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post #1 of 9 (permalink) Old 09-18-2008, 02:30 PM Thread Starter
 
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K&N Filters & Jets

Took my bike in for th 12,000 maintenance, when I told the tech I wanted him to put in K&N filters he told me that he would also have to re-jet the carbs..
I did a some research and the only thing I found was that when you did an EarJob you needed to re-jet the carbs.

Is the tech just trying to drum up work?

Thanks
Tim B
2004 VN750 in California
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post #2 of 9 (permalink) Old 09-18-2008, 03:08 PM
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He might be. He might also legitimately believe it's a need....

As I understand it, and have read dozens of times on these very forums, just putting on K&N filters, without any other changes to intake or exhaust, you don't need re-jetting. Lots of folks here have done just the same without trouble.

Save yourself a bunch of money and time; buy the filters yourself and put 'em in, and keep on riding.

The whole re-jetting issue is a hot topic- a close second only to "which oil is best".

BTW, welcome to the forums. I'd suggest you spend some time reading all around here, especially the "Verses" before you let somebody work on your bike.

Last edited by 750Doug; 09-18-2008 at 03:10 PM.
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post #3 of 9 (permalink) Old 09-18-2008, 03:15 PM
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the need to rejet depends entirely on the exact bike in question. Engine Age, Mileage, fuel condition, carbeurator condition, pipes, aircleaners all have an effect on the tuning of the bike.
Jetting and needle settings vary from bike to bike enough that it is really hard to say one way or another. If the bike wont run well by just adjusting the screws, then a rejet may be required. Some bikes run just fine with a little tweak on the screws. K & N airfilters increase airflow, which requires more fuel, requiring at least some adjustments, and depending on the engine and pipes, possibly a rejet.

The Emgo Pods on the other hand are pretty restrictive, requiring changes in the opposite direction.

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post #4 of 9 (permalink) Old 09-18-2008, 04:12 PM
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Before my 750 i had a 500. A friend suggested that I put on K&N filters to get some more pep. Did that and soon noticed that I was running too lean. Everybody I asked at that time said that I was sucking so much more air that new jets were indicated to enrich the mixture.

Went to the mechanic and once he opened the carbs to change the jets, he found that the diaphrams were streched out and needed replacement. By the time I was done with a "simple" filter and jet job it cost me hundreds of bucks.

When it was done it ran very well but the money is keeping me from putting K&N filters on the 750 because opening up the carbs and changing the jets is not a simple job. Just be aware of what you're getting into before you start.
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post #5 of 9 (permalink) Old 09-18-2008, 04:32 PM
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Where you live will add in to the factor as well. a person riding on the coast, and one riding in say the Rockies are more than likely to have different jetting needs. Especially if you change the airflow amount.

Don't know if I'd be considered old fashioned, or just low tech, but a plug chop has always been the best way to see what the engine needs or doesn't need.

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post #6 of 9 (permalink) Old 09-18-2008, 04:54 PM
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Quote:
Originally Posted by Scootergptx View Post
Don't know if I'd be considered old fashioned, or just low tech, but a plug chop has always been the best way to see what the engine needs or doesn't need.
Thats the only way as far as I'm concerned.

85 VN750 basketcase ( yes its a true 750, and no smog controls, its good to be Canadian)
It will have
a rebuilt 96 top end, rebuilt 85 bottom end
degoated, Eared
stripped, lowered, raked, bobbed,
reed valve boxes shaved
ported and polished
balanced
right side dump exhaust
heads and cylinders shaved for compression
looking for smoothbore sidedraft carbs
possibly fat bob tanks
modified vn800 or sportster drag pipes or I'll just make some

Chopperfix
Duck's Garage

Last edited by Duck; 09-18-2008 at 04:57 PM.
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post #7 of 9 (permalink) Old 09-18-2008, 05:29 PM Thread Starter
 
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Thanks. I'll order up a set of K&N KA-7586 filters and replace them myself, then after a couple of tanks of gas, I'll check the plugs and make the decision from there (I 'assume' that is what you mean by a 'Plug Chop').
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post #8 of 9 (permalink) Old 09-18-2008, 06:59 PM
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I think some of the confusion is because there are those that have done an earshave, and used K+N filters. These are small screen covered filters that clamp directly to the mouth of the carb. Some call them "pod filters" .

Now, K+N also makes filters that are replacement filters for the stock ones inside the "ears". Some say these are less restrictive, but I do not think they really make that much difference, as the stock air boxes have a rather small inlet for the air to enter and with all the other crap the air has to go through before it actualy reaches the carb mouth, I seriously doubt that swapping the stock filters for ANYTHING that still goes inside the ears is going to require re-jetting..(going on the assumsion that the bike was running fine to begin with and your not using a filter that has less surface area)

But , if you alter the intake in any way , either by removing the whole system and installing "pods" i.e an "earshave"...or simply making the intake hole in the ear larger, you will increase the flow of air enough to require re-jetting.

If you go look at the stock airbox, you will see that the air enters through a square hole about 2 inches on each side. Thus, about 4 square inches. The outlet from the filter goes to yet another box, and there it is mixed with the air from the other ear, and then split again, before it goes down the hose connected to the carbs mouth. This is where the restriction is, not in the filter itself.

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post #9 of 9 (permalink) Old 09-18-2008, 10:36 PM
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If you like your nice shinny chrome headers, you may want to jet. The first visible sign of lean mix is bluing on the header chrome. All the rply's above are mostly correct and give you good info.

The basics are, change the intake: check the plugs. Change the pipes: check the plugs. Change both (to less restrictive), go buy the jet kit and follow the verses suggestions.

The other factor is how do you ride? If you put put or ride wide open the jetting will be different.

I'm doing mine this winter so post what you do for others to share.

DT

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