Horrible rough idle, running bad. Solution:
 

A few days ago, I posted that I was having trouble getting the twinmax to zero out with the LBBS, that the idle didn't change at all moving the LBBS and that the bike was running badly.

Many wrote in to say that in this case, check the valves, 'cuz the valves being off even a small amount can cause this. Today I have solved the problem.

1. I checked the valves. One of the right side intake valves was minimally tight, so I adjusted it.

2. I checked the plugs. The right one had fine black deposits (fairly heavy for 3K) and the left one had a fine white powder. I cleaned them up a bit and re-installed them.

3. Started up the bike and it still ran like dog****. Backfiring, low idle rpm, poor power, erratic throttle response.

4. Put the twinmax back on it (after warming it up) and it showed NO CHANGE WHATSOEVER from the other day.

5. Scratched my head and walked in circles for a while.

6. I changed the plugs with new ones. Slight improvement, still pretty bad.

7. At this point I was convinced some electrickery had died, but thought about doing one last thing: I started screwing in the crossover throttle cable (right side).

8. Lo and behold, the idle picked up and smoothed out and the twinmax centered out.

9. I started over with the sync procedure and now the bike is running great.

LESSONS:
1. I'm a dumbass
2. It is possble to back out the throttle cable TOO FAR and throw off the whole sync process (I'd don't quite understand how, but it will affect the low speed sync)
3. Last time around, I had the two LBBS set about 1 1/4 turns different. The bike ran well, but as one plug saw lean conditions and the other rich conditions, the two plugs progressively differed in those two directions (probably led to the poor-ish running that first got me to try syncing and led to this whole mess)
4. Well, I guess #4 is the same as #1

the only way the throttle cables can affect the idle is if there is no clearance / freeplay in them. which there should be at idle, as the idle stops on the throttle bodies are what should be positioning the throttle blades.

has the cable come out of the holder at all? if screwing the cable adjuster down fixed it, the cable is holding up. if the cable is not sitting in the holder properly, it causes exactly what you describe.

we've had lots of bikes come in like this over the years (and we've generated it ourselves inthe workshop). usually after some sort of fuel tank lift or fiddling exercise around that area on any r 4v.

i'd look at how the cable is sitting.

badger, one of the problems when using a TwinMax is when things are way off it is hard to tell what needs adjusting and by how much. I recently changed out all the cables and had difficulty telling what was going on with the TwinMax when synching the TB's. I finally threw a carb stick mercury manometer on the throttle bodies and could see immediately what needed to be adjusted and how much. The right side throttle stop was way off at idle and the carb sticks made it easy to bring it in synch with the left side. From there, the right side cable adjustment at just off idle through 4,000 rpm was a cinch. I'm sold on the old carb stick method from now on.

brad, I had that very same thing happen to my bike when I replaced the fuel pump a while back. The right side throttle cable had pulled out of the junction box at the top under the tank and the bike idled and ran like krap. I was sure I had screwed something up and took it to the shop to have them look at it. By the time I got it there the cable went back into position and the mechanic thought I was nuts. Lesson learned.

Brad:

You are not a dumbass. If you were you would never have found your problem and solved it. People who repair computer code know that there is a 50% chance of introducing a bug when fixing a bug. Same holds true for mechanical work. Adjusting one thing can throw off something else. It happens to all of us, and more than once in a while.

i've been called worse.

we've had people trailer bikes in from miles away and we fix them without even unloading them. one of those really annoying little tricks. the cable often sits on top of the adjuster and will never go back in by itself.

if you want to see some real self introduced agro, try adjusting the throttle cable on a f650gs to reduce the freeplay.

Brad,

I'm not quite following this. I can only see the cables where they enter the bracket and for a couple of inches above that (both right and left side).

Previously, I had screwed out the adjusting barrel a long ways to be sure it wasn't pulling on the TB. That's when it ran badly, but it never came all the way out of the bracket. Afterwards, I screwed it back down, maybe 1/4 inch and the bike smoothed out immediately. Is there a picture that shows where the cable is s'pposed to route? Mebbe the previous owner hosed this up (or more likely where he had it serviced)

I agree with the "no freeplay diagnosis". In the other thread, somebody here even suggested that you adjust idle with cable slack which is obviously incorrect. Yes, I think a PO or service folks hosed it up.

I don't mean to hijack the tread, but I'm still confused about how the fast-idle system fits into this. Does the FI lever cable go into some junction box which causes the throttle cable to the right side to be pulled a bit to cause the fast idle? Which then pulls the crossover cable? My bike has progressively been developoing a rougher and rougher fast idle and I'm wondering why.

- Mark

The fast idle cable cams the main throttle wheel a small amount. In affect it is just like holding the throttle a small bit open. You might want to check your "just off idle" TB synch again to see if it is still even.

Off-idle sync is adjusted then with the x-over, right?

- Mark

They don't recommend using the fast idle for adjusting off idle synch, but I don't see why it wouldn't be the same as twisting the throttle. At any rate it is easy enough to just twist the throttle slightly to measure the synch at just off idle. That way you can watch it at various ranges at the same time. I found that a carb stick is easier to view than the TwinMax because you can just make the two levels the same for all ranges of throttle input. With the TwinMax you always have to be sure the thing is warmed up and balanced perfectly before taking a reading. I found mine to also give slightly different readings when I switched to oposite TB's too. Carb sticks are always perfectly balanced thanks to gravity. :) Just my 2c

Thanks. Yes, I'm using Stix, but over time, the mercury in the columns has become a little fragmented with a couple little smidges of mercury hanging up in each column above the main pool. I assume the errors are minor.

- Mark

if you screwed the knurled adjuster upward (out?) then you took all the freeplay out of the cable and opened the throttle blade. which causes the problems you described.

to give them freeplay you wind the adjuster down.

Huh.

That's opposite of what the manual on ibmwr sez. It sez to turn the knurled knob ccw to assure that the left TB plate is fully closed for the low speed synch.

Sounds like I started to open the Right TB plate by turning the barrel out (up, ccw whatever)

Yes, everything Brad Black said.
Definitely had negative clearance on that cable with the adjuster out. I've never heard of that typo on the ibmwr manual before, and it's been posted for years. Are you sure it said that? Anyway, and if so, it's wrong.

Quoted from balancing throttle bodies by Stephen Karlan:

<Starting the Adjustment:

Loosen the right side crossover synch cable by loosening the 10mm lock nut and turning the knurled knob counter clockwise to ensure that there is slack ['97-'98 loosen right throttle cable] . >

However, I will say in the other 2 TB synch articles, they do say turn the knurled knob clockwise.

Guess I'll cross out the counter part from this article.

Yes, definitely a typo.
Otoh, now that you're attuned, it should be pretty obvious that going CCW doesn't ensure slack. It's always good to read procedures and make sure you understand each step rather than following by rote. In that latter case, you don't always note where the procedure obviously conflicts with itself. Sounds like you have it now at any rate, and you're sure to never forget it :)