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Poor gas mileage

  #1  
Old 12-15-2016, 08:44 AM
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Default Poor gas mileage

My CBR gets about 95 miles before the reserve light turns on. I put about 3.5 gallons in each time, so I'm getting about 27 mpg. It starts, idles and runs fine, except that it has a little less low end then other f4is according to my stunter friend.

Reading mpg threads online, this seems to be pretty common. Some people get 40-45, and others get 30. There doesn't seem to be any reason why.

The first reason I can think of is riding style, but I get roughly the same mileage if I'm riding aggressively or cruising at 6k on a road trip. The only difference i can think of between me and other riders is that I'm pretty tall and don't tuck behind the windscreen. I don't think that would cause a 15 mpg drop.

Mechanically, I did valve clearances, air filter, oil, coolant and plugs 500 miles ago. I checked the fuel pressure regulator, replaced the fuel filter and checked fuel pressure, which was dead on at 50 psi and held pressure. There are no Fi lights. I checked the intake air temperature sensor, and it was in spec at 2.6k ohms. The engine coolant temp sensor was slightly off however. The spec is 2.3k-2.6k ohms at 68 degrees, and i got 2.02k at 60 degrees. I don't know if that small of a difference could cause at 15 mpg drop, but I'm going to try a new one.

Does anyone have any ideas or problems they have seen before? This isn't a huge deal, but I would like to have my bike running at 100%.
 
  #2  
Old 12-15-2016, 12:37 PM
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I used to get 45-50mpg depending on my riding to and from work. now, 80,000 miles later, its dropped to around 40. But I've never done a throttle body sync [it needs it] or changed the O2 sensor in the exhaust. I assume it will go back up once I do them.

My only other guess in your case is the motor was broken in badly and has never had optimum ring seal, unless you have a ton of miles as well. But one guy has like 300,000 miles on his F4i and I've never seen him complain of mileage so who knows.
 
  #3  
Old 12-15-2016, 07:27 PM
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I only have 30,000 miles on mine. I think it has pretty good ring seal because I tore it apart 500 miles ago to replace two gears and a shift fork, and the combustion chamber and valves looked pretty similar to low hours 450 dirt bikes I've rebuilt.

The other question I have is if the ecu actually adjusts fueling based on the temp sensor. Looking online, I've seen some suggestions that it's only used for the cold choke and to protect from overheating. If so, it probably is a waste to buy a new one.
 
  #4  
Old 12-17-2016, 02:54 PM
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If it thinks the engine is always cold it will always run stupid rich and kill your mileage.
Combustion chamber carbon build up does not indicate ring seal being good or bad, nor does it show blow by. A compression and leak down tests are the only way to confirm. Chances are pretty good your fine though, it was just an idea.
 
  #5  
Old 12-22-2016, 11:26 PM
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I may have found the solution. When I first checked the ect, I had rode the bike a few hours ago. I checked today with over a day since the last ride, and got 2.31 ohms at 62 degrees. Close enough.

After that, I tested for a vacuum leak by spraying starting fluid and wd40 around the vacuum lines and throttle body boots. At first, the leak was really bad. Spraying anywhere near the right half of the throttle body would cause rpms to drop, and a spray in the right spot could stall the engine. After three cans of starting fluid and a fair amount of wiggling the throttle bodies, I could only get the rpms to drop by directly spraying the far right throttle body boot.

The screws on it were loose. I tightened them up, and rpms wouldn't budge after fogging the entire throttle body and the vacuum lines. I'm going to put a full tank in it tomorrow and see how far it gets me.
 
  #6  
Old 01-19-2017, 02:32 PM
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At a loss here. I'm still getting under 30 mpg. I also checked the throttle position sensor and map sensor according to the manual and both were in spec. The only other odd thing is that my cold idle choke recently stopped working, and my bike has a pretty steady idle, but it varies between 1.5 and 2k rpms depending on the day. Does this point to any other problem?

At this point, the only ideas I have left are the m4 slip-on causing issues, something going on with the throttle body, or a difference in riding styles between me and other riders. However, my mileage has never really changed depending on how hard I ride.
 
  #7  
Old 01-20-2017, 02:53 PM
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Originally Posted by seraine View Post
The only other odd thing is that my cold idle choke recently stopped working, and my bike has a pretty steady idle, but it varies between 1.5 and 2k rpms depending on the day. Does this point to any other problem?
Your waxing unit is not working, just like mine now that my mileage has gone down. Common themes tend to point to a starting place.....
 
  #8  
Old 01-20-2017, 03:57 PM
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what about tire pressure?
 
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