I had mentioned I didn't care for the single Zenith Carburetor.
OK.. been putting this off for sometime... so here is another RANT:
WEBER CARBS.... yes the be all and do all and it will make this little car some sort of race horse... yaddda... yadda.
In fact they are a great carb. No Argument there. And once set up they kinda just stay set up. But that part can be the biggest expense.
These are just my opinions.... No offense meant....
PLEASE... and EXCUSE ME! All sorts of folks are just in love with the idea that we can throw out the Zenith... well not a bad idea.... and slap on this
magical Weber BS at some ridiculous price.... maybe but not necessarily, the price includs the manifold...of some sort... that may or may not bolt up properly.. spacer thickness you know..
But then, folks wonder why oil is blowing out of the dip stick...... Sort of like Carlin explaining to people why when they build houses on volcanos there is lava in the living room.
I am sorry if I offend all the proud Weber owners that have suffered through finding the correct choke and jet combination. But Hey, you get what you pay and pay for.
And better get a rolling road to set it up... or set them up.... That is the downside to this in my view. Too much technology
on a LBC.
I'm just sort of a dual SU kind of guy that can get through with what the Europeans consider stock. This is a SPITFIRE. It is not a Ferrari, Lotus, or Lamborghini.
It is just a SPITFIRE. Be happy with it or get something else.
If you want a performance car get some expensive Audi or Mercedes or one of your choice that fits your budget. This is a SPITFIRE. They are supposed to be fun
not some sort of alternative to the rice boy thing. (Not that Webers are anything a rice boy would comprehend.) Sorry all you Honda / Subaru / Toyota guys.
(Hey I own a Subaru.)
All I am saying is that bolting on an expensive Weber conglomeration and not doing other things that might make use of what limited CFM increase it has to offer,
(depending on the carb) ,is a total waste of effing time an money on these cars......
AND... about that dip stick shooting out of its holder and the oil pushing out of everywhere.... OH $HIT... yes get a catch can.... do this... do that... except
everything to figure it out... you know ... SOLVE THE PROBLEM! Hey, maybe save the oil snot up and fry your Thanksgiving turkey in it.... (Sorry!)
Typical Weber installs do nothing to deal with PCV / crank case pressure / vapor recirculation. That responsibility
is born on the owner. So usually nothing is done, whether on a Spit or other vehicle... seals are bursting... oil is
providing some needed corrosion resistance to the frame and body... but not where it is supposed to be.
The forums are full of this stuff over and over.....
If you want Webers... then fine... but figure out your crank case ventilation first. I'll stick to European stock... or at least something
that has a toe hold in reality.
You may have and keep your Webers if you wish. If it not a race car you don't need two or three of them. If you want a race car... build one for the track and keep it there.
BTW, we don't like oil on the track......
Weber = Good / Great Carb. IMHO = Over rated. Typical after market non-pro execution = Poor
Thank You. END OF RANT:
SO................ Now I feel better.... but a Weber is a great carb.... just too many poor executions of it.
I did acquire and rebuild two SU carbs. The manifold and linkage was also included.
Some measurements were made of the carb layout. You are welcome to use this at your own risk.
Here is a photo of the rebuilt carbs and a stainless steel
manifold heat shield.
Looking down on the carb and manifold assembly. The
stainless steel barbed hose fittings are a modification.
The original set up was
a set of steel tubes one could connect heater hose to. They were extremely
They were cut off, drilled out and the barbed fittings
tapped in. Also the PCV valve has been
More Photos after installation
On the throttle arm; There are two holes. Apparently cars with linkage (MK III) used the hole closer to the throttle
shaft (????). The hole on the end appears to be
used or was for a return spring back to the manifold. I am not exactly sure what all the linkage parts were from as I acquired them used.
I tried using the hole close to throttle shaft, however the ratio of the length of the two arms
provided only about half the travel needed in the cable to put the
throttle control near the correct position, i.e accelerator pedal was half way to floor at WOT.
I opened up the end hole for the coupling shaft and placed the link rod there. Now WOT is just before the accelerator is at the floor. A return spring arrangement still
needs to be devised.
Front Throttle plate return spring is disconnected to show
throttle link connected to lower hole in throttle lever.
Triumph Spitfire SU Carbs and Crank Case Ventilation:
The original Zenith Stromberg carburetor set up did not have a PCV valve.
There is an orifice on the side of the Stromberg carburetor that draws gases from the tank via the charcoal canister and from the crank case. This however is
ported on the atmosphere side of the throttle plate and not directly to the intake manifold. As the throttle plate opens and the velocity of the air past the opening
of the orifice increases, so does the venturi effect and the vacuum on the hose to the valve cover and charcoal canister. These hoses are simply "T'd" together.
One would presume on a decent engine at idle, the blow by gasses and the pressure in the crank case would be minimal thus requiring less scavenging of gasses than an
engine running at a higher speed and under load. With more vacuum at a higher engine speed / load the residual gasses / blow by are probably reasonably well taken care of.
With the dual SU HS2 and manifold, the situation changes considerably. The manifold in this photo has a PCV valve, the large round mushroom shaped device press fitted
into the intake manifold. Some manifolds had the valve mounted separately with a hose between the manifold and valve. Either way the function is the same.
The valve equalizes the pressure in the crank case using manifold vacuum. Removing the oil filler cap causes the vacuum to drop and the idle to increase
and the engine to idle a little rough as now the valve can not compensate and the mixture turns lean. Replacing the cap
the engine returns to a normal idle.
For this particular configuration, a vented oil filler cap for crank case intake air is typically used. I saw a specification that the cap vent hole should be 9/64 or .140 of an inch in diameter.
This was for a 1275 cc engine. It would stand to reason that some sort of orifice should be used, however I've not yet found
the science behind determining the size of the orifice. The size on the Stromberg was approximately .180 of an inch, on the atmosphere side of the throttle plate.
Rimmer Brothers however makes the following suggestion for a ventilated cap. This is from the Rimmer Brothers web site.
The original 2 piece oil filler cap (part no. 143393) which prevented a vacuum by allowing air into the engine is no longer available.
As an alternative, GZC1400 can be used with the following modifications:-
Remove the rubber seal from the cap.
Alternatively, retain the seal (which prevents the cap from rattling) and drill a 1/16" hole in the cap, off centre to avoid the rivetted centre plate.
Also here is where I found the piece on the orifice size in the cap.
For a good explanation of how the Smiths PCV valve works, look here.
The saga continues on the engine breather. I decided that I hadn't opened a can of worms in at least 20 hours so it was time again. I had previously flushed the steel wool filter
material in the top of the valve cover. It seemed to be clear and working OK, but still didn't feel right about it. Another stone yet to be turned.
So after removing the valve cover I started probing and rust powder fell out. This can not be good.
If you stop and think about it, here is some sort of steel fiber that has been sitting in the top of the valve cover for 40 + years. It has seen a lot of moisture.
So after quite a bit of probing and prodding this is what came out of the top of the valve cover. Some pretty nasty stuff.
A closer look at the steel wire material. I used a curved pair of hemostats to remove this. There also seems to have been a
screen on the inside end of the breather pipe coming out of the valve cover. The ID of the breather tube is essentially 12 MM
so I think that I can fabricate something to go into the tube, but be removable so it can be cleaned and inspected.
I do not remember where I came up with this idea. I probably had seen this or read it in one of the on line blogs. It appeared that
Scotch Brite stainless steel scrub pads might be a good replacement for the woven steel material in the valve cover. Stainless wont rust,
they are very pliable and inexpensive. They seem to hold up to heat very well and they don't seem to shed particles once they have been shaken out.
This is a pad that was stretched out and cut in half to see how it would hold together. It seems perfectly fine and is a whole lot better than what was removed.
I've cleaned up and repainted the valve cover and will try this in it. This material also seems fairly easy to install and to replace, so it could be added to ones PM schedule.
The pcv valve connected to the valve cover seems to work as advertised for the engine breather. I put a 1/8 inch hole in the cap. Something between Rimmer Brothers 1/16 and the
9/64 that was suggested. No particular science other than intuition applied.
In order to connect the charcoal canister, I needed a T in the hose, but also needed some sort of restriction.
There is a restriction in the center hose fitting of the canister. I was told "A .088 drill bit is a snug fit in the center hole of the canister." This was on the 3 port
canister. Unfortunately the 2 port canister
I have has no restriction in it. I believe it to be a plastic insert that has gone missing.
The following photo is the T that was made out of stainless steel tubing. A piece of aluminum rod was turned down, a 1/8 hole bored in the end and inserted in the
side towards the canister. In this photo the T has not been trimmed to length. Also for reference a standard Nylon T is shown. With the nylon fitting,
one could use some 3/8 nylon rod and make a restriction if necessary. I found the nylon after the fact. I didn't like the temperature ratings of the polypropylene and polyethylene
fittings I had seen which is why I went with the stainless. While reviewing drawings of the plastic fittings, there was a reference to a nylon fitting. It is a Thogus TT9888/N.
(And they are made in the US.)
I had to trim the end of the breather fitting on the valve cover approximately 3/4 inch to make it all fit comfortably.
Fuel Line Clearance problems:
After fitting the bonnet and installing gas struts on the bonnet. there was a clearance problem with the fuel line running between the front and rear carbs.
The clearance was tight to begin with, however adding the struts made things worse in that it would catch on the line. The original factory
installation using these carbs also had the fuel line running in front of the air filters. I tried moving the line closer to the filters,
but still didn't like the way the lines were obstructing access to the air filters and carbs.
I ended up fabricating a new line out of 1/4 inch stainless tubing to go over the top of the air filters.
(Hose clamps not installed on fuel lines in these photos.)
Someone requested a photo of the choke linkage.
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