Exhaust Valve

[knotzilla]

I just found out the reason for low compression in #3 cylinder. (see link below) Does anyone have an idea what caused the crack? Also, if someone has a spare exhaust valve for a 1980 gs850g they want to sell, please let me know. Thanks Ted

http://i42.photobucket.com/albums/e326/knotzilla/Valve-1.jpg

[bwringer]

That's not really a crack -- that's erosion from high exhaust gas temps.

I have two GS850 exaust valves sitting in my toolbox that look much worse than that!

I keep them as a reminder to NEVER continue riding a bike showing symptoms of a lean mixture. It's sort of like keeping a severed head on a stake to remind visitors to behave...

Anyway, my exhaust valves burned out several years ago, before I knew about this site. I later found out the cause of the tragedy was leaking intake o-rings, along with crumbled foam seals in the airbox.

All the above led to extremely lean running, which means extremely high exhaust gas temperatures, and leads to nauseating sights like that exhaust valve.

I rebuilt the carbs many times, I cursed, I wailed, I replaced the ignition system, I checked the air pressure in the tires and the supply of blinker fluid. None of it did any good because I had no idea those intake o-rings even existed -- the manual made no mention of them. Tragically, I continued to ride the bike despite the fact it would barely get from one place to another.

Here's a longer summary of the problem:

http://cycleorings.com/intake.html

Here's the cure:

http://bwringer.com/gs/intakeorings.html

You can still order new valves from Suzuki -- they're $30.16 :shock: from the fiche at http://flatoutmotorcycles.com , which is probably the cheapest price you're going to find.

http://www.z1enterprises.com/ is a good source for the gasket set.

[knotzilla]

My plugs are a bit on the white/grey side. Would lowering the diaphragm needle 1 notch be too much or should I add a spacer washer. Thanks Ted

[bwringer]

You do not need to make changes to the carbs if you have the stock exhaust and airbox. You do need to make sure the airbox is sealed so that air only gets in where it's supposed to, and you also need to make sure you don't have any intake leaks via bad intake boots or o-rings.

Make sure both side covers on the airbox are sealed with weatherstripping foam. You will also need to use the foam to seal the top of the metal air filter "cage" so that there's a nice tight seal against the top of the airbox.

If you have an aftermarket or altered exhaust or have discarded or altered the airbox, then, um, good luck. You will need to make jetting changes to the carbs, but there is no all-purpose recipe for doing this. You will have to experiment and read the plugs, and you'll get really good at removing the carbs.

[txironhead]

It's sort of like keeping a severed head on a stake to remind visitors to behave...

Wow, you do that, too?:-D

....the supply of blinker fluid.....

Wait! Crap! That's not listed in the manual! How do I check that?!?!\\/

[bwringer]

My plugs are a bit on the white/grey side. Would lowering the diaphragm needle 1 notch be too much or should I add a spacer washer. Thanks Ted

Oh look, there's a linky thingy I didn't see earlier. DOH!

OK, you seem to have the stock airbox and an aftermarket exhaust. You definitely want to keep the airbox -- getting these carbs to work right with pods can be challenging.

To richen the midrange mixture, you'd actually want to RAISE the needles using teensy washers -- IIRC, you can get teensy washers that will work at Radio Shack. Start with one washer under each needle and see how that works.

You also will need to play around with the idle screws and float heights to get a good off-idle transition. You might need to drop the float heights by 1/2mm - 1mm.

You may not need a larger main jet, but once it's idling well and working nicely in the transition and midrange, you might do some full-throttle plug reads and see. The stock jets are 115, so you might maybe possibly need to go to 117.5 or 120.

AFAIK, there aren't any Dynajet kits available for the GS850, but all the pieces you might need are available.

[knotzilla]

I have the stock air box and a 4 into 1 exhaust. The intake boots are in good shape. Would a slight popping noise from the exhaust during deacceleration in the 3000 rpm range indicate a lean mixture. Thanks Ted

[bwringer]

I have the stock air box and a 4 into 1 exhaust. The intake boots are in good shape. Would a slight popping noise from the exhaust during deacceleration in the 3000 rpm range indicate a lean mixture. Thanks Ted

Yes -- popping is a lean mixture. It can also be caused by intake or exhaust leaks, so make sure that's squared away. In your case, since you've pretty well gone through that, odds are it's the jetting.

With the 4 into 1 exhaust, you will definitely be running lean with stock jetting. Lean=hot=not good for exhaust valves...