1978 GS550E carburetor frustrations - spitting gas

[enriquev9]

I am finally 90% finished restoring my 1978 Suzuki GS550E. I got the tank on, new aftermarket vacuum Petcock, started her up, and went riding for the first time. After a couple of laps up and down the street the bike started to die when I would come to a stop. Finally got her home and at my garage I saw a huge puddle of gas on the floor from the over flow tube lines. This was as I attempted to keep restarting the bike. Which it would start then die.

What could be causing so much gas to over flow?
is it the aftermarket vacuum petcock?
is there a better petcock set up?
obviously the bike is stalling because of lack of fuel….so I’m diagnosing it as a petcock issue….is that correct?
could a bunch of air have just build up in the fuel lines since it was disconnected?

here is what I’ve done
Dipped and sonic cleaned the carbs
replaced O-rings
replaced needle valves (stock Suzuki)
adjusted idle air screws for optimal idle
synced carbs with Carbtune
stock airbox
stick exhaust
(I like to keep them original)

your help is always appreciated.

 

[Nessism]

Rust/debris in the tank causing the new float valve needles to hang open?

Another option is cracked overflow tubes in the float bowls

 

[enriquev9]

Rust/debris in the tank causing the new float valve needles to hang open?

Another option is cracked overflow tubes in the float bowls

Verified that the tubes were not cracked.

Could be rust or debris, but the tank appears to have minimal rusting, and there is also a good filter in the petcock.

it’s like the gas spilled out or the aftermarket petcock was starving the carbs for fuel causing the bike to die. When I had the bike running in a fuel bladder there were nine if these problems.

 

[tom203]

Since it was running ok on fuel bladder,I’ll blame the Chinese petcock..decent Japanese ones are still available for about $50..mine still works fine at 12 years old…. I check it every year!

 

[Rijko]

I hope you followed the GS Resources manual to properly clean the carbs ?
Carbs are bench synced ?
Large idling screw set too low (will work on choke but stalls when choke is off) ?

obviously the bike is stalling because of lack of fuel….so I’m diagnosing it as a petcock issue….is that correct?

​No. Could be lack of fuel, could be too much fuel, could be dirty carbs ..... etc.
If the bike runs well at higher revs and stalls on low revs, it gets enough fuel to dismiss the petcock as cause for starvation for now.
Since you mention overflowing carbs, that should be solved first - check the carb float needles and fuel level.
Even a malfunctioning petcock cannot make the carbs overflow, the float needles should stop the gas.

Unless the petcock leaks fuel through the vacuum hose ... very rare, but check that too.

When I had the bike running in a fuel bladder there were nine if these problems.

So you have made changes (fuel tank and petcock).
The new issues may be caused by that, but not necessarily.
You DID check if the bike runs well on the fuel bladder now ?
Always try to go back to a "good" situation if possible, and restart from there.

 

[enriquev9]

Since it was running ok on fuel bladder,I’ll blame the Chinese petcock..decent Japanese ones are still available for about $50..mine still works fine at 12 years old…. I check it every year!

can you send me a link of what you bought so I can compare to what I bought. Mine only cost $20

 

[enriquev9]

thank you Rijko for reminding me to manage my impulsivity and frustration. You’re right about thinking or going back to the last “good” situation and work forward from there.

I hope you followed the GS Resources manual to properly clean the carbs ?
Carbs are bench synced ?
Large idling screw set too low (will work on choke but stalls when choke is off) ?

I followed the VM carb rebuild guide off the BikeCliff site. The carbs have been dipped, scrubbed, brushed, sonic cleaned, and a cycle o-ring kit was used (what happened to them).

The bike did run on choke only but I solved that using the forum. Pilot fuel screws were not turned out enough. So I turned them out two turns and that matched the notches on each carb body. Pilot air screws were tuned for best idle on each cylinder. Those match the notches on each carb body’s also.

carbs were synced with a Morgan carbtune. That helped the hanging idle (they were way off despite a bench sync.

on the fuel bladder…. No gas leaked out of overflow tubes. Bike started and revved well. Didn’t get to drive her since I live in an apartment complex.

I really think it is a lack of fuel. The bike didn’t stall when I came to a full stop until several laps up and down the street. When that happened it kept her rolling. I did stop and turn her off to take pics. The pics don’t show any fuel on the floor. I noticed the fuel when I pulled up to my garage and kept trying to start her and get her to idle. It’s like the carbs just decided to spit out fuel.

I will pull spark plugs and check if there is a rich situation.

just need to take my time, don’t get frustrated, and go back to a good state to help diagnose.

let me know if something i said here helps the diagnosis.

 

[Rijko]

My compliments.
Following the carb cleaning guide helps a lot, using expensive Suzuki float needles instead of cheapo ones,
Carbtune sync, Cycle-Orings, coaxing/improving the bike to run better ... WELL done, you're almost there.

I take it you checked valve play too ?

Just asking because remote troubleshooting is hard but you are doing things right so we can dismiss
a lot as cause this way.

So what happens ?
You start the cold bike on choke, warm it up a bit by couple of laps in the street.
Did you turn off the choke ?

No - if the bike warms up, the choke may be too rich (possibly worsened by a high float level and overflowing carbs) and kill the bike.
Not a biggie when driving, but idle mixture is sensitive.
Yes - you have now taken away the rich mixture and rely only on the idle jet. Big change, usually the RPM are lower now.
You did not comment on the central idle adjuster knob. What happens if you turn that one in ? Will the bike idle, even if at 2000 RPM ?

Oh btw - Ed "Nessism" took over the service from Robert Barr.

 

[Rijko]

I will pull spark plugs and check if there is a rich situation.

Don't. A couple of laps in the street is not enough to judge that.
If the carbs overflow, the plugs get wet and don't show colouration indicating rich running.

Take care of the overflowing carbs first, should not be difficult because you used the new Suzuki float needles
that have good springs in them and don't stick as much as some el-cheapos.
Please re-check the tiny holes in the float bowls and float level while the carbs are on the table anyway, a small deviation spells problems.

 

[enriquev9]

I was hoping to not have to take the carbs off again lol.

But lots to check with your suggestions.

Got to fly to Denver for the Christmas weekend. When I get back I will fire her up again and give the details if what is happening. What I experienced was after my first ride on the motorcycle anyway.

stay tuned for updates.