Running lean

[henri]

Running lean

Hi,

I resynced the carbs with the correct airbox and took it for a test run. There was improvement but at around 150 Km/h in fith gear it does the same thing. The plugs on cylinders 2,3,4 burns white, with 3 almost glazing. Only cylinder one burns sandy brown.

With the the float levels all exactly the same I don't understand the coloring if only the float level determines the mixture at that speed. I set the level at 25.7 ('78 xs 11 specail) Is there anything else that can cause the bike to run lean or the plugs to color white?

I will really appreciate any suggestions.

[SFSPECBIKER79]

you could try a colder plug. to try keeping it from getting to hot and burning the electrodes of your plugs. most stock plugs are the hotter type plug. just my 2 cents.

[oseaghdha]

Hi,

I resynced the carbs with the correct airbox and took it for a test run. There was improvement but at around 150 Km/h in fith gear it does the same thing. The plugs on cylinders 2,3,4 burns white, with 3 almost glazing. Only cylinder one burns sandy brown.

With the the float levels all exactly the same I don't understand the coloring if only the float level determines the mixture at that speed. I set the level at 25.7 ('78 xs 11 specail) Is there anything else that can cause the bike to run lean or the plugs to color white?

I will really appreciate any suggestions.

You did not mention if you pulled the carbs apart.
Check the emulsion tubes, diaphragms, and main jets, fuel flow, vacuum leaks, etc.
4 into 1 headers do need bigger jets.

Every engine is different, the setup that works on one may not work on another.

[mro]

Since you have it running...
Clean plugs, and have spare set in your pocket.
Go out and putt at a constant 3000 rpm about 4 minuets, use kill switch and coast to side of road, pull plugs and check color.

Change plugs, cruse at 5,500 rpm and do same.

If plugs look good at low rpms, but lean at higher.
Early carbs, can raise/lower the slide needle which will effect higher rpms.
Raising needle > richer.

If lean at all rpm, double check for vac leaks etc, try increase float level .5 mm at a time (I don't go more than one mm from stock). If all above fails will need to re-jet.

mro

[henri]

Found the problem

Hi,

I am sorry to have wasted your time and energy. I removed the carbs yet again and I realized the two inner carbs had the fuel/air mixture screw's tip stuck in that little hole and broken off from the screw. I checked the outer two and felt if the pin was sticking out from the hole in the port on the inner ones, not even checking if it is in fact blocked. That is assumptions for you.

I am waiting for 3 replacement throttle bodies as the carb ports have already been damaged by somebody down the line trying to drill them out. This was the problem all along.

Thanks for everyones help and guidance.