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Engine and Valve cover breathers  Rating:  Rating
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 Posted: 06-03-2005 12:04 am
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Wayne McCartney
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I have a question regarding breathers. I notice on my car which is fitted with K&N air filters that the breather that comes from the volve covers is attached to a metal tube that is inserted in a hole in the rear carb's air filter housing. The engine breather that is at the rear of the block has a 90 degree angle hose that simply breathes into the engine compartment. My car is running quite rich (some smoke, stammering at idle, etc.) and I suspect the carbs are in need of rebuilding as no amount of mixture adjustment seems to rectify the problem. Is this the correct arrangement for these breather hoses? The larger engine breather in particular seems to create a nasty odor in the engine bay making working with the engine running quite unpleasant and I'm guessing the fumes find their way to the cockpit. I have noticed in photos of the original air cleaner setup that the engine breather hose appears to be fiited to the rear of the air cleaner housing. Is the original setup preferable?

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 Posted: 06-03-2005 12:33 am
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Jim Ketcham
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Hello Wayne,

The large breather hose that comes from the rear of the block goes into the "air box" on the factory original.  On later models the vent added to the top cam cover on the side of the oil filler inlet also goes to the "air box".  The air box in turn connects to the air cleaner housing.

It is undesirable to have the hose vent to atmosphere, especially in the engine compartment, both from an environmental and safety viewpoint. 

In my opinion, the air box venting also offers a bit of vacuum for the crankcase which, directionally, is a good thing to help limit seal leaks.  It is one of the reasons that I reinstalled the original type air box system on my JHs.  The main reason was that I found the Dellorto carb noise a bit too much with the K&N type filters.

Jim

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 Posted: 06-03-2005 01:01 am
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mike92782
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Hi Wayne,

I have an extra original airbox and "muffler" type air cleaner assembly that I am willing to part with.  Contact me at mike92782@sbcglobal.net if you are interested.

Mike

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 Posted: 06-03-2005 01:07 am
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Wayne McCartney
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Jim,
Thank you for the prompt reply. You have voiced my concerns precisely. My car came with the original air cleaner monstrosity in a box with the attaching hardware included. I may convert back to it. Is everyone who has converted to the K&N system dealing with the same thing or do I perhaps have an incorrect setup?

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 Posted: 06-03-2005 01:34 am
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Mark Rosenbaum
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First, from the symptoms you list, it sounds likely that your carbs do need to be rebuilt.  The mixture setting on Strombergs really works properly only when the rest of the carb is in good shape.

Next, many (probably most) JH engines smoke.  Those that have been sitting for a while smoke a lot more.  And it's even worse if the crankcase oil isn't about half a quart below the 'full' mark.  Fortunately, driving a JH on a daily basis usually reduces the smoke significantly, often to the point that it isn't really noticeable.

Other than annual engine rebuilds, about the only solution is to suck the fumes into the cylinders where they will be burned.  The conventional way of doing this is to use 'positive crankcase ventilation' (PCV) which is nothing more than allowing manifold vacuum to suck the fumes out of the crankcase, generally with a one-way valve so that backfires won't ignite any crankcase fumes.  Despite the relatively low manifold vacuum in a 907 engine at idle, this might actually have worked fairly well.  But Lotus, for some reason, chose not to do so, and my understanding of US emissions laws says that because the manufacturer didn't, neither may the owner, unless he wants to formally certify his system.  But IANAL and could be wrong.

What Lotus did do was to vent the crankcase into the air box, later adding a second vent from the intake cam cover.  Notionally this provides an equal amounts of fumes to each carburetor.  In fact, due to the locations chosen for the hoses, the rear carb seems to get about 2/3 of the fumes.  From an emissions standpoint, this may not matter much, but from a carburetor lifespan and function standpoint, it matters a LOT.

Unless K&N has changed their setup recently, their arrangement dumps all the fumes into one of the carburetors (usually the rear one).  I don't think this arrangement is anywhere near as good as the stock setup.   

To do the job right, IMHO, one needs to deliver fumes to both carbs equally.  There are many ways of doing this.  The method I chose is shown in the attached photo, though the photo does not show that the original fume hole provided by K&N has been capped off, nor the coupling connecting the central hose to the hose from the crankcase vent.  Any fluids in the system, regardless of source or nature, should drain out through the bottom of the filter rather than being ingested into the engine.

As I recall, the hoses and fittings together cost about $10-12, and this could be reduced considerably if desired.  Perhaps more importantly for those folks in California, the car even passed an honest smog test with this system in place.

Attachment: breathers.jpg (Downloaded 183 times)

Last edited on 06-03-2005 01:37 am by Mark Rosenbaum

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 Posted: 06-03-2005 01:35 am
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Judson Manning
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Wayne,

My car probably has the most elaborate and expensive solution to venting the crankcase:

http://shorpac.com/v-web/gallery/album08/910_907_hybrid2

I've plumbed the crankcase breather into a catch can to separate any liquids before the fumes get routed to the Dellortos w/ K&N filters.

To each his own solution...do what works for you, but do route the fumes back to the carbs so they can get burned.

Judson

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 Posted: 06-03-2005 01:51 am
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Wayne McCartney
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Mark,
I like the looks of that better than the original setup and I'm sure your logic for preferring it is sound. The photo brings up a couple of questions. Did you drill holes in the filter housings? Do those yellow gaskets between the carbs and the intake manifold replace the o-rings? Is the inline filter you've installed in addition to the one adjacent to the fuel pump? Thanks for the photo. I'll save it to disk for later use.
Wayne

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 Posted: 06-03-2005 02:52 pm
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Mark Rosenbaum
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Wayne,
I used a tool called a chassis punch to make the holes in the filter lids.  This is just a large hole punch.  I happen to have several of these in various sizes, left over from the days of vacuum tube electronics.  They get used about once a decade nowadays.

The yellow 'gaskets' are actually the adapter plates that fit between the carbs and intake manifold.  They're painted with Rustoleum oil-base white primer and bright yellow paint.  The only reason for doing that was esthetics.  A stock engine is just one huge mass of dull aluminum, and a few discreet spots of paint will break this up into discrete sections that better please the eye.

The filter is in addition to the one in the trunk  I've never seen any rust in it, but I don't want to find out the hard way that something has happened to the inside of a fuel line or hose.  The hose connecting the filter to the metal fuel line is covered by a length of corrugated wiring wrapper as protection against abrasion.  That stuff is useful for a lot of non-wiring applications.

One last point, now that I think of it: the hose I used for the breather setup is 3/8" fuel hose.  The choice was driven almost entirely by cost -- while a larger hose size would probably work slightly better, the fittings would have been a lot more expensive.

 

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 Posted: 06-03-2005 06:02 pm
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Jim Ketcham
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Please remember that an important function of the "airbox" is to capture the liquid and let it drain back.  If you note the airbox is designed with its hose connector at its lowest point and flanged so as not to impede the return flow.  I do not think it is advisable to have the liquids enter the carburettor or drip out of the air cleaner into the engine bay.  I think to properly handle this function and still use K&N type filters you would have to use Judson's approach.

Jim

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 Posted: 06-04-2005 04:06 am
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Wayne McCartney
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Mike,
Thanks! If I decide to switch back I'll inventory my bits and pieces, see what I need and let you know.
Wayne

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 Posted: 06-04-2005 04:21 am
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Wayne McCartney
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Mark,
Here's what I have done as a stop gap measure. In that I have the later valve cover with the breather extending to the rear carb I left that arrangement intact. I then ran a piece of 3/8 inch tubing from the large crankcase breather to the forward carb after noticing the punch out on the back of the air filter cover that I had not previously noticed. I used a fitting I had in the garage that happened to reduce the diameter of the large tube just enough for the 3/8 tube to work nicely. I theorized that perhaps both carbs would receive similar vapor though certainly not equal since the crankcase vent emits much more at least from a purely observational standpoit. I also had a grommet in the garage that fit nicely in the hole on the back of the front air filter cover through which the tube fit with a little encouragement. I know this is not final but it sure helps the stink. Thanks for your input and ideas.
Wayne

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 Posted: 06-04-2005 04:28 am
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Wayne McCartney
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Jim,
Thanks for that sound advice. Do you think that if the 90^ angle hose that comes off the crankcase breather was straight rather than angled the tendancy of the liquid because of it's relative weight would be to return to the crankcase rather than make the journey through the hose? Further would it be possible to monitor that theory by useing clear tubing for a short period of time?
Wayne

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 Posted: 06-04-2005 04:37 am
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Wayne McCartney
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Judson,
That is one outstanding looking engine bay and utterly outside my price range. The basic idea makes sense though and might be accomplished on my limited budget though without such lovely results.
Thanks,
Wayne

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