1978 GS750 Idles Fine, Stumbles/Loses Power While Accelerating - Esp. Above 4000 RPMs

[Big T]

Points and condensors new???

[cwscooge]

No, they're original, but they look good.

[David_510]

Long shot here. But check your plugs. I haven't head you say what they looked like.

Im going to suspect they are probably lean. Maybe try checking your air box for leaks. Make sure it is properly sealed.

This reminds me of when i made my custom pods for my 83 550esd, i had it jetted and it ran fine in neutral. Got on it and it had like nothing about 5000 rpms. It was WAY to lean so i had to add some foam inside my custom pods to restrict them a little more.

If not that the only other thing i can think of is maybe somewhere (either in the fuel line leading to the crab or in the carb body itself) you may have some debris causing a blockage.

[Big T]

No, they're original, but they look good.

I'd start there - condensors go bad with age and screw up the spark, which causes the engine to break up at speed

Take off the ignition cover tonight and fire it up in the dark. Lots of sparking at the points?

[KEITH KRAUSE]

Based on your description of the performance, it could be either electrical or carburetion or both.
One thing you need to do first is to return the jet needle e-clips to the factory position. One position richer on a stock bike will be too rich. Keep in mind that the carbs will have to be re-synched whenever you disturb the needles.
Then you need to do some basic tuning. Replace the condenser as others have suggested because it's cheap and also the points unless you KNOW they are in good condition. Be sure any pitting is gently filed down and the points are very parallel. Dwell must be set and then the timing adjusted. If the battery is holding correct charge then also check voltage and resistance at the coils primary and secondary sparkplug caps. Be sure plugs are clean and gapped. Be sure all harness connections are solid and not burning up, especially connections leading to the reg/rec' and stator. Spark, in a darker area, should be bluish and a solid "snap" be heard, just as a general description.
After knowing the electrical is good and returning the needles to correct position, test and get plug reads at full throttle, half throttle and minimal throttle positions. Record what you find and let us know what happens.

Also, I have to question the "weatherstripping" you did between the carbs and filter box. Are you sure there's no leaking or blockage of flow?

[cwscooge]

Thanks everyone for all of the tips and ideas. The problem ended up being the points and/or condensor (I replaced them at the same time). I have put a couple hundred miles on the bike since and it runs great!

I gotta give y'all the credit. I have learned so much from this forum since I got my bike. It's funny because I'll tell my friends that I have a forum that I go to for help and they always roll their eyes and tell me their disappointments from forums in the past or they'll warn me to take what I hear with a grain of salt. But I swear by you guys (and gals) on here; y'all are awesome! Thanks again.

[1_v8_merc]

ahh those pesky points.

at least it was something simple

[Big T]

Thanks everyone for all of the tips and ideas. The problem ended up being the points and/or condensor (I replaced them at the same time). I have put a couple hundred miles on the bike since and it runs great!

I gotta give y'all the credit. I have learned so much from this forum since I got my bike. It's funny because I'll tell my friends that I have a forum that I go to for help and they always roll their eyes and tell me their disappointments from forums in the past or they'll warn me to take what I hear with a grain of salt. But I swear by you guys (and gals) on here; y'all are awesome! Thanks again.

Post #16 strikes again!

Most of the members here don't have bikes with points, so they tend to forget the tell tale signs

Now, go save up for a Dyna S and banish those points to the spare parts box

[Nessism]

Another problem solved by basic maintenance.