1978 GS550 Rebuild Questions

[Guest]

Hi everyone!
I've got a 1978 GS550 I've been bashing my head against trying to get running. I'm pretty sure the only thing I've got left is a carb/air/fuel problem, since she keeps dying at idle, and flattens out at ~5k rpms (any suggestions on where to look for this would be amazing!). However, my fabulous boyfriend has offered to buy me whatever I need to get my bike fixed and running.

What I've done:
Reground battery
Replaced spark plugs
Replaced o-rings and gaskets in carbs, also did a rebuild kit, and have cleaned these ****ers 6 or 7 times, and synced them.
Replaced stator, r/r units
New horn and horn relay
De-rusted and sealed the gas tank

I have a Dyna ignition system, and new o-rings and intake boots on the way.

Do you guys have any other suggestions on things I should replace/fix to help my bike get running and/or prevent future breakdowns? Ie, should I do a petcock rebuild (or entirely new petcock), should I completely replace the wiring harness, should I get a new starter, etc?

Thanks!

[Mutant]

I got a 78 GS550 a couple of months ago which I learning about. This may not be related to your particular problem and I'm no expert but I'd think you should have checking valve clearances on your list of things to do.

[ilyena]

I got a 78 GS550 a couple of months ago which I learning about. This may not be related to your particular problem and I'm no expert but I'd think you should have checking valve clearances on your list of things to do.

Forgive me if this is a dumb question...is that related to the compression check? I know I've had that checked and the compression was fantastic.

[Mutant]

Forgive me if this is a dumb question...is that related to the compression check? I know I've had that checked and the compression was fantastic.

One of the more learned ones on this forum will need to answer that. What I found with mine was a lack of power round about 5000rpm on checking the valves there is little or zero clearance. That's about as much help as I can give

[koolaid_kid]

Forgive me if this is a dumb question...is that related to the compression check? I know I've had that checked and the compression was fantastic.

No. Have the valves been adjusted? If so:
First, if it dies at idle you need to adjust the idle using the Highest RPM Method
You cannot proceed any further until the bike idles without dying. Let us know when that is accomplished, please.

[Steve]

No. Have the valves been adjusted? If so:
First, if it dies at idle you need to adjust the idle using the Highest RPM Method.

Good suggestion, k_k, but wrong method.

She has the VM carbs, that write-up is for the BS carbs.

Ilyena, if the bike is basically stock (airbox and exhaust in particular), set the pilot fuel screws (the ones under the carbs) about 3/4 turn out from lightly seated. Set the pilot air screws (the ones on the sides of the carbs) out about double that, or 1 1/2 turns. That will be a decent starting point. If the bike will start and run, warm it up then let it idle. Slowly adjust the air screws, listening for the highest idle speed. Note that speed might not change much at all, but should be detectable.

By the way, idle speed for your bike is probably about 1100-1200 rpm.

.

[Nessism]

What Steve said...

...and make sure the airbox is installed and fully sealed. The bike won't run for crap without it unless you rejet the carbs.

[koolaid_kid]

Good suggestion, k_k, but wrong method.

She has the VM carbs, that write-up is for the BS carbs.

Ilyena, if the bike is basically stock (airbox and exhaust in particular), set the pilot fuel screws (the ones under the carbs) about 3/4 turn out from lightly seated. Set the pilot air screws (the ones on the sides of the carbs) out about double that, or 1 1/2 turns. That will be a decent starting point. If the bike will start and run, warm it up then let it idle. Slowly adjust the air screws, listening for the highest idle speed. Note that speed might not change much at all, but should be detectable.

By the way, idle speed for your bike is probably about 1100-1200 rpm.

.

Steve, the highest rpm method is right there. Please check again. Cliff put my method for the CV carbs in the same section as the one for VM carbs.

[ilyena]

Thanks!
I'll try that and get back to you guys. When I did the rebuild kit, I set the fuel screws at 1 turn out, and the air screws at 2.
I did also reseal the airbox, forgot to mention that!

Should I go ahead and replace any other parts or just wait until/unless they **** up?

[Steve]

Have you inspected your spark plugs after a few start-then-die episodes?

If they are wet or black, you are running too rich or simply not firing (possibly because of too much gas).

Might be best to turn the screws in a bit to reduce the amount of fuel in the pilot circuit.

What "rebuild kit" did you use? That could be part of your problem, depending on what parts you replaced. Unless your stock parts are simply too buggered up to use again, you are usually better off with them, instead of the (usually) inferior parts that come in the rebuild kits. If you need to replace any of the brass parts, buying OEM replacements is much better.

Have you adjusted the valves? Tight valves (the usual scenario) will make it harder to start when cold. Once running, they won't affect much, but valves that are too tight are more prone to burning. THAT will have a greater affect on how the engine runs, though.

Where are you? One of us might be close enough to drop by and give you a hand.

.

[ilyena]

My spark plugs were black, before I rebuilt the carbs and readjusted the screws. I haven't checked since, but I will tomorrow.

The o-ring kit I got from cycle-o-rings actually disintegrated on me, and so I bought the rebuild kits from bikebandit or somewhere similar.
I have not adjusted the valves, but she runs okay when cold.

I doubt I'm nearby anyone haha, I'm down in southeast Alabama.

Once my boots come in, I'll replace those, and do the idle mixture, and see where I am then!

Thanks everyone for your help!

[Big T]

The o-ring kit I got from cycle-o-rings actually disintegrated on me, and so I bought the rebuild kits from bikebandit or somewhere similar.

I'm puzzled by this.

You're saying that your $18 O ring kit was bad, so you spent $100 to replace them?

If you had a problem with the O rings, Robert would replace them.

He's done it for me and others

[Mutant]

I doubt I'm nearby anyone haha, I'm down in southeast Alabama.

Would that be anywhere near Mobile? I came over from England to the Convention Center last year, nice place.

[Steve]

Would that be anywhere near Mobile?

Nah, Mobile is southWEST Alabama.

.

[Mutant]

That's why we kept getting lost