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Pre-Assembly of Carb/Manifold Unit for Installation
In my limited experience (and particularly with new components) there is quite a bit of shop-type preparation work that needs to be done before installation of the components on the engine. It is suggested that the initial assembly be done in a shop environment and that the entire carburetor/manifold assembly (minus perhaps the air cleaners) be mounted at one time to the cylinder head.
To facilitate the assembly, I built a stand from 3/4 inch plywood scraps. By clamping the stand to the work bench, this allowed me to bolt the manifold in position such that it imitated the actual installation on the Lotus engine. See Pictures below.
For this process, I am going to assume that the carburetors you are going to use are in good shape and properly jetted for use with the engine.
Preparation of Intake Manifold
The new intake manifold was just that, a manifold. It did not have any of the fittings for lines, hoses, etc installed so that was the first order of business.
1. Press-fit the heater hose fitting into the end of the cooling water tube.
I actually used a woodworkers pipe clamp to press the fitting into place,
and used a little Loc-Tite as a sealant. It seemed to work fine.
2. Install the vacuum fitting for the brake servo assist. Actually, my manifold
came with two 1/4” threaded (NPT) vacuum connection holes, one on each
end. The Stromberg manifold has only one servo vacuum connection, but
it actually feeds off of the rear two cylinders. It is best to connect both
vacuum take-offs to the brake servo through a tee. It should improve both
engine operation and brake performance during deceleration versus just
using one take-off. Currently I use only one of the vacuum take-off
(#4 cylinder) on my new Dellorto manifold and have plugged the other, but I
plan to split the work among both cylinders soon. I bought new 1/4” NPT
brass vacuum fittings from a local auto parts store, but ended up using the
one recovered from my Stromberg manifold.
3. Install water temperature sending unit. My manifold did not have a threaded
hole for the water temperature sending unit, but there was a boss in the
center for one. I drilled and tapped a suitable hole and screwed my
recovered water temperature sending unit into it. I believe it was also 1/4”
NPT
4. If you are the cautious type, you might want to check, at this point, that the
manifold will actually fit over the intake manifold studs on the engine. Mine
actually took a little filing with a round file to slip on. Such filing when the
carburetors are mounted and ready to go is no fun. Believe me, I know!
5. Next mount the manifold on the assembly stand.
6. Install carburetor mounting studs. You may have to play with this a bit to get
the stud lengths right. Have to make sure the studs are long enough to
accomodate the gaskets, spacers, washers and nuts, but not so long that
they hit the carburetor housing when you are snugging up the nuts.
Although there are stud installation tools, I just jammed a couple of nuts
together and used them to install them, along with a little Loc-Tite.
Preparation of Carburetors and Linkage
The first thing you should check is that the carburetors will fit over the mounting studs. As with the manifold mounting studs on the engine, they may not be entirely square. Mine weren’t.
1. Check proper fitting. If needed, carefully use a round file on the lower
mounting holes on the carburetors and on the gasket spacers to get them
to fit. Suggest you do not alter the top holes, if possible, because it can
affect the alignment of the gaskets and spacers.
2. Install the carburetors complete with gaskets and spacers. Snug up the
nuts
3. Check the linkages. Although my linkages were new, I had to bend the idle
adjustment arm just a little to get full and centered contact with the idle
adjustment screw. Final adjustment of the linkages will be done later.
Bench Assembly
You might want to check out Soft Mount Mounting Tips from Dave Bean Engineering. I started out this way and then later totally removed the o-rings, replaced them with solid gaskets, and bolted them up with locknuts.
1. Slip the gasket spacers onto the studs and postion the o-rings before and
after it.
2. Slip the carburetor linkages together and then slip the pair of them over the
studs and up against the spacer/o-ring assemblies. You might find this
easier if you connect the choke linkage first between the carburetors as a
brace. You may also want to temporarily put a couple of nuts on the top
studs to hold the carbs in place while you fiddle with putting on the
grommets and thackerays on the other studs.
3. Tighten all the nuts per your own preference and various instructions. The
important things are to seal at the o-rings and to have the same
measurement between the carburetors and the manifold face all around.
This will assure no air leaks into the manifold, and that the carburetor fuel
levels and linkage alignments are proper. You will have to check this again
after installation on your engine.
4. Install your fuel line. My set came with a pre-made fuel line that was
protected by a stainless steel loom. You may have to purchase and fit fuel
lines between the carburetor banjo fittings. The banjo fittings can be
removed to allow room to install the fuel lines.
5. Install air horn studs into carburetor. Use a little Loc-Tite to assure they stay
in place. If you are not sure what size your venturis (chokes) are on your
carbs, now is a great time to look into the carb barrel and see. The size is
stamped onto the cylindrical choke, should be easily visible and should be
between 30 and 40 somewhere. Jot the size down, it’s amazing how
quickly you forget.
6. Install air cleaner backing plates and carburetor air horns. Make sure
gaskets are properly fitted so that no unfiltered air enters the carburetors.
Air horns are a must - they smooth the air flow into your carburetors
allowing them to work more consistently, particularly with bolt-on air
cleaners.
7. Install air cleaner studs. Use a little Loc-Tite to keep them in place.
8. Slip the filters into place and bolt on the air cleaner covers. My air cleaners
came with wing nuts, which sounds great, but it is almost impossible to
keep wing nuts from working loose, give the engine vibration. One of mine
promptly fell off after I drove a couple of miles. I ended up replacing them
all with nuts with nylon inserts. Did not want to lose one of the new air
cleaner covers.
Bench Adjustment
1. Jetting. If you do not know for sure what your idle and main jets are, now is
a good time to take a look. Just unscrew that black plastic cover on the top
of one of your carbs and you will uncover two sets of jets. The larger ones
are the main jets and the smaller are the idle jets. To determine the jet
size, just unscrew and remove the jet assembly. The main jet will have
three numbers (starting from the bottom), one is the jet size itself, one is the
air holder size and the other is the air correction size. The idle jet assembly
has two components, and two numbers - the jet size and the holder size.
Jot all of it down for future reference. If you are not absolutely sure the
jetting is the same for all barrels you should probably check at this point.
2. Install a throttle return spring. The throttles already have built in return
springs, but most people will tell you that to be sure you don’t have a
fail-open, you should install auxiliary throttle return springs. I bought a
nested (2-spring)set for Chevy products from a local auto supply house. My
air cleaner housings had a very handy bolt boss to which I connected mine
3. Install synthetic caps on any open vacuum ports on the carbs. I needed 8
caps and used bolt thread caps from the local hardware store..
4. Synchronize (initial) the dual carburetors. First unscrew the butterfly idle
screw (on the rearmost carb until the screw just touches the butterfly lever
with the butterfly valve fully closed. Maintain pressure on the butterfly lever
to assure it remains closed and adjust the spring loaded idle screw (on the
linkage between the carburetors) until the butterfly lever on the forward
carburetor is also just closed. Next, go back to the butterfly idle screw on
the rear carburetor and screw it in 1 full turn. Finally, go back to the spring
loaded idle screw on the linkage between the carburetors and unscrew it
two full turns. Caution: Do not use pressure when closing these screws or
damage to the seats will occur.
5. Finally, set the idle screws. Suggest you screw them all the way in and then
back them out 3 turns. There is a shoulder that keeps you from screwing
up the idle screws if you close them too tightly, but be gentle anyway. This
adjustment will not be perfect, but it should allow you to start the engine so
you can tune it.
Click for a larger picture
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