Help! Yet another starting problem!

[mercilor]

First off, hello - I'm a new rider on a 99 GS500EX (18K mi). This forum has been invaluable so far with links to great resources like the wiki. So, here's my scenario:

(as a note, I'm mechanically adept at working on cars, do my own maintenance, etc., but have never worked on a bike before and haven't worked on a carbureted engine in over a decade)

I bought the bike about two weeks ago, but it kept stalling whenever the throttle was unattended, even after warming up. Idle screw/choke didn't help much, as the bike would either "hold revs" (not fall back to idle) or stall. Anyway, there were lots of nuances to all this behavior, but it's all a bit moot now as I decided to trade one set of problems for another. Since the bike is naturally lean, the carbs had obviously never been cleaned AND the previous owner had put the K&N drop-in filter in, I decided to rejet to 40/127.5.

So I spent this beautiful Sunday afternoon disassembling everything, cleaning the carbs, changing the jets, putting 2 washers on each needle, resetting the mixture screws then doing three complete turns out, etc., reassembled everything (after some confusion with the hoses, which was solved by the diagrams on the wiki), set the fuel valve to prime and fired the bike up. It sounded amazing, revved beautifully, all-in-all was a reborn beast. So I let it sit there and rumble while I finished attaching the rear plastics and seat, when it dies. "Oh well," I thought, "it must just need the idle screw adjusted." If only. The bike refuses to fire up, for the most part. Idle screw all the way in, idle screw all the way out. Petcock on prime, reserve or normal. Choke on, choke off. All permutations of the above. For the most part it just turns over and sputters like it's going to start, but never quite gets the momentum up. Plenty of power - headlight, indicator lighs, etc. all fine. Occasionally it starts, just barely, under 1K RPMs - but it takes holding the throttle wide open, choke all the way on, idle screw all the way in just to keep it alive for a minute or so before it fades off again.

I'm going to disassemble and reassemble everything all over again tomorrow if I have the time, just to be sure everything's in its right place, but I'd much rather go into it with some pointers than relatively blind like I am now. Thanks for any advice you might have!

[Affschnozel]

Just to be sure check your spark plugs ,they can get fouled in instant

Otherwise sounds like float height problem

[mercilor]

Haven't had time to redo everything yet, but I did check the plugs: they're sooty and smell like fuel (though not evidently wet), so I'm obviously too rich. I have a new set of plugs, but since the others should be fine for now I just cleaned them off with a wire brush and dropped them back in (don't want  to get the new ones sooty while I'm sorting this out).

I tried to do the float test with the transparent tube, but the tube I bought was too large of a diameter for the drain nipple, so it just leaks fuel everywhere when I try to lift the other end up 

This did remind me, though, that when I was disassembling the underside of the carbs the float valve had fallen off the metal tab on the bowls. When I put it back together, I assumed that the wire loop on the valve went AROUND the tab on the bowls - is this correct, or is it simply supposed to REST on the metal tab?

[Affschnozel]

You are correct , it goes on and around the metal tab 

[mercilor]

Ok, I just finished taking it all apart and putting it all back together again. Really, the only changes I made were the position of my washers on the needles (didn't have them between the doughnut and clip) and adjusting my float height (one side was a bit off). Put it together, tried to fire it up, no luck. Swapped out the spark plugs, and BOOM fired right up, sounded beautiful. Let it warm, slowly let off the choke, etc, etc. Then after running for about 15 minutes, right as it was ready to be warm, when I went to blip the throttle it just sort of coughed (even though I'd hit the throttle a few times before and it'd responded well).  Now, it's back to what it was this morning. Will just barely start, then sputters out. I'm tired, I'm going to pick up all of my tools from the back yard, but mostly I'm frustrated. I just want to ride! Help appreciated.

[mercilor]

Is it possible my new jets are clogged already? I did clean out a bit of rust from the bowls; it's possible I loosened some up somewhere else, didn't notice, and now it's made its way into my pilot. Is there some way for me to spray carb cleaner in there without taking the whole thing apart again?

[Affschnozel]

If you cleaned the carbs and there's no significant rust residue in the tank itself , then I don't think it would get clogged so fast ...

Maybe three turns on the mixture screw is too rich ,try backing it in a 1/4 of a turn and see how that goes

Working on carbs especially on GS is frustrating , just because of the tank removal and all the fuel lines in the way ,

a makeshift tank helps a lot btw 

Edit:

Awhile ago a friend with another GS asked for help , he had all sorts of presumably carb conditions :

difficult to start ,but when it did the rpm would hang or bog down and die and plugs would get fouled fast ( just like your's )

He cleaned the carbs numerous times with no luck , I checked the float height and it was OK 

Then I checked for valve clearances and they were non existent ,all 4    after adjusting the valves it ran like new instantly 

You see where i'm gettin at ?   If the previous owner neglected checking/adjusting the valves this could be the same issue

[mercilor]

So this past week I tore down the bike and checked the valves. Sure enough, no clearance on 3 of 4 valves. So I put in thinner shims, reassembled, got a jump and fired it up. Same thing - runs fine for five minutes, then coughs off and won't come back. I really don't want to pay to take this to a mechanic, but I can't think of what else could be wrong.

[Affschnozel]

Strange behavior indeed  ,   5 minutes OK and then dies 

Try running the bike with gas cap partly open . One thing that comes to mind is that tank's ventilation is at fault causing a vapor lock

[GeeP]

It sounds to me like rust and dirty water is coming out of the tank and getting into the carbs, especially if you've found rust in the float bowls.  It doesn't take much rust at all to gum up the works, but would explain your troubles exactly.  Mine did the same thing before I cleaned out the tank and coated it with Red Kote.

I suggest you get about six quarts of Isopropyl alcohol from Wal Mart and wash the tank out.  Read my post about #3 down here for more info: 

http://gstwins.com/gsboard/index.php?topic=27969.msg297997#msg297997

I also suggest a sintered bronze fuel filter such as the one on the top right of this page:

http://www.russellperformance.com/tech_center/motorcycle_fuel_filters.htm

I have one, and it has caught more than its fair share of junk.  The beauty of a sintered bronze filter is you can disassemble and clean it when it gets full of junk.  This can be an asset if it clogs on the side of a lonely road in Southern MO, like it did to me one afternoon.   

Let us know what you find!