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March 08, 2021, 06:48:19 AM

Venting to carbs

This is a discussion for the topic Venting to carbs on the board Beach Buggy Engine and Exhaust Help.

Author Topic: Venting to carbs  (Read 1062 times)

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Reply #15 on: January 13, 2021, 09:25:42 PM
Fat fingers again matey! Deep sump?

Reason Iím asking is I have read a very interesting article from a well-respected VW engine builder explaining the reasons for and how to use them correctly which will cause a lot of folks to say NO, he's talking crap.
But.
A deep sump is not to increase oil capacity, it is to drop the oil level below the thrashing bits which will free up horse power and cut down oil misting.
It's kind of a semi dry sump if that makes sense.
So a deep sump with the pickup strainer fitted at the lowest point has the potential to make oil misting worse due to more slop above the normal level on hard cornering etc.
He recommends recalibrating the dipstick to the low mark.
Magic beans or common sense?


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Reply #16 on: January 13, 2021, 09:29:00 PM

Flags,

One more question. I can see the hose over the fan housing 👍Looks like you too use AN fittings. What size AN/ hose for your vent.
Thanks again.
Paul
All oil and breather fittings are AN 8 and with quality hose you get no collapsing


this user is offline pepsi81

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Reply #17 on: January 13, 2021, 09:40:36 PM

My breather is AN8 too, all mine are from Speedflow, yes Torques UK are cheaper.
Do you run a deep sump. Need to understand. The deep sump is footed via the 6mm bolts of the original mesh filter. So, you donít bother the oil take off, leave as is 🤷🏻‍♂️ Re: dipstick level, the low mark becomes the high👍🤔
Not magic beans, makes perfect sense to me.
Flags, really appreciate your input.
Paul


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Reply #18 on: January 13, 2021, 09:53:51 PM
To deep sump properly you would move the strainer to the plate on the sump and extend the pickup by welding not just a jubilee clip.


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Reply #19 on: January 13, 2021, 10:37:07 PM

Ok. Understand. Thanks .
More space for air to move without challenging the crankcase 👍🤷🏻‍♂️.
Am I right re: oil level. Low becomes the new high  :-\ :-\
Paul


this user is offline Dave DND

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Reply #20 on: January 13, 2021, 10:56:57 PM
Only potential benefit I can see is some negative pressure on the crankcase so effectively forced breathing when added to the positive pressure from the thread on the pulley.

My 2 cents on this - When I connected the breathers to my carbs, the negative crank case pressure cured 100% of my oil leaks - None were ever serious, just those bloody annoying little weeps around the crank seal and pushrod seals - All gone  ;-)up
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Reply #21 on: January 13, 2021, 11:16:45 PM

Appreciate your input Dave. Still donít like the thought of putting unnecessaries into the carbs.
Think itís a learning curve. Hopefully not expensive.

Best Paul


this user is offline Paul1953

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Reply #22 on: January 14, 2021, 08:19:30 AM
Just to mention the original VW design principles.....

The crankcase environment was designed to have a small positive pressure but importantly to have this as consistent as possible. Air is drawn into the crankcase quite efficiently by the "scroll piece". In order to maintain a "small" positive pressure the "oil filler tower" had either 1 or 2 "take offs". (I cannot remember if the two preceded the one or the other way round). Take the single take off as an example first tho`.... this connected to the carb air filter to allow the "induction" to draw air/oil mist back into the engine to be burn`t and so stop the crankcase positive pressure from rising above the "design" level.  It had nothing to do with emissions in 1936 as no such thing was of a concern.    The 2nd take off had a pipe leading to atmosphere further down the structure. The majority of petrol engines in "early" years had wire wool fitted to oil relief pipes/fixtures. Aircooled engines had them just inside the take off pipe area. (Mine is still in place after 45+ years).  This was in place to prevent "fire back". Early petrol engines backfire up through carb/carbs with ease if your timing or valve rocker clearances are incorrect. Visible flame at times. That wire wool is intended literally to be a "fire suppressor". 

This info is what I gleaned as a youngster from the actual VW manuals to be found at their UK main agents Mill Garages.  What I experienced practically was that... yes... the engine ran more smoothly with the tower to filter pipe in place with standard carb fitted. Yes oil leakage occured more often with the pipe off.  QED (for the mathmaticians  ;D)


this user is offline Doon L001

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Reply #23 on: January 14, 2021, 09:54:23 AM
That's interesting Paul, but you specifically say single carb.  From memory weren't the standard air filters a large pancake oil bath? If so then a bit of oil mist wouldn't make much difference and the suction on a single carb is double and smoother than a twin.

I know with my twins it was horrible and even if it could be made to run I can't really see how to balance them with one oily and one not. The only way I could image twin carbs working with a bleed pipe is if an air filter can was manufactured to serve both carbs.

Anyway my setup seems to work
Dave - Doon LWB 1st one made  ;-)up Name "Weather Permitting"


this user is offline Paul1953

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Reply #24 on: January 14, 2021, 12:39:10 PM
Hi Doon...   I say single carb because this is where 99% of my personal experience came from.  I was fortunate in that at secondary school I met the lad who was to become my best mate. He worked for a couple of years at Mill Garage and I was allowed by management to talk to him and look through the official operating manuals current to that point. In fact i was allowed to borrow them one at a time These tomes were immense but everything was backed up with drawings/schematics and lots of calculations that just went over my head. 

I have only ever owned one twin carb aircooled VW and that was a 1500 twin carbed notchback that I truly wish I still had. However I wrote it off one xmas time. This had twin carbs. Don`t remember the type. I don`t recall the "breathing" either. I am confident in saying this will have had a breather pipe to at least one carb. Cannot see why you would have two but could be wrong on this. The principle remains the same I would suggest in that the prime purpose was to maintain a small positive crankcase pressure. Unfortunately, being a "schoolboy tinkerer" and no engineer  I don`t recall why  the crankcase positive pressure was considered necessary. A carburretor utilses the "venturi" principle and the flow of air to fuel air mix is quite fast. There was never any sign of an oily mist within the carb body if you looked down the throat. It must have shot straight into the manifold and on into the piston barrels. Removing the inlet manifold showed no oil residue either so the amount of oil involved must have been really minimal. (This may be born out by the fact that type 1 engines did not "eat" oil).

There was a comment in an earlier post of this thread whereby the writer stated something along the lines that he knew vw did it but he would never let oily crap go down his carb/s.  Sadly people just jump to conclusion without really understanding what they talk about.
We. who drive modern cars daily, send crap into our engine every single day we drive them.... How so... Think egr valve, (exhaust rec-circulation valve).... This device, when working correctly, is under precise engine management control. It does not, or shouldn`t operate frequently of for long. At start up, or when falling to very low revs it should open under vacuum control from a solenoid and whilst open allow unburnt exhaust gas to re-circulate back into the engine to be burned off within combustion. Does it allow crap through into the cylinders? .... Absolutely.  Take off a well used/seized egr valve and you will see exactly the same rigid black carbonised deposits that you find in the heat riser pipe of a type 1 single carb engine. This crap is easily removed completely from a type 1 riser pipe but not so from a modern egr valve. Carb cleaner flushed thro might get it going for a week or two but doesn`t help the moving bits to operate freely.....   

My aim is never to criticise others.... I just try to pass on what I believe to be original thinking and principles. There is so much rubbish/mis-information on the web that I steer clear of it and ask my questions on here from people who run their buggies frequently and not just two or three times a year.


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Reply #25 on: January 14, 2021, 01:29:54 PM
Good write up Paul. All your comments back a lot of sense.
I intend to trial various options  ;-)up


this user is offline Doon L001

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Reply #26 on: January 14, 2021, 01:33:40 PM
Paul, I certainly don't see any criticism in what you say. I am fascinated by the complexity and thought that went into these old cars.

I had a beetle for a while and was just gobsmacked at how tough it was compared with the modern company cars that I was using that in many ways were much more comfortable and "civilized" but had zero character and were pretty fragile with a fairly short life expectancy.

The problem is we have all taken something engineered for reliability and then totally changed it. The moment we start tuning we are interfering with the design and undermining some of the assumptions in the original spec.

Peter's site and many of the posts on here with information about odd little bits of VW design are fascinating insights into why things are the way they are and long may they continue
Dave - Doon LWB 1st one made  ;-)up Name "Weather Permitting"


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Reply #27 on: January 14, 2021, 02:24:15 PM
You are right here Paul in that the moment you remove an aircooled engine out of its natural environment of the "engine bay" the operating conditions are completely thrown out of the window. What I would say/advise owners is that if you want a trouble free running then  try to maintain basics as much as you can as these principles did give this engine longevity so far past any other that it is hard to believe. A watercooled engine from 36 and many many years onward was looking at a top end overhaul at a mere 30,000 miles and at 60,000, if they ever got there, a full rebuild was required.

When I think back to the notchback, which I bought for £50 whilst owning my buggy, and purely wanted it for the engine to put into my buggy I was so impressed with the notchback that I ran it until I wrote it off. The engine went into the buggy totally original with the air filter box etc mounted remotely and the hot air hoover retained. This engine started instantly, idled from cold and the choke came off  smoothly. No hiccups at junctions and no hesitation on acceleration. 

I guess if you move the goal posts a little you can recover original parameters. If you move the goal posts a lot well it`s going to be troublesome  ;D

Am going to write up some observations that I made with my buggy in the garage where the concrete floor temperature was minus 10 degrees. It stayed well below zero for two days so I had chance for a bit of investigation....  I now know exactly what happens at a cold start up. 



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Reply #28 on: January 14, 2021, 10:47:14 PM

Think I can manage AN 10 hose/ fittings ( > 1/2 ď internal diameter) . Bigger hose better venting ?
Pauk