Weird choke behavior

[Incubus]

OK, I have two '79 Standards. Incubus is a wonderful bike. It does everything right. I am tempted sometimes to break something on it so that I have a reason to look below the gauges. The carbs are tuned absolutely perfectly. Scarily so. I truly believe either a burglar broke in and adjusted them or the Carb Fairy visited one late night. I do not believe I am responsible and can take no credit. When I first start this bike it starts on full choke. After a few seconds, when the idle begins to increase, I bump it back down to half choke and it idles smoothly. Then, after a little while more, the idle again begins to climb and I kick off the choke and the bike idles like a purring lion.

Not so with Succubus. Oh no. Succubus (the bitch) acts more like I am the one who tuned the carbs. It will only start on full choke (even at 105 degrees) and within seconds the idle SHOOTS to 4,000 rpm. If I knock it down to half choke, the engine dies. I can only transition between full choke and half choke by first getting the engine to rev with the throttle. Once it will go successfully into half choke everything seems to be OK, and the bike idles very well once I get it warmed up. It also runs very well. It is just starting it that is a problem.

Can anyone tell my why full choke acts so damn weird? Both bikes have stock air boxes and stock jetting. The carbs on both are so clean that the Bubble Boy could eat off of them. The only main difference between the two is that Succubus the Problem Child has an XJ top end on it (YICS plugged with set screws) to take advantage of the larger valves.

I believe the problem is in the carbs, but I don't know how. Any ideas?

Of course, it could also somehow be tied to the petcocks, which are inherently evil and, I suspect, have a consciousness that enables them to screw with things that have nothing to do with them. There are probably retractable tendrils involved....

Patrick

[CatatonicBug]

I had a similar issue, but everything changed to the way you describe Incubus once I installed the Dynojet kit. The only things I can suggest is to check the air jets (and the passages that lead from them to the choke circuit), and the choke plungers themselves. Be sure to remove the plungers from the carbs or at least unscrew them and clean behind them like crazy. You can only fully remove the plunger on #1 without taking the carb rack apart.

On mine, I never had the problem with it dying on half choke, but it did the 4k rpm thing on both full AND half choke until I installed the dynojet kit. I thought something was blocked because it would no longer do the 4k rpm thing. The only jets that change with the kit are the air jets and the mains, so I know it had something to do with one of those...

[Larrym]

Creature Features 2010

Patrick,

I believe that you should embrace the darkness as surely those evil forces know their victory is certain.

I suggest that you model your next steps from the pages from Mary Shelley's Frankenstein:

<Igor enters the dimly lit morgue and picks up the glass jar containing the "Normal" brain. A sharp sound startles him causing him to drop the jar. Glass shards and useless grey matter litter the floor. "Master" had charged him with the task of acquiring a brain and he knows that Victor Frankenstein doesn't respond well to failure. Igor reaches for the only remaining brain/jar available to him. "ABNORMAL" is clearly visible on the jar label...>

The rest is history, eh???

You could actually do a carb swap/transplant between the two bikes. If the problem x-fers then truly one of the carb banks is "ABNORMAL" and should be clearly labelled so as to keep your own personal laboratory servant/assistant from making the same mistake as Igor.

Also...Whenever I hear someone insist that their carbs are absolutely clean (Sanitized for your convenience...) I wonder if they actually pulled the individual carbs off the rack. Sure, that means fussing with the Tees between them but then again I don't see any way to get at the enrichment plungers/orifices. Since those plungers are the effective "choke" for cold starting and you report problems directly related to that function.....well??? Did ya "break the bank apart" or not???

I know this is all just a matter of rearranging the deck chairs on the Titanic. You're going down that road where there's evil on all sides but the one left deliberately open. Hopefully though, I'll be there with the unruly Mob armed with torches/pitchforks headed up the road to burn down your castle and rid the village of the evil menace.

Look for me way at the back. I'll be the one with a video camera...

[Incubus]

Oh, these carbs are clean, Larry. I scrubbed them so hard I may have altered their molecular integrity. When I was done I noticed electrons scattered about on the workbench.

The carbs were separated and disassembled, at least to the point where I would have had to remove the butterflies. That was not done because only a crazy man removes the butterflies from XS11 carbs.

Y'all know who you are.

And that's enough talk about "bad" brains. I'm pretty tired of it. My mom, SWMBO, my dog... and now you, Larry. Can you not recognize a unique and original mindset without suspecting abnormality? It's entirely possible that I have the ONLY normal brain....

I did consider switching the carbs to see what happens. Switching the carbs themselves would be simple. The prospect of wrestling with two stock air boxes, though, is daunting.

I was hoping someone knew an chant or an incantation - like the one I had to use for the petcocks....

Patrick

[Larrym]

Quem deus vult perdere, prius dementat...

Patrick,

I'm not advocating diagnosing and then actually repairing the offending carb bank. Not at all. I mean we already know what's wrong with'em: They're EVIL. Kinda pointless to continue on once we know that, right?

I'm in favor of just pulling the carbs off, clearly labeling them as "ABNORMAL", and then placing them on a shelf somewhere in plain sight.

Then we sit back and wait for the rest of the events to unfold.

(Likely you'll have a late night break-in with the perpetrator being afflicted with Kyphosis Scheuermann's disease...)

Do try to place them at an easily reachable height. I'd hate to think that the perp could fall from a makeshift ladder. Paid Health care isn't included in the standard "Mad Scientist/Hunchback Assistant" employment arrangement.

[Incubus]

Larry, my friend. I don't think you are thinking this through.

The carbs are EVIL: this is a point on which we both agree. But you are advocating - of I am reading you correctly - that I remove the carbs from the bike and leave them UNCONFINED and UNCONTAINED in my garage. Leaving their evil mouths open and free to spew their demon spawn willy nilly across the landscape.

This is Texas, Larry. We don't need any more evil running loose around here.

And I know that you know that EVIL is not a linear creature. There is no way to be sure where it will go and what it will ooze into. Well, actually, in all likelihood it would end up in SWMBO's rat terrier, assuming it could crowd out the EVIL already therein. I already fear sleeping with that creature in the house. She usually looks at me like she would really like to rip off my face and wear it for a mask. SWMBO thinks that is cute. It would only take a small measure of additional EVIL to make the fear a reality.

So what is the alternative? Cryogenics? Can't afford it. Better to leave them where they are, with the EVIL bottled up and unable to affect anything but poor Succubus, who probably started life as a sweet, reliable ride before her transmogrification into the dreamscape widow maker I now believe her to be.

The more I think about it, the issue with the choke probably isn't so much a high rev as it is a Banshee-like shriek of impending doom.

Or, far less likely, perhaps I have an air leak somewhere.

Patrick

[Cobia]

Patrick,

I had the same issues with airbox when removing the carbs. After getting tired of arm wrestling with an inmovable object (and skinned knuckles), I decided to go the BikerPhil route. I cut off all but about 1" off the snorkle and can get the carbs off in less than 15 mins, putting them back is just as easy. All you do is remove the bottom of the AB with the air filter and rotate the box downward, it will come out the right side with ease. Then the carbs are out lickedy split.
Good luck.
Lucky you don't have an XJ, there's but about 3/4" of wiggle room and no snorkle shortening helps.

[Incubus]

It's not actually getting the carbs off that presents the problem, Cobia. My best time from ridable to carbs-on-the-bench is about 13 minutes. It's the boots from the airbox that are a huge pain in the butt to re-install. I haven't found an easy way.

Patrick

[petejw]

hi patrick,
the float levels can affect the choke operation,
what have you got them set at?
sounds like it could be on the lean side,
how does the bike run generally when its warmed up?

[Incubus]

The floats are set at 25.7mm, Pete. Once the bikes gets past the transition from full choke to half choke it is fine. It actually has more power than my other XS. I attribute that to the larger valves coupled with the early cams.

That doesn;t mean it is NOT running lean. The carbs are coming off again anyway. I'll check the float heights again just to be sure.

Patrick