gs450 - still not running right

[bren]

i'm getting frustrated, i need help thinking through this. let me just put out some basic obvservations i've taken.

the left cylinder is way richer than the right one still.

the only way i can get it to idle evenly is to back the sync screw out really far. when i put the carbtune on there, it shows much more vac pressure on the left cylinder. but if i sync it up, it idles unevenly, and it still takes a long time to come back down to idle when i blip it.

the right pipe is running way hotter than the left one.

the left side was puffing intermittently at idle when it got really warmed up.

i looked at the plugs after about 10 or 15 minutes of mostly idling. the left plug is starting to turn brown. the right one still looks basically brand new.

• what i'm trying to understand is, is the left cylinder too rich? or is the right cylinder too lean? how can you tell?
• if the cylinders are this different, then, if there's an air leak, it's gotta be after the carbs, not in the airbox, right?
• this could be caused by the right carb still not being clean enough? or the right side float being too low? what else?

i'm looking for troubleshooting suggestions, thanks for reading

[Nessism]

Have you gone through all the items in the Newbie Mistake thread? Post up everything you have done.

[bren]

thanks, i read it again. i decided to start over on the carbs. i read through the carb dipping guide again, it says to leave the parts in there for 24 hours... the can says, 15-30 minutes. So maybe they didn't get clean enough the first time. I'm gonna leave them in there for the full length specified in the guide.

other than that, i did the carb o-rings, the valves, the boots, boot o-rings, even replaced the ignition, which turned out to just be for fun in the end. checked for air leaks with carb cleaner, for what that's worth. it's gotta just be that i didn't clean the carbs right. if that's not it, then i'm really at a loss.

[Big T]

The vacuum diaphragm on the fuel tap is bad and is dumping extra fuel into the left cylinder.

Test - remove the vacuum line from the fuel tap and plug it with a bolt. Run the bike on Prime and see if the issue is gone

[dgates1]

The vacuum diaphragm on the fuel tap is bad and is dumping extra fuel into the left cylinder.

Test - remove the vacuum line from the fuel tap and plug it with a bolt. Run the bike on Prime and see if the issue is gone

Agree with this. Simple test to eliminate the petcock.

[bren]

Agree with this. Simple test to eliminate the petcock.

sorry guys i've ruled that out. the petcock's not even on the bike right now. i'm running the bike off a gravity fed aux tank straight to the carbs

[KiwiAlfa156]

Are you sure it's running on both cylinders? Get it running and try pulling the plug lead on the side with the clean plug and see if anything changes. Replace the lead and try the other side. Report your observations.

[Zellock]

Having this exact same issue with my GS450T; I replaced the carb boots, and I'm marking it up to an air leak on the new boots. I put a liquid gasket between the engine and the boot (being very careful to keep it on the exterior of the O-Ring to ensure nothing gets into the engine area) - It's currently drying for 24 hours, then I'll throw the carbs on and test. If it fixes, I'll give you a hollar, bren.

On mine though, I could see a very tiny sliver at the top of the boot where it didn't look like it was seating properly. Thanks Jeff Bezos.

[bren]

alright, well... i let the carbs dip all night long, they should be medically clean now.

I put it all back together and started it up ... i'm not sure if it's fixed, but it's definitely different.

Now, the left cylinder is running about 100deg hotter than the right. so they swapped. but i synced it and it does seem to be running somewhat better. but still not right. once it cools back off i'll start it back up and post a video.

so that's a clue; there are several parts that I might have swapped between the carbs, i didn't take great care to put everything back on the same side that it came off of;

• the choke plungers; if one is leaking gas, it might be richening that carb;
• the floats; maybe one is too high/low. Maybe I need to run to the parts store and pick up some clear tubing and take an actual fuel level measurement.

i might try strategically swapping parts between the carbs and see if that narrows anything down.

kiwi alpha - yes, it's running on both, but it's still not quite even. it's "rhythmic", like when you're expecting it to say "ticka ticka ticka ticka ticka ..." it's saying "ticka ticka tick tick ticka ticka ticka tick tick ticka ..." and it seems to be the left one still that's not firing consistently (edit, i realized when making the video that you can't tell from the exhaust which one is missing). it evens up if i mess with the carb sync. i'll make a video here in a few.

[bren]

alright, here is a video of it running

while running, i showed the carbtune, and adjusted the sync back and forth, and then put it back to center. when i blipped the throttle, it hung up (edit, i realized watching it back, i didn't put it back perfectly centered. even still, with it spot on, it comes down but it takes several seconds).

i then showed the temps after running for a couple of minutes

[bren]

Having this exact same issue with my GS450T; I replaced the carb boots, and I'm marking it up to an air leak on the new boots. I put a liquid gasket between the engine and the boot (being very careful to keep it on the exterior of the O-Ring to ensure nothing gets into the engine area) - It's currently drying for 24 hours, then I'll throw the carbs on and test. If it fixes, I'll give you a hollar, bren.

On mine though, I could see a very tiny sliver at the top of the boot where it didn't look like it was seating properly. Thanks Jeff Bezos.

yea, interesting theory, best of luck, but mine is the same way. it's the o-ring that makes contact with the head, not the boot. the actual boot doesn't fully seat flush with the cylinder head.

[bren]

i just swapped the floats; no change. so that's eliminated.

every other part i could swap:

1. pilot jet
2. main jet + bowl (one of the mains is a little stripped so i didn't remove it when i dipped it, to keep from stripping it worse)
3. emulsifier
4. slide
5. choke plunger
6. pilot screw

i'm getting really good at taking the carbs off and putting them back on...

i hope it's not the choke plunger. if it is, i think i'll have to buy a second set of carbs to rob for parts ... i'm not finding a choke plunger assembly online, even in the parts fiche... but that would make sense that it's the choke plunger leaking. considering how many people wanted me to check that the petcock wasn't leaking fuel into the carbs...

but i have a good feeling about where i'm at ... i feel like i'm honing in on the real problem ...... a lot better of a feeling than throwing parts at it and hoping!

[bren]

1. pilot jet
2. main jet + bowl (one of the mains is a little stripped so i didn't remove it when i dipped it, to keep from stripping it worse)
3. emulsifier
4. slide
5. choke plunger
6. pilot screw

one more down. swapped choke plungers. no change.

calling it quits for the day.

tomorrow i'll start with the pilot jets. maybe one of them is messed up / still clogged.

[KiwiAlfa156]

The video was interesting. A question, when you are adjusting the carb sync and it runs more evenly, are you opening the RH carb more in relation to the LH (good cylinder) carb?

[bren]

i believe that when i turned it and it started running better, i was turning the sync screw counter clockwise, which on my carbs, opens the right butterfly. which i suppose would make sense if the right carb is currently running leaner than the left one.

edit: hang on, now i'm getting confused, lol! currently it's lefty that's running hot. let me re watch the video real fast.

edit 2: okay, so at 2:37 in the video, i realized the screwdriver was out of frame, but there where i paused turning it, it was centered up and the carbtune was balanced. when i turned clockwise, the idle cleaned up, and that was closing the right butterfly in relation to the left one. so it still stands to reason that opening the left butterfly would clean up the idle if lefty was running lean and having trouble firing. (edit 3: actually, the idle set screw props open the left carb, and the sync screw adjusts the right carb in relation to it. clockwise closes the right, ccw opens it.)