gs550 1981 GS550L Dies under 2k RPM(s)

[ProducerBill]

Thanks to all the help from this forum I have been able to get my barn find 1981 GS550L to a,,, running-ish state.

Issue is I just can't seem to keep it running under 2k RPM.

Here it is running feels stable and could run forever.

 

I turned the idle down under 2k. It just continues to lower and lower until it just dies.

For video of above see link: https://drive.google.com/file/d/1vF2FYEu3S3Nwbkj5zmFM20TLjRv-mVBY/view?usp=sharing

I am not sure that it matters but before the above I noticed that cylinder 3,4 was kind of cold 70F so I leaned out the mix and they are now up to 130-140F. So now the four temps seems to stabilize at:

1 = 135

2 = 205

3 = 130

4 = 140

Not sure if this is correct, but it did start to run better. Not sure I am doing the right thing, or if it is even related, but seemed to be a good idea.

Any ideas I would love to hear them.

[Gixer1460]

#2 is a bit out of balance and 135F is barely 60 C - at idle you should be seeing maybe around 160 - 200 C ? Low running is exclusively pilot jet!

[ProducerBill]

4 hours ago, Gixer1460 said:

#2 is a bit out of balance and 135F is barely 60 C - at idle you should be seeing maybe around 160 - 200 C ? Low running is exclusively pilot jet!

I figured the low temp was due to rich mixture. As 3,4 where at around 70-80F until I maid a mixture adjustment to lean it out. I wonder if I balanced all 4 cylinders at around 205F do you think that would help at idle?

 

Another thing I noticed was the if I set the choke to full it killed the bike. I was thinking that this was because the mix was waaaaay to rich and choking the bike just pushed it way way to rich.

 

Any thoughts?

[Gixer1460]

There's rich and rich to the point of flooding! A rich mixture that is burning still make heat. I don't know what ignition you have - if its too advanced it won't help the rich situation, too retarded will tend to be burning in the pipe so would show much higher temps (this helps turbo's spool btw). I suspect either something is blocked causing rich condition or someone has been jet fiddling and gone upsize which seems it doesn't need. Are carbs 'absolutely' clear and clean - we say over and over - an Ultrasonic clean is std. for these old carbs! Check jet sizes against workshop manual quoted sizes, if only to cross off the list - and that they are the same in every carb!

[ProducerBill]

On 11/27/2023 at 9:37 AM, Gixer1460 said:

There's rich and rich to the point of flooding! A rich mixture that is burning still make heat. I don't know what ignition you have - if its too advanced it won't help the rich situation, too retarded will tend to be burning in the pipe so would show much higher temps (this helps turbo's spool btw). I suspect either something is blocked causing rich condition or someone has been jet fiddling and gone upsize which seems it doesn't need. Are carbs 'absolutely' clear and clean - we say over and over - an Ultrasonic clean is std. for these old carbs! Check jet sizes against workshop manual quoted sizes, if only to cross off the list - and that they are the same in every carb!

I replace the CDI with "waltyotur CDI Ignition Replacement for Suzuki GS550 GS750 GS850 GS1000 GS1100 1977-1983 DS3-2" as the CDI was toast.

I set it up best I could with eng-rish instructions and the help of the internet. It seems to be ok, but I will say that it does seem that cylinder 3,4 are firing in the exhaust on the right side sometimes. Also Cylinder 2 get hotter then the rest. Based on your comments it sounds like I need to advance the timing a bit, but I am paranoid as my friend told me if I advanced to much is could damage the bike.... So I figure later is better.... base on well, knowing nothing.

So base on your above I should advance a bit.

[Gixer1460]

Ah - good old Chinky knock off of a Dyna S. If its working correctly (not a given baring in mind from where it came) it should run exactly where it is set currently. I think that model uses original ATU (auto timing unit) for advance - is this free and working correctly? Are the two notches in the black ign. rotor engaged with the pegs in the ATU, and all free to rotate? I wouldn't be playing with timing till it runs / idles. There still could be issues in the carbs and its unusual for odd pairs of cyl's or one to get a lot hotter purely down to ignition issues! Trying to diagnose problems from 3000 miles away is never an exact science!

[ProducerBill]

5 hours ago, Gixer1460 said:

Ah - good old Chinky knock off of a Dyna S. If its working correctly (not a given baring in mind from where it came) it should run exactly where it is set currently. I think that model uses original ATU (auto timing unit) for advance - is this free and working correctly? Are the two notches in the black ign. rotor engaged with the pegs in the ATU, and all free to rotate? I wouldn't be playing with timing till it runs / idles. There still could be issues in the carbs and its unusual for odd pairs of cyl's or one to get a lot hotter purely down to ignition issues! Trying to diagnose problems from 3000 miles away is never an exact science!

The ignition ATU advanced freely. As the RPM's increases the engine runs better. Makes me wonder if advancing the timing my help as it is on the edge of too retarted and just barely working. As for heating pairs it is not odd as it is cly 3,4. I do applicate your help even from 3000 miles away, unless your in Michigan,,, then get off my lawn!

Thanks!