Build a paper tube to shield the gauge.

Or, test at nite!

This is all rumor and hearsay, so believe it or not as you see fit.

The EPA tests are not all-inclusive of all engine operating conditions. The EPA puts the vehicle through a carefully defined "drive test" at certain speeds for certain distances. It is never run wide open, nor at high power. Since motorcycles in general have higher power-to-weight ratios than cars, they are operated at lower throttle openings to run at the prescribed speeds. Motorcycle makers are very aware of the test procedures. Makers jetted carburetors to run lean at idle and low power, where the motorcycles are tested. They jetted the bikes to run properly (slightly rich) at high power where the EPA does not test. (I use "low power" for power up to 1/3 rated; "medium power" from 1/3 to 2/3 rated; and "high power" for power from 2/3 to full power. This is my arbitrary choice.) Naturally, stories abound that carburetors are way too lean from the factory, but the "rest of the story" seems to be missed. Part of the issue is that most motorcycles are operated at small throttle openings most of the time, so they usually run in the lean regions of jetting.

Hello o2 fellow. I use a gauge with numbers wich is very visible in sunlight. I have posted a photo of it in my thread.

In the first round of testing I had:  152.5 Main, 55 Pilot, 3 Washers under the needle, and the air screw was at 1-1/4 turns out on the screw to run well at idle.  I had lowered the float to 29 mm as the engine has always started without the choke.  The O2 sensor showed the engine was rich everywhere except when accelerating at 1/4 thottle or less where the engine ran very lean and surged.  When lightly accelerating with throttle settings below 1/4....the O2 sensor showed the engine was lean and the bike would surge and did not run smoothly.  If you added any throttle over 1/4 the bike pulls strong and smoothly.

For the second round I installed a 150 main, 52.5 Pilot, and raised the float to the maximum factory setting of 27mm.  The idle gas screw is out just short of 2 turns for the ideal mixture as shown by the O2 meter.  This morning on the way to work the engine ran with a good mixture reading on the O2 gauge in the 1/4 to full throttle range - it runs just a bit above the middle (green) bars that shows the ideal mixture, and it pulls smoothly.  At crusing speeds and throttle settings between 1/8-1/4 at speeds above 40 the mixture is very good and in the green.  The engine still runs very lean and surges from 1/8 -1/4 throttle when lightly accelerating through the gears at speeds below 50.  The gauge will show in the green while cruising - then if you lightly roll on the throttle up to 1/4 the gauge drops into the lean zone and you can feel the engine surging.....if you roll a bit more throttle on and get above 1/4 throttle it pulls smoothly and the gauge goes up into the green.

I need to get some more fuel into the system at throttle settings between 1/8-1/4 throttle.  The info I can find says the Pilot Jet controls this range - and that the slide needle is more involved in the 1/4 to 3/4 throttle range.  I might try opening up the mixture screw a bit - but that will make the idle too rich.  I could also try going back to the 55 pilot....however the engine still had the surging with the 55 and it showed rich during normal cruising with this jet.      

Anybody have a suggestion on how to richen up the 1/8 to 1/4 throttle mixture?  I may be able to get a tiny bit more height in the float level - but I am at the maximum setting the manual allows.

verslagen1 wrote on 09/28/12 at 07:50:46:


Thanks - I will give that a try and see what happens.

Third try is a charm.....well.....sort of.

I took the carb apart and removed two of the three washers on top of the slide needle, and just left one.  The bike no longer has the flat spot between 1/8-1/4 throttle - but it has become too rich everywhere.  The O2 gauge shows it is rich, and it does not run as well when you are rolling off the throttle and it surges when slowing down.  First thing tomorrow morning I will put one washer back in.

I am pleased with how this simple narrow band 02 sensor is working.  It may not be as flexible as a Wide Band sensor and gauge - but it does let you know how the jetting changes you have made affect the engine.  Without the gauge you would know that the engine stumbles or surges.....but you would not know easily if the problem was caused by being too rich or too lean....the gauge clears that up and tells you where you can improve things.  If you were tuning a race bike and looking for maximum power then a wide band O2 gauge might be worth the extra money....but I already had this one from a previous project and thought I would give it a try.

couple of easy ways to lean her up a bit

remove the snorkle

remove the air box door.