It ran fine after valve job - won't now!

[49er]

I think Paco13 has suggested the most likely cause. You probably have had some gunk in your auxillary tank drawn into your carbs. You will need to give them a through cleaning, especially #2.
While you have the airbox and carbs off the engine, replace the weathering strip that should be completely sealing your new K&N filter. Your engine will run lean until you fix that seal. While your working on the airbox, check the condition of the seals on the end caps as well! They also need to have an air tight seal.

[JMHJ]

Ok guys, I think I'm in business again, but I don't 100% know why.

I did some more plug swapping on cyls 1 and 2 and ended up replacing the #2 plug with one of my old ones (I saved 'em since they didn't look bad).

All cyls seemed to be working after that (although exhausts 1 and 2 weren't as hot as 3 and 4) and I took a test ride. After a short warmup, the bike seemed to run nice and strong, and all the pipes were hot when I got back.

So maybe something was wrong with a plug? It looked ok, and I didn't see any bristles in there. I still don't know how swapping plugs 3 and 4 brought cyl 4 back online, but maybe it was something else I did .

I will see what tomorrow brings. I'm leaving the fuel supply (a 20oz pop bottle with a hole in the cap for fuel line, with an inline filter above the carbs) hooked up overnight. Hopefully it will run again, and I can try the carb synching before putting the tank back on.

Thanks to all for the suggestions. - Mike

[TheCafeKid]

Also a SUPER dumb question probably, but if i had never been told or asked i may have never known back when either, but on your new plugs, did you pull off the lil screwcaps on the plug side of them? Yeah i know...but like i said, id have never even thought of it either...

[JMHJ]

Yeah, I took them off, and saved them too .

[TheCafeKid]

Welp im certainly glad its running better. Maybe you just got unlucky and had a couple of bad plugs, or wirebrushing them did something that you couldnt see. Id get a new set however and see if that at all makes any difference just to be sure.

[82Shafty]

1) I'd make sure your vacuum operated petcock is supplying the necessary fuel that you need

2) Make sure that the vacuum line going to the petcock does not have any tears, seals well on the nipple, and does not kink when you reinstall the tank.

3) you could always check the amount of fuel that comes out of each bowl and verify that it is of equal quantities.

4) after it runs and you dial it in, I would try some water in a spray bottle around your spark plug wires and coils to make sure that none of the insulations is breaking down.

5) A bad plug can cause two cylinders to go down with the wasted spark theory.

[RobGS850L]

Just my .02 worth. I've noticed on my 850 that the carbs do take awhile to fuel up when they are emptied. The bike runs real bad if at all while the carbs are filling back up. Also gravity plays a big part in remote fuel sources. The weight of the fuel has to be enough to get through the needle and seat assy. and also not so much as to have too much pressure to keep the needle from seating. I run a longer fuel line and vacuum line from the tank to the carbs and then raise the tank on 2 2x4 blocks. Gives me room enough to make all my adjustments and lets the bike run as if it were in a normal all put together situation.

[chef1366]

I mentioned bad plugs but deleted my post thinking it was too simple.

[bwringer]

I'd cast a jaundiced eye toward the plug caps. If you're using the stock coils, new NGK plug caps are cheap and widely available for a total of around $15-$20 a set, so it's worth doing whether or not you're currently having a problem.

If you're using aftermarket wires and coils, you'll also want to double-check the innards of the connectors.

And yes, sometimes you just get a bad spark plug. It's rare, but it's happened to me three or four times.

Are you using the correct original NGK plugs?

[paco13]

Now hold on a minute, In your description of your aux. fuel supply you made no mention of a VENT. If you don't have a vent hole in the bottle it is not gonna gravity feed the carbs very well. Might be cause of problems. You weren't getting ample fuel to the bowls.
Do you have a Vent?

[82Shafty]

Now hold on a minute, In your description of your aux. fuel supply you made no mention of a VENT. If you don't have a vent hole in the bottle it is not gonna gravity feed the carbs very well. Might be cause of problems. You weren't getting ample fuel to the bowls.
Do you have a Vent?

Quick; somebody poke a hole in the bottle!!!

[JMHJ]

Good to go now, as near as I can tell

Yes! I think the fuel setup was the main problem. There was no vent to speak of, other than between the line and the hole in the cap, which wasn't much . Once it was flowing well it seemed fine, but I guess it didn't work consistently. I think I will try to use the tank next time also. Either that or at least actually vent my bottle.

I did get the carb synching done today, but had some trouble with the poor running in the middle of it. Thankfully though, after tweaking around with the fuel, it smoothed back out long enough to get it done. I set the outer cylinders with slightly more vacuum than the middle ones. I hope that's right.

I got it all back together this evening, and took a ride to fill up, and otherwise test it. The bike definitely has more power now than before, so something musta went right.

I still think one of the plugs is bad too, and I've got an old one in place of it. I may swap the new one back in there before too long to verify. Can't afford another set of them just now. I've also got the original coils, wires, and caps on there as far as I know. I accidentally rode several times last year in heavy rain without any problems, but those parts are a year older now.

Thanks for all the replies! I think I've learned a few things, and I hope I'm good for a while now. - Mike

[paco13]

For sync and adjust I usually just turn the tank around backwards and sit it were the seat would be and bungee it down. I use longer fuel and vacuum lines to reach carbs, just watch for kinks. On bikes were the frame/tank shape doesn't allow this I use an old plastic push lawn mower tank strapped to the frame with an inline valve and filter, and block the vac port for petcock.

Yes still sounds like new plugs are needed.