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KN air filter and weird behaviour

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4.5K views 12 replies 7 participants last post by  Yellowspider  
E
#1 ·
Hello,

Decided to install the KN air filter on my carb bird. The carburetors were synced and cleaned but the mileage was still bad.. around 250 km with one tank... so way to rich... after the KN the mileage went up to 320 km per tank which looks good and sounds like a range....but I feel some hesitation in power....under 6000 rpm when accelerating the engine hesitates a sec than goes... if I go easy on the throttle behaves like lack of gas... on off on off and so on......checked again the tubes for gas and the vacuum and everything seems to be in place....

Any idea???
 
#2 ·
The K&N filter can cause issues, depending on what you have done in the way of mods to your exhaust and induction system. The filter seems to upset the CV carbs ability to cleanly open the slides of the carbs as they are vacuum operated not direct lift slides (When you twist the throttle grip the slides do not open as you twist, they only open if there is enough engine vacuum to open them). To see the difference in performance and ride-ability try putting the OEM paper filter back in the air box.

T.
 
#4 ·
Some light reading for you. There my not be a solution in the following threads but it will give you something of an education perhaps. The easy fix is to remove the K&N and get the bike back to a near stock set up. Old fart talking here, I continue to run stock induction and exhaust system on my XX for both the quiet exhaust note when on tour and for the easy of (lack of) tuning required. But of course that is just me. Sorry but this most likely will not solve your issues.

T.

http://www.cbrxx.com/engine-airbox-exhaust-fuel-delivery/13013-jaws-right-problem.html

http://www.cbrxx.com/engine-airbox-exhaust-fuel-delivery/10928-call-arms-carb-experts-hear-me.html

http://www.cbrxx.com/engine-airbox-...exhaust-fuel-delivery/17138-davids-carbie-xx-fpro-mods-help-required-gents.html
 
#6 ·
Never had a carb version but perhaps removing the grills on the ram on the front may increase air flow, also have you checked the vacuum pipe is not kinked on tank when you put it back? Or try reposition the vacuum hose like I did on my FI which helped a hundred fold. Just some ideas? Like I say never had a carb version but I'm sure other people have had a K&N in carbs and not had a problem but who knows??or perhaps setting up the carbs with gauge with K&N installed?
 
#8 ·
reddave101 said:
......... the grills on the ram on the front may increase air flow......
Click to expand...
The above line struck a cord and brings to mind an often forgotten bit of duct work that is required for the carb'd XX induction system to function correctly. That often lost bit of plastic (x2) are the "Air Guide Plates". I'll attach pictures of the plates and there location below. reddave, thanks for the memory jog. The carb'd machines nose cone airinlets do not have direct inlet trunking directed to the airbox as does the fuel injection machine. The grilled nose inlets on the carb'd XX direct the air toward the oil cooler for the most part, but of course there are ways and means for the air to find it's way to the airbox also. Where as the FI model taps into the "Ram Air" possibilities of the nose cone, the carb'd machines have much short airbox inlet snorkels that measure approx. ? 6 inches (at most) in length, and they simply draw air in from the underside of the fuel tank and dash panel surround fill panels. at a guess the idea is to draw from something of a steady state or calm air supply, because when the Air Guide Plates are missing (easily left out or miss placed) they performance of the machine suffers big time. Unless direct lift carbs are installed the idea of Ram Air on the carb'd machines may be very problematic with the stock CV carbs, at a guess. Here are the pictures of the Air Guide Plates and a couple archive part micro-fiche shots of the carb'd and FI airbox systems.


T.
 

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#7 ·
I've had a K&N filter in a carb model for about 16 years with no trouble. However, I also fitted Remus race cans and a stage 1 dynojet kit. The dyno test shows a smooth power curve with more power throughout the rev range.

I expect just fitting a free flow filter is not a good idea without the other mods, the K&N was always recommend when fitting race pipes along with a dynojet kit.

Ian
 
E
#9 ·
so last night went back to the stock filter and went for a test.... and the bike behaves different... much more power and pulls from low gears.... no more hesitation ... but will test more during the weekend.....I have some shorty exhaust but yes.. probably the filter and the exhaust is not enough.. should be a rejet and some dyno testing for the lean and so on... maybe the vacuum hose is not ok... any idea of a part number for the vacuum hose? like the Honda part number? checked again the hoses and they were all seem to be in place... probably with the stock filter the fuel consumption will go to hell... so I don't know... will try and find a Honda dealer to see if they can mess with my carbs....sometimes on the engine break I hear pops on the exhaust... not normal like on other bikes but almost as long as the engine break is... so if is from 8000 rpm I hear pops until 2000 rpm... might be the case that something does not seal and lets fuel in even when it should not?
 
#12 ·
FI birds run rich (as tested by Beestoys) so they take a K&N easily with no issues. I've been running mine since 2011 and checking the plugs to verify. Earlier birds (carb'ed) are probably tuned right on the edge and the increased airflow tends to push them lean. This will give you exactly what you are feeling regarding hesitation before "it goes". Additional evidence is that your mileage went up which is a sure sign of leaning the motor out.

I would stick to OEM filters unless you plan to re-jet and change them accordingly to your environmental conditions (dusty conditions require more frequent changes). Without tuning there is no real benefit to the K&N.
 
#13 ·
Too rich : pity of the fuel.
Too lean : pity of the engine ��.

I agree with the above: Stay oem or review filter+jets +exhaust as these should be in harmony.

I have a carbie and, based on feedback from this forum, I stick to OEM filters.
 
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