K&N FILTERS
I've done my own research a few years ago, not aware of the information in forums, and maybe it's intresting to share. I have a CB72 (1967) and I ride it almost daily (more that 5000 km a year).
Changing the air filter from time to time got more difficult (expensive) each year, so I replaced the original paper for the foam and oil solution. It works great, and it's a safe way to filter the air (including the air from the air vent from the cilinderhead hoses). I could use a K&N filter but I like going for original as possible. But put in mind that changing the setup of an engine, if it is an other air filter (usually with higher air flow like K&N), or other exhausts, it will effect the mixture. A few years ago I wrote about Dynoyet tests of different exhausts on my CB (if anyone is intrested I can share this info on this forum), but I also found out that the original setup isn't ideal. Dynojet tests back in in 2002 (original setup, including original air filter and rebuild motor) showed that the engine was running a little lean, and in some area of the RPM range very lean (that is an explanation for overheated small ends and for blowing holes in pistons). I changed the carb setup, and the problem was solved. Changing to another air filter (more flow) showed again a leaner mixture on the dyno specialy in the mid and top rpm range, I had to change the carb setup (more fuel), to make it work. I have the (late) power yet version carbs, very early (stainless) exhausts, self made stainless downpipes, early type cams. To make a long story short, beware of changing the air filter with a more modern (high flow) material. A very easy way is to "read" your spark plugs from time to time after the change. Jensen
Jensen - you're right about the leaning of the engine with the addition of filters such as the K&N's. I'm running Amal (626) MK1 Concentrics on my CB77, and we've made the necessary adjustments to ensure proper mixture for my particular setup. I'm also running TOGA/Norman Hyde Goldstar mufflers which flow much more than the stock arrangement.
I'll try to get the part number for those filters this week -- sorry for the delay, but work has taken control for the moment!
Great info! Yes, I am a big fan of KandNs. Once they are in I'll stop playing with my new Vespa engine and do my total tune up on the CB77 including valve adjust, mixture, points, condenser. Following the instructions in the honda305 faq - thanks for that too!
Right now, according to the plugs, I'm running rich so I think this may actually get me closer. Currently I have Oval carbs Points factory pipes without baffles Original air filters... dirty but I did brush them.
Bad News -- Can't find the part number for the air filters, but if you measure the filters and just look on the K&N filter chart for the closest match, then that should work, or call K&N and quote them the numbers I posted that are on the ends of the filter itself and they should be able to figure out which one it is. As well, you'll need to weld a collar of some kind onto the mounting bracket so that the filter will have something onto which it will clamp. You could use a piece of exhaust pipe or even a reducing sleeve for a muffler. You will also need to be very careful in the welding as the metal on the bracket is very thin, and the collar metal might be thicker (I'm sure all you welding experts out there know the process much better than I).
Dyno Experience .. a new thread ?Hi Jensen
I'd be interested in reading the results of your dyno experience .. perhaps it should be a new topic ? I have a CB72 running old rechromed silencers with most of the internals gone and VW baffle tubes fitted; the carbs are all on std UK settings but I don't have any alternative jets. She runs fine except on the last 1/4 throttle or so but without alternative jets the only method I've tried to adjust the mixture is to play with the float level ( not ideal I know ). As the silencers are starting to crack up I've got a pair of David Silver replica's ready to go on but again they would need setting up... I'm thinking of booking some time on a dyno with a gas analyser but its a bit pointless until I have the ability to easily change the jet sizes .. was your experience positive ? Hoping to get the top end performance sorted as supposed to be going to the Coupe de Moto-Classics at Dijon with it and would like to do Spa later in the year as well. cheers Phil PS - Vince, see you have some ACE Cafe stickers on your 305 .. let me know if you are after any other stuff as our section of the VJMC should be going up there in the next couple of months and they are always at Brighton in autumn.
Hi Phil -- Thanks for the Ace Cafe offer. I actually got the decal from the cafe at '59 Club Day' in September of 2005. As far as other stuff goes, I have my requisite Seaboot socks, Defender boots, Davida helmet (even a brand new Cromwell helmet before they were discontinued the first time around), Perfecto jacket, Belstaff etc etc so I think I'm covered for now -- unless they do up some commemorative VJMC Day regalia or something like that. BTW, are you on the Classic Bike forum as well????
In terms of performance increases with the K&N filters, my seat-of-the-pants perception is that there is a noticeable tweak in performance, and it seems to be throughout the entire range. Mind you, we did also adjust the Amals, and I have the Toga exhaust system, so I think the addition of the filters rounds out this particular system nicely. The Amals may need a smaller main jet once the warmer weather sets in, but we'll deal with that easily if it's needed. And yes yes, the vent filters are officially installed on the bike, so no worries about potential 'raw' air contaminating the engine, though I'm still a bit of a Doubting Thomas about that likelihood. I should be picking the bike up next week from 'the masters' Bob Wolf and John Grainger of Wolf Cycles (the weather should be much more agreeable than the current 18 degrees farenheit) and I'll post photos of how they have been installed. John ended up using a pair of filters from Drag Specialties rather than the K&N's because their mounting bracket worked better for him, but they're basically the same type of filter. This is the Drag Specialties mini crankcase vent filter.
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