• Required reading for all forum users!!!

    Welcome!
    Register to access the full functionality of the GSResources forum. Until you register and activate your account you will not have full forum access, nor will you be able to post or reply to messages.

    A note to new registrants...
    All new forum registrations must be activated via email before you have full access to the forum.

    A Special Note about Email accounts!
    DO NOT SIGN UP USING hotmail, outlook, gmx, sbcglobal, att, bellsouth or email.com. They delete our forum signup emails.

    A note to old forum members...
    I receive numerous requests from people who can no longer log in because their accounts were deleted. As mentioned in the forum FAQ, user accounts are deleted if you haven't logged in for the past 6 months. If you can't log in, then create a new forum account. If you don't get an error message, then check your email account for an activation message. If you get a message stating that the email address is already in use, then your account still exists so follow the instructions in the forum FAQ for resetting your password.

    Have you forgotten your password or have a new email address? Then read the forum FAQ for details on how to reset it.

    Any email requests for "can't log in anymore" problems or "lost my password" problems will be deleted. Read the forum FAQ and follow the instructions there - that's what we have one for...

  • Returning Visitors

    If you are a returning visitor who never received your confirmation email, then odds are your email provider is blockinig emails from our server. The only thing that can be done to get around this is you will have to try creating another forum account using an email address from another domain.

    If you are a returning visitor to the forum and can't log in using your old forum name and password but used to be able to then chances are your account is deleted. Purges of the databases are done regularly. You will have to create a new forum account and you should be all set.

'79 550E intermittently weak at 6K rpm

roeme

Forum Mentor
Past Site Supporter
Hey Forum,

I can't shake the feeling that my daily rider developed an issue. It most likely is an intake O-Ring issue - if it's even an issue at all -, but nonetheless, I'd like to pick your brains for other possibilities, so I don't need to take apart my bike multiple times.

The reason why I wrote "If it's even an issue" is because my senses might be off, as I had to ride a loaner bike for some time, a 90ies Yamaha TDM 850. That's way way more power than I'm used to from my GS550E. Nonetheless, I can't shake the feeling that she used to pull better, and that the power band/curve fluctuates.

From a standstill, the bike begins to really pull at around 2500 to 3k, and then kicks in between 5 to 7k - but hitting a wall at 8500 to 9000, it's time to shift up to get more pull.

On the highway, it's worse; depending on the incline, in 6th gear, I just really can't get beyond 6k (120kmh / ~75mph). Shift down, I manage to push beyond 7k, but that's about it.

However, I also had rides where she almost effortlessly got into redline, which puzzles me a bit.

This is all somewhat unreliable information:
- I notice this stuff during normal riding/commuting, and I cannot afford to troubleshoot & test my bike in traffic too much; also, to really get a picture, I would need to go faster than the law :)
- A said, warped perception because of loaner bike
- Newbie rider; not really wound her out until recently
- No Idea how much power the 550 brings to the table anyway; air resistance, i.e. riding position really makes a difference I feel
- Never checked systematically against engine temperature (i.e. at which point after taking off the issues develop)

That being said:
- The valves have been adjusted just recently by a shop - didn't have time to do it on my own, but I trust them, and had them report all measurements to me
- The points have been replaced by the same shop (because of an accident, more on that later), so these should be good (also, I noticed this issue earlier)
- The spark plugs and caps have been replaced a while ago
- The R/R has been replaced with a SH775
- When requiring choke to start up, RPM do increase as the engine heats up (strong hint at intake O-Rings, right?)
- When I measured temperatures around exhaust collars, cylinder 1 measured hotter than all others (around 130?C, #4 at the same time measured 119?C), indicating a leaner mix than the others

I'm not sure wether I'd need to sync up the carbs as well, or check the timing advance.

I'm not looking forward to this work (the dreaded 550 airbox....), so I'd check as much as possible when I have her apart. Any hints?
 
"- When requiring choke to start up, RPM do increase as the engine heats up (strong hint at intake O-Rings, right?)"

yes, this would make me suspicious. You need all 4 cylinders being fed correctly (and together) .
 
Update: After the issue went away, appeared again (which I mulled over a bit in another thread), went away again, it finally came back today, and stayed.
So at least I'm sure now that there is an issue - the ping-pong above made it very hard for me to determine if there's something going wrong.

Currently, everything is fine up until 4000, but between 4500~5000 rpm the bogging begins. The engine also sounds different, as if the mixture is off - similar, but not exactly the same when starting up with choke and playing with the throttle tad bit too much.

- I did run briefly with choke - boy did she protest when I wanted to open the throttle.
- Switching the petcock to reserve made no difference, so I assume a proper fuel flow and the petcock in good enough working order.

My hypothesis is that around these RPM, the vacuum becomes strong enough to suck false air through an aged intake O-Ring.

From what I know and read so far about carbs; if I were to have an issue, the issues would be mainly correlate with throttle position, not RPM - please correct me if I'm wrong here.

Blech. Not looking forward to removing the airbox.
 
Last edited:
Oh, completely forgot to update this thread.

Did take off the carburetors last Friday, and as soon as I had them off, noticed a inlet vacuum screw loose.

Ugh...oh well, since I had them off, proceeded to replace the intake O-Rings. However, since I only detached the airbox, not disassembled it, I was unable to reach all screws with the impact driver. And the chedar is strong with these screws. As it was getting late, and I had no other means of transport available, I just replaced #4, and put everything back.

Fired right up, with no choke required whatsoever.
 
Back
Top