Right hand side running hotter?

[Lars S]

Just happened to read (in the Autobook 865 for VW411) that the early carbed version of the 411 had a bigger main jet for the righthand side (cyl no1 and2) than the lefthand. The righthand side had jet size 175 and the lefthand 150.
I would guess this is because of the righthand side runs hotter.

Always thought that the lefthand runs hotter with its oil cooler arrangement just like the Type1 engines....also heard that valve dropping is most common for no 3 exhaust valve even on Type4 engines.
Any input...?


//Lars S
_________________
Porsche 914 -72, Bahia Red daily driver
VW411 2-d -70, White, sold
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold
Husqvarna 118cc, -47, Black, Sold

[raygreenwood]

If I am remembering.....I think the left hand carb contains the central idle system.

I am not a carb expert....so this is pure thinking it through speculation.
The central idle system left hand carb supplies fuel to the right hand carb for idling and a little air with it.

Unless I am misunderstanding it.....this system operates along with the choke when stone cold but also may operate whenever the vehicle has come to a stop and the main throttle flaps are cold.
Its possible because of a bit of overlap....that this circuit feeds some fuel to the right hand carb for a slightly wider portion of throttle opening.

Its also possible as you are thinking.....that VW could already see some of the temp imbalance during running from left ro right that is attributed to cooling...and moved to balance that a bit with fueling.

From looking at my Haynes manual....it is actually the air correction jet that is larger on the right. The left shows 155 and the right shows 175. The main jets for both are listed at 135.

With the central idle system supplying extra fuel...perhaps the larger mainjet is there to supply some extra air.

Dont even ask about the bus version of these carbs. The Haynes has no less than 6 combinations based around US emissions to all others and manual to Automatic and 1.7L to 1.8L.

And.....the "Without Guesswork" book is worthless for this question because its US only.....and we had no official carbed versions shipped here.....

There may be a little more method to at leaat the madness looking at bus specs simply because there is more info available for the bus.

So...in the bus specs.....its also interesting that the bus specs ....in the Haynes.....only list air correction jets in the 175 size.....for 1.8L engines. The 1.7L engines have 155 air correction jets....and of course this is just in the prelude to the chapter so it does not list the different size for both carbs.

So going back to the without guesswork book for the bus:

1.7L up to July 1972: main jet 137.5 and air correction 155 left and what appears to be 150 right. It is written in a split column left snd right like this. 155/050.

But.....from August 1972 for 1.7L manual transmission specific
Main jet 127.5 and main jet 140 for both left and right.

For the same date from August of 1972....the 1.7L with automatic transmission:
Main jet 137.5 and air correction jet 175 for both left and right.

For 1.8L....both manual and Automatic transmission from November through 1973:
130 main jet and 175 air correction for both sides.

Its possible....two things are happening.
1. due to the fact that none of the manuals we have for 411/412 are "official".....we are seeing some mixing of specification in writing. Hard to say.

2. A part of the difference for 411/412.....is that the right hand carb is also compensating for the vacuum take off for the automatic transmission.

Not sure. Ray

[Lars S]

Thanks Ray!
Did not think of the central idle system guess we have the answer there. Also you are right it is the air correction jets that differs (not the main jets).

From the swedish "Without guesswork" book from 1970 I can read that the carbed V-engines had 150/175 air correction jets (L/R) and the carbed Z-engines had 160/160.
Auto and manual cars are listed separately with the same jets.


//Lars S
_________________
Porsche 914 -72, Bahia Red daily driver
VW411 2-d -70, White, sold
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold
Husqvarna 118cc, -47, Black, Sold