GS550L hard to start after sitting for a few days

[MatBirch]

Trying to work out the last few bugs on my wife's bike. It's a 1980 550L. If it sits for a few days, it starts very hard usually. I followed all the tutorials, and did a full rebuild of the carbs with new o-rings and carb boots w/ o-rings. It runs absolutely beautifully... Once it starts. It seems like it's not getting fuel and should have the petcock switched to prime, yet if you even think about touching the throttle, it will flood and die. It just seems wierd to me no fuel one second, too much the next...
I've read posts here about the stupid petcock that's not really petcock. I think it should be able to go more than a few days before needing to prime again shouldn't it?

thanks gang!

 

[tkent02]

Those 1980 petcocks are screwy. Prime really doesn't prime until it gets opened by a bit of vacuum. Once it gets opened by vacuum it stays open until you turn it away from Prime.
I think my 550 starts better using Prime after about five days, not sure exactly. I either ride it almost daily or it sits three weeks or more when I'm gone. It's not a 1980 though.
Just thinking out loud here, I don't know what to tell you except those petcocks without the lever suck big time.

 

[eil]

Are you using enough choke?

When did you last adjust the valves?

After it's sat for a few days, open the carb bowl drain screws and see how much gas comes out. I think each one holds something like 1/4 cup. You should not have to prime the carbs until they've been sitting for months or intentionally drained (which is what you should do when you know it will be sitting for months).

yet if you even think about touching the throttle, it will flood and die.

If that happens, then it's not dying because of too much gas, it's dying because of too little. (Opening up the throttle allows more air through.)

You can check the tank, petcock, fuel line, and carbs for fuel obstructions but those are usually more evident on the road than when starting up.

 

[tom203]

Just get new 1980 petcock and eliminate it as possible problem for many years. Once you understand how it properly works, you can probably learn to cope with it!

http://www.georgefixs.com/1980-gs550-gs750-gs850-gs1000-gs1100-petcock/

 

[Steve]

Eil asked what I was going to: have you adjusted the valves? Tight valves will cause hard starting, especially when cold.

.

 

[MatBirch]

Sorry guys, I should have added more info! I just thought you all have followed each and every one of my posts on this bike from day one, and have all my stats memorized'
This build began a couple years ago, and started from the ground up. Since I got it on the road it has maybe 4 tanks run through it, as my wife gets used to it and learns to be a motorcycle rider. Easily less than 500 miles at this point...

Valves were done to the loose side of spec.
A new factory petcock was installed.
New choke, throttle and clutch cables
Fully serviced carbs, torn down, dipped cleaned, o-rings, and synched.
New plugs.
Relay mod on coils, with new plug caps.

I use the choke to start when cold. "Enough choke"?? Is there an option here?? Pull it all the way out and go...
If it tries to fire and you give it a little throttle, it dies immediately. Then it becomes even harder to start, and sometimes won't at all. Often times I can smell gas at this point. That's why I feel it's flooding.
The times it all goes correctly, I pull the choke all the way out, don't touch the throttle, give it a quick crank to get a little vaccuum going, then hit the button. As it catches, let off the button. Sometimes it's right away, sometimes it takes a few tries. Once it rumbles to life, I still touch nothing. Let it lope along for maybe 5-10 seconds, then slowly roll a little throttle on. If I get this far, it now idles like a dream, and rides even better.
Unfortunately, the times we fight with it far outnumber the times we don't.

 

[JTGS850GL]

I use the choke to start when cold. "Enough choke"?? Is there an option here?? Pull it all the way out and go...
If it tries to fire and you give it a little throttle, it dies immediately.

Something else is still wrong, but never try to give it gas while on choke. Kind of defeats the whole fuel addition circuit.

When it does fire up, what RPMs are you seeing with it on full choke? It should jump to some pretty high RPMs. Something in the vicinity of 3500-4000 or so. I usually have to pull the choke back once it fires and the RPMs take off in order to get it to settle into a 2000-2500 RPM range. A few seconds later I can ride off. By the time I'm at the end of my driveway I can shut the choke off completely.

 

[tkent02]

Shouldn't need full choke unless you're in sub zero temperatures. Just a little bit should do it.

 

[chuck hahn]

Like Matbirch said....."If it tries to start and you give it a little throttle " .. You never twist the throttle ever. It starts with the choke and if it wont start with just choke youve got a fuel delivery problem or the carbs are gunked up. But that doesnt seem plausable due to your having dipped and all new orings etc etc.

Last thing that will also effect starting..even without touching the throttle..is the idle knob turned up too much. try turning the idle out a turn and see what it acts like.

And check for spark on all 4 plugs too.

 

[JTGS850GL]

Shouldn't need full choke unless you're in sub zero temperatures. Just a little bit should do it.

Agreed. In the summer I usually only need a half choke. If I use full choke they will start well but take a couple of seconds for the RPMs to jump up. Starting it at half choke causes the RPMs to jump off right away and stay at around 2500. In the winter it's full choke to start but quickly down to half choke after a few seconds.

People who think these bikes are cold staring natured simply have never had one running right. None of my bikes has any problems starting in hot or cold weather.

 

[chuck hahn]

And the OP needs to remember that gas does evaporate from the bowls and after a few days they may be a tad low..thus yes its gonna take a few extra seconds for the bowls to refill and to fire up. So that or set the petcock on prime and then start it after a few seconds..being sure the petcock goes back to the ON position immediately.

 

[MatBirch]

Ok, so played a little more-
Tonight, I even had to resort to starter fluid. Even with that, it would not fire for the longest time. Crank and crank. It would give little pops on release of the button, it seems. Just wouldn't catch and roll. I had to walk away for about five minutes to let the battery rest. Came back and it fired right up first try????
Good spark on all 4
When it does start, it definitely does not "jump up" in rpm. It fairly stumbles and struggles to keep going for a bit, till it warms enough (5-10 seconds) to give it a twist. Then it will settle down and idle great. JTGS makes it sound like this should have a high idle solenoid or kickdown like a car has.?.?. I know with my '80 Honda CB750, even with the choke, I hit the button and twist at the same time and BAM!!!!!!

Tonight I was struggling with fire on #1 at idle. Pipe was cold until I shut down for a few minutes, started it again, and revved it up to about 5k. It was fine after that. If that's part of the problem, it's definitely fuel, not spark.

I did play with the idle knob a bit, but it didn't seem to make a difference in starting, just idle rpm once it was running...

thanks again!!

 

[DimitriT]

For a motor to run you need three things:

1. compression
2. fuel mixture
3. spark

Compression is the result of properly functioning top end: valves are sealing correctly, bores and piston rings are within spec. You can and should measure compression on a new bike to understand the state of the top end.

Fuel mixture is the result of a properly functioning carb and intake system. For cold starting the most important items are a sealed intake (no air leaks), a functioning enrichment and idle circuit, and a functioning and correct float valve and fuel level. It's hard to measure the enrichment circuit but the fuel level is easy to measure using a fuel level measuring tube.

Spark is easy to measure. You look at a spark plug off the head. But timing may be off so its also good to verify timing.

Doing all these things will tell you what you need to know so you can fix the problem.

 

[tkent02]

It would give little pops on release of the button, it seems. Just wouldn't catch and roll.

Sounds like an electrical problem, not enough voltage until you release the starter button, then it sparks once and fires the mixture. If this is the case it may well spark with the spark plugs out and no compression going on, but when it's compressing air with the plugs in the starter draws too much power, there's not enough voltage left for the ignition to make a spark. How much voltage do you have at the coils while the engine is cranking with the plugs in? The 1980 electronic ignition won't run on low voltage like the points type ignition will.

Tonight I was struggling with fire on #1 at idle. Pipe was cold until I shut down for a few minutes, started it again, and revved it up to about 5k. It was fine after that. If that's part of the problem, it's definitely fuel, not spark.

This does sound like a fuel thing. Go through the pilot circuits again.

 

[chuck hahn]

I would put in new plugs and check / clean all the connections and clean up all the harness grounds.