Suddenly started running rough...any ideas?

[arbik]

Hi guys,

So my bike suddenly started running rough. It back fires on shifts and deceleration, and runs VERY rough. It also is down on power and sounds like a harley. I checked both plugs, and they both look good, and there is no fowling.
This and the popping tells me, I'm good on the fuel side, and there is combustion in the chamber, at least enough to not foul the plugs. Maybe the timing is off?
A friend of mine thinks its the hall effect sensor. Thats 300 dollar part, so before I take the plunge on that, I have two questions.

1. What else should I check?
2. Is there a way to check the hall effect sensor?

Thanks,

-arbi
2004 Rockster

[R4R&R]

You have an '04 Rockster? That should be a dual spark, correct? What happens if you unplug the secondary plug (on the bottom of the cylinder)? My bike did the same thing and it turned out to be one of the primary coils (the actual log plug cap). If I pulled the secondary plug wire off of one cylinder - no difference. If I pulled it off the other the bike would die. Then I swapped the primary coils and the problem moved.

You will have to remove the secondary plug covers so you can easily pull the wires. My symptoms were reduced power (it was hard to pass cars) and it idled like a Harley!).

[Sunbeemer]

Man what a great resource this board is! You ask a question and somebody who has been and there done that tries to provide answers.

Anyway, having said that...I don't have any experience with this, but have read that this can be the result of incorrectly synched throttle bodies. Especially if you've recently removed your tank, the right side throttle cable may have pulled out of its seat above the throttle pulley on the side of the throttle body, which causes badly out of sync fuel delivery between the two throttle bodies. This can also be caused by a small stone or debris caught between the throttle pulley and the cable. That should be easy to see and clean out.

[MikeCam]

Good answer John...and good diagnostic technique as well....very good.

I would only add one minor alternative....water in fuel, clogged fuel filter, clogged/faulty charcoal canister, and/or clogged air filter might also do those things.

But I think John nailed it on the first try.

M

[Arjen]

So my bike suddenly started running rough. It back fires on shifts and deceleration, and runs VERY rough. It also is down on power and sounds like a harley.

My wife experienced similar problems with her R1100RS a few years ago and our dealer discovered a little rock/stone somewhere stuck between one of the throttle cables/bodies...

[wncbmw]

Check the cheap stuff first. I had rough running, loss of power problems on a group rain ride once and a can of Dry Gas to remove the water fixed the problem within 15 miles. Cheap enough to try!

[bobminor]

Check those throttle cables before you do anything else. I can't count how many threads I've read on the other boards in which the symptoms you describe turn out to be a hung up cable on one of the throttle bodies.

[gbq]

Just had it happen to me last month. Idled rough and then ran like it was 20% low on power. Idled 300 RPM lower than normal and especially noticeable with a lack of power > 5000 RPM.

Problem was coil. Covered by warranty! Good luck.

[arbik]

Hi guys,

R4R&R and gbq were right.
It was the pencil coil on one of the main plugs.

Cost me $95, since my bike ran out of warranty on 9/24/06.

Well, at least she's fixed now.

Thank you very much guys,

-arbi

[tor1150r]

Pardon the ignorance, but which part is the coil?
Is it the hooded cover that slides over the spark plug??

(I know, I know...I should have some mechanical knowledge, but I'm learning as I go)

[R4R&R]

Good job - glad we could help! I guess I jumped to my conclusion too soon (even though that was my problem), and you should've done the cheap things first (run a couple tanks of gas through, use gas 'dryer', etc.)

tor1150r, yes, the 'pencil' coil he refers to is the ingition coil of the main plugs on this bike, and it is the long part that slides onto the sparkplug, essentially the sparkplug wire boot. The "two spark" bikes have an additional sparkplug on the bottom of the cylinder, and those plugs are fired by a shared coil tucked up under the gas tank (I think).

[arbik]

R4R&R,

I knew it wasnt the gas. I just knew it was an ignition issue, but the reason I wasnt sure, was that I'd never worked on anything dual spark.
When you said you had that problem, the rest was easy to diagnose.

But...I gotta say, I'm pretty happy with the design of this bike.
I mean, ok, the coil shouldnt go out at 22K miles..but, if a coil goes out, you can still keep going. Sure, you loose about 20% power, but you're still firing both cylinders and you can keep truckin' to your destination...

gotta love redundancy.......
...can you tell I'm a System Engineer?


-arbi

[gbq]

arbik,
Glad you found the problem with minimal hunting.

gbq

[Sunbeemer]

What (bad) luck Arbik! I can't believe they wouldn't cover that when you were only 4 DAYS OUT OF WARRANTY!!! That's not something that should've failed this early, and I would consider it a mfg. defective unit, and they should too. Shame on them.