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Floats: I thought I knew what I was doing there for a minute...

  • Thread starter Thread starter Austin550
  • Start date Start date
A

Austin550

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I'm working on a 1981 GS550 that I bought last fall, bottom line is it won't start, or run for that matter now. After a complete carb rebuild I got it running (but not without half a can of starter fluid). Sounded really good when revved up; timing is good, compression is solid, fuel delivery was, at the time,...iffy. So I decided to make it "better"...

One cylinder was cutting in and out, leading to a really sporadic and unstable idle. I believed it to be a float height set too low. So I raised the fuel height by bending the tang closer to the floats (to avoid confusion, I mean the float moved up towards the carbs at the point in which the needle shuts off the gas, letting more gas in.................right?). Only, now the problem is worse; I can't get it to start at all. It barely gives it the old college try and begrudgingly puffs a few times.

I have a translucent polypropylene fuel line so I can see the fuel in the line; if I disconnect the gas tank and crank the starter, the gas level doesn't go down at all in the fuel line and the spark plugs are completely dry. Why would raising the fuel height cause no fuel to get to the engine?

I thought I knew what I understood the float height adjustment, but apparently not. Am I missing something really obvious? I ordered the fuel height gauge here: http://www.ebay.com/itm/271428455754, so maybe that will shed some light on the situation. Until then, any thoughts?

Thanks,

Austin
 
You went backwards essentially cutting fuel off completely before the bowl gets sufficient fuel in it. I set the float heights on my bikes so that the molded line on the side of the float is parallel with the carb bowl surface. I've never used a float height gauge etc and have never had an issue. I might could get a pic of the orientation I use on my 850 carbs for you tomorrow for reference.

Edit: Was bored anyways so here ya go.
YFMKCF0.jpg

Also make sure you have the vacuum line from the carbs to the petcock connected as this could also cause fuel starvation.
 
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Interesting, that appears to be how I have mine set now, but I'll take a look since I'm going to have to take them off anyway.

I may have incorrectly described the direction i bent the tang. If I were to take a picture of the way they were set previously, the parting line on the float that you referenced would have been angled way up (with regard to the carbs being upside down like in your pic). Wouldn't that make the fuel level lower because the float is sitting lower when the gas is shut off by the needle (the "lower" in the last sentence is with regard to the carbs being upright, opposite of your picture). So, with the carbs upside down, like in the pic, the solution would be to move the float down towards your orientation so the fuel has to fill the floats more to push on the floats and shut it off. Sorry for all the confusing ups and downs. Will get pics tomorrow.
 
Why not just measure them the way the service manual describes it to you and know that it is correct ? It is not that hard
 
That's exactly what I did to set the floats, use a caliper to set the height of the floats to the service setting. If memory serves, it was .84" to .92" off the carb body. How I messed up the first time is I did that measurement with the needle spring depressed all the way.
 
Haven't had a chance to pull the carbs off yet, but here is a picture using the float height gauge. The fuel height (red line) doesn't seem unusually low does it? Is it possibly too high? Would a high float level create the symptom of not sucking in gas?

When I crank the starter, the height fluctuates slightly, but the plugs remain completely dry, indicating no fuel getting to the engine.
 
Update:

I was actually able to start the engine with some convincing. Turns out, it is only running on the two right cylinders now. The left exhaust pipes were bone cold whereas the right two were scalding hot.

So maybe float height isn't the issue; as you can see from the attached image vs the image in my post below, the right side and the left side are dead on with each other as far as float height is concerned. But one works, and the other doesn't.

I've tried running it with the idle mixture screws in various positions to no avail. Any ideas why the left two won't take in gas? Cylinders have good, consistent compression across the board...

Austin
 
Initially it was on the side stand, but I moved it to the center stand and the problems persisted. Both float height measurements were done with the bike on the center stand.
 
A half a can of starter fluid is enough to cause serious damage to your motor. ether washes all the oil off your cylinders. You might use it once to see if it fires, but a half can.:eek: If the float level is measured the same as the VM carburetors, your level is about perfect. You might start looking somewhere else for the problem, but lay off the starter fluid.
 
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Full disassembly, dip.
New o rings.
Reassemble.
Set float height, bench sync and set mixture screws 2 turns out and master idle screw 2 turns in, all as per the tutorial on Cliffs site.
Assure you have spark on all plugs.
Make sure your petcock vacuum line is hooked up.
Should start.

Which of the above have you not done correctly?
You are obsessing on this float height thing.....something else is wrong.
 
Sorry, half a can was an exaggeration.

loud et, the only thing I can think wasn't done correctly on your list is maybe the cleaning wasn't thorough enough. Maybe the pilot circuit was really gummed up and just needed more time in the dip, I don't know. Otherwise, to the best of my knowledge, everything on your list has been done correctly.

Although, I'm not familiar with the "master idle screw". Is that a VM carb thing? I'm running CV carbs.

The reason I obsessed about the float height initially is that at one point, I had three cylinders running relatively smoothly, but I knew I had set the height too low. I thought if I raised them all the same the fourth one would kick in and it would run better. Now only two of them run.
 
Here's the thing about the side stand. If the bike is on the sidestand a long time, it will have the left side carbs clogged up unless the petcock is sealing absolutely perfectly. Once the fuel evaporates out of the bowls the floats fall down, the fuel valve is now open. When any fuel leaks down the fuel line from the petcock it goes into the left carburetors, because it's up hill to the right ones. Even a slow leak will keep resupplying fuel to the left two carbs, as it evaporates up it leaves a mess in the pilot jets, choke feeds, other places in the lowest parts of the left carburetors.
 
Bent tangs and needle valves

Bent tangs and needle valves

I had this issue on my GS1150ES. I had bent the tangs too far but only because the needle valves and the little spring in the needle valve were knackered and it was necessary to bend them that far to obtain the correct float height reading. But clearly it was a bend too far:

P1110149.jpg


I replaced the needle valves completely (don't tell Steve that I used K&L carb kits though) and you can see the difference.

P1110144.jpg


P1110150.jpg


Now the tangs are at a more acceptable angle. And the bike works.

P1110140.jpg


I also had rebuilt the main jet needles incorrectly. Check them too.

Greetings
 
Thanks for the pictures, that first pic is similar to how I had mine set. Definitely bent too far.

Regarding how it was kept over the winter, it was actually leaning against a concrete block, which kept it relatively upright, but if anything, it would have been leaning to the left very slightly. Perhaps this made the left two more gummed up and I need to be more thorough on the cleaning.

Back at it I guess.
 
Well, good news, apparently the problem was that my bench sync wasn't done well enough so one cylinder wasn't firing. I had to do some tweaking of the sync screws while it was running to get all four cylinders firing. But I was able to ride it for the first time just the other day. The pilot circuit is still kind of groggy, but once the needle starts opening the thing shoots out of a cannon. It probably just needs to be synced better - with actual gauges instead of tapping the exhaust pipes with my hand to make sure they are all firing.

The bad news is that it leaks way more oil than I anticipated. I think the lower cylinder gasket (mates with crankcase) is the culprit. The oil drips right onto the ground for the back wheel to run over. Probably going to be a safety issue. Kind of a bummer...

Austin
 
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