Zenith WIP & WIA Carbs

[AlpineII]

Planning on doing an overhaul on the Zenith carbs this coming winter and have a few questions. I have 1 pair of WIP's on the car that runs not too bad (Vizard mods, KB grind) but the front carb leaks at the fuel line connection. I am certain they are not original to the engine, which has been competely rebuilt.

I have four other complete pairs of Zeniths, two pair on manifolds. When looking them over and trying to decide which two to rebuild I noticed there appears to be differences between them. This I gather is due to the by-pass jet valve on WIA carburators.

So do I have this correct and is the only external difference between the WIA's and WIP's is the diaphram for the by-pass jet?

Is there a performance difference? I run the cooper wire mesh filters.

 

[husky drvr]

Eddie,

There is a difference in the way the idle mixture is adjusted between early and later WIP's as well. The earlier WIP-2 carbs have a fuel adjustment at the throttle blade for mixture control. The later WIP-3 carbs have an air adjustment on the top cover to control idle mixture.

 

[SIVAllan]

WIA Initial model, three screws are used to secure the throttle body to main body

WIA--2 Four screws are used to secure the throttle body to main body

36 WIA--3 Air regulating screw is fitted instead of volume control screw

42 WIA Initial model

42 WIA--2 Special short throttle body

42 WIAT As 42 WIA but fitted with thermostatically operated air strangler

42 WIATD -- Similar to 42 WIAT but fitted with throttle damper for automatic gearbox

36 WIP Initial model, three screws are used to secure the throttle body to main body

36 WIP--2 Four screws asre used to secure the throttle body to main body

36 WIP--3 Air regulating screw is fitted instead of volume control screw

"P" signifies the power jet circuit is not incorporated, not being necessary on certain applications

from Zenith carburetters service bulletin SB.201 (will post to web soon hopefully)

Allan

 

[Bill Blue]

WIA Initial model, three screws are used to secure the throttle body to main body

WIA--2 Four screws are used to secure the throttle body to main body

36 WIA--3 Air regulating screw is fitted instead of volume control screw

42 WIA Initial model

42 WIA--2 Special short throttle body

42 WIAT As 42 WIA but fitted with thermostatically operated air strangler

42 WIATD -- Similar to 42 WIAT but fitted with throttle damper for automatic gearbox

36 WIP Initial model, three screws are used to secure the throttle body to main body

36 WIP--2 Four screws asre used to secure the throttle body to main body

36 WIP--3 Air regulating screw is fitted instead of volume control screw

"P" signifies the power jet circuit is not incorporated, not being necessary on certain applications

from Zenith carburetters service bulletin SB.201 (will post to web soon hopefully)

Allan

My how you've learned! A few months ago you did not even know Zeniths were not supposed to be on later Series cars.

Fun, Isn't it?

Bill

 

[Series3Scott]

Don't forget everyone, in addition to the Forum we also have a regular club website - see if this link to our technical section will help too......

http://www.saoca.org/technical/zenith-carbs.htm

 

[SIVAllan]

Bill, this forum makes learning fun, and the interaction here provides a sound education!

It is fun to learn Sunbeams in more depth, and will make the eventual driving more enjoyable as well .

Allan

 

[AlpineII]

So is there a performance difference between the WIP and WIA's? The concept of the extra fuel delivery during accelleration via the Bypass Jet seems to make a lot of sense.

 

[Chuck Ingram]

Scott
Now I know why I feel so far from it all.
Seeing you are in the center of the Sunbeam universe I now see just how far we are out in the great white north

 

[Series3Scott]

Scott
Now I know why I feel so far from it all.
Seeing you are in the center of the Sunbeam universe I now see just how far we are out in the great white north

I'd be glad to trade you, as it's hotter than you know what today here in Cincy - I'm ready for some "great white north" weather!

 

[SIVAllan]

So is there a performance difference between the WIP and WIA's? The concept of the extra fuel delivery during accelleration via the Bypass Jet seems to make a lot of sense.

I'm not the one to answer the question at this point, but a clue is found in the referenced bulletin:

Power jet:

"In the WIA type...Upon opening the throttle...the depression is reduced, which allows...This action admits a further quantity of petrol (over and above that supplied by the main jet) to the main discharge jet."

From there fuel goes through the venturi into the engine.

I certainly yield to anyone who knows the Zeniths WIA vs WIP <s> but it looks like more fuel would equal more performance.

How much more - marginal? substantial? - needs experience to answer.

 

[RootesRacer]

The goal to tuning a carb is to meet the driving objectives.

Cars without a carb with a power valve have to be jetted rich across the board, or jetted lean across the board.

Put in a carb with a power valve, and the engine can be jetted relatively lean in the idle to mid range (running off the main jets as a lean mixture), while when the throttle is opened, and manifold pressure is lost, the power valve essentially allows the main jet to be enlarged, and more fuel is provided, which is load based.

Because I've spent some time with an O2 meter on an alpine and similar motor, I can tell you that an alpine will idle nicely with as lean of mixture as 13.7/1 AFR.
In order to get maximum economy, the engine will want mixtures in the 13 to 14/1 AFR range, but maximum power is developed at 12.0 to 12.5/1.

This said, tuning the main circuit to achieve 14.0/1 with enough manifold vacuum to inhibit the power valve, then setting the power valve with a final AFR or about 12.25 will yield a decent compromise between economy and power availability.

Oh, and the empirical difference betwen 14 and 12 AFR is about 15% more combustion energy.

 

[SIVAllan]

The goal to tuning a carb is to meet the driving objectives...

, but maximum power is developed at 12.0 to 12.5/1.

This said, tuning the main circuit to achieve 14.0/1 with enough manifold vacuum to inhibit the power valve, then setting the power valve with a final AFR or about 12.25 will yield a decent compromise between economy and power availability.

Oh, and the empirical difference betwen 14 and 12 AFR is about 15% more combustion energy.

If I understand this correctly from idle to throttle with a properly adjusted WIA carb = + ~15% gain in combustion energy.

In a comparable carb, a WIP for example, with out the power jet, would the change from idle to throttle be significantly less? wild guess +12--13%?

 

[husky drvr]

If I understand this correctly from idle to throttle with a properly adjusted WIA carb = + ~15% gain in combustion energy.

In a comparable carb, a WIP for example, with out the power jet, would the change from idle to throttle be significantly less? wild guess +12--13%?

Allan,

Not really. Max power with either type carb should be nearly identical because that depends on the engines pumping ability. The carbs are calibrated to supply a given amount of fuel for any given air flow through the carb. The difference is that the WIA can be tuned to run somewhat leaner in a cruise ( high vacuum and steady low to mid rpm condition ) to improve economy. The engine produces far less than max power while cruising so there is not a need for a rich ( max power ) mixture under those conditions.

 

[AlpineII]

So it seems to me that I would be better off in the long run setting up a pair of the WIA's if the overall performance is the same but I gain the economy of having the leaner mixture on idle or highway cruise speeds.

 

[P. Scofield]

Eddie,
there are several good re-builders over the pond. I think they do rebuild or direct exchange for yours. Someone here can probably point you in the right direction. (Scott C)
Just a rebuild kit is really a waste if you have any kind of mileage on them. They will re-bush your throttle bodies and insure you have NO air leaks. There are some NOS Z's floating around out there. If you feel like talking to English folk in the middle of the night and making tons of lead calls (there are some that make this a hobby) you can probably find some. But they will run you better than $250 each.

Good luck and let me know what way you go. Maybe we should do a group rebuild?

P

Planning on doing an overhaul on the Zenith carbs this coming winter and have a few questions. I have 1 pair of WIP's on the car that runs not too bad (Vizard mods, KB grind) but the front carb leaks at the fuel line connection. I am certain they are not original to the engine, which has been competely rebuilt.

I have four other complete pairs of Zeniths, two pair on manifolds. When looking them over and trying to decide which two to rebuild I noticed there appears to be differences between them. This I gather is due to the by-pass jet valve on WIA carburators.

So do I have this correct and is the only external difference between the WIA's and WIP's is the diaphram for the by-pass jet?

Is there a performance difference? I run the cooper wire mesh filters.

 

[Andrew]

Zenith Rebuilds

Eddie,
Maybe we should do a group rebuild?
P

Hey Scott:
Now this would be a great thing to do, I could use this help!
Is this possible?
Regards,
Andrew

 

[Series3Scott]

Ian and I have done it before with overdrives and transmissions - we box up our stuff and send it in one big package over the pond to a certain UK rebuilder; helps to share the cost of the expensive shipping.


We can certainly do the same with Zeniths - I need to get mine rebuilt some day and back on the car, though my Weber is running so nice I'd hate to replace it. What has held me back is choosing the right rebuilder - there's a number of them in the UK, and none I've found here in the US with whom I'm comfortable.

Has anyone tried some of the rebuilders over in the UK?

 

[SIVAllan]

In addition to the high speed jet, some Zenith comparative info hunt 'n pecked from various sources:

WIA/WIP comparative info

*S I Carb Venturi mm Main jet Idle
36WIP2 28 130 50

*S II 36WIP2 30 142 50
36WIP3 30 142 45
36WIA2 28 112 45
36WIP2 28 112 45
**Harrington
Lemans
36WIP2 28 150 45

***S 3 36WIP3 29 127 45

*Chiltons
**Glenns
***Haynes

The Haynes book indicates the above for gauze air filter carbs. Dry element filter carbs
Have different specs.

The club document @ http://www.saoca.org/technical/Zenith 2.pdf
presents more thorough comparative info; the above is just to indicate differences at a glance. The CS# on the club document indicates which air filter type (I think). That number is located on the top plate beneath the W model type and will likely be faint. I base this conclusion on the #1744 found there on Air-pine's carbs.

I took the S IV's carbs to a shop in north Atlanta:
http://www.carbspec.com/index.htm
I can't recommend them (or not) as it is too soon to tell, and offer the URL only as a potential rebuilder option.

 

[AlpineII]

Just a little update. I have had the bodies redone and have had full bushings installed. It cost me $50 at a local shop for the machine work and bushings. Is there anywhere to acquire new bypass pump shafts with diaphrams? They must have really stuck as they were really sloppy!

 

[jumpinjan]

Rebuilding Zeniths is not a problem here, IF.......one can get the correct parts. What I have seen in rebuild kits are all junk except for the gaskets.