Recently bought a 1993 GS500E. I installed a new rectificer,battery,ingition,plugs,gas cap, and many other things. First thing I did was clean out the carbs, Let them soak in a ultrasonic cleaner and then replaced the gaskets on it. Heres my problem. I can start the bike in any temperature on a cold motor without the choke on. Just a second on the starter and it fires up. It idles to about 3,000RPMS on cold then if I blip the throttle it will go back to the 1200 RPM idle range. I can leave it idle all day like this no problem. If I try and ride it like this I wont be able to ride more than a mile without the motor starting to cut out and bog on me. First thing I thought was a fuel problem right? Well I unscrewed the drain screw on the carbs and they are all still full of fuel. I can even see the fuel flowing in the fuel filter. Alright so the bike stalls out, I could sit there all day on the starter and the thing wont start back up until the engine completely cools down. ALSO it does burn alittle bit of oil ( I believe its oil) when I start it up cold. But after a few seconds it doesn't burn the oil anymore. I thought maybe it would be a leak around the carbs so I sprayed choke cleaner all over and couldn't find anything. I made sure the throttle plate on both carbs were about the same gap in each (As I do not have a vacuum guage yet). There is one valve on the intake side that it out of tolerance since I cant fit a 0.0015 feeler guage in it. I don't see if that would be the problem. I'm stumped on this one.

Quote from: garagemonkey on August 18, 2016, 05:05:28 PM
*snip* There is one valve on the intake side that it out of tolerance since I cant fit a 0.0015 feeler guage in it. I don't see if that would be the problem. I'm stumped on this one.

Very well could be the problem.  I had bikes that would do the very thing you're talking about.  Turned out to be tight valve clearance.  Bike would get hot, stop running well, I'd park it for an hour or two, fire it up and it'd be fine until it heated up again.

If that didn't do it or you have some doubt then perhaps check to make sure the coils are operational at high temp.  Occasionally these can malfunction at higher temps.  Do it the easy way first, pull the plugs (don't burn yourself) and check for spark.

It could still be the carbs.  I'd open the tops and check to see if they were reassembled incorrectly at some point.  It can be easy to get the sequence of the needle assembly mixed up.  Check to be sure the choke slide is not binding up and causing the bike to over-fuel.  This happens a lot on these carbs and would explain the way your bike starts initially.

Good luck...have fun with it too.  It's like solving mysteries.   

I have a carb rebuild kit on the way since I took the carbs apart and the gaskets seen better days. Everything seems to be in tip top shape though other than the orings and gaskets. http://gstwins.com/gsboard/Smileys/New_Smile/woohoo.gif What I did notice however was the fuel would only flow from both petcocks if I slowly turned the valve on the tank. There would be only about a 1-2:00 turn area where the fuel would start flowing. Every other turn would be off. Then on the petcock I noticed that the fuel would only flow from the reserve valve and not from anything else, including prime. I took it apart and found no dirt or anything. I think it would be better just to replace both petcocks. But that goes with one of my questions. What would a vacuum problem be like. How could I tell if I have a vacuum problem in the bike.

FWIW it sounds to me like the pilot needle is set too rich. Starts cold without choke and dies when it gets hot ... that's what mine does too.

I'll let you know if fixing the pilot mixture fixes mine, in my other thread. But worth it to check your plugs, see if it's running rich.

Of course if you do the carb rebuild then you will fix this as a matter of course. Or make it worse, or make everything worse, and have to dial it all in

Quote from: garagemonkey on August 18, 2016, 05:05:28 PM
I can even see the fuel flowing in the fuel filter.

If it's an automotive filter, remove it, if it's a MC Fuel Filter carry on....

Try without the fuel petcock

You guys thinking it's an insufficient fuel problem, I don't think the symptoms support that theory.

It sounds to me a lot more like a too-rich problem, where the bike will only run OFF CHOKE when it's COLD.

Poor fuel delivery (filter/petcock/etc) would not have this effect.

IMHO ... but I'm no expert on these bikes. Just learning about my own.

Quote from: mr72 on August 26, 2016, 01:59:17 PM
You guys thinking it's an insufficient fuel problem, I don't think the symptoms support that theory.

It sounds to me a lot more like a too-rich problem, where the bike will only run OFF CHOKE when it's COLD.

Poor fuel delivery (filter/petcock/etc) would not have this effect.

IMHO ... but I'm no expert on these bikes. Just learning about my own.

As soon as I read "filter", that potentially problematic item has to be taken out of the equation because the bike does not come with one.

I got my valve shim removal tool today. Took the intake shim about and it was 0.009tho off tolerance. Thankfully the bike shop guy let me just swap shims. I garage ran the bike with no tank or air filter on to see how the carbs ran. It seemed like when I gave it throttle it reversed the flow of fuel and shot a stream (not a mist) of fuel back out of the carb where the air cleaner would be installed. As for the choke situation I discovered that my starter cap ( choke plungers) were old and   leaking so it was constantly sucking air in through there. Might do a rejet of the bike after I do a complete teardown of the entire carbs and get a full size picture of the carb diagram.

The thing shooting mix out the carbs could be a timing issue, as well as a spark timing issue.
However you can have some of that reverse flow issue just from a engine that revs up and back down. So there is a fine line between normal and bad behavior.

Cool.
Buddha.

I did a carb tear down today and discovered I installed the diaphragm springs wrong. Instead of going on top of the needle to compress them they were inside the needle. Rookie mistake. So I got the bike to idle and rev up. Not sure how fast these bikes are suppose to rev up. I know from dead idle if I hammer on it it takes a second or two to actually rev. I read that's the job of the pilot jets. Anyways I notice at idle one diaphragm wants to slowly move up and down maybe 1/16 or so but the other side doesnt move at all. It will move though when I give it throttle. My guess is the carbs need syncing.