Carb piston valve question - left cylinder dysfunction

[adwags]

Hi,

Last week I purchased a 1999 GS500E with 6,700 miles (my first bike).  This group has been a great resource during the short time that I've owned the bike and while doing research before purchasing.  I ordered a Haynes manual from Amazon using the forum link.  This should help supplement the Clymer manal I got with the bike.

Anyway, I'm troubleshooting some problems and wanted to see if anyone has had a similar experience (didn't see an exact match when searching).  The previous owner had stored the bike in his garage for about a year before pulling it out and sending it to the local shop to bring it back to a road-worthy condition for sale.  I have the recepts...they cleaned the carbs, changed the oil and break fluid, installed new plugs, etc.  It didn't quite run right when I looked at it, running like crap at low RPMs and then surging.  I figured this could be due to the fact that there was a hose hanging off (which I later discovered was the air box drain) and that it had been sitting for a while.

The third day I rode it (in stop and go traffic) at a stoplight the RPMs shot up to 5k and wouldn't come back down.  I killed the engine, fllipped the throttle to see if it snapped back and then restarted.  Same problem.  The choke was off (fully forward)...I never even use it.  I then turned down the ide and managed to get the bike into a state where no matter what I did it wouldn't idle.  I limped home holding the RPMs up manually at stops.  After it cooled down I readjusted the idle screw and got it to idle fine.

The next day I realized that the right cylinder was much hotter than the left.  I followed some of the troubleshooting threads on the forum and eliminated electrical problems (tested resistance from the igniter harness through the coils).  I pulled out the plugs one at a time, grounding and cranking the engine to check for spark.  Both plugs looked okay (tan).  The left side sparked and had compression but I didn't smell fuel...the bike would idle on the right cylinder.  The right plug sparked but the engine wouldn't idle and I smelled gas within the cylinder.

So I pulled off the carbs and check that the floats looked symmetric between the sides (haven't tried measuring yet).  I then opened the tops of the carbs to check for symmetry.  I pulled up gently on the center of the left piston valve to check for movement and it snapped back down fairly strongly.  The right side was totally different, the diaphram lifting up and off easily.  I lifted the left piston valve a couple more times and it eventually popped off.  There was quite a bit of resistnace, almost like there was a vacumn under the diaphram.  I'm thinking that this was causing the left carb to kick in only at high vacuum.  Does this make sense and has anybody ever run into this problem?  I can't see how the piston could become stuck down.  The left side seems fine now, moving freely.

Sorry for the long post!

Thanks,
Adam

[The Buddha]

What ... no ... diaphragms comming off or not isn't a problem. Look for 2 little O rings right infront of the diaphragm. One missing (especially left) = your problem. 2 missing = bigger problem.
You have a vacuum line leak more than likely.
Cool.
Srinath.

[adwags]

Hi Srinath,

Nope, all of the rings are in place, especially the little ones (I've seen the warnings about losing them).  It was just weird because I lifted the piston up and in snapped back down (as opposed to needing to be pushed down by the spring on top of the diaphram).

I figured while I have the carbs off I should update the main and pilot jets and insert washers per the jetting FAQ for an otherwise stock bike.  Maybe turning the jets out and replacing them will clear out some debris.  I guess I'll see what happens when I put them back on.  Is there anything I couuld gain by further disassembling the carbs and checking around?  Any further ideas would be appreciated.

- Adam

[ducati_nolan]

While your carbs are apart, give them a real good cleaning, and blow out all the orfices and jets with compressed air after soaking in carb cleaner. I know you have receipts that the bike shop did this, but you know how some shops can be. Make sure there is no varnish or scores in the bole that the throttle slides ride in. When you put the thing back together, but some oil on the slides, so they work smothly at least for a while. Two stroke oil, marvel mystery oil, or WD-40 should work fine fithout fouling anything.

While you are putting the carbs back on, make sure your intake boots are in good condition and don't leak. Get out the manual, and make sure all the fuel and vacume lines are routed correctly and you don't have any uncovered vac fittings. This should do it.

If you still have a problem, do a compression check, and check your valve clearances.

If it still dosen't work, get drunk  then start kicking the sh*t out of the thing. Keep drinking and start lading your gun  then let out all your aggresions.

[adwags]

  I've taken the drinking and kicking approach before but not with carbs!  Seriously though, I'll try giving everything a good cleaning and see what happens.  Thanks!

[Egaeus]

I had the same problem.  It was after I cleaned my carbs.  Then I cleaned them again.  It ran better after the first time, but there was still some varnish in the pilot jets that loosened up and plugged them again.   I recommend cleaning them again.  That, and probably a rebuild.  The o-rings in my 99 were shot to hell. 

[adwags]

Just thought I'd post an update.  The bike is back in one piece now and runs like a dream.  I actually can't believe that I bought it running like it had been before but now I'm glad that I did.  It was running like crap when taking off (nearly stalling...bogging) and then surging...now it's smooth from the start and sure runs/sounds better on two cylinders than it did on one!

I cleaned/lubed the pistons, replaced the air filter with OEM and replaced the stock pilot/main jets per the rejetting matrix (plus added the washer).  I also attempted to balance the carbs but not sure if I actually did any good.  The air/fuel mix screws were already exposed and were way out (9 on the left and 10 on the right).  I couldn't really get the feel for adjusting them so just set them to three turns out.

Thanks for the help!  If anybody in the San Diego area ever needs help with any of this stuff I'd be happy to assist.  It really makes a huge difference.

[pandy]

Welcome!!!  Glad you got her running well!!!   

P.S. Tequila is still an option;  ya' just don't have to do the kickin' part now!