First Start After Rebuild - Choke/Idle/Carb help?

[ryamatt]

Hi,
It was a landmark moment and personal victory for me today - my first XS650 project actually started. I've been working on this one for 3+ years now, and I don't think the bike has run for more than a decade. However, since I committed the cardinal sin of changing the ignition, charging system, and rebuilding the carbs and top end all at the same time, I am going to be chasing things for a while. But it started, so I am pretty happy. I'm looking for a little input and help from you guys and where to go next - it runs, but will accept no throttle input without dying.

What I got:
76 XS
New cam chain, guide and tensioner
Stock head, no porting work
Stock cam, valves and springs
New pistons and rings, first oversize
HHB PMA - although I am running straight off a battery as per PAMCO Pete's advice when tuning as I am eventually going to run battery-less/kick only with a capacitor
PAMCO ignition in middle advance position as per Pete
Stock BS38 Carbs, rebuilt with good diaphragms and 135 mains 30 pilots about 2 turns out on the idle screws
Running stock headers only for the time being, no mufflers

What's happening:

1st start-up: Choke ON; Starts on first or second kick. Once running, idles ok but is clearly only firing on left cylinder. Exhaust is strong out of the left pipe, just pushing air on the right. Right cylinder is cool to the touch and when shut down and plugs pulled, the right plug is wet and stinky. I am able to give the throttle a 1/8-1/4 twist and the left side responds fine, but right remains limp. It idles on its own pretty ok.

2nd/3rd Start-up: Choke ON and everything happens as described previously, but when I turn the choke off as it idles, the right side cylinder fires up and both sides are running as they should - right side heats up and exhausts are similar. However, it will accept no throttle input without dying/stalling. When this happens and I re-start without the choke on, it fires up but will not accept any throttle.

Other than what is described above, I have not yet hit it with a timing light or adjusted anything with the ignition.

So, any ideas on the dead cylinder and throttle issue when choke is off?

Thanks.

 

[TwoManyXS1Bs]

*whew*, Glad you edited that typo. I fell outta my chair on that one.

Your bike sounds like the typical 'cold natured' issue. Can't take throttle until it's warmed up.

Try blipping the throttle while simultaneously blipping the choke.
Hard to explain, but it's a way to overcome momentary lean-out during throttle opening.
The trick is in the timing of those two.
If you can get it to catch and the revs come up ok, then may want to revisit the pilot circuit.
If not, then a more thorough carb inspection, like bowl fuel levels, needle jet, jet needle, main circuit.

 

[gggGary]

do a hot water dip on both floats cracked/leaking floats are very common on old carbs.





cracks aren't always this obvious.

 

[ryamatt]

Both sets of floats are brand new, so I wouldn't think they'd be leaking yet. I set the float level when I installed them a long time ago but I am going to pull them and check to make sure they aren't sticking or anything.

 

[5twins]

If you have the carbs off and haven't done so, do a bench sync. Your non-running one cylinder at start-up may be as simple as the sync being way off. If you can get the bike to start and idle around 1100 or 1200 (no faster), you could check the idle timing with a light. Dial that in correctly and the full advance should be very close too. Once you figure out your problem and get the bike to rev, you can check and fine tune the timing at full advance to insure it isn't over-advancing at all.

If you're using a '76 carb set, you may be a bit rich. You're 2 up on the pilots and 5 up on the mains. The needles are going to most likely need to be leaned a step with those large mains. The stock mix screw setting for this carb set is 1.5 turns out. With the larger pilots, you shouldn't need more than that and will probably need slightly less (1 to 1.25 turns out). The way the right cylinder doesn't fire with the choke on could be because of your overly rich jetting and mix screw settings.

 

[ryamatt]

I was able to spend some time on it this evening. I have some other jet sizes so I went down to 130 mains and 27.5 pilots and put the idle screws to 1.5 turns out. While I had the carbs off I think I got a decent bench sync done. It took more kicks than last time to get it going but the weather has turned and it has been cooler all week. While idling, the right side was pumping air very nicely but was still not firing. While letting it warm up a bit with the left side firing, I heard a few random, deep sounding thunks that sounded like they came from the right side of the bike inside the cases. I shut it down and decided to call it a night. I'm going to drain the oil and investigate as much as I can to the cause of the strange noises before starting it again.

 

[peanut]

wise to check strange noises in a new built engine so I know you'll be tied up with that a while but...
Just to satisfy my curiosity did you actually verify that you had a consistant strong spark at the plug on the dead cylinder ?

You need to make sure that you never turn the engine over with a spark plug wire /cap disconnected when you've got an electronic ignition naturally ...I use these testers. They are as cheap as chips and you don't need to fart around trying to hold a loose spark plug to a ground point whilst kicking over the engine .
http://www.ebay.com/itm/6-AND-12-VOLT-IN-LINE-SPARK-PLUG-PICK-UP-COIL-TESTER-IGNITION-DIAGNOSTIC-TOOL-/351065230532?hash=item51bd1e4cc4:m:mZgqzwu3iY3ehaJfLRsHa7Q&item=351065230532&vxp=mtr