Cheap 'Pod' filters - why you shouldn't - Public service posting

CB400 t carbs are not 'jettable'
There is a 'kit' that may help but you can't 'jet out' the over rich condition on transition from primary main jet to secondary main jet
Back in the 80's Leon Moss completely re-worked the carbs for Honda to 'go racing' in Super Stock class, there was all sorts of drilling, piping and machining inside the bodies (carbs on CB750/900 dohc are near enough the same as 400)
 
Just as an FYI, I have UNI long foam flters on my GT750 on BS40 CV carbs and out of idle curiosity I pulled them off tho check to see if they obstructed any air bleed holes. The straight one on the center carb seemed OK (just) but the two 15 degree angled filters had much smaller inner flanges that partially obstructed the air bleeds.

Nothing that couldn't be ported with Dremmel and sanding drum, but a nasty discovery. It will be interesting to see what difference it makes to the Air:fuel ratio and general running - if the snow ever leaves.
 
I've learned a lot from this post :

1. If you're new to DTT and working with motorcycles, prepare to be bitchslapped at some point.

No but seriously, I have a few questions :

1. I recently purchased the cheapie pods and returned them because I noticed the restriction of air myself. I'm buying some K&N universal cone shaped pods instead. Should I go with the UNI foams instead?

2. The XS750D uses the Mikuni Mark 1 BS carb. Should this carb not be run with pods at all? In that case I've just made a huge mistake by ripping the airbox out :(



ive-made-a-huge-mistake-gob-arrested-development.gif
 
K&N are probably better in that the ones I have looked at have no step, but the small step in a UNI can be reduced in 5 minutes with a Dremmel. Don't go mad though and clean out the dust you create with the dremmel.

Those carbs are pretty much the same as an XS650 or a GT750 Suzuki and people fit pods on both of those without too much drama. But you are right that a stock airbox is easier to jet ...
 
Re: Re: Cheap 'Pod' filters - why you shouldn't - Public service posting

kopcicle said:
That's got CV's? Take a #2 phillips screwdriver, heat the tip with a torch until cherry red and plunge it into your eye. It will hurt less. Really. Bikes with CVs have airboxes. Bikes with slide needle carbs have pods. Even Mark Dobeck, former owner of Dynajet, cops to a loss of midrange using his kits.

And for the other eye heat a 3/4" drill bit chucked up in an air drill ...

I can get BS34's to almost work on the 998-1100 with one serious caveat . They will pull hard with the throttle arbitrarily pinned OR they will mix fuel cleanly at part throttle cruise . Pick one I don't know how to give you both . Mark Dobeck and I went back and forth for most of a summer getting several of my customers bikes and my 998 urban terror two wheeler running right . The customers are probably still ****ed even though I neither recommended nor supplied this serious impediment to performance . In the end I knew neither was right (thanx for the flash runs Ron !) But the one that was the best and closest to right got me the most grief . That guy thinks I'm an idiot and in ten years hasn't wasted an opportunity to say so . Funny that the last two guys to touch it asked how I was able to get it so close . The one that isn't so good , that guy thinks I'm magic .

just a partial list

various attempts at
springs
needles
needle jets with and without discharge shields
pilots
mains
main air bleed
air horns within the air filters
closer to or further away from the head
adjustable cam sprockets
different headers ....

All because in one case the owner wanted to look like all the other cool kids
and the other thought it was a pain to get the carbs in and out with the stock aribox

coincidently both of these mental midgets went from 35-36 mpg to 30-31mpg and might have gained a couple of hp on top at the expense of having me spend untold hours filling a huge hole around 4k .

So I was asked recently if I would jet another 998 for "pods" ( is it that hard to say individual air filters ? really?) good thing I kept my notes .

Sure I would . With an eddy current dyno and by the hour ...

~kop
Click to expand...

I dunno. Kop makes it sound like putting pods on a CV carb like the Mikuni and getting it to work right is as hard as rocket science. I don't have any expensive equipment to calibrate with either..aside from a carb sync and my ears.

I should have just stuck to airplanes :p Seriously. The inner workings of aircraft engines seems less complicated to me at this point!
 
Even more worrisome is that he says he got them to 'almost work'. If he couldn't do it, I as a novice don't stand a chance I'd think.
 
Carbs work on pressure differentials and changing the filter changes those pressure differences and the balance is delicate. Some Keihin carbs are extremely difficult to tune after a change in air filter and for sure it's easier with a stock airbox. People have be re-jetting CV carbs for years on the 650 twin.

I'd look at what they do as a starting point. The motor is different but reading some of the 650 threads will give your more insight.
 
Yep, join the XS650 Garage on proboards, they have a complete section on the 650, you'll just have to make allowances for different sized carbs on triple but the information will work on Mikuni CV
 
Re: Re: Cheap 'Pod' filters - why you shouldn't - Public service posting

crazypj said:
Yep, join the XS650 Garage on proboards, they have a complete section on the 650, you'll just have to make allowances for different sized carbs on triple but the information will work on Mikuni CV
Click to expand...

Went ahead and did that. Hopefully someone will steer me in the right direction once my pods get here. Also thinking about sending the carbs off for ultrasonic cleaning.
 
I have cleaned a few sets of carbs for guys on DTT. When you get a quote, why not see if I can match it or beat it. :)
 
Re: Re: Cheap 'Pod' filters - why you shouldn't - Public service posting

teazer said:
I have cleaned a few sets of carbs for guys on DTT. When you get a quote, why not see if I can match it or beat it. :)
Click to expand...

I'll definitely message you, teazer. Would be more than happy to have an experienced DTTer do the Job.
 
If you have a look at the original carburettor incorporating the principle of constant depression, the SU, you can see that it has a separate channel from under the piston to the relatively calm air inside the air filter. On the Mikuni, on the other hand, that channel ends right inside the carburettor throat, in the turbulent air entering the motor. I can imagine that this makes the Mikuni a lot more sensitive to modifications in the inlet.
 
Re: Re: Cheap 'Pod' filters - why you shouldn't - Public service posting

harrydahl said:
If you have a look at the original carburettor incorporating the principle of constant depression, the SU, you can see that it has a separate channel from under the piston to the relatively calm air inside the air filter. On the Mikuni, on the other hand, that channel ends right inside the carburettor throat, in the turbulent air entering the motor. I can imagine that this makes the Mikuni a lot more sensitive to modifications in the inlet.
Click to expand...

Hi Harry, thanks for the input. I see that you've built a beautiful XS650. What kind of carbs are you using on that and how has your experience been with fitting pods on it..
 
Thank you, manas!
It has the original Mikuni 38's, with some no- name pods, when I bought it. Changed them to velocity stacks from Dime City, but I am a bit concerned that the stacks make the Mikuni's port holes a bit shrouded. Maybe I will try and attach a short pipe between the Mikuni's reference hole and the bell mouth, to get undisturbed air into the hole. Later, I plan to put the velocity stacks inside Uni filters to get better air filtering
 
Re: Re: Cheap 'Pod' filters - why you shouldn't - Public service posting

harrydahl said:
Thank you, manas!
It has the original Mikuni 38's, with some no- name pods, when I bought it. Changed them to velocity stacks from Dime City, but I am a bit concerned that the stacks make the Mikuni's port holes a bit shrouded. Maybe I will try and attach a short pipe between the Mikuni's reference hole and the bell mouth, to get undisturbed air into the hole. Later, I plan to put the velocity stacks inside Uni filters to get better air filtering
Click to expand...

Interesting! I'd like to know what happens after your modifications..
 
Was thinking about doing some modifications to the Mikunis, but before that I decided to do some testing. I attached the carburettor to a vaccumcleaner. The hoover sucked air through the Mikuni and the flow was enough to lift the slide all the way up to the top. Then I tried both with and without the velocity stack attached, but there was no difference, so I'm leaving the carbs as they are, for the moment. However, I did modify the Dime City velocity stacks, to the rid of them shrouding the slide hole in the carb intake.
 
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