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FXDX high fuel consumtion


Hello All,

Long time not here,this is the second time I bring my 00 FXDX to the dealer (not an official one but a HD specialist). When I bougth the bike, it has a very low fuel consumption but runs poorly (it was parked for nearly 2 years). I changed the not-legal exhaust pipes by US stock pipes bougth on Ebay and had a huge maintenance. Now the dyna runs very fine :) but I notice a huge increase in fuel consumption : 31,3 miles par gallon (7.5 l/100 km) !! The mechanics does not understand what happens, he checked and cleaned again the carburator but I still have this poor mileage :-( . The dyna is a 00 model, 8700 miles, with stock US pipes and SE air filter.
Can it be some kind of electronic problem that only a dealer with a scanalyzer can find ?
Possibly the carb has had larger than stock jets put in to go with the changed pipes.My guess is that the reason the bike ran poorly before the carb was cleaned is that the jets were clogged, thus the low fuel usage.First thing I would look at is the jet sizes.

Are the plugs very black and sooty? I am not a big fan of reading plugs, but after a ride (don't idle the bike, just shut it off) and pull the plugs. If you can post some pics. Also while the mechanic was in there what jets were there in the carb. I pray to God that he didn't just clean the carb and not check the jets and the needle. Stock? Aftermarket? I am willing to bet that whoever had the bike prior to you had the carb rejetted and now that the stock pipes are on the bike is way rich.

Or you can replaces the stock metal slide with a plastic one, and a lighter spring. Unless you've other mods(pipes and air cleaner) you don't need to change the needle and jets. The lighter slide gives better throttle response. That's been my experience, anyway.

Do a plug check.Maybe even try getting 3 sets of new plugs and check the first set after you let it warm up at idle without the choke.Next set check at 1/3-1/2 throttle(kill it with the kill switch) Pull the plugs and make a note of what color the insulator tip is dark brown -tan is what you want.Next with the other new plugs run 3/4 throttle for a mile or so and kill it with the kill switch and recheck the plugs.If in the first step you have a black sooty plug chances are the choke is not off all the way or the air/fuel screw is not out far enough.On the second check if the plugs are sooty your slide is not right or you needle and jet tube are worn.
On the last check that will tell you if your main jet is too big or too small.Black sooty= BAD too big of jet.White = VERY BAD too lean brown-tan good.
BTW 32mpg is all I get on my old shovel.
Doing the plug checks even using the throttle chops will not give you very good results since the tetraethyllead has been removed from fuels many years ago. What you see now is the color from the additive packages in the fuel mostly which shows up in a redish brown color to different degreese usually depending on the brand. IF you get any color on your plugs at all, it will be very difficult to tune using this as a basis for jetting. Mostly white/clean insulators are the order of the day now. Thank you EPA:17:
Has anyone possibly changed the Main jet in the carb???
My buddy had the same problem with a used scooter.
Changing to aftermarket pipes and Air filter usually and should create a problem. This would require a larger main jet in the carb. (usually)
If you changed back to stock pipes etc; then the big jet will cause a larger consumption of fuel (rich)..
See any black sooty smoke when ya cranker 'er up or accelerate??? This is raw fuel ..
Check the main jet and the slow jet also...