilot fuel screw adjustments.
I doubt your uniform dark plug reads are because the carbs aren't vacuum synched yet, but the vacuum synch must be done for best performance and plug reads aren't accurate without the vacuuum synch. Without the synch, fine tuning the pilot fuel screws isn't possible. You wouldn't know if a rich/lean plug read is related to vacuum or poor screw adjustment per cylinder.
The ignition timing must be correct before the vacuum synch too. Is it?
 
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