Wont Start

[Barkdog]

Hey, I've had an ongoing rebuild project on  my 2002 lemon GS500.  Everything is finally back together, but I cant get her to start.  It is getting spark.  The timing is right.  Fuel is getting in the cylinder.  Anyone with a knowledge of mechanics have any ideas?  Is there a trick to priming it?

One strange thing I noticed is that if I try starting it for a while... like holding the ignition for 10-15 seconds, gas will squirt out the carb into the airbox.  Is that indicating a clog somewhere?

[The Buddha]

Was happening on Gino's bike... it busted my knuckles for a week, and finally we took out the new plugs it had, and put in old and dirty ones, and it fired up instantly. New plugs sometimes are bad.
Cool.
Srinath.

[Barkdog]

I've got the old plugs in there.   I testedthem out, and they are firing.  I occassioally get a backfire when I'm trying to start it.  I suspect there is a carburation issue happening here.  Maybe not enough gas, or too much....

[destroyer]

If that bike has been sitting a while you will have to tear the carbs down and clean them.  I have a 2000 model I rebuilt that sat around for 8 months to a year and the carbs were completly clogged.  Took me two cleanings to get all the crap out.

Stephen

[etam]

similar problem here...

I removed the signal generator to check for oil leak (crankshaft seal leak) and while still waiting for seal (mid next week).. I put it back and want to go out.. but it won't start:

battery is good 12.3V;
it cranks; signal generator is spinning (didn't put cover back on);
it was running fine 3 days ago except oil leak; and started on first crank;
should be enough gas in tank;
couples loud back-fire does it mean something??
bike in center stand; side stand up;
spark plugs changed 50km before; put back old one?

Any idea?

Thanks!

[MarkusN]

I had the GS only backfire on me when it was tuned way too rich and the new sparks got carbon fouled within about two weeks of riding.

[etam]

Haven't checked continuity of ignition system yet.. but one thing I notice is that when signal generator rotor spins, it doens't really touch the 2 terminals on either sides, there is a small gap, is it normal?

Actually, how does ignition system works?  Let me try and please correct me:

* press start switch -> turn on ignition coils
* ignition coils -> fire up spark plug at different time -> combustion
* at the same time

(A) signal generator coil spins the signal rotor and crankshaft (big induction force from signal generator coil to turn the crankshaft??) or
(B) the other way? crankshaft spins the signal generator rotor? but then what turn the crankshaft?

sigh.....

[Kerry]

The crankshaft gets its initial spinup from the starter motor.  As the crankshaft spins, the signal generator thingie passes over a pair of pickups which in turn "signal" the spark plugs to fire.

The resulting combustion causes the engine to "catch" and become self-sustaining.  (No more need for the starter motor.)

I don't know all the details about the spark timing (or sequence or advance), but I understand that each time a plug fires for one cylinder, the other plug fires at the same time.  ("Lost spark method", or some such thing.)

[etam]

ic... and I am seeing sparks from both plugs (don't know if they are strong or weak though; no comparison) or in other words, the gap between signal generator rotor and pickups doesn't matter then (??).

okok.. check continuity tomorrow morning.

Good night and have a nice weekend!

[Kerry]

Cool!  I was afraid that an old thread with a lot of related diagnostic info didn't exist anymore (e lost the first few months worth a while back).  And yet ... it lives!

If you would, go to the 2nd page of the thread Narrowing down the problems to a broken bike and scroll down to my 4th post on that page.  You should be able to start from there, and test what I'm interested in by the time you get to the bottom of the page.

You're welcome to start at the very beginning of the message thread and wade through the whole thing, but there are several wrong turns and detours in there....  

[etam]

ok.. I think I check as much as possible:

* signal generator harness on left side is good and correct ohm resistance (3 connectors plug) and continuity of both plug ends.
* both ignitions coils; primary/secondary resistance are within spec (I just moved the gas tank a bit backward; don't want to mess up the fuel lines).
* continuity of 4 connectors plug is good (left side)
* I double, triple check spark plug.. and they are yellow, not fat blue, and it is dancing around the electrode.
* I put in 2 litre of gas to tank
* still cranks.. but no catch
* no more back fire as I sometimes start without choke and/or throttle

What else missing? suggestions?

Please don't tell me to open up the engine top

[Kerry]

Wait a sec - do you have ONLY 2 liters of gas in the tank?  If so, the only way to get any of that fuel to the carbs is by using the PRI setting on the frame-mounted petcock.  OK, the RES setting might work, but I wouldn't count on it....  In fact, even on the PRI setting you may have to tilt the bike to the left to get some fuel to drain out of the tank and down the RES (front) hose.

Otherwise, everything sounds good.  I'm about to get out of the house with my wife for a while ... I'll go back over the whole thread when I get back.

[etam]

oops.. I mean I added extra 2 litres in.. should be more than enough in the tank.  To recap, it was starting fine (start on first crank) before I removed the signal generator to make sure where is leaking.  

Actually, as of today, the bike is in my possession for 8 days, after 2nd day ride for 45km (just practice around small streets), I noticed it was leaking... and asked here to finally confirm that it is leaking through crankshaft oil seal.  It only leaks when the bike is running.  Oil level is still above low mark.

Signal rotor is spinning and there is spark in plugs and I assume that I put it back signal rotor correctly.

I called the seller and hope he can help me out.

Kerry, thanks again!

[edit]side stand down: won't crank; kill switch on; won't crank

[cernunos]

Try a new set of plugs...you said you get a yellow spark is one clue, spark dancing around is another. It's one thing for a plug to fire out of the engine and another to ask it to fire under compression. Compression increases resistance for the initial spark voltage to overcome. And yes, the GS500 is loved by me...as is this forum.

Cernunos

[Rema1000]

I had a weird problem last fall, where the battery seemed fine, but when it was cold, the engine would not catch... right until the moment I let go of the starter button.  Then it would catch!  This would never happen if I hooked-up jumper cables to a boat battery I had sitting nearby.  My guess was that the bike's own battery was strong enough to turn the starter for a while; or it was strong enough to give a healthy fat blue spark; but not healthy enough to do both at the same time.

So I'd recommend trying to start using jumper cables at least once, just in case there is a battery problem contributing to your yellow spark.

[Rema1000]

couples loud back-fire does it mean something??

The only times I've had backfire, is if I press the starter button for a few seconds, and the bike turns and turns but no catch, then I release the starter button.  Then I  push the starter button again, and the engine turns and turns, _then_ I get a backfire.

I have never gotten a backfire on the first time I try holding the starter button; only if I try to stort, then relelase the starter button, then try again.  So my theory is that there is too much gas left from the first starting attempt.

It may be more successful to just hold the starter button on and see if you can get the engine to catch.  If you are jumping from a car battery (see previous post), you can hold the starter button for quite some time (say, 30 seconds... but let the starter cool for 30 seconds after that!).   If you are wondering if fuel is getting to the engine, you can try giving  a squirt of some gas into the air filter... or even a small squirt of ether ("starting fluid").  I've used ether to start lawnmowers, etc. after they have sat unused for a few years.  But my GS has never gotten that bad.

[Kerry]

As I probably said in that old thread, I had a weak yellow spark too.  I also had a few backfires, although I don't think I mentioned that before.  However, I could get the bike to start.  It only ran on one cylinder though, which made sense because of the broken connection to one side of the signal generator circuit.

The odd thing was that I actually got that weak yellow spark on BOTH sides.  I still haven't figured that one out....  

Anyway, I'm coming to the end of my useful suggestions.  I will second some of the others' ideas: 1) Jump with a car battery, just in case yours is getting "low" and  2) Try some starter fluid just to have another "data point".

Otherwise, my last suggestion at the moment is to hook up with another Toronto-based board member and meet them with the appropriate socket and wrench for removing their right-side engine cover.  (Don't worry folks - this won't hurt ONE BIT.)  Take a long, hard look at how everything is mounted under there, and make sure yours looks the same.

One last thing - I wouldn't even consider pulling the engine apart for this problem.  If the bike ran right before, it should run right again.  The main issues are carburetion and ignition, and my money is still on the ignition side....

[etam]

Just tried jump start with my car's battery (car running) with very original plugs and NO start.

Seller showed me to change plugs on first day and they are NGK DPR8EA-9.  Since bike won't start, I put back original plugs (originals are still brown) as one of new NGK plugs is kind of black, guess that's because I was running with choke on longer than needed and couple back-fire.  All 4 plugs show yellow spark.

Anyway, I will go get some new plugs tomorrow and try again.

Appreciate all the tips!  Hope other people find it useful.

[etam]

OK.. it starts now after seller told me to rotate the signal generator.

There are 2 holes on crankshaft.
1 notch and 1 hole on generator.
And 1 metal pin to line it up.

When I first removed generator, metal pin stay with crankshaft and I have 19mm wrench to turn it around couple time and forget the orientation.  When I put it back, I line up notch with locatin pin as described in Clymer.  Apparently, the pin should be in other holes of crankshaft.

Anyway, if it doesn't start, rotate it.

I can take some pictures later.

ok.. I am ready to change crankshaft oil seal, do I need addition sealant for crankcase cover? or new gasket is good enough?

[edit] I search.. looks like sealant is not needed... didn't mention in Clymer as well.

[etam]

ok.. all done.. 15km test drive and no more leak!

picture of signal rotor:
http://members.rogers.com/subaru0/gs500/signal_rotor.jpg

picture of crankshaft:
http://members.rogers.com/subaru0/gs500/signal_generator6.jpg

Apparently, I need to line up metal pin of crankshaft to hole (not notch) of rotor... or maybe I can move the metal pin to another hole in crankshaft.

Thanks all again!