1983 GS550ES Fuel Delivery Issue

[joeman001]

Hi All,

Im not even sure what to list this as so I just put it here.

So basically I have an 83 GS550ES that looks like it just rolled off the showroom floor because it was kept in a guys living room for 30 years but under all the glamour this thing has some sort of serious air fuel mixture problem that I can not figure out. I thought It was the intake o-rings but I replaced those to no avail (they were very flat though). The main problem is that when its running it will idle around 1100 rpm at start and then slowly rise to about 2000 and then if you give it any amount of throttle it will immediately rocket up to 5000 rpm and never come back down.

A list of things we have tried:

-Cleaning the carbs
-confirming correct jet size
-made sure all the vacuum lines are in good order and in the correct place
-checked the float bowl level
-checked the slides to make sure they fall at the same time
-greased the boots at the airbox to carb boots
-I used WD40 on all boots when installing to make a good seal
-replaced boot clamps
-checked diaphragms on the carbs
-cleaned fuel pet cock and ensured it was delivering adequate fuel and the vacuum was pulling fuel from the petcock in ON and RES positions
-checked coil packs to make sure they spark the plugs
-new spark plugs (correctly gapped)
-New battery
-went over the carbs like 4 times.

The last thing I did one it was check the fuel petcock filter to make sure it was clean and I just tried starting it after priming the carbs with fuel and putting it in the RES position (only 1 gal of gas in tank) and the damn thing wont even start now. It just cranks and cranks and cranks. Am I missing something thats stupidly obvious here? or is this just the bike from hell??

Anyways sorry for the rant and long post I appreciate your guy's help in advance.

Thanks,
Joe

[tom203]

“It’s running it will idle around 1100 rpm at start and then slowly rise to about 2000 and then if you give it any amount of throttle it will immediately rocket up to 5000 rpm and never come back down.”

these things are sensitive to “choke” position . Once bike is sorta warmed up ,you need to keep backing “choke” off or it will race just like you’re describing...especially with throttle applied.

You have done lots of work......but I would have replaced the o-rings at carb boot/ head interface.

[Rich82GS750TZ]

What do you mean by “all the vacuum lines”? There is only one. From the front of carb 2 to the smaller or the 2 nipples on the petcock.

[roeme]

Those are VM carbs? Then it could be that the "butterfly" part connecting the throttle cables to the combined throttle shaft came loose (It's what happened to me).

If it doesn't start at all however, then there must be a different issue.

Try dropping down a teaspoon of gasoline down each cylinder (through spark plug hole). If you get it to fire, your problem is with fuel/air mixture/delivery. If not, it's spark/electrics.

Tackle one issue at a time.

Just because it looks pristine, doesn't mean it has more than a few issues common to bikes of this age.

[joeman001]

I guess shouldnt have said vacuum lines what I meant was i connected the one vacuum line from the petcock to the carb and then i connected the two lines that vent the carbs to atmosphere, plus the fuel line itself

[joeman001]

Hi Roeme,

Im not sure what a VM carb is but looking it up looks like youre talking about the single barrel carbs. These are the Dual Barrel carbs for the 572cc engine for an 83 gs550es. Not sure what the problem is but i threw a clear vinyl fuel line on yesterday to check fuel flow and it doesnt pull any fuel on the On/Res positions with the vacuum line connected, and when i try to use prime it doesnt send fuel through like it should. I checked the petcock and it is very hard to turn but it looks like the valve inside works correctly and the piece the vacuum operates on looks like it goes back and forth ok. I think its getting a serious lack of fuel for some reason. I only have around a gallonish of fuel in there so maybe its just low on gas and prime wont work? anyways thanks for your help.

-Joe

[joeman001]

Hi Tom,

Like i said in the post above I did just replace the O-Rings at the intake because i thought that was the problem but it isnt. Im pretty sure the choke is working because when i had the carbs apart i could see it moving back and forth when i was using the choke lever. Is there anyway to check to see if the chokes are getting stuck in the choke port in the carb while they are installed? Again i have tried running it with the choke on/off and it was running like i described with the choke completely off. Thanks again

-Joe

[tom203]

Ok, it was early and I missed the o-ring replacement....

“and when i try to use prime it doesnt send fuel through like it should.”

add some more gas.....if it still doesn’t flow in “PR” ,get a new petcock - don’t waste your time fiddling with or admiring a 40 yearold petcock . Measure bolt centerline spacing on petcock..lots use a 44mm spacing. Determine whether you must have petcock outlets facing towards front or if there’s room to face them back, cuz later is more typical.
Understand that this cold start system is an enricher,not a “choke”....it sends an extra dose of fuel into carbs throats to aid starting . Do not use any throttle during “choke” application or you defeat its purpose.

[rphillips]

There should be a very fine filter attached to the pet cock, inside the tank, check to be sure it isn't clogged. Even with a non working pet cock, it should be wide open when in PRI position. Just my opinion.

[Cipher]

There should be a very fine filter attached to the pet cock, inside the tank, check to be sure it isn't clogged. Even with a non working pet cock, it should be wide open when in PRI position. Just my opinion.

Yes wide open on prime.
Disconnect the fuel line from the carb and fuel should flow on prime.
If it does then it should also flow if you suck on the vacuum line whilst it is in the other 2 positions.

If you have fuel flowing from the petcock reconnect the line to carb and remove the float bowl drains. Fuel should flow from these if all is well.
There are tiny dome shaped filters attached to the float valve seats but I had mine apart after 30 odd years and they were clean as a whistle. These are a royal pain in the ass to get out without damaging them so as long as fuel will come out of the bowl drains do not bother.

So two things to check in the fuel flows path.
Confirm these and we can move on.

Tom from Maine was right about the choke position. The bike will warm up quickly and you will get a rapid rise in RPM so you have to drop the choke back incrementally during the warm up. But thats not an issue now go check for fuel flowing.

I once had a gelationous and semi varnish buildup inside the petcock which required it be dismatled and cleaned.
You cracked open the carbs and did farm more difficult things so if you get no flow its worth a check.


Also remove the gas cap when your doing this.

[BigD_83]

get a new petcock - don’t waste your time fiddling with or admiring a 40 yearold petcock .

I spent countless hours searching for a new petcock with the exact configuration needed for the '83. The little fuel door is not compatible with the petcocks that were used in the '84 and later...

[joeman001]

Hi rphillips,

Yes when i took the petcock apart yesterday the fuel filters were extremely clean and I even blew them out with compressed air to make sure. Took the top piece of plastic too to make sure that the two ports inside the filter werent clogged for the RES/ON side. Im going to try to add another gallon of gas and see if prime works and try to take the gas cap off and see if it works as mentioned above. Thanks for the advice!

-joe

[joeman001]

Yep same problem here!

UGH- cant believe how few parts there are for these bikes left in new stock or new old stock!

will keep trying on this one. I dread the thought of sending it into the local dealer for a $125 per hour service charge

-joe

[joeman001]

HI Cipher,

I will try what you have suggested for like the third time. Me and my dad are working on this. Hes an ME and has plenty of experience in this kind of stuff and is stumped like me. When I first drained the gas tank I used the PRI feature to drain it and it was gunning out like no ones business. We have also opened the float bowl screws a few times while monkeying with it and there was definitely fuel in the bottom of the carbs. Like you said with your carbs after 30 years they were clean as a whistle. I made sure to blast it out with carb cleaner just to be safe. I also checked the float bowls and used a dial caliper to check the float height. I have no idea what is wrong with this thing. Give me a day or so to get the time to run your test and ill get back with you (Didnt want to not respond since i responded to a few others on here). Thanks for your help.

-Joe

[joeman001]

OK.

So I was completely wrong and the fuel petcock is working totally fine. The float bowls were full of gas still which was stopping the fuel from flowing to the carbs. I also took a look at the carb and the guy before me drilled out the air/fuel mixture plugs and turned all the screws to like 3 to 3.5 turns when its supposed to be 2.5. I turned them all back to 2.5 and now the bike is starting (although i had a lot of trouble getting it to start but now it starts fine) but even with the choke on/off it still rockets up the in the RPMS. I tried adjusting the idle screw as low as it would go and still no luck. Instead of idling at 5-5.5k RPM though it fluctuates between 3.5 to 4.25 RPM now. Also it no longer starts out at around 1-2k rpm idle its just straight to 4K rpm with whether its on choke or no choke. Do you guys think I should turn the screw more to around 2 turns instead? I don't feel like that's going to make a massive difference though. Honestly I'm running out of ideas and the bike when I first got it had 175PSI compression on all cylinders and I am getting really worried that the engine is going to be destroyed by the time i get this thing fixed since its constantly running lean. I've heard horror stories about valves being eaten alive by lean conditions. Anyways thanks for all the help, if any of you in the Cincinnati area know somewhere or one who knows these bikes well enough to work on them please let me know because I might have to take this in to a dealer and pay an exorbitant amount of money to have this fixed.

Thanks, Joe