Frustrated with GS

[nslav]

Hello,

I bought a 93 GS to learn to ride and provide some entertainment for the summer... but unfortunately all it has provided so far is several weekends of frustration.  I noticed and fixed several problems myself, but now I am seriously stumped.  I replaced the stock air box with a K&N lunchbox and rejetted using the suggested 140/40 1 washer setting from the wiki (I have the stock exhaust).  This was intended to be a modification I would do at a later time, but after finding some sort of dead animal + nest in the stock air filter I decided to do it immediately to get rid of the smell.

After doing this, I fired up the bike.  It started and ran, but was chugging a bit up to about 3000 rpm.  At this point it would run pretty smoothly, but the revs would hang around 3000 when I released the throttle.  I also noticed that after the bike was shut off the carburetors were both moist with gas.  I tinkered with the pilot air screws and the idle screw a bit, which did not fix the issues.  Searching this forum revealed that what I was dealing with was probably a vacuum leak, and the gas leak could be caused by incorrect float height.

Today I set out to fix both these problems.  I pulled the carbs off and checked the float height as carefully as I could.  Both floats seemed to be incorrect, so I set their heights each to around 15mm.  I then reassembled the carbs and put them back on, this time being extra careful to make sure they were seated correctly and the clamps were tightened enough.  Fired up the bike, and since my idle screw was set high it revved up to about 4000 rpm and sounded fantastic.  I let it warm up a bit and lowered the idle to around 1200, and the chugging started again with a vengeance.  I'm not sure how to describe it, but it sounds almost like the bike runs on only one cylinder when between 1000 and 1200 rpm.  I played around with the throttle, choke, idle screw, pilot screws, but nothing seemed to help.  At this point I killed it, and noticed that the left hand carb was fairly wet with gas... again.

The only thing that I seemed to have fixed is the hanging revs.  Is there anything that could cause the carbs to leak like that, besides incorrect float height?  I could probably pick up some fuel hose to check it using that method, but I tried to be very careful when I was setting it.  The gaskets around the outside of the float bowl were a little stiff, could this be the problem?  Also, does anyone have any ideas as to why the bike would run so horribly until about 3000 - 4000 rpm, then sound great after that?

Sorry about the long post, but typing it all out made me feel a lot better.  This is the part where I was planning on asking for a cliff to push the bike off of, but my attitude isn't quite so poor anymore 

Thanks,
-Nick

[DoD#i]

Starting right in with modifications can be a problem. If you were starting from no problems, you invite adding them by mucking with stuff - of course, if you were starting with problems, it can be tough sorting out what problems you started with and what you might have inadvertently added though inexperience. Drop the stock airbox in a bucket of bleach-water, replace the air filter, no more smell...

Thus my boring old person advice to sort out any maintenance issues and put on 3000 miles before going all modification-happy. Too late for that, as usual.

You may have a bad float needle, where even if it's set right (height-wise) it leaks due to not actually sealing. The tubing to check float height is good because it doesn't lie, and it doesn't assume.

The improvement in running at high rpm may be that you are finally using enough fuel at that speed to overcome the tendency of the left one (from your description) to flood out and not run. Running on one cylinder can be diagnosed by checking (carefully, they give a nasty burn) for heat at the exhaust - also by yanking the plug wire on each cylinder - if one has no effect, and the other causes the thing to die, you've got a diagnosis.

As for the float thing (and some other possibles) check this recent thread.
http://gstwins.com/gsboard/index.php?topic=48213.0

While I'm not a big fan of hauling your bike to someone else (good ones are very hard to find) it can be worth it to have a knowledgeable mechanic go over a bike, especially if it's your first one. OTOH, where is you at, perhaps a GS Twinner can drop by and offer advice.

[LOUiE]

i find the clear hose method of checking the float heights to me more reliable.  I would try that method.  yeah, much more reliable.

It also sounds as if something isn't sealing right in your carbs.  Perhaps the your needle valve and seat aren't sealing properly, hence the overflow of gas.   look at hte tip of the valve if it's the least bit worn it might need to be replaced.  Or it might just need a good solid cleaner.  An aerosol cleaner and a toothbrush does wonders.   An easy way to tell if it's not sealing, is watching to see if your airbox drips when idling.   if so, one of the carbs isn't sealing right.  If one of your sparkplugs is wet too, it could be this problem.

Also check your mixture screws.  It's on the bottom of the carb by the float bowl.  They may have a brass cap over them, in which case don't touch them.  But if they don't I would make sure they're turned the same amount out.  I'm not sure exactly what the screws should be at with the K&N lunchbox, but the stock setting is 2 1/4 turns out.  Use the synch method (search the wiki) to sync them if you can.

good luck!

[nslav]

Thanks for the quick replies.  I should have time tomorrow afternoon to check out some of those possibilities.  Regarding the float needles, one thing I did notice when I had them apart is that one of them seemed to have a tendency to stick.  I cleaned it off and the condition improved some, but perhaps this is part of the problem?

I live in Amherst, Massachusetts.  If I were to take DoD's suggestion (which at this point seems like a good idea to me) and take it to a professional mechanic, does anyone have any recommendations of where to take it in this area, and how to get the bike there?  I rode it around the block last weekend when it was in a similar condition, and it seemed to do okay above 3000 rpm, but I am a very novice rider and I do not feel that I could safely get it very far on the open road.

[DoD#i]

You're about an hour and a half east/south from me, and I haven't got any other reason to head over that way at present, so I'm going to punt - 3-4 spare hours are not happening for at least a month. But there are some folks closer to you, I'm pretty sure.

Go ahead and see if you can get it running better by fiddling with or replacing the needles. Better, even if not perfect, may let you ride it to the shop, at least, sparing all the crummy options below.

Your best bet is a friend with a low-bed trailer - much easier to get the bike into and out of intact than a pickup truck. A pickup truck and 2-3 spotters/helpers is the other option, and a flatbed tow truck is the money option. I guess the u-haul truck or u-haul trailer is a probably less money option. Bike shop my have a truck themselves, probably costs less than either the u-haul or the tow-truck option if they do.

For any of those you need bike tiedowns - usually can get a set of 4 at any auto parts store or aisle. 6 or 8 is better, but 4 usually works. You want to compress the suspension about halfway with the straps connected form the top of the bike to tiedowns lower than that. If you have 6, tie one set from the bottom, to keep it from creeping sideways. Drive moderately, in any case.

[nslav]

Okay.  I am kind of against a wall here because I am moving to a new place across town next weekend, and the new place does not have any sort of garage.  I also keep fiddling around with the motorcycle instead of packing my stuff!

The good news in that regard though is I will have to visit u-haul no matter what for the moving.  If next weekend I still haven't gotten the bike running good enough to limp it to a shop, I can rent something that would be able to haul it as well as my other belongings.  Hopefully I will be able to ride it though, hauling does indeed sound like a pain.

[commuterdude]

You've got a bad frame petcock which has a torn diaphragm.   It is leaking allowing gas into the vacuum into the line to the left cylinder, flooding it out..   Replace the frame petcock with the unit recommended in the wiki for the Honda dirtbike.

[nslav]

That is an interesting thought about the petcock.  Would there be any way to confirm that?  It seems to me if that is the problem it will not leak unless there is vacuum present on the hose, so I can't just pull it off and see if there is fuel dripping out of it.  I guess I could suck on the hose a little bit and see if I get a mouthful of gas, but I think I'll shelve that idea because it sounds pretty dumb.  Because of the holiday I was unable to buy hose to check the float height... I have to be out of town tomorrow but hopefully Wednesday night I can check that out.

[DoD#i]

While buying hose, buy some "vacuum caps" (little caps to plug an un-used vacuum port).

Remove the petcock vacuum line. Plug its port (makes a nasty vacuum leak if you don't).

Run on prime - if your problems vanish, that was the problem (and you may well see gas dripping, without vacuum, too). If the problem persists, that wasn't it.

Or, if the vacuum hose is fresh and flexible, just clamp it shut with vise-grips (this shatters old brittle hoses.)

[nslav]

I figured I would update this thread now that I've got things sorted out a little better (even though its from two months ago )

Just before I moved out of my place I had the bike trucked to my dad's house, and we worked on it on the weekends throughout June.  After doing a compression test and ruling out problems with the petcock, we rebuilt the carbs.  This succeeded in stopping gas from leaking out after the bike was shut off, but it was still chugging really badly at low RPMs and hanging up at 3000 on the way back down.  We noticed a crack in the plastic piece of the driver's side carb, but spraying starter fluid at this didn't seem to have any effect on engine RPM.  Nevertheless we sealed it up with epoxy just in case.

At this point I took DoD's advice and changed back to stock jetting and bought a new element for the stock airbox.  When running the bike in this configuration with the airbox off, we noticed that gas was shooting out the back of the driver's side carb when the engine was chugging at lower RPMs.  We lowered the float height in that carb, which greatly reduced the amount of gas coming out (now it is barely visible) and eliminated the chugging.  With the airbox off, the revs weren't even hanging up anymore.  The next weekend I came back and put the airbox back on and put the bike back together, and it runs very smoothly.  I did notice that the revs hang up sometimes, but it is running very well otherwise and at this point I just want to get out and ride.

I took it the 80 or so miles from my parents' house to Amherst this morning, and it ran strong the whole way.  I think all it needs now to be really rideable is new tires.

[DoD#i]

Glad that helped a bit. Put on another 2920 miles and _then_ get back to modding it.

One local dealer has a supersport "with full muzzi exhaust" and something like 474 miles on it for sale used.

Guy could probably have saved the price of the new seat for it and the new underwear and pants for him by scaring the Shine-ola(tm) out of himself with the stock exhaust, but noooooo!

[The Buddha]

You replace the O rings in the float seat ?? - that can cause it to leak/overflow.
Spitting gas from one carb vs another - well the plastic top crack will not cause it to leak, and it really wont act like a intake leak either that much. If it lets in air into that part that is covered by the plastic part that cylinder will have a diaphram that will not slide up with increasing throttle position. It will make for a bike that caps off at 4-5-6-7-8 K under load depending on how much air its letting in. If its the size of a pin prick, it will barely make 4K. It is that sensitive.
I'd sell you a top for 5 bucks and $5 shipping for an 89-00 carb.

One other reason you can have 1 cyl spitting into the carb can be that its out of synch or the valves are hanging open in that cyl.

Cool.
Buddha.