GS1000G carb rebuild done - but she still won't run :(

[ChrisMA]

Background:

After I bought my new-to-me 80 GS1000GT last fall, it ran fine for a few weeks, then started idling and running inconsistently (racing then lagging, stalling out at idle). This deteriorated over a couple of short rides, and then wouldn't idle at all (would stall unless I was holding the throttle open). Trying to start it up (on the sidestand), I saw fuel coming out somewhere behind the #1 carb, I gave up and decided to do a full carb and valve job.

Over the winter, I did a compression test (I don't have the #s in front of me, but they were well within spec), and adjusted the valves (a couple were just below spec before swapping shims). I did the full carb teardown, cleaning, dipping, and rebuild, following both of the detailed pictorial guides (including all the little channels, etc). Carb #1 was seriously crudded up with rust powder (or some sort of brownish powder) behind the needle valve screen, which I'd hoped was the cause of my fueling issues. No other gunk though, everything looked pretty clean. After the carbs were re-ganged, I did a quick bench sync test (butterfly valves looked to be spot on).

While I had everything apart, I replaced all of the carb o-rings, along with the rings on the intake manifold boots (all from cycleorings). Replaced all of the the fuel and air hoses with Suzuki OEM. Airbox is stock, and already had new (flexible) boots from the PO. Replaced the air filter with a UNI foam filter (freshly oiled). Filter seal was worn down and the rubber side seals were torn, so I re-sealed everything with foam insulation tape following the guide.

Fast forward to this weekend, when I finally had enough free time to put everything back together. Went to start her up in preparation for doing a carb sync, only to find that the exact same problem was happening: fluctuating rough idle then racing (though this time it wasn't spitting fuel). I recall seeing some white puffs of smoke out of the right exhaust pipe, but couldn't take my hand off of the throttle to feel behind both pipes. As the engine warmed up, I was able to reduce choke, but the same race/stall cycle kept happening until I finally reduced choke and it stalled out. After restarting (partial choke), the engine raced up to a VERY high RPM (not sure if it was redlined, but it was high), then immediately stalled out. After that, it would turn over, but no ignition. Checked the headers, pipe 1 was burning hot, the other 3 were only warm. Engine isn't seized (I can turn it over by hand). No fuel leaks or noticeable smell of fuel.

As it stands now, I've put her back in the garage, and am going to step away to regroup. I plan to do another compression test, and a vacuum test. If anyone has any thoughts of obvious things to check, or even just words of encouragement, I'm all ears. I'm fearing the worst, though I'm not really sure at this point what the worst is, other than a season without a running bike.

Thanks in advance...

Chris

[hikermikem]

What does the inside of the fuel tank look like ? If it's chunky rusted you may be cleaning those carbs again... try running the bike using a remote fuel tank. I use a tank from an old snowblower I junked years ago, you get the idea...

[ChrisMA]

Good point on the tank. PO said he'd cleaned the tank, and it looked clean at a glance. There are couple of bubbles under the paint, which I'm hoping are just a surface thing (paint job will wait until I get it running). Petcock was new, I didn't pull it to check out the filter and lower tank. Over the winter, the tank was mostly drained, though there was a bit left sloshing around which I didn't drain (I really don't know why, it would have taken 30 seconds... my bad). I guess if there was enough rust to crud up #1 last fall, that could explain #1 running hot this year.

In retrospect, I really should have fully drained and inspected that tank before putting it all together...

[ukjules]

Agree on the remote tank to test.
I have cleaned my carbs (on my kwak) time after time after i chemically cleaned my tank and put it back on without a filter ! (residue as you state)
time after time it produced results as you experience ! and blocked jets.
A remote tank of known clean petrol removes this from the list of possibilities.

Also check electrics - plugs, caps, ht leads, coils, timing. (it doesnt hurt and can be done while having a coffee break)
Carb boots on correctly ?
air mixture screw set ? (to colour of plugs if you have run it long enough to effect)

Otherthings that have produced what you state: (from my own expereince)

Kinked fuel line !! dont underestimate this one
throttle cable routing
choke cable routing
vacuum pipe on correctly - bungs in if have them ?

[ChrisMA]

Thank you both for the good suggestions

Kinked fuel line !! dont underestimate this one

Very possible. I left my new fuel line extra long (temporarily) as I'd planned to perform the carb synch with the tank connected but physically off the bike. The extra line very well may have compressed or kinked during my test.

Electronics is definitely something on my to-do list. I'd rechecked the spark plug leads (which are fairly new), and the ignition fuse, but I have not taken out the multimeter yet.

Suspect #1 is definitely the fuel tank. In hindsight, it seems silly to me that I knew that there was a rust blockage, but I didn't take the time to more than glance into the tank. I'll pop the bowls and check out the screens, and I fully expect to find carb #1 clogged up again (as my test was run on the sidestand). Follow with a tank cleaning (which reminds me, I need to order a gallon of evapo-rust today...). My follow-up test will be done from a known clean plastic tank or other container.

I've also broken down and ordered a new set of intake boots. The old ones weren't cracked or brittle, but getting the ganged carbs into them was a b!%@#, involving bar clamps and more pressure than I felt comfortable applying to 37-year-old aluminum. It will be worth the extra $ to have a soft set of rubber going forward, and eliminates one possible leak source.

Thanks guys for your suggestions... I'm out of panic mode, and I have my next steps lined up for when I manage to get some free weekend time.

[Tom R]

Is the vacuum line from the petcock to the #2 carb hooked up? Do you have the leverless petcock? It was only on a few model years and is a horrible design - not that it really makes a difference because when they work they're fine, but the prime position is a pain to use and doesn't work that well anyway. You can test fuel flow if you put the fuel line into a container, a Gatorade bottle or the like is nice because they're clear, and apply vacuum to the diaphragm line. Usually takes very little vacuum for fuel to flow... and if you get a mouthful of gas you know the diaphragm is bad. If it needs a lot of vacuum, the petcock could be hanging up. There's the petcock screens and individual screens on your carbs to filter out any of the big stuff, you could check if they're mucked up too.

[JTGS850GL]

Time to verify and adjust vacuum sync. If the bench sync isn't close enough it will only run on a few cylinders. Make sure the pilot screws are at 2.5 turns or more to start with. Put on the vacuum gauges and see where you are. My bet is that you're going to be way out of balance.

[Nessism]

Did you verify the choke pick up tube were clear? Passage in the float bowl for the choke tube are open? Hold up the pilot jets to a light to make sure they are open? Set the pilot screws to 2.5 turns open? Replace the spark plugs? Verify spark for each cylinder?

Assuming you did all of the above I'd do a cold start and carefully check each header pipe to see if they are getting hot. Could be the bike is only running on 3 cylinders unbeknownst to you. Also, make sure the petcock is working properly. No fuel should flow unless there is vacuum pulling on the diaphragm. Also, no raw fuel running back down the vacuum tube and into the carbs that way.

Good luck and hope you figure it out soon.