Hi everyone!

I just bought my first motorcycle, a 1994 Suzuki GS500E, and at 400 bucks, I got a steal of a deal. There are a couple things I need to do (bleeding the brakes, replacing the chain and sprockets, etc.), but there are also a couple things I'm not sure what to do to fix yet.

There are few things that seem odd with the throttle, and I'm betting that at least two of them are related. The first being that when I crank it, it hesitates around the 2-3k RPM range, the problem seems to lessen a little bit the longer the bike warms up, but it never really goes away. It also doesn't seem to have any issues if I just ease onto the throttle.

Another issue is that if I hold the throttle at 2k RPMs, after a few seconds, it'll shoot up to 6k and just hold there. This issue doesn't really appear when holding at higher RPMs.

The last issue, that may or may not be related, is that the RPMs seem to drop slowly compared to what I think it should. My roommate has a 95 Honda Shadow 1100 that will drop from very high rev (no tachometer, so I don't have a specific RPM) to idle in one or two seconds. If I rev up to 6k or so, it seems to take about 3-4 seconds to drop down to idle.

All in all, the bike is ridable, I've been having a great time, plus I'm just glad that I'm finally on two wheels. 

Thanks in advance! 

The second issue you mention, a delay in revving down to idle, is commonly called "hanging idle" and usually the premise is that it is running lean.

However, your other issue makes me think you have a vacuum leak. So I'd check there first, then deal with the lean/hanging idle.

http://gstwins.com/gsboard/index.php?topic=71047.0

Vacuum leak can cause the rising and hanging idle, I'd start there.
Spray some carb cleaner around the carbs and a change in idle will indicate a leak.


What air filter and exhaust are on the motorcycle?  I wonder if it's jetted inappropriately as well.

So I went out on a ride last night and checked for a vacuum leak when I got home. I sprayed some carb cleaner on the intake boots and noticed an immediate change in idle (noticed after each one individually, both are bad), so I definitely have to get those switched out.

I'm not sure about the intake, but the exhaust is stock except it has 2 holes drilled into the baffle. I haven't had the opportunity to pull apart the carbs yet, but I'm thinking about getting a rebuild kit to make sure the right jet sizes and everything are in there. However, if it's already having an issue of running lean, I wonder if I should go with one size higher on the jets.

Thoughts?

You really should read the wiki. Top of every page. http://wiki.gstwins.com

It has a ton of great information for exactly what you are dealing with. I only gave my link on the vacuum leak thing because there isn't a wiki on it.

There are a ton of places for a vacuum leak to occur, not just the intake boots. So definitely replace the intake boot o-rings (and maybe the boots too), but while the carbs are off, seriously replace every single o-ring in them. That's my not so humble opinion. And replace every vacuum hose.

You know to be very careful with carb cleaner. Don't spray it on any rubber part (including those intake boots!) since most carb cleaner will degrade or readily dissolve rubber parts. Most importantly, don't spray it in your carbs while they are together, not unless you have taken every rubber part out (all o-rings) ESPECIALLY the diaphragms that are under the covers. Carb cleaner will straight up destroy those diaphragms. And it's not nice to paint either. Anyway, that's why I don't recommend the spray-carb-cleaner method of finding a vacuum leak. On a GS500E there are so few o-rings to replace and so few places for a vacuum leak to occur you are just way better off ruling it all out. By the way, be especially careful with the "little o-rings" that are beneath the vacuum ports on the carb covers. They easily get lost and you wind up with a very hard to find vacuum leak.

You should probably jet up one size on the pilots (to 40) if you are at a low elevation. If everything else is stock, the stock main jets are probably ok but you might consider jetting up one size there too (125) if you are at a low elevation. I have 40/127.5 in mine with stock everything except Yoshimura "slip-on" (it's actually bolted/welded) and from a mixture perspective it's perfect. It's probably safe enough to change these jets while the carbs are off and then tune it once it's together, but believe me further tuning is a fool's errand until you are absolutely sure there are NO vacuum leaks. You cannot tune it with vacuum leaks.

Good luck.

Thanks for your help. I knew that carb cleaner could cause damage to paint, but I wasn't aware about the damage it could cause to rubber. Luckily I sprayed it on after I had been running the bike for awhile (I had just ridden the bike home), so the carb cleaner evaporated very quickly, and I had only sprayed it on the boots.

I had already planned on rebuilding the carbs while I had them off anyways, part of why I was thinking about the jet sizes. I found a rebuild kit for both carbs for just under $50, and I should be able to get new jets for about $20-25. But for the intake boot, O-Rings, and the single vacuum hose (since I have the 1st gen), do you have any recommendations on where I go to purchase? I'm trying to keep costs down as much as I can, I don't have a whole lot of money to invest, unfortunately.

Quote from: CLBreen on November 03, 2016, 12:53:48 PM
I had already planned on rebuilding the carbs while I had them off anyways, part of why I was thinking about the jet sizes. I found a rebuild kit for both carbs for just under $50, and I should be able to get new jets for about $20-25. But for the intake boot, O-Rings, and the single vacuum hose (since I have the 1st gen), do you have any recommendations on where I go to purchase? I'm trying to keep costs down as much as I can, I don't have a whole lot of money to invest, unfortunately.

I'm not sure I'd go with a rebuild kit. You can away with not replacing the main jets so save your $12 there and get the 40 pilots from Buddha here on the forum or elsewhere, like $10-12. Then just get specific rebuild parts, like a complete set of o-rings including intake boot o-rings from here: http://www.thisoldtractor.com/for_sale_dr350_orings.html  and then get float needles on ebay or elsewhere, they are cheap. You can probably recycle the bowl gaskets. You do this and the whole job will be like $30-40 or less in parts. Don't forget the o-rings on the pilot adjustment needles (screw on bottom of carb).

Somewhere around here I posted a whole list of which o-rings to get. You might be able to search and get part numbers. I bought them one or two at a time and paid for shipping each time like a fool. Don't be a fool like me. Get them all at once.

Maybe a little overdramatic about the carb cleaner.

Does it eat rubber/plastic?  Yes.  Will spraying it on/in the carbs damage it?  No.

Unless you're dousing your carbs in it you wont harm anything.  You use so little and it evaporates WAY too fast to do any real harm in the vacuum leak test.  A split second spray is all it takes.

Cleaning the carbs with it is done with the carbs apart and at that point if you didn't take the seals out you deserve to ruin them...

Just to give an update, a few nights ago, the vacuum leak got a whole lot worse, and I hadn't chance to purchase the parts I needed yet. Seeing that I new that the primarly cause of the leak was either with the intake boots or the o rings underneath, I went ahead and went over to O'Reilly's and bought some o rings that were very similar. They didn't fit exactly, but I had already spent awhile taking the bike apart, so I managed to make them work and it created a good seal.

I put the bike back together wrong, as I found out, but it's primarily running alright now, I think I just have to make some adjustments to the idle and fuel mixture screws.

I still want to take everything apart and replace everything else, but I'm glad the bike is working in the meantime, thanks for your help.

Quote from: CLBreen on November 09, 2016, 11:59:21 AM
I put the bike back together wrong, as I found out, but it's primarily running alright now, I think I just have to make some adjustments to the idle and fuel mixture screws.

Did you get it put back together correctly eventually?

FWIW if you have the stock pilot jets (37.5) then I'd say set the idle mixture screws to three turns out and leave it alone because you can chase your tail a LOT trying to dial that in if you don't have everything else sorted. The bike will run and probably close to right on the money like this. Then set the idle speed so that it doesn't have a hanging idle.. basically as low as you can get it without it drooping.

Ride it for a while this way tinkering with the idle speed in tiny increments until it idles right and then do a plug check to assess the mixture situation.

Did you get it put back together correctly eventually?

[/quote]

I did! I found out that I plugged the hose from the fuel inlet on the T in between the top of the two carburetors into the vacuum line on the petcock, and had just left the vacuum hose unplugged on accident. Once I realized what was wrong, taking the airbox back out showed me the exact error of my ways, haha.

Yet another update!

So after I replaced the intake boot o-rings with my emergency surgery, the bike ran great for the first day. Then the second day... Not so much. The hanging idle issue got waaaaay worse. Like the RPM's wouldn't drop at all as I went to change gears. So today I decided to pull the bike apart again and try cleaning out the jets, seeing as I already had carb cleaner lying around anyways.

Pulled the float bowls off, and they're just covered in buildup, the guy I bought it from probably lied to me when he told me cleaned the carbs. (Unless he was talking about the outside of them, since the outside was spotless, haha.) Not to mention, as soon as I pulled the float bowl gaskets out, they practically fell apart. So full rebuild on the carbs it is.

Igck!

Well, at least we're heading down the right set of tracks now.