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Terrible mpg on f4i

  #1  
Old 03-19-2019, 07:14 AM
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Default Terrible mpg on f4i

Hi, I have a 2003 f4i, I have had it for around four years and never got good fuel economy, maybe between 25-30mpg, I never figured it out exactly. My commute was fairly short and I never really did much long distance at given speed so I just put it down to the way i was riding it. At some point the fuel economy went down, I was getting 120kms from a tank. I had some holes in my down pipes which I thought might have been the problem, I was getting lots of pops and bangs from the exhaust, then the holes got much bigger, I took quite a while finding a replacement exhaust and getting it changed. Now that I have it done I was hoping the mpg would have gone back up but if anything it seems worse. The bars came up today on 80kms since filling it up which is the worst I think I have ever gotten from it.. Looking at a convertor it might be something like 15mpg, hard to know accurately but it certainly is way too low..

Few points..
The auto choke idles at somewhere just over 2k revs and turns off after a couple minutes riding the bike.
When I got it back from the downpipes being changed the idle was a bit low, I just adjusted the idle screw a little bit so its back idling just over 1k revs.
I came off it at low speed and then didn't use it for several months.
I completely ran out of fuel and did not change the fuel filter, I was trying to find out if this would be an issue but couldn't find a good answer.
It has a non stock slip on exhaust.
The mileage on it is 36k kms.
The back of the exhaust is a black, it has been since not long after I put it on a few years ago, it has been serviced several times and the spark plugs checked, I kind of presume the mechanic would have said/done something if the spark plugs were showing its running so rich that there is a problem..
I think the air filter should also be ok, I have only done a few thousand kms since the bike was last serviced and it would have been checked.
There is no smell of petrol from the bike, the smell of petrol makes me feel sick, I would notice very quickly if it was there.

I am not great on mechanics but if there are any simple things I could do to try and diagnose the problem it would be great..
 
  #2  
Old 03-19-2019, 08:04 AM
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Have you looked at the Fuel Pressure Regulator,
 
  #3  
Old 03-19-2019, 08:15 AM
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I was just reading about it and looking at the cost of replacing it, seems it is very common to fail. This is why I mentioned not smelling petrol, it seems you should if its not working as fuel is leaking out? The local Honda dealer just quoted me 250 euro for the part alone. I am trying to find one available online in Europe as it seems it should be much cheaper..

Is there a definitive way to know if it has failed or is not working correctly?
 
  #4  
Old 03-19-2019, 08:20 AM
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I am reading about it now, I mentioned there not being a smell of fuel as it seems if it is not working then there should be as it will leak petrol? Perhaps this is not necessarily the case though? I just rang the local Honda dealer and was quoted 250 euro for the part which seems ridiculous as it is about 50 euro in America

Anyway, is there a way to tell if it is not working or do you need to replace it to know for sure?
 
  #5  
Old 03-19-2019, 09:09 AM
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Pull the small pipe off if it leaks its malfunctioning, but it is not always the case ,video's on You Tube
 
  #6  
Old 03-19-2019, 11:39 AM
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Ok thanks, I will have a go at checking it.
 
  #7  
Old 04-13-2019, 04:21 PM
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So I got my bike serviced and i had the fuel pressure regulator changed. I had about half a tank left and the reserve bars came back on at exactly 80 kms. The mechanic was saying he though it was the lack of an 02 sensor, I was pretty sure the original exhaust didn't have one when I took it off and then looking online it seems like they were not sold with them. If anyone had any other ideas what it could be.
 
  #8  
Old 04-13-2019, 06:04 PM
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When the bars are showing, it it really empty?
 
  #9  
Old 04-15-2019, 03:12 PM
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Forget the gauge, how many gallons are you putting in for how many miles traveled? Some F4i's just seem to get bad mileage. I don't know if they were broken in wrong and not getting a good piston ring seal or what, but that's just how it seems to go.I used to get 50mpg but now I'm down to about 40. Maybe the coils are weak, I dunno.
 
  #10  
Old 04-16-2019, 11:47 AM
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I filled my tank this evening,

16.4 Litres, 92kms on the clock. It is possible i put slight more in than the last time I filled it, so call it 16L of fuel used to go 57 miles. That works out at 18.5 mpg.

I worked out the fuel consumption when I got the bike and it was somewhere around 25mpg so something has been wrong for ages but 18mpg is awful, I cant go out for the day on it without thinking about where/when I would get fuel.
 

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