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

RoadRash

New Member
harrydahl said:
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.
:eek: :eek: :eek:

Dude, why are you hooking your carb to a vacuum, and what they HELL did you think that was gonna prove?!
 

crazypj

Split personality, I fake being smart
Sounds like a pretty reasonable way to test in my opinion.
Probably had too much vacuum though, need to have some sort of bleed so slide just lifts all the way without filter then try again with filter.
Slides rarely lift all the way on bike, they barely move until 5,000 rpm
 

manas

New Member
No expert but I would think that a vacuum cleaner might not imitate the exact pressure differential but wouldn't exceed the design specs of the carb. I don't think vacuum cleaners are all that powerful, at least household ones. I might be wrong.
 

crazypj

Split personality, I fake being smart
Topic was covered a few years ago on the XS650 garage board, slides don't lift until around 5,000 rpm, the airflow through motor isn't as high as you would think
 

manas

New Member
That makes sense. I was just pointing out that I don't think a vacuum cleaner would damage the carburetors.
 

teazer

Active Member
DTT BOTM WINNER
PJ, do you mean that they don't even start to lift until 5500 on an XS? IS that true of the BS34s and 38s?

BS40 on a GT750 lift with a blip of the throttle - probably closer to 3000 but I never stopped to check. Maybe next time I have it on the dyno I'll pop the pods off and watch the slides.
 

crazypj

Split personality, I fake being smart
Yep, the slides are a fair way up when fully seated.
If you open throttle gradually you can get a pretty high rpm before they lift
When you blip throttle they flutter
 

harrydahl

New Member
Well, that wasn't my experience. As soon as I opened the throttle the slides started lifting. I was surpriced that the vaccumcleaner managed to draw so much air. Also tried to attach both carburettors to the vc at the same time, but that was too much for it, the slides only went up halfway, but I could confirm that they lifted the same amount, indicating that the carbs seem to be syncronized. Anyway, the purpose of the test was to see if the velocity stack had any harmful effect on the carb, but could not notice any difference with or without the stacks attached. But as I wrote before, I did some modification the the stacks, so now they have the shape similar to the cooling tower of a powerplant (hyperboloid).
 

RoadRash

New Member
I guess my concern was that it was not going to be an accurate comparison cause an every day vacuum isn't gonna give you the same velocities that they would see on the bike. Way too much velocity to test with, IMO, so of course you're gonna get the same results with or without the stacks.
 

RoadRash

New Member
By the way, sorry if I sounded heavy-handed in my initial reply. Wasn't my intention. Funny how writings don't always read like the writer's emotion.
 

manas

New Member
Re: Re: Cheap 'Pod' filters - why you shouldn't - Public service posting

RoadRash said:
Way too much velocity to test with, IMO, so of course you're gonna get the same results with or without the stacks.
Really? My guess was that while you wouldn't have such a sustained period of suction, the rate of suction as well as the dynamic pressure would be greater through the Bernoulli's tube. I guess we could roughly calculate it if we knew the displacement and the average time the slide is open for. Actually never mind, I think all you would need is the time taken for the intake cycle and displacement.
 

harrydahl

New Member
RoadRash said:
By the way, sorry if I sounded heavy-handed in my initial reply. Wasn't my intention. Funny how writings don't always read like the writer's emotion.
[/quote

That's OK, sometimes it's not easy to understand, what the other fellar is trying to explain :)
This is how the velocity stacks look like now.
 

Attachments

crazypj

Split personality, I fake being smart
Cool, works for me ;)
David Vizard uses a shop vac for a DIY flowbench, it's in a couple of his tuning books
The electronics to go with it are about $700~1,000, need to be doing quite a few heads/carbs/filter checks to justify that outlay though (still way cheaper than a $5~10,000 dollar bench 8) )
 

Rich Ard

doin' the backstroke in an estrogen ocean
DTT BOTM WINNER
Re: Re: Cheap 'Pod' filters - why you shouldn't - Public service posting

harrydahl said:
This is my "flow bench", made up from a vaccumcleaner, a beer can (Carlsberg, not my favorite..) and some masking tape...
It's good enough for who it's for ha ha! Good idea.
 

harrydahl

New Member
Just beware that the carbs are clean,you don't want gas fumes into the vacuum cleaner, might be a surprise.....
 

crazypj

Split personality, I fake being smart
Motors are sealed on new ones, Mythbusters did a bunch of tests (I wouldn't deliberately suck gas through vacuum though)
 

harrydahl

New Member
Well, what do you know....You learn something every day! Unnecessary knowledge: the vacuumcleaner is an Electrolux, who owned Husqvarna motorcycles ("Husky") for a brief time, but then sold it to some Spanish or Italian company. I believe the brand is now owned by BMW.
 

kopcicle

antidisestablishmentarian
crazypj said:
Yep, the slides are a fair way up when fully seated.
If you open throttle gradually you can get a pretty high rpm before they lift
When you blip throttle they flutter
Teaz I can confirm this

~kop
 

Bobby Joe

New Member
Wow...putting this on my list to check. Good find. I would almost be more worried about the filter properties over the rubber boot.
 
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