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There are three Dellorto floats available. They all look similar, but they have different weights. For a given fuel level, each weight float must be set to it’s own corresponding height.
A heavier float will naturally ride lower in the fluid, and a lighter float will ride higher. So, in order to produce one standard fluid level (27mm / 1.063” down from the carb body / float bowl's rim), a heavier float must be set to a lower dry-height, and a lighter float must be set to a higher dry-height. If the proper heights are set, then all three float weights will result in the same standard fuel level in the float bowl. IMHO, the heavier 10 gram float provides a more constant fuel level and running condition. However, float weight is a very real factor in the carb's overall jetting set-up, so don't go changing it unless you know how to jet a carb from scratch.
The weight & part-number are engraved on each float. The basic part number for all the floats is 7298-_ _, with two final digits denoting each weight.
7298-01 = 10.0 gr, set to 16.5 - 17.0 mm (bigger number = lower).
7298-02 = 8.5 gr, set to 15.5 - 16.0 mm.
7298-03 = 7.0 gr, set to 14.5 - 15.0 mm (smaller number = higher)
Float Drop = 25.0 mm
If the incorrect float weight is fitted, then the stock spec float height is no longer valid either. Change the float height along with the float weight... it's a package deal. However, Lotus wasn't shy about playing with the float height (deviating from standard) as a means of tuning the overall mixture. If in doubt about any float height differences (?) between Lotus model-specific and Dellorto generic specs, follow Lotus' recommendation for your engine. Stay with original spec unless you really know what you're doing.
I agree that the Viton inlet valves are better, but they're different and require a different set-up procedure. The rubber tips take a compression-set shortly after installation, and cause the eventual float height setting to end up higher / richer.
When using the standard, solid metal tipped needle valves, set the float heights and you're done. However, when using Viton needle valves, install them, set the float heights and finish the installation complete with filling the carbs with fuel. Give the needle valves a couple of days under load to take a set, and then re-adjust the float heights. You can cheat by initially setting the float heights about 0.5mm lower (larger number... ie, 17.5mm becomes 18.0mm) to compensate for the small compression set the soft tip takes, but then you're guessing, and it may not come out spot on.
This applies to new Viton valves. Used valves have already taken a compression-set and should be okay after the initial setting.
Regards,
Tim Engel
Op mijn vlotters staat 7298.01 en 8,5g en toen ik eigenwijs als ik ben ze lekker toch heb verbogen naar 15.5mm (dell'orto vlotters schijnen niet verbogen te mogen worden) reed de Alfetta toch ineens stukken beter.
Wat de auteur schrijft over lotus, zou dus ook voor Alfa kunnen gelden en de opmerking over vitonnaalden is natuurlijk waar.
Chris
