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1978 GS550 throttle chokes when under load

  • Thread starter Thread starter edwinastafanus
  • Start date Start date
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edwinastafanus

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Hey all!

New to this forum, and new to GS ownership! I just picked up my first bike, and it's a beautiful 78 GS550.

Anyway, it runs pretty good and idles relatively smoothly. It'll rev nicely all the way through the RPM's while it's in neutral, but when I'm in gear and driving, it'll start to really choke when I hit about 3k RPM. It seems like the more I crank on the throttle, the more the engine wants to choke out and die.

Does this just sound like a dirty carburetor to you? I have the VM22SS carb in there with pods.

Thanks in advance for any help!
 

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Has it been jetted to run with the pods and the modified exhaust? What are the details of the carbs as it sits now? Those pods are considered cheap trash here, you would do yourself a favour if you replaced them with K&N or APE pods that are much higher quality.

Does it surge and buck when you get into the problem range? Or does it just bog and want to die? What throttle setting is that at? Carb circuits are based on throttle opening, not engine RPM or road speed so you need to know how much throttle you are using when it coughs. Typically if it will rev well in neutral but won't pull a load that is a symptom of being lean.


Mark
 
Hey Mark! The previous owner said he never had to change the jets on the carb, which would be concerning, but he's a pretty experienced builder with 5 or 6 bikes on the go at any given time, so tough to say if he should have changed them or not. To my understanding, all the jets are the factory size right now, how do I know if I have to rejet? I'll replace the pods asap!

It's more of surge and buck, but sometimes it will bog as well. It seems to be at about 50% throttle usually where the problem occurs. If it's running lean, is that just a symptom of poor tuning or synchronization?

Really appreciate the help!

Edwin
 
Last edited:
edwinastafanus said:
Hey Mark! The previous owner said he never had to change the jets on the carb, which would be concerning, but he's a pretty experienced builder with 5 or 6 bikes on the go at any given time, so tough to say if he should have changed them or not. To my understanding, all the jets are the factory size right now, how do I know if I have to rejet? I'll replace the pods asap!

It's more of surge and buck, but sometimes it will bog as well. It seems to be at about 50% throttle usually where the problem occurs. If it's running lean, is that just a symptom of poor tuning or synchronization?

Really appreciate the help!

Edwin
Click to expand...

If the jets have not been changed then you will need to rejet to suit the modifications. Surging indicates a lean mixture, bogging indicates rich. Running lean is a symptom of not being tuned correctly. First thing to do is pull the spark plugs and show us what the electrodes and insulators look like. Post a good close up pic of all the plugs. Second is to open up a carb and see what jets and needle are in place. While you are doing that check the air and fuel screws and note how many turns out they are set. Do this before you bother with new pods, both the K&N and APE pods will flow more air than those paper element cheapies and make the lean condition worse. To check what throttle position you are at put a piece of tape on the throttle housing and mark off the throttle position from 0 to 100% in 1/8 increments (of full travel). That lets you tell at a glance where you are on the throttle and which carb circuit you are running on.

If you haven't already, go to BikeCliff's site and download a service manual for your bike: http://members.dslextreme.com/users/bikecliff/


Mark
 
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