So I got about 100 amazing miles out of the new top end before I ran into serious trouble again.

I'm sitting at a stop light on the offramp of the freeway when the GS just dies...like I turned the key. Couldn't get it started and had to truck it home.

Just pulled the fairings off. Definitely getting a spark and it seems like I'm getting good compression. Maybe I should invest in a legit compression tester to really see.
Also checked the petcock to make sure fuel was getting to the carbs.

I really don't know what is wrong this time. It had been running so amazingly great since I rebuilt it. Seems weird that it would just decide to jump timing or something sitting at idle when I've had the thing up to 90 mph.
Anyone got any ideas (simple things that could be wrong) before I go drop some $$$ on a compression tester or another top end?

I thought I was ready to start having fun again with this bike, but I guess it has a different agenda for me

I got a compression tester 

THink I could borrow it? I would ride the bike over and use it in your bike cave but....the bike is broken!

Yep.
PM me what's convenient for you.

Given the work you've done on it, I would suspect mechanicals first, but if it died like you turned the key and you didn't notice anything obvious happening (loud grinding, misfire), take a look at the electricals. Did you pull the engine to do the head work? Maybe your ground wire isn't secured tight enough?

I woukd doubt compression suddenly went out. The bike would do something even with bad compression.
Like mentioned, most likely electrical. Or the timing chain could have jumped. Or the timing rotor slipped.
Too bad you can't bring it to the Bike Cave.

I agree it's likely electrical as well. One of your connectors might've just come undone, although you did say you were getting spark.

At least no one said "the only 3 things you need for a motorcycle to run are compression, spark and fuel", haha as if that's ever any help. If all you had to do was throw some compression, spark and fuel in a bucket to power a motorcycle I'd making hand built motorcycles in my basement. I completely understand how those things are relevant and important, but still.

Curious, you said you've had it up to 90 MPH. When I was rebuilding my top end some of my research and the BF said to treat it like a new engine. I.E break in period like it says in the manual. I know Flick didn't touch 90 until he had a 1000 miles in or two weeks. Think you might of been to hard to soon?

Mary

Its possible I rode it too hard to soon. I thought the break in thing was only for bottom end work, but what do I know?
If something had gone wrong at that speed I wouldn't have been too surprised, but it happened at idle.

I installed a manual chain tensioner during the rebuild, so that could have something to do with it, but again, if it was good up to redline, it seems weird the timing would get off at idle. I should be able to borrow adidasguy's compression tester soon. If the compression is in spec ( which I doubt ) then I can start figuring out whats wrong. I doubt it is electrical, because I am getting a spark.

What is the proper method of doing the compression test? Or do I just attach the gauge and hit the starter for a few seconds?

We've got a video for that     http://www.youtube.com/watch?v=6PH0BnemyPQ&context=C3d5e5a0ADOEgsToPDskKg71t1i6d-OmLfjzOfzpWY

-Jessie

Thanks for the video link!

One more thing.

The spark plug is emitting a yellow spark. It should be blue? Any chance that this is the problem? Probably just weak because the battery was nearly dead from trying to turn the engine over many times.

It could be the condition of how you're looking at the spark. Wheel it in the garage/shade and check it out in a darker area.


I agree on the break-in period that it's only the bottom end (including pistons/jug) that needs to break in. If you just did new valves, you lapped them already, so nothing there needs time to expand and sit properly like it would need to in the bottom end.

I never thought I would be happy about this, but it looks like my bike is having fuel delivery problems! 

lol....

So I got some aerosol engine starter and sprayed it into the air box while cranking the engine and she started right up.

So, maybe a ripped diaphragm in the petcock? Could be something carb related but I don't know anything about carbs so I don't know where to start. Maybe bad gas from sitting for 3 months while I worked on the bike?

The good news is, it looks like the engine internals are fine. This is just a huge coincidence that it happened within 100 miles of the rebuild. I'm not afraid to get down and dirty with the carbs, I just don't know where to start (help  )

Dies it work in PRIME? If not, then you have a kink in a fuel line or blockage somewhere.
Do you have gas in the tank?
Did you add a fuel filter in-line?
Pinched line?

if PRIME does work, then check vacuum line to the pet chicken. (and be sure there is gas in the tank)
Could the in-tank petcock fuel screen be clogged up?

Did not work on PRIME (first thing I tried on the side of the road).

Yes, gas in the tank.
No in-line fuel filter, just the stock setup.
Not a pinched line.

I'll go see if the in-tank fuel filter looks okay, but gas comes out just fine from the tank-mounted petcock.

Given how abruptly it happened, I'm with adidasguy on the vaccum line being torn/off. You've lost vacuum somewhere, a bike wont just shut off if you've got bad gas.

Carb diaphragm could have ripped, air filter could be clogged, pet c.ock clogged, or carbs just too gunked up.

Does fuel flow from the float bowl drains?  If not, look for a restriction in your fuel lines/petcock.  If it does, check for clogged jets.

-Jessie

Man, I wish you could limp it over to the Bike Cave. I'd love to help solve this. Got petcocks and whatever else needed to being it back up to snuff. I LOVE solving problems!

A little progress...

Took the tank off and started messing around with all the petcock and carb lines. Seemed like the vacuum line had been pinched by the air box. I thought it was weird that it took 100 miles for the problem to manifest after the rebuild, but whatever, the bike started drinking the fuel in my temporary tank.

So, I put it all back together and started it up. But the bike will only run for <5 minutes before it dies and refuses to start. Next day I try to start it, same thing. Runs fine for a few minutes at idle, sounds mostly normal then dies and refuses to start. Next day, same thing.

At least I sort of got it running. Anyone got any ideas why it won't stay that way?

Shot gunning it I would guess that you are getting insufficient fuel flow.

-Jessie