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Discussion Starter #1
anyone have issues with road wind hitting the filters causing lean conditions? as soon as i hit 65mph the wind starts to effect my bike. i have to give it about half throttle or more to get it to clean up and that in turn causes me to start speeding. i've got real K&n filters on it. and it runs perfect at all RPMS and at all throttle levels. so long as i'm under 65mph.

I first thought that it was a petcock flow issue. but i turned the petcock off as it was sputtereing and running poorly at 65mph and slowed down and it still had plenty of fuel in the bowls and didn't exhibit any symptoms under 60mph.

so thats all i can think that could be causing it. I think i may try wrapping something around the filters and see if that fixes it.
 

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I'd say it's FAR more likely that your jetting is on the cusp of being wrong or the needle needs to be moved.
If WIND is effecting your jetting then the jetting is too close to being wrong.
An engine under load in 5th gear will run different than it will at other times in other gears. Run it up to 65 in 4th gear and see if it does the same thing.
Sounds to me like it's tied to throttle position, under load, in 5th gear.....which means a carb issue. If you haven't rejetted for the K&N filters then that's almost certainly your problem.
JohnnyB
 

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You have the old standard air + pod issue. I don't think the problem is from a too lean issue as it is from being too rich. From my own experience with my bike and pods is the air flow around my legs at higher speeds creates air turbulence to the pods. I've found from experimenting that if I move my legs around a little the air turbulence changes and I see a change in the engine performance. This is why airboxes are designed the way they are to provide positive air flow at all speeds. I'm seriously thinking about adding some sort of direct air intake from the front of the bike directed to the pods on my bike. The other alternative is to re-install the standard airbox with a K&N filter. I'll have to get back to you with my further investigation. Again - I think the problem is caused by air turbulence and being too rich not too lean...
 

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Discussion Starter #5
okay. i tried it at 65 in 4th. still have the issue.

i also tried using old K&N filters with more oil and dirt on 'em. it got about 35% better i would say.

its very possible that my carbs could be the issue. i ran 125 jets earlier this week and it did the samething as now with 130 jets.
I don't think its too rich, because when i pull the needle up the jet to let even more fuel in, it clears up and gets better.
BMartin, i look forward to seeing what you find. please post it in this thread for us and i'll do the same if i find any fix for it. i'm thinking about wrapping a papper towel around the filters of something and trying that out.
 

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if it's not a race bike, rather than go through all that bullshit, why not go back to the air box? i agree pods LOOK better, but then again, so does the clean, minimalist appearance of no front brake...or fork brace. boxes were a result of major engineering improvements and as far as i'm concerned, putting pods on a road-only bike is a technological regression for the sake of appearance.

...of course, if you're the kinda cat that likes to tinker as much as he likes to ride, then hats off to your efforts bro! i hope you get it sorted out and i look forward to reading about your success! direct air induction is straight up cool! i guess what i'm saying is that it's kinda like reinventing the wheel. or in this case, re-engineering an airbox.
 

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i am going to say this is a jetting issue. we run a "pod" style filter on my dirt tracker and if it is jetted correctly, it will run the same at 30mph as it will at 80mph. You are correct in your thinking about air turbulence, it does have its affects, but not THAT much affect. also, in theory, i would GUESS that the factories use airboxes on stock bikes not because of the power gains, but for filter protection. They need a bike to perform well, sure, but they also need to protect it from bone head owners who are not going to take care of their bikes as well as enthusiats like we do. too many bone head customers that dont maintain and open filter element...you start getting blown engines and a bad reputation. however, you place that filter in a box where it only pulls air from relatively "clean" spots, and the filter will stay MUCH cleaner. so if you think that it is too rich, you need to go DOWN in jet sizes. also, your needle, it only affects 0 to 20-25% of your throttle opening. after that you pilot takes over from 25-50% then the carb comes up on the main jet. keep that in mind while you are tinkering. a little tinkering and some test runs and you'll get this fixed...plus hey, thats extra riding time!!!
 

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Folks - the effects we are talking about here effects multi cylinder MC's where the pods are directly behind the engine. Pampadori - I'm getting my bike on the road this weekend - the weather here finally broke. I'll have to get back to you on this but I still am thinking it is an air turbulence issue which is effecting the carb operation. You can also try out moving your legs on the bike (blocking or unblocking) and see if you notice a change also. BTW - you never mentioned what kind of bike your talking about....
 

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quote:Originally posted by bmartin

Folks - the effects we are talking about here effects multi cylinder MC's where the pods are directly behind the engine.
...no shit. hence, "dirty", inconsistent intake. turbulence. why do you think moving your legs around works?
 

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no, he was shooting me down on my explanation about my single cylinder race bike...
 

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show pix of your setup

too short of a filter is much more likely than dirty air turbulence especially for an inline

the reversion slug does need room to expand before hitting the back of the filter

next on my list would be adequate fuel bowl venting

run your fuel bowl vents up into clean air

they are much more affected by dirty air than the clean air intakes

and I run two bikes with forward facing carbs, one even have multiple facing carbs and both have open velocity stacks
 

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I'm running pods on my SuperIII and it has any issue though it's a faired bike.
I ran pods on my Speed Triple previously without a issue.
I agree about the bowl vents wanting 'clean' airflow, any kind of pressure variation in the bowl will readily (and negatively) effect fuel metering. We mocked up a ram-air setup on an old GS drag bike and it caused all sorts of problems until we took measures to be sure the float bowls saw the same effect as at teh carb mouths.
 

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I'm going to weigh in with johnnyb. The chances that the wind is creating an over pressure is borderline impossible. The best wind tunnel tested ram air boxes at triple digit speeds generate just slightly above ambient pressure. My bet is a bum needle setting. I had the same situation w/ my vfr, a hideous stumble at 5500 rpm. I had to rev through the flat spot which made being smooth a joke. I went for a custom needle set that was tapered and designed for my header. problem solved, she rips.
cheers, bcr
 

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well some of the japanese carbs are known to have inadequate fuel bowl venting for anything marginally above stock performance levels and carte blanch going to jetting some of those without correcting that real problem first is somewhat as useful as peeing up a rope

and I do agree that if moving your legs around produces notable change

one either has some really obtuse funky aerodynamics going on or your carbs have some tuning problems

most UJM's I've had will barely run at all once the stock air box has been removed

and replaced with nothing, velocity stacks, or aftermarket pods

until errors have been corrected and jetting has been dialed in

in fact I cannot recall one that would run right after removal of the stock airbox without retuning

even if everything else; pipes, ignition, porting/valving, cams, etc were left stock
 

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Discussion Starter #15
well after reading sohc4.net (a honda cb350-cb750 only forum) this must be an issue with most all of the cb750's. i've had the bike for a while now, about 2 years. and its not so big of an issue that i'm going to put the box back on. it runs really well usually and its not like i drive on the interstate much anyway.
If i do anything, i'll most likely build a shield around 1 and 4's filters like this...

that shouldn't take long to make and may just be the trick. But i apprieciate everyones thoughts.
 

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Back when you could still find these cheap I used to buy every one I found and use them:

http://cgi.ebay.com/ebaymotors/1973...ryZ35597QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

They use the stock carb to airbox rubbers and I would just buy unifilter blocks or sheet and cut them to fit (you need the center removed on the blocks to get the airbox effect).

They always worked great. Looking at how they are constructed it would not be hard to make a filter setup similar our of plate steel or aluminum
 

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The dyno testing we've done on our 200cc honda twins has shown them to be unbelievable sensitive to the intake tract up stream of the carb inlet. Hack is right about that, they are very sensitive to the reversion pulse.
JohnnyB
 

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Appreciate the back JB, be a shame to see earnest people be lead astray by the herds of non-tuners

Choking out half the filter with ether a shroud or the riders hams........ and it affecting running tells me there is a lot more wrong with the jetting and filter itself than well protected carbs running in allegedly dirty air

even HD's running velocity stacks on the salt have zero problems and if so, cocking it forward or aft about 7 degrees does the trick

picture that carb and stack actually parallel to the air flow


interesting is to note what happens on either one of my open velocity stacked forward facing setups at speed

reality is it is very anti-climatic but the whole setup was totally un-tunable until I enlarged the fuel bowl vent and actually put the vent in very clean air

the other reality is it would be quite different if both that I run weren't tuned to 2nd 3rd and 4th intake pulses

and my lil flatty goes slightly positive manifold pressure just past 70 mph


but even for non-force fed applications

not allowing the reversion pulse room to expand is the kiss of death to full range tuning

this is why you see XR and other flat-trackers running those very long bodied K&N's

they have long rod:stroke and huge ports with big nasty cams

put a pancake filter on it and say goodbye to either topend or that powerless 4000 rpm idle and say hello to beating your head against the wall trying to get your jetting "settled in"
 

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I've got no technical data to back it up, but so far it's appeared to me that the larger volume of still air in an air box/filter that my carbs can draw from the easier it is to tune, with fewer "anomolies" at various rpms. If I plan the intake length from valve head to carb inlet properly, then give it a big dead air space to draw from, it seems real happy. No gobs of power to be had, just consistant carburation at just about any throttle position. My guess is the high frequecy, low pressure pulses from a short stroke, 12,000 rpm engine are more forgiving than other applications.
JohnnyB
 

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a classic and common example would be the very thin, air bending pancake K&N's used on single carb 650 triumphs and then on certain custom 71 and up Oil In Frame Tri/BSA's

that reversion slug has them dripping raw gas at certain engine speeds which is largely dependent on the exhaust system

and often they are impossible, at least without a handy set of carb drills and the willingness to file on slides and/or needles... to get dialed in since the pilot jet is both hidden and fixed......

and the slide cutaways are in hugely coarse increments compared to mikunis

it is really easy to physically see and feel this reversion

just remove all filters and watch with your eyes thru the engine range

hold your hand behind the bellmouth and it will get wet with fuel

to be consistent........ the carbs have to be tuned in that range to actually be enriched THREE times and the filters must not interfere

which will mean when you un-restrict the exhaust........ some circuits will need to be made leaner

becomes more pronounced with straight pipes or megaphones

do nothing but remove the mufflers from your triumph......

it will require smaller main jets

sounds bass ackwards wrong but it's very true

put a megaphone on the straight pipe and it will require uncommonly lean slide cutaways
 
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