So in a previous thread I ran into some issues after not stabilizing my fuel over an extended and very cold winter.

Ended up flushing the tank and spraying some carb cleaner in and having the bike run smooth as never before.

http://gstwins.com/gsboard/index.php?topic=66612.0


Since, I have had more failures to start. I chalked that all up to being cold and the bike being fickle. Today I went down nice 14 degree (Celsius) day and tried to start it to no avail. Switched out my battery for my girlfriends and it roared into life for about 30 seconds and only if I was giving it throttle.

After a few more moments it started to bog and unless I kept the throttle wide open it would die and even when I did it sat around 2K. If I let it die and sit for a few second it would start up and rev a bit but soon end up at the same fate.

It feels just the same as when the bike it down on fuel and I need to switch over to reserve. Doesn't seem to matter which setting the petcock is on and it has a full tank of fresh fuel (about a week old)

The nice weather is starting to roll in and I don't want to be stuck on a CBR 
What should I be looking for? Vacuum leaks? Bad petcock? Grime clogging my tank petcock?

Thanks again for any help.

Check your spark plugs and air filter, replace if needed.

Check for vacuum leaks next. If that doesn't get you going, start at your gas tank and recheck and reclean everything all the way into the carbs.

When did you last clean and sync your carbs?

Carbs got a decent spray down of carb cleaner 2 weeks ago, but due to a PO stripping the screws I was unable to actually pull them apart for a full cleaning, and  they haven't been synced since I took ownership a year ago.

The plugs were replaced at the same time. Currently there is no air filter in the bike. (waiting on a replacement).

I'll attempt a vacuum leak check if I can get it started this week.

No air filter could very well be your problem.  Too much air making the mixture more lean than it already is, would be a real pain to get running, especially when cold.  By your description, I was initially thinking it was fuel starved for one reason or another, but being an air hog would have a similar effect as well.

- Bboy

Quote from: BockinBboy on May 05, 2014, 06:59:53 AM
No air filter could very well be your problem. ......
- Bboy

+1 on that.  It's quite possible that previously you may have been running rich and the lack of Air Cleaner didn't make too much of a noticeable difference.

You've done so much carb cleaning ect, that if the carbs are now clean, adjusted and functioning the way they should, perhaps you're just "way lean" now..

Kind of like when someone leaves the snowblower in the shed all spring, summer and fall without draining fuel / using stabil etc.  They get so gummed up, the only way they'll usually seem to start is with starting fluid, no air cleaner and wide open choke! And then they only run for a few seconds.  After the carb is taken apart, clean, rebuilt and re-adjusted, they are usually on the lean side.  It only takes "a spec" of varnish, dirt, rust etc to cause issues.

Hmm, I didn't think of it that way.

When I first rode the bike it was horribly rich and spewed black smoke under heavy acceleration. When I pulled the filter this spring it was quite damp and the bottom part had come off making it just a spongy tube not doing anything.  When I took the airbox and carbs out I just left the filter out thinking it wasn't doing anything anyways.

Will replace and see if it helps.

Thanks again.

I see... its possible you may have several things going on here then.  I would suggest trying to get everything as close to stock as you can.  That is a proven setup guaranteed to work.  Once you have it running well stock, you can then add a change or a mod one at a time. 

- Bboy

So I took another stab at it. Noticed that the airbox wasn't on super tight and that the boots were misaligned, tore them down and put them back together.

Started it and it would idle but only at 1000rpm and without any throttle it would slowly drop to 500rpm and then die.

At a while of this (2-3 minutes) it wouldn't start without a heavy amount of throttle. Put the old airfilter in - no change.


Seeing as I didn't disassemble the carbs when I sprayed them with carb cleaner could I have ruined any of the gaskets in them? Would that lead to these kinds of issues?

I just don't understand how it could have run so beautifully one day only to not even run the next. I knew this bike might be some work but at this rate I'll be wrenching more than I'll riding this year.

You should take apart your frame mounted petcock and clean it/blow any debris out of it. They can get clogged pretty easily and not allow gas to the carbs. Also, once you finally crack your carbs open, make sure you blow anything and everything out of the main fuel passage ways. My old GS had three or four decent sized chunks of debris in the main fuel passage way, and after that it started up just like fuel injection (okay maybe not that good, but you get the idea).

You may also want to think about replacing the fuel lines. Gunk is probably everywhere depending on how long the bike sat. If you are worried about it taking forever to clean the carbs, it only takes one night to take everything off, take carbs apart, clean them, and reinstall everything. At this time you should also put the new air filter in. I did my first carb clean in one night, and that was my first time ever working with carbs. Very easy to do.

Good luck 

In reading this thread you said you had bad fuel and cleaned the tank and sprayed the carbs. This sounds like a dirty pilot circuit which is common with bad fuel and storage without clearing the carbs out. Spraying carb cleaner into the carbs will not clean this out...they need to be torn down and cleaned IMO.

Well I guess that means I have no option but to pull the carbs apart and do a full cleaning.

Any ideas what the best way to get the stuck screws out? If I cut the heads off can I pull the top off and use pliers to get them out, or are they threaded all the way?

First thing to try is to get actual JIS screwdrivers (if you haven't already stripped the heads).  To get those stubborn screws, use a dremel to cut a slot and use a flat head screwdriver to get them out.  You can also use an impact driver with a flathead screwdriver at that point; just don't be too rough or you will deform or crack the aluminum.  Replace the JIS screws with stainless steel socket head cap screws.

I agree on the full cleaning of the carbs.  Remove all jets and clean them (except for the air jets on the airbox side; they are tiny and strip too easy, and don't often need to be removed to clean).  Clean every passage with carb spray and compressed air.  Check all orings for condition, if they are squared/flattened or cracked replace them.  If a float bowl gasket leaks, replace it.  If the gas seals on the inlet T leak, replace them (requires splitting the carbs).

A few things that are often missed with cleaning carbs are these:

1. Old float needles that don't seal anymore cause flooding.  It's best to replace these with OEM (not cheap) needle valve sets.
2. Mixture screws not removed to clean the pilot circuit completely, and/or pilot jets not removed and cleaned properly
3. Emulsion tube is hard to remove, so people don't take it out and clean it thouroughly.  Best to remove this from the bottom by finding a screw with the same thread as the main jet and using it to tap the tube up and out.
4. Small jet integrated in the bottom of the plastic float not cleaned out, so the choke/enrichener circuit doesn't function properly
5. Vacuum leaks due to carb boots or airbox boots, missing vacuum port oring under the diaphragm cover, or leaky and/or stiffened diaphragms

Did I miss anything?

Ask me how I know on any of the above...

Another common way that I get stripped screws off (all too often) is to file down the edges with your common diamond pattern file, and then gripping the filed down areas with a pair of pliers. Good luck.

You will find that the carb rip apart/rebuild/ and put back together is surprisingly easy.

So I finally got around to cleaning up the carbs. Replaced a pilot jet because it was stripped but every thing else in there looked fine.

After getting them back on the bike it started up almost instantly. Idled okay but a bit rough.

The issue is now the throttle seems to hang a long time around 3500 after accelerating. There doesn't seem to be any power. And it feels like it putts, under only slight throttle it seems on and off instead of a solid power curve.

It was also smoking a lot out of the left side cylinder when it first started.

Could there be something wrong with the actual motor now?

I also fiddled around with the mixture screw a bit and that seemed to make a bit of a difference but still hovers at 3000-3500 rpm.