CB1100 Idle speed instability problem

[peterbaron]

Hey guys, I experienced the Idle speed instability problem for a while but it was luckily solved. I bought my bike with 5k miles and it was only after the 16k miles mark when I started experiencing very low idle to the point that it stalled a few times. I tried several things trying to fix the problem, I adjusted valves, cleaned injectors, changed spark plugs, air filter, (among other services and inspections like disconnecting the power commander and resetting procedures) and nothing helped. I was about to give up and just accept that my bike was just another CB that suffered from this common disease. Then, while I was cleaning electrical connections, I remember that I was using a cheap battery from Autozone and decided to replace it with a motobatt battery. The cheap battery from Autozone was only a few months old, but one day when I was riding far from home, the stock battery decided to give up. I was 2 miles from autozone and it saved my life. I never suspected the reason for this problem could be the battery because it would start right up every time. I had the battery tested and it was good, but maybe it was fact that it had lower specifications than those required by the cb1100 charging system and it was causing the low idle problem. I waited 3000 miles to report my problem/solution just to make sure the problem was solved. I know that my case can be an isolated case but hopefully it helps someone one day. cheers.

I'd expect that cleaning electrical connections may have been the "cure".
To evaluate a battery, check voltage key off, key on and while cranking.

1. KEY OFF battery voltage, at the battery: Normal is 12.8, acceptable is 12.6 (standard lead acid battery, not AGM) to 12.8 for no load. If just taken off a charger, voltage may be 13 point something. The battery needs to sit for a while before a reading is useful. In the case of a bad cell, the other cells overcharge and give an almost normal reading, until load is applied.
• If lower, then battery is discharged and needs charging or
• Battery has a bad cell

2. KEY ON battery voltage (headlight on): Normal is not under about 12.5 initially, but will decline the longer that the headlight is on, without the motor running. Under no load, 12.5 volts indicates 50% discharge, but under load, it is just voltage drop.
• If lower, then battery is discharged and needs charging or
• Battery has a bad cell or
• Battery cable(s) have high resistance

3. KEY ON battery voltage while cranking: Normal is not under 10.5 volts
• If lower, then battery is discharged and needs charging or
• Battery has a bad cell or
• Battery cable(s) have high resistance or
• Starter is drawing too much current

4. If the bike is running, battery voltage at about 2,500 RPMs should be 13.8 to 14.8
• If not, then check stator resistance and regulator ground
• If the stator is not shorted to ground and resistance is within spec, the regulator or regulator ground is suspect

Nonetheless, glad that you solved it.

Hey guys, I experienced the Idle speed instability problem for a while but it was luckily solved. I bought my bike with 5k miles and it was only after the 16k miles mark when I started experiencing very low idle to the point that it stalled a few times. I tried several things trying to fix the problem, I adjusted valves, cleaned injectors, changed spark plugs, air filter, (among other services and inspections like disconnecting the power commander and resetting procedures) and nothing helped. I was about to give up and just accept that my bike was just another CB that suffered from this common disease. Then, while I was cleaning electrical connections, I remember that I was using a cheap battery from Autozone and decided to replace it with a motobatt battery. The cheap battery from Autozone was only a few months old, but one day when I was riding far from home, the stock battery decided to give up. I was 2 miles from autozone and it saved my life. I never suspected the reason for this problem could be the battery because it would start right up every time. I had the battery tested and it was good, but maybe it was fact that it had lower specifications than those required by the cb1100 charging system and it was causing the low idle problem. I waited 3000 miles to report my problem/solution just to make sure the problem was solved. I know that my case can be an isolated case but hopefully it helps someone one day. cheers.

Dang it! I knew I shouldn't have traded-in my CB. : )

I have "moved on" with my Street Twin, but I haven't lost curiosity for what will become of this issue. I have the ST for less than two weeks and it's a nice bike, but I can't help but feel that it will be "bait" for a new CB somewhere down the line.

Glad to hear your problem has stayed away!

Yep, and you may have solved it! But you did give several reasons for trading it. There, feel better?!

How are you liking the Street Twin?

Max suggested (via email) that disconnecting the battery may have "reset" the ECM...so, more than one possibility.

Max suggested (via email) that disconnecting the battery may have "reset" the ECM...so, more than one possibility.
....and if I can add something::: ignition OFF

when both terminals DISCONNECTED from the battery, join disconnected NEGATIVE and POSITIVE CABLES!! (NOT battery!! ) together for 15 min, prior reconnecting'em back to the battery terminals....

pb

p. s. Good work SportsterDoc