Mikuni RS38's - velocity stacks/filters??

[Leblowski]

I raced my slabby with 29’s bored to 33’s in the rain at spa with ram air filters for two days no problems

[canamant]

My experience of running bellmouths with no filters is limited to race bikes.  However I've never seen any significannt piston/bore /ring/valve/seat wear.  Admitedly the mileages aren't sky high (thousands rather than tens of thousnds of miles) but race bikes operate right on the edge in a very dirty environment very very close to other bikes with high wind speeds  and race tracks are surprisingly dirty places too. I'd happily run open or very large mesh strainers on a road bike without worrying about engine damage.

 

[Dezza]

Bellmouths often seem to be now presented in conjunction with brown seat covers and exhaust bandages on 'customised' cb550s and similar so this is a big plus point for any sort of air filter.

[Gammaboy]

On 4/4/2018 at 1:51 AM, Flatline said:

Like these?? The twin or single filter??

There's a version of these that Ramair make that's deeper on one side - they come in the correct spacing for Air/Oil cooled suzukis. Them, plus the 50?55?mm long Mikuni bellmouths work very nicely on the RS's on mine.

 

FWIW, I believe most top level motorsports run air filters these days.

 

[Gammaboy]

These ones.

Gives a little more "still air" volume, and a little more filter area.

Ramair MS006 is the part number.

[nlovien]

MS006 with 55mm stack length is what I use - interesting discussions in this post, the question " can anyone show actual erosion / debris  wear " running unfiltered  - or effect of air entry restriction  into the stack - can only offer my own experience

I've observed screwing up the carburation by fitting tea strainers to stacks on 33mm mikuni smoothbores - possibly could have tuned it out but simply run without - great - run same set up with and crap 

I've not observed short term wear damage - forsure I'd presume long term accelerated wear but actually gauge this ? dunno - recon a wet carb left to let fuel creep into the head/bore probably causes more damage

Erosion wear shouldn't be an issue, if I recall port flow is optimised at around half erosion velocity  - ok there will be accelerated flow across valve seats as valves open which could cause wear but its not something i've observed

Carbon build up that then gets displaced - clean air in - make micro deposits inside combustion chamber - rattle this about and flow it out the ex - the best filtered air ending up contaminated is std practise

carbs! - big yes, erosion yes, sticking due to fine debris yes - basically filter for the benefit of the carbs - definitely yes

free still air at stack entry coupled with smooth radioused entry ? this is not bike specific, this is common gas flow - laminar versus turbulent flow issues - and its back to the gas velocity for effect - the higher the velocity the greater chance of turbulence = pressure = less flow  - valuable fine tuning stuff which may show only when up at the high flow demand - will have more effect if you run smaller ID / longer stacks - ok so more important on say 33mm carbs versus 38mm feeding the same engine - - basically this is inline with why a plenum or airbox 

[MeanBean49]

On 05/04/2018 at 2:28 PM, kokolis said:

I ve run pods, bellmouths, for years, raced on street circuits.

If you keep the airbox on what so ever bike, you ll have her for life.

So basically what your saying is what I said was right. In the application were taliking about a mesh filter will not affect performance!

Like I said in my experience ive run no filter for 5 years now, i strip and check everything every 6 months and I have never found an issue. My intake sits 6 inches from the road, i fail to see how a set of carbs in still air under a tank in the middle of a bike are going to be very suceptible to much FOD at all. Probably why ive never had any issues running carbs on open bellmouths ever.

I guess if i was doing 10's of thousands of miles in all conditions it might change that a bit. But i dont.

This is my experience based on actually doing everyrhing I have said previously. Back to back  dynoing, lots if riding and maintenance. If others have had different experience then thats fine

[dupersunc]

My carbs are all exposed to the spray off the rear wheel. 

I can see no reason what so ever to run with out proper filters.*

 

 

*Ok maybe if you are loopy enough to fit a greatbig snail in such away that the air filter would mean you can only lean the bike like an IAM instructor.

[Solcambs]

Interestingly - I had a conversation with a mate who is an F1 engineer at a recent winning F1 team. He has an RG500 gamma, and a slabby. When he saw my build he dropped me a note and said "you are running filters aren't you?" - Open bellmouths = guaranteed early failure. Carbs ingest crap period. This degrades oil, wears rings, reduces engine performance exponentially until failure. Open bellmouths look cool ... but unless you have very low service life on an highly tuned motor ... not worth it!

I also spoke to FrankMX .. who sells those filter sets, and also sold me my FCRs ... and his advice was that IHHO the filter he was selling worked best with a non-airbox set up, and hardly affected the power against completely open. Drop him a mail - he's a knowledgeable guy, and very open to questions.