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My dad has a '98 Low Rider that gets poor gas mileage compared to my '99 Twin Cam Dyna Convertible. His bike is only able to go about 150-160 miles and mine is able to go 200-210 miles.

His bike is stock except it has Screamn' Eagle slip on pipes and the Screamn' Eagle high-flow air cleaner setup. However, the carburetor is the stock CV...it has been rejetted by the previous owner. I took the carburetor apart and I believe it has the stock needle. The jets are #170 and #42.

The pipes are black as can be and the plugs get carbon build up fairly quick. His bike runs excellent...we just want to get better gas mileage as we like to take long trips sometimes. His bike only has about 18,000 miles on it.

Any help would be appreciated...
 

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Try a 165 main. Make sure the A/C to carb mouth is nicely matched. Open the A/C hole that mounts to the carb if needed. Make sure the air fuel screw if tuned for smothest idele after you rejet the carb. Keep the filter clean.
 

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Sounds like the idle jet may have been redrilled too big. My '86 Lowrider Sport had a sooty front pot and a lean rear. Replaced compliance fittings with a rigid manifold. Rear run good front now very rich. Checked idle jet size marked 50, checked hole size with a drill .80mm Way too big. Asked as to what size idle jet I should have with my opened up Cycleshacks and K&N air filter. Told to go from the 50 standard to a 52 thats an increase of only 0.02mm not the 0.30mm that someone else had done. Purchased a new jet stuck it in and haven't looked back. No sooty plugs and good economy. I wouldn't change the main jet as most of your running that affects economy is on the idle jet or the transition from it to the main jet. The CV carb idle jetting with your engine mods should be about a 48 I would think. Also check that some clown hasn't also drilled the main jet and check for excessive shimming under the needle
 

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1997 Road King with a carb and EV27 cam

Heavy Breather, Dyna Ignition, EV27 cam, slip on mufflers.

My gas mileage prior to changing the cam was an average of 38 mpg with a high of 44 low of 33 when riding over 80 mph. My private mechanic put in an EV27 cam, Dyna ignition and re-jetted using a dyno. HP went from 50 to 66, but mileage went to 33 no matter how I rode. Before Sturgis 2011 I checked my plugs and found they were almost black. My wrench had put in Champion plugs when Harley offers no replacement type. That may not have been the problem. I suspect that testing jetting options caused the fouling even though the engine ran perfectly. I dropped the carb needle jet one notch and put in new Harley plugs. My mileage went to 42 average with a high of 49 and a low of 35 when riding at 80+ mph. Now I have the best power and economy.
 
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