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Discussion Starter #1
(Sorry if this was already asked, but i have searched and found nothing)

During the winter and the COVID lockdown i've got plenty of time to take care of my burg, so i changed the engine oil, air/CVT/oil filters, and since i did'nt know how much old they was, i installed two new spark plugs (the older ones were almost new and perfect).

Now lockdown is off, so i'm back at office from two weeks. This means 42km per day... and i noticed that now my mileage is lower than the last year. It was about 19~20 km/l, now is about 16/17 (i'd let you do the math to convert fuel consumption from the metric units to boots per hamburger or whatever unit you're using :p ).

Question is: what should i look for? is the air filter able to makes such a change? or are the spark plugs?

I kept both the old parts, I can mount the air filter easy but the s.plugs are a pain to install (more if your hands type is the neanderthalian one) so i'd avoid to tamper with them if there's no real reason to do it.
 

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I’d run a second tank of gas from a different vendor and see if improves.
 

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Discussion Starter #3
3 full tanks (13 or 14 liters), 3 different vendors, 2 different brands,
 

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The stuff you did shouldn't change the mileage except to make it better. One thing I notice is that at my place it as been windy almost every day and when going for a ride, bad mileage going against the wind. Make sure the hand brake is off and check that the brakes are not dragging.
 

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3 full tanks (13 or 14 liters), 3 different vendors, 2 different brands,
Well you can rule out bad gas....I’d check filter seal and then replace spark plugs with the ones you pulled out.
 

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Mine varies a good bit, depending on many things...terrain, wind, traffic, temperature, length of trip, average speed, and primarily, how squirrely I'm feeling with the right hand.

If you haven't already I would run a couple tanks with injector cleaner or Seafoam. Could be a little sludging due to sitting for a while. I don't see the need to put the used parts back in. I assume you checked the plug gap before installing?

Are these numbers what you have calculated at fill-ups or just going by the dash display? My trip computer varies from actual calculated and by different amounts. From what I understand the computer basically counts the injector pulses to calculate fuel economy, so if an injector is dirty it seems it could affect the calculation.
 

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Discussion Starter #7
If you haven't already I would run a couple tanks with injector cleaner or Seafoam. Could be a little sludging due to sitting for a while. I don't see the need to put the used parts back in. I assume you checked the plug gap before installing?
The cleaner is an idea i did'nt had, thanks!
Yup, i checked just to be sure, but the plugs were brand new.

Are these numbers what you have calculated at fill-ups or just going by the dash display?
Calculated: i fill with 13 or 14 liters, do the math and then reset the trip A.
The computer is ALWAYS worst than real math, but the difference then and now is consistent (i mean: it also says that i do 3km less per liter than before).
 

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the plugs may not have the caps seated tightly and be missing occasionally, I haven't done them yet but I do understand they are very hard to get seated right and can cause poor perfomance and mileage problems. maybe some rpm readings at speed would help diagnose, ? Eh ignore me I'm an idiot, a steady 3 km difference wouldn't be a loose plug.
 

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Discussion Starter #10
I do understand they are very hard to get seated right and can cause poor perfomance and mileage problems.
My guess is that i could feel some missing sparks. The burg is smooth as usual.
Anyway, while changing the plugs is a nightmare, i can try to give to the caps a shake and see if they're well set.

Have you ruled out that your bad mpg might be with winter blend gasoline, and your previous good mpg with summer blend? Probably not it, but something to consider.
uh... i don't even know if a thing like that exists here.... anyway, in the case it is something that is done here, i doubt that the two fill-up i've done in the past week were made of "winter gasoline". we're already hitting 28°C, so it is a nice warm springtime :)
 

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I have changed plugs on my 2005 Burgman 650 when I had that one. Also checked valve clearance. I know how hard it is to get to but not impossible.

One thing that hasn't been mentioned is to ask...
Did you check the gap for the new plugs?

I find new plugs may or may not have the proper gap out of the box so I check every time. I don't think the air filter would cause this issue. I also don't think the other things would cause there to be a sudden change from before the maintenance performed to after... all of a sudden. I also agree that you would likely notice, at least a little, if one cylinder was missing. Even only once in a while. A 6 cylinder motor is sometimes hard to tell. Even a 4 cylinder motor can even be hard to notice if it's only once in a while and you're not putting it under stress. A 2 cylinder would be noticeable. A 1 cylinder would be like a slap in the face every time it happened. Besides, it would be rather coincidental for this to not be something related to what you did.

First thing I always do when I notice a problem like significant mileage change or other operational change is to ask myself what changed recently(?). I go looking for other things only after I check and make absolutely certain that it wasn't something I did.
 

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Discussion Starter #12
One thing that hasn't been mentioned is to ask...
Did you check the gap for the new plugs?
Yup. It was correct.

I have a "young" mechanic on the other side of my office block, which was a Suzuki mechanics before starting his own activity. ("Young", being me 50, is somewhat a stretched word :LOL:)
He told me that some aftermarket air filters can "choke" the engine. So, being the easiest of the steps back i can take, i'll re-install the old one and see what changes. We will have at least a week of rain here (what else can you expect for when the lockdown ends? :rolleyes: ) so it will take some time to get the test result (i dont like to ride on rain).
 

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I guess I was assuming (for no apparent reason other than that's what I always use) that it was Suzuki air filter, so it seems reasonable to try the old one back in. I don't know how sensitive FI is to airflow...old tech carbureted engines can be very particular about such things.
 

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For us SI challenged folks, in MPG that was originally around 46 MPG and went down to around 39 MPG.
 

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Discussion Starter #20
O.A.T - outside air temperature
OH! Thanks.

So:
I will see 5 mpg change with o.a.t. but I'm sure Parduz has taken that into account.
Nope. I did'nt noticed anything like that the last year. The only time i ate so much fuel was when i took the highway and kept about 90MPH for a pretty long time.

Anyway this week i have the oldair filter on and the tires pressure exactly at 2.3 / 2.7 (they were a bit low). I'll see and the next one i'll use the new filter again (keeping the tires exactly at the same pressure).
 
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