Bike Alterations

[hrc2002]

As looking on Dave Mawers website, I seen that he has used a kitchen sieve (not sure on the spelling) as the vents on his seat to prevent all the dirt getting in.

And I wondered, as a seive doesn't restict airflow, could it be used elsewhere?

Such as the cap for the air filter, over the end of the silencer to stop all the mud getting in and many many more.

However, the sieve will reduce the ammount of dirt that enters, but there will be a build up of dirt, which isn't good for the air filter. But the silencer may be an idea? I've had to take apart my silencer to remove all the mud build up that it creates due the conditions I ride in being so muddy.

Just an idea, what are your opinions, corrections, ideas..?

[bigfoot]

You should never restrict the air flow out of your exhaust, especially on a two stroke. The sieve woud be fine for low volume air flow like intake but would greatly reduce the air flow of an exhaust.

I'd advise you not to even try it.

[ridgrunr]

Not sure what a kitchen sieve is (piece of screen?), but I do put a piece of screen mesh across the air filter intakes of my bikes. It helps keep a lot of the big chunks, grass, bugs, etc out.

A few years ago we had a meet that had sections in the beaver ponds (real bever ponds). One particular section, the first of the day, had been set that so that it dropped into the water, made a left turn then back up out. The water looked about twelve inches deep, but there wasn't a track one in that velvet muddy bottom. "Oh it's not deep", the trials marshal assured me. Not wanting to get my sidis full of water on the first section, I decided to go ahead and ride it, how bad could twelve inches of water be? So I rode first (thinking I'd ride it before it got all rutted up), nosed the KRoo off into the water and about died when it started submerging with no bottom in sight. Dowon down down into the three feet of dinosaur turds in the bottom of that pond the KRoo dived. Man the thing had no bottom. Grabbing the brakes of course did no good as the thing turned into a submarine. I hopped off, and stood there waist deep in water frantically pulling on the bars trying to keep the thing from disappearing, with only the rear fender of the KRoo showing above the water. Two guys jumped in and helped pull the bike back to shore. I was p****d! p****d that the marshals would set a section that they hadn't tried to ride first, and p****d that I hadn't walked it before riding it.

Of course the bike had drowned out, and I could just imagine how that engine had sucked in gallons of dinosaur turds, which I knew would kill it. I pushed it back to the pits, determined to find a big club and then go find the marshal after I saw how much damage was done. I took off the fender and discovered that the picece of screen mesh I'd put across the air box intake was indeed plugged with mud and grass, but other than a tiny bit of water in the bottom of the box it had not ingested anthing. I sopped out the water wrung out the filter, and the thing started first kick. By time I got back to the section, they'd changed it, so everyone else got to go around. I demanded and got (who'd argure with an enraged KRoo pilot?) a reride. The new section went right over a behive in an old hollow log, lots of gyrations as guys rode those those swarming bees. Course they were good and wound up by time I got there , but that's another story in itself!

The moral of the story is, that mesh screen over the airbox intake saved my bike. I've put one on every bike I've had since the U2 incident.

[social climber]

In reply to bigfoot,

Unless there are massive airleaks betwen the airbox and engine (which will cause their own problems...) the Volume of air ( lets say gas to avoid arguments over air / exhaust fumes), through the airbox in a revolution of the engine, and through the exhaust for the same revolution,should be roughly the same....

To demonstrate this, run your bike with the airbox off the next time you have occasion to do so and put your hand over the carb intake to see the sort of suction it generates.

In the U.S. where Public land access demands a DOT approved spark arrestor, the most common one was called a sparky, basically a metal tube made to slip over the end of the exhaust with a wire mesh screen inside the end of it.

[bigfoot]

Social Climber

The air you pull in on the intake stroke is cold in fact the velocity it comes in at cools it well below the atmospheric temperature. The air going out the exhaust is very hot as it's just supported a flaming fuel vapour. Air expands very dramacitally when it's heated meaning that you are expelling a vastly greater volume through the exhaust than you are taking in through the carb.

I've never used a spart arrestor on a bike so can't comment on the construction. A car one is specially designed to cool the air by accelerating the hot air through a series of relativly thin openings. The increase in velocity again cools the air reducing the likelyhood of a spark surviving. This is the same philosophy as used for possibly spark or flame producing electrical equipment used in flamable gas environments. The enclosure has a very thin gap between the body and the lid. As a flame generated inside the enclosure rushes throught the gap it cools and won't light the gas on the outside. Becuase the enclusure is not sealed there is also never a buildup of pressure inside that could cause it to explode.

I'll get off my high horse now.

[social climber]

oops, forgot that an engine is not a closed system and also forgot about thermal expansion.......

My physics teacher would be so proud!!

[glenn]

Hi

Just to add my thoughts on the subject. In my mind any thing that could restrict the flow of air into the air box will have an effect on performance. a properly set up 2 stroke engine pulls in aproximately 16 -18,000 litres of air for every 1 litre of fuel. And opviously anything that restricts this leaving the engine will also have an effect also. this is why it's so important to keep air filters clean.

[steve]

To filter the vents on the seat is probably not going to do any harm, however I wouldn't advise sticking anything directly to the intake on the airbox unless you are increasing the size of the intake to compensate.

Are you finding any debris passing through your 'well oiled' foam filter?

Do you grease the lid of your airbox?

A certain world rider I worked for used to use tons of sticky red grease, not only under the lid of the airbox, but underneath the seat/mudguard aswell. The chief engineer at the factory used to tease him about all the 'strawberry jam' he used!!

[hrc2002]

Hi steve and others,

I have very little ammounts of anything getting though my filter. I was just curious as to if anyone has done this before.

Although now it comes to think about it, adding a thin mesh to the airbox would not be a good idea, for that it would collect the dirt and block the airbox.

However, adding a small peice to stop dirt and crap going into the silencer doesnt seem a problem to me, I know that if you restrict the airflow of the silence the bike will 'suffercate' and die out, or a slight restirction will cause a loss in power and make the bike run s**t.

But, It is a very, very thin peice of mesh, inwhich you could perfectly breath though and I wouldn't image it to restict flow that much. But I'd rather not risk it.

HRC

[t-shock 250]

Does anyone actually have a problem with dirt getting in their tailpipe??

Very unlikely i'd say, sounds like a solution to a problem that doesn't exist!

[hrc2002]

It is in the mud holes of Debryshire. Not so much now, as it is beginning to dry out, but when its wet it turns to really thick mud, and it flings up off the tyre and all over the airbox, fender, my back, my helmet and the silencer.

Not a serious problem, I was just curious.

Cheers All!