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Old 04-21-2011, 04:50 AM
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Default Horrible gas mileage after spark plug change?

Hi everybody,

I changed out my spark plugs about two weeks ago and my gas mileage is a lot lower normal. I would usually get up to 250km before the reserve light would come on but now I keep barely hitting 220. That's 30km per tank less!

I've also noticed a power loss. It felt a bit ball-less but I thought it might have been due to some brake drag (which I got after removing the front wheel to change the fork oil). I cleaned it up and it helped a bit but was still missing some power. I main reason I noticed it was because I kept hitting the rev limiter when going for it. I only hit the limiter once before in a year. This basically comes down to me giving it more gas to compensate for a loss of power...

I did some Googling and mostly got car related results. The consensus was people using spark plugs with either a different sized gap or heat range..

The ****ty thing is that a friend and I both changed our spark plugs (my F4 and his Gixxer) and although I put my old ones back in a box, he had apparently tossed all the plugs in the garbage.. I can't compare the plugs now so I'm wondering which plugs I should use. I'm going to call the dealership who sold me the plugs to see if they gave me the wrong ones but I haven't had a problem with them before... Has anyone of you experienced a similar problem? (The plugs were made by NKG btw. Not the more expensive iridium plugs though.)
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Old 04-21-2011, 09:04 AM
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Assuming that they are the correct plugs did you verify the correct gap before you installed them? Does it seem like it idles rough or anything? I once installed a new set of plugs and accidently cracked an insolator. Although it ran it just seemed like it was idling a tad rough. When I pulled the plugs back out I discovered the problem.
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Old 04-21-2011, 07:09 PM
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Quote:
Originally Posted by RoadiJeff View Post
Assuming that they are the correct plugs did you verify the correct gap before you installed them? Does it seem like it idles rough or anything? I once installed a new set of plugs and accidently cracked an insolator. Although it ran it just seemed like it was idling a tad rough. When I pulled the plugs back out I discovered the problem.
I didn't check the gap before installing. I installed the plugs on the Gixxer and the manual didn't ask for it. I forgot my own Haynes manual so I didn't think of measuring them (thinking it was a plug and play kind of deal). When calling the dealer they also didn't mention anything about measuring the gap. I read in the manual that it does tell you to measure. I'll have to get a gauge tomorrow and see what happened. I'm hoping one is faulty, or that a vacuum line is loose which would be an easy fix instead of something more serious.. I also bought a new air filter today because I'll be rummaging in there anyway.

I've been able to feel the loss of power but just today I felt the bike idle a bit weirdly..

We'll find out tomorrow what is up, I really miss the power.
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Old 04-21-2011, 09:01 PM
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Doesnt sound serious. Probly just the plugs. Did you maybe cross. A plug wire or something? Good luck
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Old 04-22-2011, 08:03 AM
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I didn't cross wires but I just finished up the job (and air filter) and plug #4 was loose enough that I didn't need the wrench to loosen it... Perhaps I was just lacking compressing. I also tested the plugs for spark and everything else was fine!

I'm about to go on a ride so I hope to be back to normal again.

(PS: Didn't expect that much sand and flies in the old air filter .)
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Old 04-22-2011, 11:25 AM
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I'm a bit **** on things like spark plug torque. I always use a torque wrench when tightening them. Hopefully, that was the cause of the low power problem.

Were the gaps all correct?
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Old 04-22-2011, 01:54 PM
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Quote:
Originally Posted by RoadiJeff View Post
I'm a bit **** on things like spark plug torque. I always use a torque wrench when tightening them. Hopefully, that was the cause of the low power problem.

Were the gaps all correct?
I'm very **** about torque specs and I always use my torque wrenches (except for fairing stuff). I forgot to bring my spark plug tool so I used the one my friend had in his Gixxer toolkit. Mine is solid and you can use a 12mm (I think it is) socket to tighten it. His is hollow and a bit different, I couldn't use a 1/4 socket to tighten it with my small torque wrench so I tried to improvise ('making' an adapter for a 1/2 socket to a 1/4 wrench) and failed. I couldn't use the torque wrench in the end so I didn't tighten it enough. It feels better now but I'll have to wait till the amber light comes on to see if I'm back to my old mileage.

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Old 04-23-2011, 10:55 AM
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Hi. Read somewhere recently whislt researching the F4 like yours that you should only use iridium spark plugs. Might be relevant, as you say you didn't replace the old ones with iridium ones? Worth a try if your consumption is still higher than it was before the spark plug swap.
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Old 04-23-2011, 11:24 AM
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Glad to hear all is well and back to normal with you bike.
I am sure the MPG will be back too. A loose plug will play havock with a motor.
Happy trails Be Safe
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Old 04-23-2011, 06:43 PM
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Quote:
Originally Posted by highwaypatrol View Post
Hi. Read somewhere recently whislt researching the F4 like yours that you should only use iridium spark plugs. Might be relevant, as you say you didn't replace the old ones with iridium ones? Worth a try if your consumption is still higher than it was before the spark plug swap.
It's the F4i (FS) and up. that use the iridium plugs Mine takes the normal NKG's.

Everything is back to normal though, the loose plug was the culprit!
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Old 04-23-2011, 06:43 PM
 
 
 
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2000, change, changed, gap, gas, low, lower, mileage, neon, normal, plug, plugs, plymouth, spark, torque


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