Pulled the bike out today for a carb balance.Started it up and let it warm.Went for the idle screw and BANG.Backfire!Blew the vacuum caps off the left carb along with that side of my K&N lunch box filter.Pulled the carbs to find the diaphram on that side blown to hell.The top of the slide hit the cap so hard that it left indentations in it.Any clue why.I have checked the valves.They're in spec.New plugs.Carbs were gone thru over the winter.The ignition system checks out fine using the Clymer manual technique.Tank is clean with new lines,fresh petcocks(both) and a brand new filter.It was running fine until this.All I want to do was some fine tuning. :dunno_white:
A really BIG nasty gremlin???? :o
Quote from: Teek on July 02, 2008, 12:21:37 AM
A really BIG nasty gremlin???? :o
I checked the Mikuni site.Appears the only thing that can cause this is an air leak or clogged main jet. :cookoo: My carbs are better than new internally and my intake boots are in like new condition.No other places for air leaks. :dunno_white: I will not attempt to start it again until I solve the problem.I can't afford new diaphrams every time I start the bike. :cry:
Chain tension for cams OK???
Maybe the valves jumped timing.
If it happend with the throttle closed the problem is related to the pilot system. It wont be the main jet if it happened on tickover. You have ruled out timing and air-leaks, that only leaves an incorrect (probably lean) mixture as the cause. So its down to a blockage in the fuel/airways of the pilot circuit, wrong pilot screw setting.......or, and this is my best guess......its still incorrectly pilot-jetted for the K&N.
Did you pull the plug on that cylinder and have a look at it?
Quote from: birdman on July 02, 2008, 08:36:04 AM
Chain tension for cams OK???
Maybe the valves jumped timing.
This was checked during the valve check.
Quote from: sledge on July 02, 2008, 09:22:03 AM
If it happend with the throttle closed the problem is related to the pilot system. It wont be the main jet if it happened on tickover. You have ruled out timing and air-leaks, that only leaves an incorrect (probably lean) mixture as the cause. So its down to a blockage in the fuel/airways of the pilot circuit, wrong pilot screw setting.......or, and this is my best guess......its still incorrectly pilot-jetted for the K&N.
Did you pull the plug on that cylinder and have a look at it?
This happened while the bike was idling with the choke off.Engine was warm and outside temps were in the low 90*F.My jetting is spot on for my set up.40/142.5/1 washer 2.5 turns.Everything has been clean and double checked.I replaced all fuel lines,fuel filter and installed a freshly mod no vacuum petcock.Rechecked the fuel levels in the float bowls.That's spot on.Pulled the plug and it appears to be running rich.They were black and sooty.This could be from using the choke for cold start up.I never really rev'd it to burn any carbon off the plugs.I had to replace the left carb body,but the replacement was in good shape after a good cleaning.All my fuel lines are correct.I have another set of carbs.I may clean them and rejet them.Give it another go.Could I possibly have broken loose some carbon, got it stuck in the intake valve, hanging it open ever so slightly.I may pull the intake boots and have a peep down the intake ports.
mine used to backfire wometime when i was starting it...
the little flange/ring thing that holds the header on was loose...
both sides
fresh air into the pipes + fire (exhaust) = BOOM in the pipe
Quote from: starshooter10 on July 02, 2008, 04:02:44 PM
mine used to backfire wometime when i was starting it...
the little flange/ring thing that holds the header on was loose...
both sides
fresh air into the pipes + fire (exhaust) = BOOM in the pipe
That's a backfire thru the exhaust.No problem there.My bike backfire thru the left carb and blew it apart inside.I've done a lot of carb work but never experienced this before.I am very particular about my bike.Everything as to be spot on an rechecked 3x before I will even connect the battery.Especially when dealing with the fuel system.I blew up,literally exploded,an 82 full size Bronco because my boss was rushing me.I didn't recheck everything.The metal fuel line wasn't seated correctly and leaked fuel onto a bad spark plug wire.By the time I went 50 feet to grab an extinguiser,I was laid out on a concrete floor from the explosion.Luckily,we start vehicles outside that have had fuel system work.It burnt to the ground before the fire department could drive around the block.So I now check everything 3x or more before I start the bike.Thing that worries me is, the bike was running fine, just vibrating a lot.I knew the carbs were slightly out of balance from where I had rejet.I didn't take time to rejet until I got the exhaust completely finished.So,I am at a loss.The teacher becomes the learner,on this issue. :thumb:
Yea my 89 did that a couple times. Back in 98.
Yea lost a diaphragm, and the vacuum spigot cap. Then till I replaced it it was terrible. heck it barely ran.
Post back here what happens.
Cool.
Buddha.
I have the unmolested all original 89 carbs.Mix screws still have there brass caps.They run ok with the stock exhaust.Sooooooooo,I'm going to break them down, clean them, and move my jets over from my rejetted 90 carbs.I'm also going to try checking the intake ports for carbon and junk.May be a valve hanging open.Hope to report back soon.
Mmm.. I have the same problem (from the left carb), some time now. I first noticed it when I rejeted and installed the lunchbox. Later I went stock again and it still persisted. Then I realized that I had this problem even before the rejeting (Same idle characteristics like sudden drop of rpm, though you don't realize it's a backfire when you have the airbox on)
Today I checked the valve clearances, the left cylinder Intake AND exhaust valves where less than 0.03mm, so I guessed this was the cause of the problem.. But now this makes me wonder...
Quote from: ben2go on July 01, 2008, 08:47:24 PM
I have checked the valves.They're in spec.
I still haven't messed with mine.I got the carbs done just haven't put them on and tested them yet.My girl friend had 2 strokes in a month and ended up in the hospital 3 times.Then her mother had eye surgery and we spent 6 days away from home.When I get my shipments out and everything here back in order, I will try another test and tune session.
Sorry to hear about your girlfriend. I hope that turns out for the best.
Carb problems seem like the smallest of your worries, but I hope you get that figured out as well.
Keep us posted.
WOW!I forgot all about this thread and I am back to somewhat of the same issue,again.
Problem 1-Occasional backfire through left carb,when idling,at a stop.
Problem 2-Occasionally requires a lot of rpm 3000-3500 to pull off without stalling.
Problem 3-Power level is off until 4000-4500 rpm.Then she screams.
Problem 4-Slow to return to idle,but has a stable idle.
So far I have completely dismantled and cleaned the carbs.I replaced all soft parts except float needles.I set the float height where the fuel level is at the split between the float bowl and carb body.Three turns out on the enrichment screws.My carbs only have a pilot jet and main.I haven't sync'd my carbs yet.Working on putting together a yard stick manometer.I did a valve adjustment while the carbs were soaking,and installed new plugs.
I believe I have narrowed it down to these issues.
1-Float level to low.
2-Enrichment screws need another half to one turn out.
3-Carb slide needles need another washer to enrich the mixture.Sorry can't remember the specific name for those needles.
4-Carbs out of sync.
Any other things that could be causing my issues?
Bike Specs
Exhaust-Right side D&D muffler from a Hayabusa.
Air filter-K&N lunch box
Carbs-40/142.5/1 washer/3 turns out
Reminder
Fresh valve adjustment and new plugs.
Quote from: laserred97gt on July 26, 2008, 11:10:55 AM
Sorry to hear about your girlfriend. I hope that turns out for the best.
Carb problems seem like the smallest of your worries, but I hope you get that figured out as well.
Keep us posted.
Thanks.She has gotten better since I orginally posted this.
Spark Plug Pics.
LEFT-The side that back fires through the carb.
(http://i205.photobucket.com/albums/bb17/ben_2_go/Motorcycle%20Stuff/sparkplugleft.jpg)
RIGHT-The side that seems to run normally.
(http://i205.photobucket.com/albums/bb17/ben_2_go/Motorcycle%20Stuff/sparkplugright.jpg)
Have you tried swapping the left and right coils?
Quote from: Big Rich on May 22, 2011, 04:53:12 PM
Have you tried swapping the left and right coils?
Good idea.
I have not, but they both check out when tested with my electrical meter.I know,it could be an intermitten problem after the coils warm up.I will give the swap a try after I double check for a vacuum leak at the carb boots.
Quote from: ben2go on May 22, 2011, 12:11:41 PM
Thanks.She has gotten better since I orginally posted this.
Thats great!
On the carby thingy, another thing could be ignition advance.
If I am not mistaken pre 04 models have two pick up coils.. could it be that the one of them is misplaced slightly??
The left plug seems to be running a bit richer than the right one.
Quote from: lamoun on May 23, 2011, 03:13:09 AM
Quote from: ben2go on May 22, 2011, 12:11:41 PM
Thanks.She has gotten better since I orginally posted this.
Thats great!
On the carby thingy, another thing could be ignition advance.
If I am not mistaken pre 04 models have two pick up coils.. could it be that the one of them is misplaced slightly??
The left plug seems to be running a bit richer than the right one.
I checked the ignition pick ups.They are tight and there is no adjustment on mine.I do have a 5 degree advanced ignition rotor,but that wouldn't cause only one side to back fire.I agree that it appears the right side is running just a little lean.Over all the plugs look pretty good.
Yesterday I readjusted the carbs and balanced/sync them.I installed new plugs and gapped them to .030in.Swapped the coils from side to side.The bike rode like a dream.This morning I started it up and the back firing through the left carb is back.I went for a quick 20 minute ride.The back firing is gone but now the left exhaust valve is knocking like h377.I just did the valves when I did the carb clean and balance/sync.I guess my weekend will be spent tearing down my bike to check the valves,again.
ben2go: what ended up being the cause for the backfiring out of the carbs and slow takeoff from a stop? I'm experiencing the same problems with my newly acquired GS.
Quote from: J banning on February 10, 2013, 06:44:37 PM
ben2go: what ended up being the cause for the backfiring out of the carbs and slow takeoff from a stop? I'm experiencing the same problems with my newly acquired GS.
I had weak voltage to the coils and bad spark plug wires.The wires can be purchased at any NAPA for a few dollars.Pull the rubber boots back at the coil and the spark plug caps.Then unscrew the spark plug caps then unscrew the wires from the coils.Righty tighty,lefty loosey just like usual.I did the ignition coil relay mod and posted it. http://gstwins.com/gsboard/index.php?topic=62039.0
Ben just beat me to linking his mod thread that included his fix. A good thread it is.
- Bboy
Quote from: BockinBboy on February 10, 2013, 07:48:38 PM
Ben just beat me to linking his mod thread that included his fix. A good thread it is.
- Bboy
Thanks.
Ben, thanks for the update!
woops old thread.
Quote from: J banning on February 11, 2013, 12:46:08 PM
Ben, thanks for the update!
You're welcome.I clean one set of carbs to the point that they wouldn't stay together before I started looking at the ignition system.Also,a regulator on the verg of going bad can cause some of the same symptoms.The coils get weak voltage and causes miss fires until the engine hits peak charging output which is usually between 3000 and 5000 rpm.There is a write up around here on using a mosfet based regulator rectifier.That is the way to go.
Quote from: Funderb on February 11, 2013, 07:22:28 PM
woops old thread.
No biggie.Post up.
Ok, I know that this has been beat to death, but I am having the SAME problem with the left carb. Along with this, my battery has been acting strange. 2009 F model:
1. From Idle, carb will backfire on the LH side. Only off of idle. Jets 20/65/142.5. Lunchbox, stock ex. Mixture 2.5 turns.
2. I ride year round, even when it's cold (sub 40*F).
3. Carbs clean and just synched, valves in spec.
4. Battery will go dead trying to crank below 30*. Stock Yuasa YB10L-B2. 2 years old (bought bike new in 2011) Water level OK. Jump or charge, and it's OK for a while, then will crank slower until dead.
Wonder if it's the regulator. I have the stock one. Time to get out the multimeter.
Quote from: jestercinti on March 14, 2013, 03:15:32 PM
Wonder if it's the regulator. I have the stock one. Time to get out the multimeter.
You get a Karma Korn just for using the word
multimeterMy bet would be a battery not holding a charge. But with your
multimeter you will be able to tell.
If you do need a regulator, I have a box of them. Or best is pay the $100 for a MosFet one. Give your baby the best.
Adidas, a Multimeter is the BEST $10 I spent at Pep Boys. I get them free now with a coupon at Harbor Freight.
I should have a contest like John to give them away as prizes to noobs.
Quote from: adidasguy on March 14, 2013, 03:32:08 PM
Quote from: jestercinti on March 14, 2013, 03:15:32 PM
Wonder if it's the regulator. I have the stock one. Time to get out the multimeter.
You get a Karma Korn just for using the word multimeter
My bet would be a battery not holding a charge. But with your multimeter you will be able to tell.
If you do need a regulator, I have a box of them. Or best is pay the $100 for a MosFet one. Give your baby the best.
I agree.However,that didn't solve my problem.It helped.Check the entire charging system.It took me doing the relay mod to get rid of my problem. http://gstwins.com/gsboard/index.php?topic=62039.0
Well, I checked my charging system using the Haynes manual, and several trusted documented methods (GSTwins, GSresources).
It's the stock Yuasa battery. Thinking of going maintenance free this time. My water level keeps fluctuating. Some may say that has to do with the regulator, but I checked it 4 times, and it appears OK. Stator is OK as well.
If I still have the issue, I'll try the relay mod. Looking at the diagrams, it makes sense. There are a lot of switches and connections in the circuit for sure!
I would think it is the battery going bad. Mine didn't last much beyond 2 years (2009 and stock battery).
Measure battery voltage.
Later, like next morning or in a day, measure again. It should not go down.
Riding: you're not riding for 12 hours so if the battery is going bad, it might never get recharged. On a charger for 12 hours is more charging than when riding for a couple hours. Riding you may only be putting back 90% rather than 100% to keep it charged.
I have a voltage monitor on my bikes. It seems around 3k RPM is the tipping point between using power from the battery and charging the battery. If you do lots of short rides, you may never be at high enough RPM to fully recharge the battery. If your battery is going bad, it could take a lot more to recharge it.
Try battery. I bet that is it.
Yep. Most of my trips are 10-20 miles. Short jaunts here and there.
Battery is on my short list.
I'm going on three years on my AGM Scorpion battery from battery stuff.My bike sits in an outbuilding for three months during the winter.My bike always starts right up after sitting.I been very happy with this battery.