GS500 1993 Will not start, was seized

[notelrat]

I have a 1993 GS500.  The bike sat for over a year and water got in I believe the left cylinder (memory failing but that one has the worst compression).  I removed the crank case cover a few months ago and using a large socket wrench I was able to get the bike un-seized. 

The reason the bike sat so long is I took it apart to clean the carborators because the right cylinder was not firing at below 3500 rpm so it was having trouble idling and accelerating from a stop.  During this time I installed fuel filters into the lines because there was rust in the tank.  After putting the bike back together problems were even worse, the right cylinder still wasn't firing correctly and now it was no longer rid able with the power band totally out of wack, it would bog than accelerate than bog again, as if it were a fuel problem (yes the filters are installed in the right direction) or the something was still wrong with the carbs. After this it has sat for the last year and a half.

In the last 2 weeks I have returned to this project.  I took the carburetors apart and somehow even though the bike has been inside most of this time, there was water in the gas lines, airbox and the carburetors. Also a large mouse nest in the air filter. It was a real mess in the carbs, and there must have still been rust in the lines.  Upon cleaning the carburetors and putting it back together, the bike was able to fire up after pulling the plugs and squirting some gas in.  It would fire up and run for maybe 15-20 seconds tops than die.  It did this a few times than it refused to start up at all and than gas starting coming out of the airbox drain line, so one/both floats were not operating correctly.

I broke the carburetors down again, the right one still had some junk in there, cleaned them out again briefly and put it back together.  No more fuel leakage, the floats are back to operational, it must have just been some sludge under the needle.  Still though, I can not get the bike to fire up at all now, with starting fluid in the airbox, gas under the plugs.  It won't fire up and run at all after firing up last week (but than it would die as if it were fuel starved..).

Compression in the left cylinder is at 75psi, the right cylinder is about 140psi.  Squirting some oil in the left cylinder will get the compression up to 140, so there is definitely a problem in there, a broken ring, something, but I assumed that it would at least still fire up on the right cylinder, but than again this was the cylinder that was originally having problems at idle.  With oil in the left cylinder (it gets 140psi compression with oil) and gas in the right, it will kick over and sound like its going to start the first second or two of starting but than it dies off again. 

I have replaced the plugs, charged the battery and I am jumping it off of a car battery.  I assume that the engine might be screwed and need to be broken down further but the fact that it won't start up at all anymore is perplexing. I didn't want to remove the exhaust in fear of ringing off a bolt, but that is the next step because I know there was some sort of nest in there as junk starting firing out after it started last week, still turning the bike over results in exhaust coming out so its not totally plugged.

Suggestions?  Thank you

[radodrill]

First off, the fuel filters are hurting your fuel flow thus making your starvation problems worse.  Instead of filters, I'd opt for new fuel lines and a thorough tank cleaning.

[notelrat]

Well one of the fuel lines I replaced, and I did clean the tank (months ago now) but the tank rusting I dont think will be ending any time soon, the fuel filters arent stopping it from starting I dont think.

[radodrill]

the fuel filters arent stopping it from starting I dont think.

Depends a lot on the filter; most are designed for systems with a fuel pump, these are over-restrictive for gravity-fed systems and typically result in fuel delivery issues.  If you have a filter that's specifically designed for gravity systems, then it wouldn't be as much of a problem.

[BockinBboy]

Take off the tank and take out the tank filter - clean it, and make sure there aren't any holes/tears - a clean and functional tank filter should really be all you need.  Too many times fuel filters on the lines cause fuel flow issues to warrant them necessary.  If the tank is less than half full and a filter is restrictive enough - it could prohibit a bike from starting, even more so if there are other problems at play which would cause it to be hard to start anyway.

In a case such as this, I'd do a top-down approach to eliminate possible problems all down the way.  If you intend to keep the bike and ride it, I'd replace things along the way... If not, I'd ensure things are clean and work as they should along the way.  Start with fueling (and air), then to spark, then to sort your compression issue... Its systematic, and it starts with the cheaper/quicker stuff first.  Use stock configuration, line routing, etc on everything - its a proven setup guaranteed to work. Start with the tank(fresh fuel), tank filter, tank petcock, fuel lines to frame petcock, frame petcock, fuel line to carbs - check through those fix, clean, or replace as needed before going to the carbs.  You can bybass this if you do an auxiliary gravity fed tank setup to eliminate all those variables to focus on the everything after that for the time being too.

At the carbs you determine if you need to open them up again, assuming the jets have already been cleaned - specifically pilots and choke circuit for starting issues.  Check float height with the clear U-tube method.  If that doesn't check out, open 'em up and figure out why - clean/fix/replace as needed.  Now you are at the airbox - make sure fliter and box is clean and double check for any possible leaks - clean/fix/replace as needed (note the manifold connections are a 'popular' leakage area).  The other part of air that most often gets looked over by assumption is exhaust, and since you mentioned a possible issue in there, I'd definitely sort that out... Then you can move onto spark/electrical - have your meter handy if your strong spark doesn't check out on both sides.

This systematic approach is the only way to ensure you're not going to be shooting at a moving target, and its the only way to do it with a bike that has been sitting, because so many little things may or may not go bad... I understand you may want to see it run, and then figure out the littles to make it run better... but it did run, so you know it can - now its time to get it to keep running, and therefore its time sort out the littles.

I will say I'm not familiar enough with compression issues to be comfortable doling out much advice on that... I would say that higher compression with oil should indicate some more specific things to look at - so if someone has some experience there that would probably be helpful.  That could tell you something right away to look at or fix, but regardless everything else that feeds the engine have to be gone through if you want a bike that's been sitting to run reliably.



- Bboy

[Crasm]

Did you take the jets out and clean them? Have you checked the diaphram for damage or splits?? Have  you cleaned the needle seats out , have you tryed draining fuel and putting fresh in?? Have you checked that your actually getting a spark??

Lots of things for you to look at and check

[notelrat]

Update:

Have removed fuel filters from the lines, removed petcock and checked for debris (there was none) replaced spark plugs, removed exhaust and blew threw to try to remove debris. Upon putting the exhaust back on, the bike fired right up and ran for about 30 seconds, than died again.  Got it to run another time or two, now it is not starting again.  The right cylinder was not firing as consistently as the left, it was about 220 degrees while the left was 400 (even though left is getting worse compression) so we switched the ignition coils from one side to another to see if that helped the problem, but haven't got it started again since.   Could there still be something in the exhaust preventing it from starting?