Bringing a GS500E basket case back to life - but with a couple of glitches

[hawk73]

I swapped a laptop for a 1996 GS500E that the PO told me he had gotten less than a year before completely in parts.  He had put it back together and ran through quite a few new parts but had not been able to get it to run properly.  He could only start it with choke on and a shot of carb cleaner then the bike would erratically jump to 3500 rpm for no reason and have to be shutdown to stop it.  He had decided he had put to much time and money into it and needed to get rid of it.  I enjoy a challenge and loved the looks of the bike so I went for it.  Well I have went through the carbs and removed and cleaned every single needle, jet, oring, float, slide, diaphram, etc and cleaned and reassembled (several times).  PO had installed OEM stock replacment jets, needles, and orings so most of stuff in the carb is new.  I can now with choke on get it to start immediately (choke enriched needles and slides had not been cleaned there was a fine black silt all over them).  It will not run when I turn the choke off and with the choke on the max RPM I can get is 4500.  Through the forums today  I think I found one mistake and that is I am testing and adjusting with the air box off (I am used to Hondas and this being OK).  I assume doing this is making it so lean it will not run except under full choke?? 

Note all below here has been done with airbox off that I didn't realize was a potential problem for tuning until today.

Completely stock except for clear inline fuel filter and 5/16" fule line.
Needles and jets have been replaced and idle/air mixture screw cover drilled out.  Have tride screw backed out 1, 2, 3, 4, and 5 turns.  Around 3 turns was best but improvement was almost negligable.
Both cylinders 110 psi compression (This is with throttle closed not openf)
Both carbs 5 lbs vacuum
Both spark plugs light tan in color
Both carburators torn down and all jets, needles, orings, gaskets, etc checked and cleaned. Enrichment needles removed and cleaned - smooth operation.  Emulsion tube, slides, needles, diaphrams, and slide plastic removed and cleaned.  All good.
Good spark on both cyliners
Will only start with choke on.  Must figit with throttle to keep running.  Will not idle or run at all if choke is turned off.  Can't get over 45oo rpm.
Fuel valve on frame is new.  Checked on both prime and on.
All vacuum lines hooked up and working.
If overflow T is capped engine stops running in seconds.  (Just did this to make sure that there was no obstruction in the T)

--------------------------------

Tonight I will put the airbox back on for any additional testing and tuning.  Any other suggestions would be greatly appreciated.

Thanks.

The main reason I went ahead and Got this bike is because of the community of other GS500 owners and thier wiillingness to help each other.  You don't find that many places any more.

[The Buddha]

Yea new sheite when the old sheite wasn't bad - common hobby for people.
You want to send me the carbs ... complete re-jet and light clean (yours dont need it, but hey I open it all so cleaning happens when you do that and adjust synch and air screw etc - $45 and return shipping.
I have see come impressive sheite ... in your cars I guess 1 or more O rings being bad/missing/poorly installed as the culprit.
Cool.
Srinath.

[beRto]

Sounds fun! Good luck on the rebuild. 

As Srinath suggested, it is possible that you are missing an o-ring in the carbs. Assuming you have a Clymer/Haynes manual, use the carb diagram to verify that you have all of the o-rings correctly installed (otherwise you can search for a parts fiche diagram online).

In particular, there are a couple of tiny o-rings in the top of the carbs that are easily misplaced when the carbs are taken apart. Omission of these tiny o-rings causes a lean condition.



EDIT: o-ring in question is #26 on the Bike Bandit carburetor schematic
26: O RING    482468-001     $2.45

[hawk73]

Ok.  I have the airbox on (what engineer ever designed such a pain in the rear piece of plastic.....  I digress) and the tank.  I can start in on choke and rev it up.  When I shut choke off it tries to die.  If I work very quickly with the throttle I can keep it running and get it to tack up to 9k.  as long as I keep it above 4k I can easily work the throttle.  If I let it drop below 4k then it dies really quick.  In essence I have choke and half to full on but no idle.  My idle air mixture screw is set to 2 right now.  Just so I know what is the factory air filter supposed to look like??  It looks like the one I have is aftermarket washable type.  Without rejetting would that lean it out enough to cause this problem?  Thanks for all your help and advice on this board!!

[ben2go]

Ok.  I have the airbox on (what engineer ever designed such a pain in the rear piece of plastic.....  I digress) and the tank.  I can start in on choke and rev it up.  When I shut choke off it tries to die.  If I work very quickly with the throttle I can keep it running and get it to tack up to 9k.  as long as I keep it above 4k I can easily work the throttle.  If I let it drop below 4k then it dies really quick.  In essence I have choke and half to full on but no idle.  My idle air mixture screw is set to 2 right now.  Just so I know what is the factory air filter supposed to look like??  It looks like the one I have is aftermarket washable type.  Without rejetting would that lean it out enough to cause this problem?  Thanks for all your help and advice on this board!!

Unless you have a K&N drop in WITH restricter,it will cause a lean condition.Also aftermarket and performance exhaust will cause a sever lean condition.I would post a link to the performance section of the GS Wiki,but I can't seem to get on that site now.Have you checked the engine to carb boots for cracks?Those are sneaky and hard to see some times.

[hawk73]

Ok.  Since I did not have a restrictor for the air filerI did the next best thing, I blocked half of the airbox intake with a rag.  Improvement but still not there.  With the choke on throttle range and response was much improved.  Finally I was able to start it without the choke also.  It would stumble and die below 2K.  Controllable throttle response.  Since this worked I blocked more of the airbox intake.  Results tapered off.  I think it started to go overrich.  I checked plugs after this and instead of being a light brown they were sooty black, to rich.  Since my problems weren't cured just closer I decided to take the tank, airbox (I would love to strangle the engineer that designed this piece) and carburators off to check the engine side boots.  I took pictures and will try to attach.  The engine side is clean and shiny.  There is a trace of a red like silicone around edges though.  The boots themselves are not cracked or split but the surface that mates to the engine is not shiny and smooth.  It has black buildup. The o-ring seems in good shape but one of them had the same red silicone stuff half way around the oring and the other one had trace amounts.  My question:  Should the boot surface that mates to the engine be smooth and shiny to match the engine and make a good seal?  Also is it a good idea to change these o-rings?
Boot Surface<img src="http://a3kncg.bay.livefilestore.com/y1pCtn0vymn4pYMOXWzO8FJSCHt59qABrNlRA3yNQAF5usnWkqsTMGRZWwjIRamGzSEdZP9CpVAhzwSPDcVXO1Ljg"></img>
Engine Surface<img src="http://a3kncg.bay.livefilestore.com/y1pCtn0vymn4pYa_XNy6UfdwsB9uWZMr4NdLxdCoOwp45bdsL6IjDXZNp9xJiisja5FRbWYo6SdrVhjEfoT2nCJxQ"></img>
Tore down bike screaming to be on the road<img src="http://a3kncg.bay.livefilestore.com/y1pCtn0vymn4pZgms6KT27LP5J5KllZkbaG2z9M0TUxQ5qfKmDBZsSmCj7Fa8DHWza8J7uqQdwv3C8kSLNSH9Umew"></img>

[hawk73]

One other question haw many inches of vauum should the test ports on the carbs show?

[rnicholas]

The boot surface should be clean.  Depending on the age of the bike, shiny not necessary.  I would clean them off with some light degreaser and reinstall.  Typically the cracks that cause the problems are in the sides of the boots, yours seem fine based on the pic.

I would check the jets to see what size they are.  If the PO replaced with stock jets, but put in an aftermarket filter with no restrictor, then you need to rejet with bigger jets.  As you said, when you restricted the airflow, you could make it rich.  Now you need to properly jet to find the right balance. 

You could also try turning in the air screws as far as they go, and see what that does.  That would reduce your air flow at idle-i'm 99% sure as this is how I diagnosed my problem of too rich/lean-though some smarter person than I may say I'm wrong. 

[hawk73]

OK. Progress  I have cleaned the carburator boot metal side surface so that it is clean and smooth.  The o-ring seemed good plus it was on odd size so I put a small bead of right stuff in the oring groove and them nestled the oring in it and let sit for 2 hours.  I then put the carbs and airbox together before putting back in back (doing it this way has its advantages and disadvantages).  I reinstalled the carb boots to the engine and then installed the airbox carb assembly and reattached everything.  Since I still have the aftermarket air filter I had set the air mix screws all the way in and had a rag cover 3/4's of the air inlet to the air box.  Start on choke was good but still had to baby the throttle a bit to get over 2k.  Once there I had full (hallelujah) throttle control and tacked it up to 9500 rpm after letting warm up for a couple of minutes.  I then shut the choke off and as long as I kept it above 2k I had full throttle response that was smooth.  I am attributing the stumble and die at 2k or below to the after market air filter and air mix screw combination not being able to find a sweet spot so I am getting an OEM air filter tomorrow and will be setting the air mix screws to 2 turns and testing.  I think I am there as the valve train is quiet, no clicking ( I haven't measured valve clearance yet) and throttle response out of the idle circut is great.  I will update tomorrow after new air filter and air mix settings.  Thanks again everybody for your help.    .....after this it will be to putting in new front fork seals and oil.

[Travis-Mc]

Kind of thowing this out there, but could it be an ignition or timing problem?  Did one of the PO's put a V&H adjustable on there or do the advancing mod?

[hawk73]

The exhaust is stock.  How can I tell if the advancing mod has been done?

[scottpA_GS]

Did you adjust the Idle screw properly?

[hawk73]

I have adjusted the idle screw and set it at just a hair below where the choke enrichment fades out of being effective.

[Travis-Mc]

The exhaust is stock.  How can I tell if the advancing mod has been done?

http://gstwin.com/diy_timing_advance.htm

look for oval holes and scribed lines.

[hawk73]

I will look for the timing stuff tonight and see if the mod has been done.  Interesting thing and question.  I have everything together and running decent except that the motor will rev to 4k and sit there without the choke and idle screw turned down.  The only way to bring it down is to shut it off or pull the vacuum caps off of the carburator tops. It is like the system is holding excess vacuum and forcing more fuel in to and keeping it reved up.  I have checked the vacuum at the carb ports and it shoes 6 inches.  What is it supposed to show?

[Travis-Mc]

I'm surprised you're not getting more help with this issue..  maybe you have everyone stumped.   If I get some time tomorrow, I'll check the vacuum on my carbs.

[hawk73]

I have gotten a stock air filter now and have it installed.  I didn't have time to test run but as I do I need to find out a couple of things.

1.  How much vacuum should the carburators be pulling through the test ports at a specific RPM such as 2k, 3k, or 4k?
2.  On the idle/air mixture screw is it the more you screw it in the leaner the idle mixture or richer?
3.  What is the factory idle/air mixture screw setting?

Thanks for everybodys help.

[ben2go]

I have gotten a stock air filter now and have it installed.  I didn't have time to test run but as I do I need to find out a couple of things.

1.  How much vacuum should the carburators be pulling through the test ports at a specific RPM such as 2k, 3k, or 4k?
2.  On the idle/air mixture screw is it the more you screw it in the leaner the idle mixture or richer?
3.  What is the factory idle/air mixture screw setting?

Thanks for everybodys help.

1. Vacuum numbers vary depending on the condition of the engine.A valve out of adjustment will cause some weird vacuum signals.
2. The tighter the screw the leaner it will be.
3. This varies from bike to bike.Mine was 2 and 1/4 turns out.Most are 2 to 3 and 1/2 turns out.

[hawk73]

Thanks for the info.  I will go ahead and check my valves also.

[ben2go]

You're welcome.