I was trimming my quill to start on this opus when a search for images found this site:
https://static1.squarespace.com/static/5c6dec53b10f25d4edf0b3f7/t/5d0190c39c74c3000181649b/1560383685667/TR250_TR6+Carbs+Part+I.pdfhttps://static1.squarespace.com/static/5c6dec53b10f25d4edf0b3f7/t/5d0191191376fd00017521ed/1560383774528/TR250_TR6+Carbs+Part+II.pdfhttps://static1.squarespace.com/static/5c6dec53b10f25d4edf0b3f7/t/5d01913a9c74c30001816be3/1560383803991/Carbs+III.pdfParts diagram can be found here:
https://jbcollier.smugmug.com/Lotus-Europa/i-vq2kJsJ/AThe information and procedures are detailed and (mostly) accurate. A couple of additional points/corrections:
1) Never adjust carbs without first checking your valve adjustment and timing (initial and advance): variable venturi and constant depression carbs are VERY sensitive to tight valves.
2) Dexron 2 or 3 automatic transmission oil is the best choice for damper oil as it does not react with the rubber diaphragm. Engine and other oils will eventually cause the diaphragm to swell and distort.
3) The information is accurate if you want to maintain all your emissions equipment as stock. I would recommend disabling some of the emission equipment. Details below.
4) Simpler to find used later TR6/7 dashpots when converting to adjustable needles. Rather than using an adjustable needle from another engine, put a Euro spec TC needle into the adjustable needle holder (details below).
5) Do not drive out the adjustable dashpot’s retaining clip as described as it can damage the dashpot damper bore. Use a hook tool to flip the retaining clip onto its side and it then easily slides out. Use a tool like the second one from the bottom:
https://public.snapon.com/R_RRD/Objects_lg/images/SGASA204AG.jpg6) Always fit a new needle and needle jet when doing a major overhaul on your carbs (details below). Spring loaded needles constantly rub against the same spot on the needle jet. This wears a groove in the needle jet and makes mixture adjustments problematic even with new needles. Thankfully major overhaul kits from Burlen now include the needle jet.
7) Anything other than slight throttle shaft play is unacceptable. Unmetered air dramatically affects the mixture setting across its range. Usually you can just fit new throttle shafts and the play disappears as the brass throttle shaft is designed to wear first. Otherwise the throttle shaft bores have to be machined out to accept bushings. I have re-bushed four or five pairs but it is best left to a machine shop if you don’t already have the reamers.
if you are not keeping your emissions equipment, then also remove the whole idle air bypass/heat system including the secondary throttle butterflies. Plug holes as needed. It is best to keep the funky carb spacer as it provides a beneficial ram effect and is tapered to match the intake ports at one end and the carb bores at the other. Myself, I would plug the internal openings with Devcon aluminium putty and shape to smooth airflow. The balance tube is a plus so don’t plug that.
9) Unisyns are not a good choice for syncing the carbs. When placed against the carb they also cover the breather which alters how the carb runs. This tool works well:
https://www.holden.co.uk/img/090_033L.jpg/prod_large—————————
Changing the needle jet
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required: a hydraulic or mechanical press (you absolutely cannot use a hammer), punches and deep sockets of various diameters to suit, a good quality, digital vernier caliper (mechanical is fine if the resolution and operator skill are sufficient) that reads in 0.01 mm increments
- completely strip the carbs
- place a reference mark on the old needle jet with a felt pen
- using the vernier caliper, measure the installed depth of the needle jet. Measure it multiple times until you get a consistent reading. This is usually in the 2.90 to 3.10 range.
- carefully support the upright carb body so it is level and use the press to push the old needle jet out the bottom of the carb
- flip the carb body and push the new needle jet part way in after lining it up by referencing the felt pen mark on the old needle jet
- go slowly and stop and check the depth frequently
- get as close as you can to the original depth
- within ± 0.05 mm is fine
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Disable the temperature compensator*
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- #39 in the parts diagram
- remove the two retaining screws and remove the compensator and the large and small flat rubber seals
- remove the two screws holding on the plastic cover
- remove the screws holding on the bimetallic spring
- examine the tip of the plunger
- if the plunger tip is fine, reassemble and tighten the middle “adjusting” screw right down so it stays sealed permanently
- reinstall the compensator with new large and flat rubber seals
- if the plunger tip is damaged then you will have to machine up a brass plug to fit the bore of the carb in a light press fit
- lightly bottom the idle trim screw (#46)
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Disable the bypass valve
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- #34 in the parts diagram
- remove the three screws and the valve
- use the old gasket (#35) to make up a new gasket with only holes for the screws, not the vacuum and air passages
- reinstall the valve using the new gasket
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Disable the evaporative emissions to the carb*
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Each carb has a large brass outlet on its side that supplies vacuum to the evaporative emissions canister. Remove the hoses and plug the outlets.
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Change needles in an adjustable holder
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https://jbcollier.smugmug.com/Lotus-Europa/i-2XBqDgL/AThe actual needles in the fixed and adjustable holders are of the same design.
The adjustable needle is retained by either a very thin spring pin or a section of the holder push in, and, sometimes, also a pressed on plastic collar.
https://jbcollier.smugmug.com/Lotus-Europa/i-S5n2BFv/AThe fixed needle is held in by top of the holder folded over a washer.
https://jbcollier.smugmug.com/Lotus-Europa/i-JnTS2qr/ATo remove the needle from a fixed needle holder, simply grind/file away the folded over edges and remove the needle.
To remove the needle from an adjustable holder either:
- use needle nose pliers to gently remove the spring pin (easily damaged): or,
- carefully bend the tang out of the way.
The plastic washer can be removed by carefully pulling the washer down the needle.
Now fit the Euro spec needle into the adjustable needle holder. Either refit the spring pin or bend the tang back in place. If your holder has the bent tang, it will most likely break off. Simply drill a hole through the holder in the same position and fit a suitable spin pin.
I think that is everything covered.
* these two affect the carb’s internal air pressure changes in which lifts or lowers the damper height at any given air flow and thus the strength of the fuel/air mix
