Hey all, just did a valve clearance check on my '92 GS and after putting it all back together, the starter will spin and the engine will turn over but it just won't catch. Gas is getting to the carbs, just replaced the spark plugs and got their clearances to spec, but I don't know what it could be.

Any ideas?

-jrtaylorthird

how did you check that gas is getting to the carbs?  was it running fine before you did the check? did you have to replace any shims or was it just a feeler check and put back together?

It was running fine, valves were still in spec. Cleaned the carbs and put the stock airbox back on.

Reverse the spark plug wires?
Ground something by accident?
Have you pulled a plug and checked for live spark when cranking it?
Do a compression check to ensure the valves are really doing what you think they are.
Did you pull the timing chain apart, thus resulting in bad timing?

Quote from: jrtaylorthird on September 08, 2016, 11:06:55 AM
...Cleaned the carbs...

I would guess something went wrong here.

Float needle missing, forgot to put the pilot jets back in, main needle stuck/misaligned, fuel and vacuum line reversed, etc.

Alright, so I'm not sure what you mean by checking for a "live spark" when cranking. I unplugged the spark plug and kept it attached to the black cable and when I hit the starter I didn't see any spark. Should I see it when it's attached to that black plug on either side?

if it was running fine before then i'd think the problem narrows down to human error.  try walking back through your process and double check things that can easily be  overlooked perhaps.  turn the tank petcock back to on?  double check all hoses are going to the correct locations and fitted properly? make certain that your new plug gaps are good and firing and that the boots are back on securely?  i've read about people forgtting to put o-rings back in their carbs and having some problems.  really hard to tell with little info but back tracking might be a good place to start,  oh and make sure your kill switch is in the ON position!  

Quote from: jrtaylorthird on September 08, 2016, 11:24:12 AM
Alright, so I'm not sure what you mean by checking for a "live spark" when cranking. I unplugged the spark plug and kept it attached to the black cable and when I hit the starter I didn't see any spark. Should I see it when it's attached to that black plug on either side?

you need to ground it on something like the frame

I had the different parts of the carbs in little plastic containers and labeled them too, I'm really particular about tiny things like that. So I know it's nothing missing or improperly placed. Hoses are good, gas is getting to them and both petcocks are on "On" and I primed the frame petcock then set it to "On" also.

There seems to be some sort of "bloop" noise every time the engine makes a full rotation. It's coming from the front-left side and I have no idea where that came from.

Quote from: jrtaylorthird on September 08, 2016, 11:32:48 AM
I had the different parts of the carbs in little plastic containers and labeled them too, I'm really particular about tiny things like that. So I know it's nothing missing or improperly placed.

Yeah but it is trivially easy for a float needle to bind or get stuck in the wrong spot without you noticing it, or for the main needles (on the slides) to get hung up on the orifice so the slide is stuck open. It's likely to lose the "little" o rings when putting the tops back on the carbs, which without making extreme adjustments to the idle speed and mixture settings, would prevent the bike from starting due to a huge vacuum leak.

It's also pretty easy to get the carbs misaligned in the boots on either end of the carb, or to forget to tighten the hose clamps holding boots on either side of the carbs, etc.

Seriously, you may have to pull the carbs back off and retrace your steps.

Quote from: mr72 on September 08, 2016, 12:30:50 PM

Quote from: jrtaylorthird on September 08, 2016, 11:32:48 AM
I had the different parts of the carbs in little plastic containers and labeled them too, I'm really particular about tiny things like that. So I know it's nothing missing or improperly placed.

Yeah but it is trivially easy for a float needle to bind or get stuck in the wrong spot without you noticing it, or for the main needles (on the slides) to get hung up on the orifice so the slide is stuck open. It's likely to lose the "little" o rings when putting the tops back on the carbs, which without making extreme adjustments to the idle speed and mixture settings, would prevent the bike from starting due to a huge vacuum leak.

It's also pretty easy to get the carbs misaligned in the boots on either end of the carb, or to forget to tighten the hose clamps holding boots on either side of the carbs, etc.

Seriously, you may have to pull the carbs back off and retrace your steps.

I was just gonna suggest a vacuum leak due to those little O rings being missing, specifically because of your thread lol.

Perhaps the "bloop" sound is a large amount of air being sucked in during the downstroke due to such a vacuum leak? 

OP, I know you feel like you re-assembled everything perfectly, but there are a large amount of pieces especially in the carbs that can easily be installed incorrectly or lost. As someone who has worked professionally in electronics repair, let me tell you, no matter how meticulous you think you are there will always be a time where you forget to plug something back in or forget a screw.

Good luck getting your bike started up!

Alrighty. Spent about an hour just taking the carbs out and giving them a once over, looking at pictures and whatnot just double checking and from what I can tell, it's all there and in the right place. Nothing's stuck, everything's to spec and we're good to go.

But now I've tried starting it so many times the battery's just crapped out on me. So I'll wait for my father-in-law to get here with his charger and we'll give it a go later. Spark plugs (when tested right) only had an intermittent yellow spark, but that may have been due to low battery...?

I don't know. I've only been riding for about a month so everything I've learned has been since then.

Quote from: jrtaylorthird on September 08, 2016, 01:13:40 PM
Alrighty. Spent about an hour just taking the carbs out and giving them a once over, looking at pictures and whatnot just double checking and from what I can tell, it's all there and in the right place. Nothing's stuck, everything's to spec and we're good to go.

Did you specifically verify the "little o-rings"? Because if you took the carb tops off, then there's a pretty good chance they are gone!

Quote
Spark plugs (when tested right) only had an intermittent yellow spark, but that may have been due to low battery...?

maybe or could be bad ground. Basically you can really only check that the ignition is not COMPLETELY dead by doing the plugs-out spark check.

Also, you are starting it on choke right? Choke cable is connected and working?

Good luck getting it going. There are a dozen things that could make it not start. If it were me, I'd assume it was something I forgot or messed up, because that's always what it is. You seem pretty confident everything is spot on, but you never know.

Alright. So for the weak plugs I'm thinking it may just be bad ground.

Also I've never had a choke cable, the bikes always started without it and I didn't realize it was supposed to be there until I was going through my Haynes manual and there was no other cable other than throttle. So THAT'S great.

I'm on my way to see the rocket launch over at Cape Canaveral at 7 tonight. I'll get back to it tonight or tomorrow