Unfiltered Intake Air.

BlackJota

BlackJota

Senior member
Location
Sunshine Coast Australia
I have noticed a number of bikes on this forum and on the streets with Carburetor Velocity Stacks. I'm sure they can serve a purpose
and they do look really good, and a lot of the older bikes came with them fitted as standard.

But it begs the question, has anyone actually had any engine damage / wear caused 100% by the fact that the intake air was unfiltered.
And I mean by riding on sealed roads only, not dirt roads.
Also, has anyone noticed no adverse wear or damage over time to their engines using Velocity stacks or open carburetors.
 
Can't answer re sealed roads, but my SF1 bores were totally destroyed after long term travel - airbox fitted but no air filter. I went from Melbourne to Darwin and down to Perth with long stays in between over an 18 month period. and quite a lot of dirt.

I have never since and never will ride my bike without quality air filtering - whether on sealed roads or not. But good question to ask and hopefully some high-mileage riders will chime in.
 
I can't give a definitive answer because I've always run an airbox with some sort of filter but I agree with other comments that it would depend on how far you are going and the roads.
One of the first things I did when I got the AE was source a proper type airbox and foam filter because even a lot of sealed roads I travel on are fairly narrow and involves excursions from either party to travel on the bare verges with plenty of dust and debris.
Seems illogical to me to travel any sort of decent distance (at least in Oz) without some sort of filter.
 
I'm not really questioning if you should or should not have air filters, I was asking about peoples experience who have or are using Velocity Stacks and if any damage / wear has been caused over time, or not, by normal sealed road riding.
 
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Just a bit of info re DNA Filters, I cleaned and reoiled mine a while back after a good few years and there was quite a bit of fine crap that was in the sink afterwards. Kinda expensive but it lasts for 3 or 4 cleans and oils so that's YEARS


 
One of my old customers was an air filter mfr, this is going back to when Australia actually manufactured things. I asked what the best air filter was for engine life (meaning paper or foam) but the answer was:

Don’t tell anyone, a really dirty one, the layer of dust and shit creates another barrier. May not be for easy breathing though.
 
chrisk said:
One of my old customers was an air filter mfr, this is going back to when Australia actually manufactured things. I asked what the best air filter was for engine life (meaning paper or foam) but the answer was:

Don’t tell anyone, a really dirty one, the layer of dust and shit creates another barrier. May not be for easy breathing though.
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Yep, I got told the same thing from a customer who worked as tech support for a filter company. He said engine manufacturers come to them with details on size and flow required, then they design a filter that achieves the requirements about half way through their lifespan. So a new filter has too much flow and less filtration. Ironically, by the time it gets to the perfect spec, people throw them in the bin and buy a new one.
 
BlackJota said:
I'm not really questioning if you should or should not have air filters, I was asking about peoples experience who have or are using Velocity Stacks and if any damage / wear has been caused over time, or not, by normal sealed road riding.
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No personal experience (I always run with some kind of filter) but my much older brother Bob used to race a little open-wheeler car. It had a JAP V-twin engine with AMAL carbs and open inlet trumpets. He raced on sealed roads or race tracks, but he'd often go through clouds of dust from other cars that had run off into the gravel. By the end of his first race season there was enough scoring in the cylinders for it to need a re-bore. He fitted air filters after that did several more seasons. He'd lift the heads occasionally to check the bores and they were fine. The car was still going well when he sold it.

For anyone interested in historic racing cars, Bob's car was a JAT, built by John Trowbridge in Tasmania (JAT were his initials). He built around 40 of them. The first one had Goggomobil running gear and engine. The Goggo 2-stroke engine was a bit gutless so later versions used other engines. I managed to find the photo below on internet. It's one of the early Goggo powered JAT's. My brother Bob's car was red and had a considerably more powerful 1000cc JAP V-twin engine. I was only about 8 or 9 when he got it (Bob would have been 20 or 21). He raced it for several years and I remember it well. I used to go along to many of his race meetings. He let me drive it once with him sitting behind me between me and the roll bar, telling me what to do. There was enough room because I was quite small and had to sit well forward to reach the pedals. Bob used to fly light aircraft too and would take me flying with him. He was a very cool older brother. RIP Bob.

1959-jat-chassis-no-1.jpg
 
BlackJota said:
I have noticed a number of bikes on this forum and on the streets with Carburetor Velocity Stacks. I'm sure they can serve a purpose
and they do look really good, and a lot of the older bikes came with them fitted as standard.

But it begs the question, has anyone actually had any engine damage / wear caused 100% by the fact that the intake air was unfiltered.
And I mean by riding on sealed roads only, not dirt roads.
Also, has anyone noticed no adverse wear or damage over time to their engines using Velocity stacks or open carburetors.
Click to expand...
No problem on the bores of my SFC after maybe 30 000km.
My S is unfiltered, on original bores. Near 60 000 km. It'll out live me.

Paul
 
In my experience the Dellorto carb slides wear out fairly quickly. They wear quickly anyway but I would say it increases the wear rate.
 
pf1 said:
In my experience the Dellorto carb slides wear out fairly quickly. They wear quickly anyway but I would say it increases the wear rate.
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The slides can be replaced, albeit they are getting pretty expensive. Carb bodies wear out with them and they are not cheap, but it gives a good excuse to upgrade so Mik or Kei. My SF2 carbs were totally gone after a year without filters, but the cylinder bores hadn't suffered appreciably. Stanco had no replacement filters and I hadn't worked out an alternative, and I listened to people who said they weren't needed.
 
Zandvoort, isnt that smething like "on sand"? in UK speak?
not quite sand yet, still in rock formation, waiting further grinding
ouch that looks very abrasive.
CLEM
 
My 3C hasn't seen an air filter since around 1980, only an empty air box fitted. The pistons and barrel I removed a few years ago to replace with 78mm slugs showed no undue or unusal wear, these had done about 60000km from new. Rings and bores would be quite OK for at least another 20-30000km, the upper ring grooves started showing normal signs of wear. No excessive wear in the carbs either, everything sort of normal.

Climate here is on the wetter side of things, dust would be the exception and road surfaces are generally quite OK.

piet
 
I can only think of the 800km of bulldust i rode on the old Fitzroy Crossing section of the only major route through NW Oz. That and countless long miles riding on outback roads - when I decommissioned my speedo in Perth with 62,000 miles on it the ridges in the bore were huge and the top rings in several pieces - 0.4mm OS didn't clean it up - it was straight to 0.6mm. It was a credit to the motor that it still ran fine - just a tad gutless - i realised once it have been rebored and the head reco'd.
 
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