Made my running bike not run by a failed carb sync

C

CADC07

New member
Hello y'all. 2003 YZF600R Thundercat. Bought for $850, no fairings. Runs. My first supersport bike.

the bike ran for a solid 20km up to 8-9krpm. Wants to die off light throttle from idle

Really need a hand right now if anyone has advice. Currently struggling only because my neighbours have gone livid at the amount of exhaust coming from my bike/gas from the tank coming on/off while I was working on it and I can barely do anything to it anymore. I'm hiding my work and making sure theres no smells currently :(. my garage shuts but we're a connected unit, our garages /homes are connected just a wall between.

No more carb syncing while its running. (we're technically not allowed to do repairs, I've rebuilt my front end suspension 2x on another bike and WAY more, we got a couple rare complaints but it was never a huge issue)

So, I bought this bike 3 days ago, it runs, but has a massive throttle hang/delay/hesitation specifcally between 1-4K RPM.

I figured it was the carbs, so I took them apart, cleaned them, and to my astonishment they were spotless.

Every jet was quite quite clean. Not sure what the problem was, I put the carb back on, and tried starting it. Had nearly an entire day of troubleshooting, just to realize the bike won't start without the airbox. Lol.

Got starting and idling okayish, still has the same hesitation and hanging up to 4K. Jets are crystal clean, and I cleaned them anyways. I did the pilot, main, and idle, float bowls are correctly set, everything is attached.

Put in 4 plugs, spark is good. So, I start to sync the carbs to see if thats the issue. I got overzealous with my adjustments, caused the bike to rev crazy high, panic adjusted the carb sync screws, and then I spent another 2hrs going back and forth trying to figure out what the correct vacuum pressure is for the carb sync. No adjustments corrected the vacuum on cylinders 3-4, they are both somehow low on vacuum. Under throttle or high idle they would climb to about 11inHg though which was hopeful.

When I was adjusting the carb, I had cylinder 3at 5inHg and cylinder 4 at 1inHg, after I had 1 and 2 sycned to about 11inHg. so I started adjusting it to bring cylinder 4 up. I got 3 and 4 even for a short while, then the bike wanted to die on me. I wasn't giving throttle inbetween revs in retrospect. My mistake, one of many.

I figured I went too far, so I backed up a few, figured I was close, and started touching the last adjuster screw. This is when I panicked bigtime, and somehow the revs shot up. It's super loud, and yea I knew I was gonna get in trouble so I tried to stop it ASAP. That messed everything up. Now the second and third adjuster and messed up and the bike doesn't want to run. If I give it carb clean and really force it, it will run and die off in not too long, or climb up in revs and "idle"at 3-5k if it does wanna run.

I figure my only option now is to take the carbs off and "bench sync" them, and just hope thats enough to get it to run, then I can take it to a parking lot and do it properly this time, being extremely slow and careful with my fking sync adjustments. This has been a painful mistake. I needed to be way more careful, and count exactly how many turns I left from baseline so I could reset it.

Also if anyone has an easy way to make an external fuel bottle to hook up to my carb while im syncing, I would fking love you so much. Also what or where I can get fuel line cheap lol. I've had my gas tank on and working around it has been a nightmare.

Phew. Thank you for reading if you did. Appreciate any help. Please try to read as much as you can if you want to give advice.
 
CADC07 said:
I figure my only option now is to take the carbs off and "bench sync" them, and just hope thats enough to get it to run,
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After the "bench sync" done with a small drill (1/8. 1/16?) to make sure they all opened at the same time my old SOHC ran very good. It's the only sync it got. I'd say start there.
 
Don't even consider the shite they call fuel line at crappy tire. That clear stuff goes rock hard after one season ...or is it one use. Pay extra and decent stuff that stays pliable and usually comes in blue or yellow tint. FWIW the blue tint is way cooler than yellow. I'm sure switching to blue line on mine Wing would be good for almost 1/2 a second.
 
timtune said:
Don't even consider the shite they call fuel line at crappy tire. That clear stuff goes rock hard after one season ...or is it one use. Pay extra and decent stuff that stays pliable and usually comes in blue or yellow tint. FWIW the blue tint is way cooler than yellow. I'm sure switching to blue line on mine Wing would be good for almost 1/2 a second.
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I normally just use black. For this case, it seems like he is looking for something to feed the bike while the tank is off so the cheapest option should be fine.
 
CADC07 said:
Also if anyone has an easy way to make an external fuel bottle to hook up to my carb while im syncing, I would fking love you so much. Also what or where I can get fuel line cheap lol. I've had my gas tank on and working around it has been a nightmare.
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If you search for "aux fuel tank" on Amazon, there are some for about $20 if that's in your budget. Some bare tanks meant for mini-bikes or go-karts also come up for less that you could use to make your own by adding hose, but $20 is pretty reasonable for a tank with an on/off valve and hanger.

Where are you located in the GTA? Maybe a local GTAM'er would be inclined to come out and help.
 
GreyGhost said:
I'd hope if he was balancing carbs that his mixture was close to correct before he started (assumed he, playing the odds). If he has mixture problems and balance problems, he's making his life unnecessarily hard.
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The random revving etc are all symptoms of overly lean so is not starting without the airbox.

Sent from my Pixel 5 using Tapatalk
 
Just a thought...sure you don`t have a pinch or kink in the fuel line and any vacuum hoses are plugged into where they should be. When I used to drain carbs for winter storage I`d pull the gas line off the tap and pull the vacuum hose off the tap too, and stick an allen key in the hole so there was vacuum. As the gas emptied from the carbs, running them dry, it would pick up revs noticeably for a few restarts until empty.
 
If the carbs were squeaky clean, somebody was in there before you bought the bike.

I’d check the jet sizing, make sure it’s correct for your bike, consider exhaust type and any air box mods. Perhaps the last owner rejetted incorrectly.

Stock pilots are 38, mains 148, mixture screws should be 1.5 turns out as your baseline. Consult the exhaust supplier for recommendations if you have an aftermarket setup.

If you’re turning the mixture screw more than 2 turns, the pilot may be too small. If you are turning it in less than 1 1/2 turns, the pilots may be too large.
 
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