flooding/petcock issue

[kevsgs]

I've been trying to get my 83 gs550 es going for a while, I've been doing a bit of fixing it up, but I'm having a problem with flooding. I've been reading the forums and it sounds like I have a petcock issue but thought I would throw this out to the experts for some opinions and advice. When I got the bike it had a flooding problem, which from what I've read seems to be somewhat common of a problem. At first thought it was a valve seat/o-ring/needle valve problem. Completely cleaned carb, O-rings looked good, needles and seats looked good. So we thought maybe it was a float height adjustment that was needed. We could set the float height so extreme that no fuel would flow in so I knew o-rings were good. After taking carbs on and off many times opted to just put in new set of valve seats and needles. Also tried using a different set of valve seats and needles before new OEM ones were installed. Every set including new ones would all react exactly the same, they would stop the fuel flow when set way above factory recomended height, and as we slowly backed it off, (.025" at a time), they would go from no fuel to flooding. So I then found this site, and reading some of the forums sounded like it was a petcock problem. So tried it all again. Sure enough we had the petcock on "PRI" and the float bowls would just flood. I pulled off petcock to make sure nothing wierd was happening and it seemed to work like normal. Well before taking it off I could turn the switch to what I thought was off but was actually on and no fuel would come out even with the engine running. After taking off petcock the fuel finally stopped flooding out, by not puting in PRI position anymore, and would stop the fuel when the engine is off. So half my problems solved. But now the problem is when the engine is off, no flooding, but when it is running and the throttle is not being turned, so its just sitting at idle it continues to flood. I thought the valve needles should keep this from happening, is this just normal for this carb? Doesn't seem like it should be doing this. Does anyone have any advice? Is this normal?

[kevsgs]

replacing petcock

I do realize the next logical step is to replace petcock with new OEM, which is what I plan on doing, but after thinking it was the valve needles and seats and replaced them and that did nothing, I just wanted some more input before I do replace petcock because it seems to be functioning as it should be. I also know the floats are fine as well.

[koolaid_kid]

Testing the petcock

If the carbs start flooding immediately after turning the petcock to PRI then you have either the float level set too high or the needle and seats are leaking. I personally left mine on virtual PRI* for hours while tuning the carbs.

*Virtual PRI is using a temp tank attached to the handlebars so I can remove the fuel tank to adjust the carbs.

I suggest the following:
First, test the petcock -
When set to PRI, fuel should flow all the time.
When set to ON or RES, fuel should not flow when there is no vacuum (engine off).
When set to ON or RES, fuel should flow when a vacuum is applied (to the vacuum line, you can suck on the vacuum line to simulate the engine running. Be careful on this one, if the diaphram is leaking fuel could get into the vacuum line.
More in the next post (testing the carbs).

[koolaid_kid]

Testing the carbs

Remove the carbs and place them on your workbench or working space. Be prepared for a fuel leak by putting them in a pan or something to catch the fuel.
Make sure the carbs are perpendicular to the ground to simulate being on the bike on the centerstand.
Now, using a temp tank (I use a radiator overflow tank purchased at the local auto parts, about $10) attach the tank to the carbs. This simulates the real tank being on PRI. Try to match the distance of the fuel level to the carbs about the same as your tank when it is full of fuel.
The carbs should not overflow for at least 5-10 minutes. If they do, you need to remove the fuel bowls and check the float level. Be sure you are measuring correctly (found on BassCliff's site, latest version of Mikuni carb rebuild doc). Also remove the needle and clean both the needle and the seat with carb cleaner.
Repeat this procedure until your carbs no longer leak for a minimum of 5-10 minutes. Once they no longer leak you can reinstall them.
Also, get a whiff of your engine oil. If it smells like fuel, you need to change the oil and filter. Don't bother to do this until the carbs no longer leak.
Best of luck, hope this helps.

[kevsgs]

will try again

Just checked the petcock like that this weekend. The fuel flows in PRI position, and does not with the motor off, no vacuum. You can suck on the vacuum line and it will then pour out the fuel. When the engine is running and set just to on for petcock, it will still flood the bowls. So does this mean it is a valve seat and needles problem? I just replaced them with new OEM. I've tried taking them off and repeatedly adjusted in small increments. I can set them so high that they don't allow any fuel in, and then slowly back off at 0.025" increments, but as soon as they start to allow fuel in they just continue to fill until flooding in the PRI position. With engine off they will fill but not overflow with petcock in just the ON or RES position. As I said they are new OEM factory sent valve needle sets, I don't understand why they won't stop the fuel at the appropriate level in PRI position though. But I will spend today taking them apart and trying to clean them thoroughly again, and slowly raise float level and see what happens. Thanks for the advice.

[koolaid_kid]

Your petcock passes the tests, so concentrate on the carbs.
If you have not done so, download this document: http://www.mtsac.edu/~cliff/storage/...d_Tutorial.pdf (a link also exists on BassCliff's website)
Pages 55-57 shows how to set the float level. It must be exact, +/- 1mm. Don't bother with playing with varying levels; even if it does not leak it will not run correctly with the float level set incorrectly.
Once the float level is set correctly, then you can start on the needle and seats.
If it still leaks, it is the needle and seat. Did the o-rings come with the new seats? If not, you need new ones.
Again, don't bother playing with different float levels. You also need to use a caliper rather than a ruler for accuracy, as shown in the tutorial.

[sedelen]

Just checked the petcock like that this weekend. The fuel flows in PRI position, and does not with the motor off, no vacuum. You can suck on the vacuum line and it will then pour out the fuel. When the engine is running and set just to on for petcock, it will still flood the bowls.

I'm not familiar with the '83 GS550es petcock. I'm wondering if it is a 3 position, Prime, On, and Reserve, or the 2 position, On and Prime. You stated above while in Prime fuels flows but doesn't with the motor off because of no vacuum, then suck on the vacuum line and it will pour out, and when the engine is running and set to on, it will flood the bowls.
Well, Prime is a gravity flow position, fuel should flow whether the engine is on or off. And "On" is the position which works with the vacuum line. Could it be that you have your petcock positions miss identified?
And that is one reason why a bike should only be put on Prime for short periods, like if the bike hasn't been run in awhile, then once started put back to on, otherwise you run the risk of overflowing the carbs, since the "Prime" position always allows fuel to flow.
The "On" position should stop the flow of fuel when the engine is turned off, as there's no vacuum to allow the fuel to flow. If your petcock is working properly, and you have it in the "on" position, no fuel should flow to your carbs and they won't overflow.

[kevsgs]

another failed try

Well broke it down again, factory spec for float height is 0.81 in. (+-.o4"), which is where I had it set using the calipers. I tried setting it to 0.875 in. and it still flooded. I set the higher depth and turned petcock to PRI position, I know its the PRI position because its the only time fuel flows without any vacuum, I did this while I had the tank on the bench and the carb sitting just about how it sits while on the bike. It was actually stopping the flow of fuel, so I put it back on the bike. Then when I put it on PRI it flooded till I turned the petcock to the on position. Then it only flooded when the motor was running. While carb was out I cleaned and inspected the brand new valve seat and needle and both looked perfect. The O-rings looked good, and when floats are set so high that it wont allow any fuel in, wouldn't this mean the O-rings are good? But they are cheap so just to make sure thats not it I'm ordering new ones after I'm done here. I didn't order the O-rings with the valve needles because I had 6 sets that all were good and have tried multiple ones to make sure that wasn't the problem. But I don't want to chance it being something as dumb as that so I'm ordering new ones. I'll let you know how it turns out after I get the new ones in. If anyone has any other suggestions, I'm wide open to them. Thanks.

[cowboyup3371]

You're floats are not set correctly as .81 inches equals 20mm. Check your measurements in mm and then compare against what the book says for your bike. I think it should be ~23mm

[kevsgs]

Just checked the numbers again in the manual and they are 0.81in (20.5 mm).

[kevsgs]

The new O-rings should be here by Friday night, really can't believe I didn't just order them with the new valves and needles, hopefully that fixes it or I am truely lost, with new valve seats and needles and petcock seems to function properly, the o-rings are all thats left that would be questionable for it to work. I'm trying to stay hopeful.

[kevsgs]

"I think it should be ~23mm"

In 83 they switched to a different carb, I believe they only ran this carb for about three years, lucky me trying to find parts for it.

[cowboyup3371]

Yea sorry for the misinformation; just looked at your service manual

[kevsgs]

So correct me if I'm wrong, but if my petcock is working as it should, the only other possible reasons for flooding would be the valve seat, needles, or the o-ring right? Even if the petcock is on PRI position, for this year and model, the float valve needles should be stopping the flow of gas and not allowing flooding correct? I cant wait to get this flooding fixed, when the engine is fired up the motor sounds very strong, very excited about getting it out on its first ride.

[koolaid_kid]

There are only 3 reasons they should overflow:
1) Needle/seat has contaminates.
2) O-ring is not sealing correctly.
3) Float level is too high.

I am in the middle of testing just such a scenario. I have a bank of 1100E carbs that I have connected a temp tank to. After 1 hour passed one needle and seat started leaking. I consider that a failure. If a cleaning of the needle and seat does not fix this, I will replace them because that is a failure IMHO. I am a bit pickier than some, but I have left this configuration on for literally hours at a time with no leaks.
The carbs have been rebuilt with a cycleorings set of orings, using Nessism's rebuild guide, which is what you should have done when you cleaned your carbs.