Barely runs(too rich?)

[bbancsov]

So i just got done doing my top end motor rebuild and carb cleaning and am having some issues. First off the bike would only start when i had the throttle at WOT. After it started it was backfiring left and right (im thinking the ignition timing isnt 100%) spot on. Will look into it after i get the carbs sorted out, i pulled them off to clean them and now the bike starts when i hold the throttle open but it doesnt rev and stumbles as i let off the throttle to eventually stall. Going through the carbs i've noticed their not the stock jets.

Cliffs:
- Was running really rich
- Fixed small oil leak behind ATU, reinstalled
- Was backfiring through carbs (sparks, pops)
- Runs very rough now, stalls when let off throttle
- Still suspected to run rich
- Pulled carbs apart, check jets compatibility

1979 XS650 Special
- BS38 carbs
- K&N Pod Filters
- Wrapped stock exhaust
- I can't get the pilot jet out to see what size it is, here are some pics.

What do you guys recommend i do next?

 

[5twins]

I don't know why guys do this, throw their fucked up carb set back on a fresh rebuild, but I see it all the time. I guess they don't realize that carb set could very well be the reason they were rebuilding in the first place.

If that is a 145 main I'm seeing in there then it is very rich. With the K&Ns looking to be your only mod, you only want one, maybe two sizes up on the mains (137.5 or 140). You're going to need to get the pilots out, whatever it takes. There's a good chance that whoever put those large mains in bumped the pilots up as well. If you even do need bigger pilots, all you'd want is one size up (#30). Both the main and pilot size increases will require that your needles be leaned a step. I'll bet that wasn't done which is also contributing to your overly rich condition.

If you marked the timing plate when removing it before the rebuild then installed a new timing chain and put the plate back on those marks, your timing is off. You'd best correct that before running the bike too much more. Messing with the carbs will do no good anyway if the timing is off. You're not going to improve the way it's running, only heap unnecessary abuse on your fresh rebuild.

 

[bbancsov]

The cam timing is on, its the ignition(points plate that might be a hair or two off) It was static timed not finely tuned. So im going to fix that tonight, the carbs came like this from the PO and the bike ran fine before the rebuild so it's hard to believe that it's running so rich now when i didn't change the jets. Oh well, so the 145 main has to go down? I'll get the pilot out as well, here's a photo of the other jet. I think these may not be stock as well...

 

[5twins]

Those are probably the stock needle jets. There's not much available to change them to. If original, they'll be stamped "Z-2" on the side. With the way it is hard to start and requires wide open throttle, plus the fact it won't run at lower speeds, I'd say your pilot circuit, and probably the choke jets too, are plugged.

 

[bbancsov]

Yes they say Z-2 on them, just pulled the main's, both say 145. Pulled one pilot and it says 27-5 or 275 can't really tell. But the other one is plugged for sure, i also can't get it out so i 'm going to let that sit for a bit and soak and try it again. It's weird that they're plugged when i put brand new in line fuel filters in. What exactly are the choke jets? Do they have something to do with the plunger that is set to lift when choke is on?

 

[5twins]

Those are 27.5 pilots and are the originals (with no air bleed holes). When you install brass jets, they don't have to be really, really tight, just a bit past snug. They seem to get tighter on their own the longer they're installed, don't know why. Use a small or stubby screwdriver for installing your jets. That way there's less of a chance to over-tighten them. Put them in with a full size screwdriver and you're pretty much assured of getting them in too tight. A proper fitting screwdriver is key as well. The jets are soft and the screw slots bugger up easily if the screwdriver doesn't fit well. I use a knurled bit holder because it's small enough not to over-tighten with and there are a multitude of bit sizes available. You can find just the right sizes or even grind one down if need be.

The choke feed jets are near the bottom of the bowls off to the side. If plugged, the chokes won't function because they can't draw any fuel in. That makes cold starts very difficult and may be why you need to compensate by using large throttle openings. The choke jet is pressed in and can't be removed. You'll need to poke or blow it clear with compressed air .....

Here's how to tell if they're clear .....

 

[bbancsov]

I'll check and clear those tomorrow. It looks like im going to need new pilots, the one that was stuck would not budge, i finally got it out but its beat to hell. So should i go with 27.5 pilots and 137.5 mains or 140's?

 

[5twins]

Since you're basically stock except for the pods, I'd say go with 137.5 mains. Even they may require leaning the needle. If you do that, you'll need #30 pilots.

 

[bbancsov]

Leaning the needle would mean that i go up 1 step or down? I haven't taken the needle apart yet so i'm not sure what level its set at.

 

[Downer]

Move the clip up one