Running Rough 2500-3000 RPM Cruising

[vur]

Hi:

I have been trying to trouble shoot a 1980 XS1100 Special that a friend of me has recently purchase.

SYMPTOM:

Once the bike is warmed up, the bike runs rough/bogs when run in the 2500 to 3000 RPM range when cruising. It appears to be running excessively rich in this mid-range cruising speed. Plugs are black.

When the bike is cold, or above 3000 RPM when warmed up, the bike pulls really strong. Which makes me think the mid-range mixture is off.

ITEMS CHECKED TO DATE:

A pervious owner seems to have altered the carbs with richer main needles. After dropping the needles to their lowest setting, it was still running rich 2500-3000 RPM. Installed the stock needles (which were leaner) in the stock position (middle clip position) and it is still rough 2500-3000 RPM with minimal improvement (still rich). Will trying dropping the stock needles all the way down and see if things smooth out.

main needle/jet combination.

The main jets, pilot jet are all stock and pilot screws are set per stock (2 1/4 turns open).

I have sync'd the carbs.

Carbs have new inlet valves, inlet valve seats and O-rings (bike was running gas out all over the place, this has now stopped).

OTHER THOUGHTS/QUESTIONS:

- Timing Advance: Vacuum advance diaphragm is good. Could a sticky mechanical advance (not checked yet) cause the above symptoms?

- Someone may have previously installed a modified cam in the engine (might explain why the bike pulls really strong at top range, and why the carb needles were different from stock)

- Anyone have any other thoughts?

THANKS in advance for any insights.

VUR
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[TopCatGr58]

Hey Vur,

You've provided some mixed information, because the 80 Special carbs are not supposed to have "adjustable" needles, they are supposed to be the fixed, one position kind!! You mention new float needles, seats, O-rings, which also directs us to the 80-81 series carbs, the earlier models didn't use a rubber O-ring around the float needle seat.

You say Mains are STOCK, but you don't quote their size!?!?

Stock should be 110's across for mains, 42.5 for pilots. Since it seems that someone was in there before putting in adjustable needles, then they could have also put in NON-stock pilots, see recent thread about
"hard to like this bike" and you'll see a diagram about the different styled Pilots that can be put in these things, VM vs. BS, and if VM, they will make it very rich and foul plugs easily!

Float height should be 23mm.

Pilot screw setting is 1.5 turns out, but then adjusted per bikes performance!

Have you ruled out the PU coil wires getting faulty, see tech tips, repairs for info and photos and such!

HTH? T.C.

[xs11widowmaker]

Take Topcats advice and check your pilots. My 81 was runing rich for over 2 years. I just put the BS pilots in and its a world of diferance. I may even be a litle lean right now.
these guys on this sight are the best there is, take there advice and you will be amazed. Thanks again for makeing my hard to like bike my best bike ever

[vur]

Mains are 110, Pilots are 42.5

Floats are adjusted to 23.0 mm

I will try the pilots 1.5 turns out.

Have not checked the PU coil wires yet. Would this not cause erratic operation over various RPMs, not just a fixed band (2500-3000 RPM)

Thanks for the suggestions. We'll get this figured out one way or another. I will should be a great bike once this bug is fixed!

VUR

[barberad]

Is the exhaust and air filter stock? If not, should't the settings be a little different?