worsening fuel economy 1994

Happy Christmas all !!!!!

I bought my 1994 in 2000 with 22,000kms on it and now it has 176,000kms. There's been numerous changes through the years but.... about 16 months ago I noticed a slow - average - decrease in the trip meter k's each time I'd fill up. I haven't been to any track days in that time so my riding is roughly the same .... commuting, occasional country ride, occasional hooning for a while... I just checked my plugs, valve clearances and then balanced the carbs and the economy is the same - roughly putting 18litres in at around 240kms on my tripmeter. I used to average 280kms on that meter. The bike feels roughly as strong as it always has so I'm assuming that the compression is not the issue. I'm going to build an oxygen sensor but still haven't figured out how far down the muffler to push it to get an accurate first reading. So whilst I'm assessing that aspect and due to the 176,000km's, I'm going to start assuming that the jets need attention. Particularly the needle jet /holder. Or would there be enough wear in most of the jets to warrant a new carby kit, if so which is the best? Are Factory Pro standard kits appropriate? I hope to fit the jets and needles without removing the carby banks.
My K&N gets cleaned about once a year, just after a particularly dusty rally. I'm having trouble getting motivated but feel a gradual movement towards getting better economy again. Due to the slowly decreasing value of the bike and the slowly increasing workshop rates, I'm going do this work myself. I'm also presuming that the trip meter is roughly accurate by comparing my distances on my trip meter with other bikes doing the same country rides. It's all very interesting and even though my inertia is a bother, the diagnosing is one of the joys of long time ownership of this reliable, versatile bike!

Thanks ladies and gentlemen!!! And a happy new year ......

 

I have no experience with the VFR, but my Suzuki RF900 suffered from worn emulsion tubes that caused very poor fuel economy and eventually started fouling plugs. The emulsion tube is the orifice that the needle reaches into, and on the RF the slide could wiggle a bit and that caused the emulsion tube to wear a bit oval instead of the perfect circle that it should have been, and that meant more fuel was entering through the mainjet than was intended. I fitted new emulsion tubes and voila, problem solved.

I doubt that the main jet or low speed jets could wear as they only have fuel passing through. The other other wear item would be the floats if their valves are not closing as well as they should, leading to higher fuel levels and richer running.

 

Sounds to me like a degrading, leaky or stuck open thermostat, which is a common problem with the complicated dual-actuator thermostat used on these bikes.

What did your plugs show--were they dark and sooty, or white and ashy colored? This is reading the insulator below the tip, not the threads and ground electrode.

Good luck opening the carb bowls or replacing jets without pulling the carb rack--never tried it, didn't know it could be done, but i suppose there's a first time for everythang...

 

+1 on reading the plugs. Slightly lean could be a partially plugged pilot jet(s). Treating a tank of fuel with the magic in a bottle of your choice, berryman, stp, sea foam, mystic, type stuff may do the trick without disassembly.

 

Hello Guys and thanks a lot for the suggestions.

Terry , my manual shows the needle going into the top of the needle jet then the main jet is screwed into the bottom of the needle jet. Is the needle jet your emulsion tube? Possibly I only need to change the needle valve and needle as per your suggestion that only these two parts are actually touching...

Kenny I've replaced the thermostat about 2 months ago and all the plugs were a lovely grey/tan.

Jay, It was the 2 / 7 / 07 when I last adjusted the pilot screws so I'm going to check it again.

Thanks once again guys and Happy New Year

 

Happy New year. Needle adjustments are most noticeable in the mid range if everything else is close. Hope you get it right without too much hassle.