91 with various problems

[bthritch1015]

So, I bought a bike which was ridden very hard I think....  I bought a 1991 GS500 with 17800 miles and I thought it ran fine (I thought) when I bought it.  It's my first motorcycle, previously I have had a bunch of 50cc scooters.  After I bought it I found I had poor (borderline) compression in both cylinders and idled around 3000rpm (which I did not know was wwwwaaayyy too high until I started looking into it) so I tore apart the top end, cleaned up everything and put new gaskets, and piston rings.   Now my compression is good.  I put in a carb replacement kit (all the gaskets but the floats are fine), and discovered that one of the diaphragms was distended as a result of a broken spring so I replaced that diaphragm and spring.  The air-filter box had been replaced with an aftermarket filter and an aftermarket breather for the crank case.  I built a carb balancing tool as described on multiple sites and I am planning on balancing the carbs tomorrow.  They were way out of alignment which I think was a result of the previous owner trying to compensate for the broken diaphragm spring.  I have it idling at around 1100 rpm, but it isn't smooth, which I imagine the carb balancing may fix.

Ok, so I have two main questions... the first is, what do I do to compensate for the aftermarket air filter?  It hasn't been re-jetted, should I do that?  I spent some time looking into re-jetting and that seems to be easy (buy new jets of a larger size), but I am not sure what I am supposed to do with the needle.  I see people talk about using a number of washers, what does that mean?  Does that mean they bought a new needle and used a certain number of specific washers to raise the needle to the correct height?  Any clarification would be great.

My second question relates to the transmission.  I have discovered that I can not get to 6th gear.  It shifts fine through 1-5, but will not shift into 6th.  Before I go tearing the transmission apart, I would like some information on what are some possible problems and what I should look for.  It seems to me like the clutch is a little worn out, meaning power gets to the tire when the clutch lever is out further than I would expect.  It has no problems shifting, but I do have some problems getting it into neutral when stopped.  If I am moving, neutral is easy to find, but when stopped it can take some up-shifting and down-shifting to finally find neutral.

Ask me any questions, and thanks for any information provided.

[Big Rich]

What kind of intake/exhaust are you running? With that info, you can pm Buddha and he can get you the exact jets you need.

Getting into 6th could be a bent shifter fork, but wait for some other ideas to pop up first. The transmission will only go from one gear to another after a gear is fully engaged (from the front sprocket rotating). So you can't sit on the bike while it isn't moving and click through all the gears. Pop it into 2nd, rock the bike a little, then pop it into 3rd, etc, etc. That would explain you neutral.

[bthritch1015]

So you can't sit on the bike while it isn't moving and click through all the gears.

Well, I have not been able to find 6th while moving either, and I can find 1-5 while sitting and driving. 

Thanks for the info about pm'ing Buddha.  I still don't know what "washers" is supposed to mean when talking about re-jetting (I am referring to information on this page http://beergarage.com/GSJet.aspx).  It has a K&N clamp on air filter, and I believe it is the stock exhaust.

[crzydood17]

whats the lever feel like when trying to go to 6th? Remember theres 6 gears but only 5 upshifts. 6th the pedal should be hard as a rock and not want to move up at all. What are your RPMs at 60ish mph. Do you know if its the stock sized sprockets?

If you only get 4 upshifts and the pedal feels like it can move up one more then you might have a problem with shift forks. If you get into 6th but its like neutral you might have bad teeth inside the box. I don't know the internals of the GS tranny but most share forks for 5-6th and if you get into 5th fine 6th should be ok too.

[bthritch1015]

whats the lever feel like when trying to go to 6th? Remember theres 6 gears but only 5 upshifts. 6th the pedal should be hard as a rock and not want to move up at all. What are your RPMs at 60ish mph.

down 1, up 2, 3, 4, 5, 6 right?  I'm going home early today to work on the carbs so I will double check my counting.  I did count them off a few times last night, but it is possible I was tired and couldn't count correctly four different times .  The pedal will move up slightly when I try for 6, but not much.  It feels much like when I have a hard time getting it into 1.  Oh yeah, probably should have mentioned that.  Sometimes it doesn't want to shift into 1.  When that happens I roll the bike about a foot and generally can get it to engage at that point, which also works most of the time when it does not want to find neutral.

I haven't had it to 60 since before I re-built the top end.  I'm still in the break-in phase where I am not supposed to exceed 5000 rpm, and I had to replace to fork seals last weekend which meant no highway driving prior to that.  I haven't wanted to put many miles on it while the carb's are not synced and I am unsure about the fuel-air mix.  I don't want to damage the work I have put into it. 

I don't know anything about the sprockets and if they were modified. 

[ryott52]

The sticky shift into first is pretty normal, especially if you're coming down from neutral. The issues going into sixth are a bit less common though. Occasionally my bike will give me a false neutral going into sixth, usually happens if I don't press firmly up on the shifter.

[noiseguy]

I always leave room to push my bike 6" to engage first gear.

If you're not riding interstates, you probably won't need 6th for awhile anyway. I'd leave it alone for now if not. I only use mine for extended cruising at +70MPH... 5th is fine for highway. Just saying. If your gearing seems lower, check your sprocket count to see if it's stock, or been changed. And their condition while you're at it.

Get it rejetted first. The lean jetting likely contributed to the low compression... stock rings should have lasted past 17K miles. Or run down a stock airbox.

Also, check your valve clearances if you haven't yet. Tight valves are common and cause similar issues to carb problems. Tight valves break and kill engines. Set them on the widest end of the tolerance.

Washers go under the needle valves between the needle clip and the diaphram... raises the needle a bit in the hole.

Make sure all the o-rings are in place on the carb... the tiny ones under the diaphram cover get lost, often, and cause a vacuum leak.

Bhudda is the best source for carb bits, o-rings, jets, and needle valves for these bike.