Won't Rev Past 4 or 5k?

[vroomvroom]

Hi everyone,

This is my first post. I've done a bunch of searching and been hitting dead ends.

I bought a 1978 Suzuki GS750E a few months ago and have slowly been getting it back up and running. I have been fairly successful getting it running well from idle to half throttle. Idle is still a bit weak but other than that I got the bike to be fairly responsive up to half or 3/4 throttle when revving it in neutral. It was bogging out when trying to rev but I richened the needle jet and it worked great.

My big problem now is that under load I can't get the bike past 4 or 5k RPM. It bogs out. But its not the typical "too lean" bog. It sounds more like its hitting a rev limter when I crack the throttle past halfway. There was one night when I first got it running that I did get the bike to really accelerate stongly. But I have never experienced that again.

Some threads have pointed me towards a faulty ignitor while others say cam timing. Can anyone help me out? Is there a way I can retard or advance the spark on this bike?

Any info would be greatly appreciated.

Thanks

Steve

 

[Steve]

With a '78, you don't have an "ignitor", unless someone has upgraded your points.

What all have you done to get the bike where it is now?

Have you adjusted the valves?

Have you PROPERLY cleaned the carbs?

Have you replaced the intake boot o-rings?

Have you checked your points and condensors?

Have you checked your plug wires?

Have you checked your spark plugs?

.

 

[GSNewbie]

Make sure you have the rubber plugs installed inside the float bowl. They are the tallest thing next to the main jet and are critical. Not having them will cause this.

Oh, ya, and everything Steve wrote!

 

[vroomvroom]

I will have to take a look at this, GSNewbie. I don't recall seeing any rubber plugs when rebuilding the carbs. Thanks!

 

[blowerbike]

the VM's have rubber plugs???????????
i haven't look at the insides in so long....thought only the BS carbs had the pilot plugs...

uhuh,
the VM's don't have these rubber plugs...there pilot's are exposed..

 

[vroomvroom]

Steve. I bought the bike in kind of rough condition. Stock bike but it has crappy, UNI pod filters on it. I live at 5-6k feet above sea level. I wrapped the main body of the pods with duct tape to limit airflow originally. I don't think that did much though.

Carbs-have been properly cleaned with all the smaller parts getting overnight soaked in Berrymans Chemtool. New O-Ring kit still needs to be installed.
Needle Jet was in middle setting and now raised to the richest setting which made a huge difference in mid throttle response.
Valves- Not adjusted.
Have not replaced the intake boot O-Rings but I haven't noticed any vacuum leaks there.
Have not checked points and condensers yet. I've never done this before so I will have to learn that.
I seem to be getting good spark and the plugs are brand new.

Thanks for your help.

Steve

 

[vroomvroom]

Thanks! Good to know!

 

[vroomvroom]

the VM's have rubber plugs???????????
i haven't look at the insides in so long....thought only the BS carbs had the pilot plugs...

uhuh,
the VM's don't have these rubber plugs...there pilot's are exposed..

Thanks! Good to know!

 

[GSNewbie]

Sorry, I didn't catch the year... I don't know on them since I yanked mine. They are here in a box, so I guess I could check.

 

[78550GS]

Adjust the valves and do the O-rings.That will be your best bet for a base line. You will be stabbing in the dark and chasing your tail until these are done.

 

[cowboyup3371]

The carb bodies also need the overnight soaking not just the little bits. There are passages inside you won't see that will clog up.

 

[GSNewbie]

Don't forget the manifold o-rings as they can crack too. cycleorings.com had them I think.