Occasional miss/bog at idle - Gas in airbox

clofan · 04-18-2016, 12:42 PM

Having some issues with the GZ lately. I've developed a small-ish oil leak, I think it's coming from the valve cover as oil is visible on the very top fin. I had a leak at the acorn nut near the spark plug, but it went away (or at least greatly reduced) when I re-torqued the nut.

Next, it will start and idle/run, and do so OK. After maybe 30 seconds to one minute of idling, it will miss one revolution and bog down, stopping the engine a few seconds later. Interestingly, in some brief (but by no means comprehensive) testing I found I could replicate this by leaning the bike on it's kickstand. It would seem to idle longer if it is straight up, but as soon as I lean it on the kickstand it will miss, bog, and die. It will still miss/bog/die if it's straight up too, but I wonder why leaning it forces the issue. After it dies, it is harder to restart-- I have to give it a decent amount of throttle and it blows soot out the tailpipe after a few hard revolutions.

I have also been finding gas in my airbox after running. This has lead to an overly rich mixture, with visible smoke/soot out the tailpipe when running. I think this may be the cause of the miss/bog/die from the previous paragraph. I have been in the carb and the floats are good, the only modification is the needle shim mod which I plan to undo. While I have the carb out, I will drill the factory mixture cover so that I may have access to it.

Any thoughts on this? I plan to change the oil and filter (1500mi since last change), check timing, replace spark plug, undo needle shim mod and recheck floats. I just replaced the air filter yesterday, with no change in condition. I will eventually replace the valve cover gasket and maybe the upper head gasket too, but I realize that requires removing the engine from the bike so will need to dedicate a weekend with a buddy to help me with that. I think I can still ride with the oil leak until then, as long as I keep an eye on the level.

alantf · 04-19-2016, 04:42 AM

When you lean the bike on the kickstand things change - This suggests a problem with the sidestand relay. It's designed so that if you put the bike in gear with the sidestand down, the engine will cut out (to stop you riding off with the stand down) I suggest the first step is to check and clean the plunger, possibly using an aerosol contact cleaner to blast the cleaner into the switch, then putting the stand up and down a few times, then repeating the blast of cleaner.

clofan · 04-19-2016, 01:04 PM

Hmm, I will give that a shot; however, I don't think it's related to the switch because 1) I'm in neutral during the entire process and 2) the kickstand is down, even when I had the bike straight up. Doesn't hurt to clean the contact, though!

I haven't thoroughly tested the leaning thing yet, but it seems like it has something more to do with the carb fuel bowl or maybe aeration when the engine is at an angle.

clofan · 05-06-2016, 11:39 AM

Just a quick update. Compression when completely cold is 150psi. Checked valve clearances, got ahead of myself and loosened the locknut on one so I had to adjust it; the other three were within spec. Took the carb off and removed the needle shim mod, back to stock. Also drilled out the idle mixture cap, so I can adjust that now (left @ stock for the moment).

Warmed the bike up in prep for draining the oil, it started easily and maintained idle OK. It would miss and bog occasionally, after about a minute and a half of running, then more frequently until it dies. I think it's doing this due to a too-rich mixture, because there's black smoke out of the tailpipe and after-fires when letting off throttle after revving.

Drained oil, promptly spilled it all over my damn garage.

With oil drained, I plan to take off the side covers and 1) check my transmission as it's been slipping between 1st and 2nd occasionally and 2) check my QuikSteel repair from this thread: http://www.gz250bike.com/forum/showthread.php?t=6938 Also plan to replace oil filter.

I forgot to check if there was any gas in the airbox after warming it up last night-- got a bit distracted on the cleanup and called it a night. Spark plug is super carbon fouled-- I cleaned it up to warm it, but will replace it with a new one once I get it all back together and full of oil.

04-18-2016, 12:42 PM	#1
clofan Junior Member Join Date: Mar 2014 Posts: 29	Occasional miss/bog at idle - Gas in airbox Having some issues with the GZ lately. I've developed a small-ish oil leak, I think it's coming from the valve cover as oil is visible on the very top fin. I had a leak at the acorn nut near the spark plug, but it went away (or at least greatly reduced) when I re-torqued the nut. Next, it will start and idle/run, and do so OK. After maybe 30 seconds to one minute of idling, it will miss one revolution and bog down, stopping the engine a few seconds later. Interestingly, in some brief (but by no means comprehensive) testing I found I could replicate this by leaning the bike on it's kickstand. It would seem to idle longer if it is straight up, but as soon as I lean it on the kickstand it will miss, bog, and die. It will still miss/bog/die if it's straight up too, but I wonder why leaning it forces the issue. After it dies, it is harder to restart-- I have to give it a decent amount of throttle and it blows soot out the tailpipe after a few hard revolutions. I have also been finding gas in my airbox after running. This has lead to an overly rich mixture, with visible smoke/soot out the tailpipe when running. I think this may be the cause of the miss/bog/die from the previous paragraph. I have been in the carb and the floats are good, the only modification is the needle shim mod which I plan to undo. While I have the carb out, I will drill the factory mixture cover so that I may have access to it. Any thoughts on this? I plan to change the oil and filter (1500mi since last change), check timing, replace spark plug, undo needle shim mod and recheck floats. I just replaced the air filter yesterday, with no change in condition. I will eventually replace the valve cover gasket and maybe the upper head gasket too, but I realize that requires removing the engine from the bike so will need to dedicate a weekend with a buddy to help me with that. I think I can still ride with the oil leak until then, as long as I keep an eye on the level. Login or Register to Remove Ads
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04-19-2016, 04:42 AM	#2
alantf Senior Member Join Date: Nov 2008 Location: Tenerife (Spain) Posts: 3,719	When you lean the bike on the kickstand things change - This suggests a problem with the sidestand relay. It's designed so that if you put the bike in gear with the sidestand down, the engine will cut out (to stop you riding off with the stand down) I suggest the first step is to check and clean the plunger, possibly using an aerosol contact cleaner to blast the cleaner into the switch, then putting the stand up and down a few times, then repeating the blast of cleaner. __________________ By birth an Englishman, by the grace of God a Yorkshireman.
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04-19-2016, 01:04 PM	#3
clofan Junior Member Join Date: Mar 2014 Posts: 29	Hmm, I will give that a shot; however, I don't think it's related to the switch because 1) I'm in neutral during the entire process and 2) the kickstand is down, even when I had the bike straight up. Doesn't hurt to clean the contact, though! I haven't thoroughly tested the leaning thing yet, but it seems like it has something more to do with the carb fuel bowl or maybe aeration when the engine is at an angle. Login or Register to Remove Ads
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