Only running on one cylinder.

[draggindakota]

2001 VS800 with 13k+/- miles. I can't get this damn thing to run on both cylinders at idle and it's driving me nuts. I know it has to be something simple, because it ran good before I tore it apart. At higher RPM's it will run on both, but at idle it only runs on the front cylinder. Confirmed by pulling plug wires. And also confirmed that the rear coil is firing. Cleaned the plugs as well.

Long story short, I had an electrical issue (R/R plug melted) so I took the opportunity while the bike was apart to do some other work like installing a new fan switch, clean the carbs again and install a new o ring on the front bowl since it had been leaking. I had plans on re-doing the carb sync since it wasn't 100% at idle. The bike ran fine, but on first start it took a few seconds for the rear cylinder to catch and at low speeds was a little jumpy I guess you could say. After cleaning the carbs I tried a bench sync like I've always done on sport bikes and threw everything back together. I've since backed the sync cable out to it's original location pre-teardown but still get nothing at idle. What am I missing here?

[Lechy]

Do a carb synch using a "U" tube manometer, then adjust the AF screws. Replace the battery earthing cable and make sure all surfaces are bright and make a good circuit.
All adjustments for the synch are on the front carb, rear adjuster is for idle, forward adjuster is for running. It's a bit of a balancing act but take your time and you will get it right.
If you still have problems, check the boots on the carbs for correct fitting, leaking boots will give a problem. Pull the covers off the carbs and check the diaphragms for correct seating, pin holes or tears, make sure the slider for the main jet is not hanging up.
Your low running jet could still be blocked so use compressed air to blow out the lines.
Then get back to us with details of what you have done for more ideas.
There are loads of odd-ball things that can make these bikes run like crap and troubleshooting can be a bit of a 'mare.
Check your spark plugs, you should not be using resistor plugs (designated by an "R" in the number).
Could be as simple as dismantling the innards of the plug cap and cleaning up or replacing the rubber boot on the end of the cap.
[emoji41]

[draggindakota]

I've been trying to do a carb sync, but it won't run on the rear cylinder at idle so I'm not getting anywhere. I could do go ahead and do the 2500 rpm sync but what's the use at the moment?

Since the r/r plug melted I went through and checked & cleaned all the battery and electrical connections. When I had the carbs off I soaked all the jets over night in Seafoam, cleaned all holes with a guitar string and compressed air (same process I use any time I clean a carb) and checked the floats & needles, checked the float heights and the diaphragms. Also pulled the plugs and cleaned them (stock replacement NGK's) and pulled the plug wires apart, cleaned and trimmed the wires. I also inspected the boots and intake manifolds while the carbs were off, and have taken the rear boot off and re-installed several times trying different things.

The one thing I'm not entirely sure about is the rectifier. I suspected it was bad, hence the melted ground wire in the plug, but it seemed to test out ok after I cut the plug out ad hard wired it. I may go ahead and swap it though.

[enforcer]

To decipher whether it's a fuel issue at all, have your checked for spark at idle? If you have spark, it's not your r/r (which I doubt it is anyway) Could be a partially clogged pilot jet, misadjusted mixture screw, or you're not doing the static sync correctly. To do a static sync, put and equal gauge wire under each butterfly and take the slack out of the idle sync cable. Also, when performing the idle sync, make sure you have slack at the grip.

[Lechy]

Fire the bike up, get it idling on one, turn the butterfly quadrant on the rear carb and see if it comes up to idling on both cylinders. If it does, you are way out on the synch.
Just a thought, remove the tank, on the front air box is the cable splitter sometimes one of the cables can slip out of its seat.
[emoji41]

[draggindakota]

Yep, getting good spark at idle on the rear. I checked the plug wires, trimmed the wire, cleaned the caps and reinstalled to be sure. With it running at idle you can hear the exhaust popping trying to run on the rear as well. Just the slightest pressure on the throttle brings it online. When it's idling, if I adjust the sync cable to the toward the rear carb the bike starts to sputter and die, so I don't think it has anything to do with the sync at this point. Just seems like it's not getting air to the rear.

I thought maybe it was the throttle cables, as the rear carb cable jacket is separated from the adjuster on the carb end. Been that way since I bought the bike though. I pushed it back in, secured it in place and lubed the cables with 3 in 1 oil. Also completely disassemble the grip again to make sure it wasn't hanging up in there.

One thing I did do was adjust the float heights while the carbs were apart. It's possible that I messed up on that. Does anyone have the pic of the reference marks on the carbs for fuel level check? I had it bookmarked on IA but, well that ain't workin right now so...

If that fails I guess I'll pull the carbs again and start from scratch.

[enforcer]

Again, your diagnoses is incorrect. If the float was set improperly, that cylinder wouldn't run at all. It sounds like your static sync is still off. Does it try to fire when you turn the idle screw in? That screw adjusts the idle for both carbs, but if it's too low on the rear and you tighten the sync cable until the front runs, the rear won't. Turn the thumb screw until the rear fires then adjust the idle sync until it's somewhat smooth. You can use your sync tool to fine tune.

[Lechy]

Re-read my last post.

[emoji41]

[draggindakota]

Thanks for all the suggestions guys. I finally got a couple days to dedicate to working on the bike (out of necessity - my truck engine took a crap ). The separated rear throttle cable was giving me fits, so I glued it temporarily. I also had the idle adjustment screw backed out all the way for some reason. Might have been going from memory of one of the walk throughs on IA or just out of frustration lol. But cranked that in finally got it synced up as good as it will get until I get the new throttle cable. Its actually running better than before and the r/r seems to be working fine. Not sure why it suddenly decided to melt wires but oh well. Thanks again

[enforcer]

To anyone reading through this, looking for answers to a similar problem, every situation is different. It's important to reason through the issues you're having and not just jump to conclusions and start replacing parts. Troubleshooting requires going through a thought process and eliminating possible culprits first before deciding what the issue is and that holds true for anything with moving parts.