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Esprit S2 federal carb change from Zenith to Dellorto - Fuel System/Carbs - The Lotus Forums Jump to content
williamtherebel

Esprit S2 federal carb change from Zenith to Dellorto

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Hi Guys, I am thinking of changing my Federal Esprit S2 's Zenith carbs to Dellorto's. However I've been told that I will have to change the cams as well. Is this correct? Will changing the carbs make much of a difference in the performance?

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William, there's no reason to refrain from converting to Dellortos from the Strombergs, other than perverse attachment to originality. The IR form of carburetion exemplified by Dellortos or Webers is optimal for the broadest range of performance. Stiffer cams will in fact trouble the Strombergs more quickly and surely than they would the full IR carb set-ups. If you want to really take the Dellortos to their utmost potential I suggest you examine the work done by American, Keith Franck, logged on his forum, "Sidedraft Central", hosted on Yahoo.

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I did the carb swap on my S1, when I had it. Didn’t swap the cams but did swap the sprockets over. Exhaust goes on intake and visas versus, you flip the sprockets as well. If you look at your sprockets as they are now you’ll see that the inside face of the sprocket has the reverse markings to the outside markings. So the inside face markings on the exhaust sprocket are actually intake markings.  It’s been 8 years since I did it and the car was sold 2 years ago so I’m relying on memory but Tim Engle posted a write up on the s1s2s3 yahoo group about it.

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From the Golden Gate Lotus Club.....

CAM TIMING


You may have noticed those little colored dots on the cam pulleys and jack shaft pulley. Those are the cam timing marks. Early 907s will ahve a red and a blue dot. Later 907s will have a red, blue and yellow dots. Also embossed on each pulley is "in" or "ex", additionally there is a dimple on one side of each pulley. The pulleys for all three, cams and jack shaft are identical. So, what is needed to be done is to use these three identification markings and timing markings to set the engine timing to European specs.

 

First loosen the pulley retaining bolts on each cam. Set the engine to TDC, check timing not only at the flywheel but see that there are tow dots aligned at the cams. Now, the timing belt can be removed. The air box, the alternator and V-belt must be removed first. Then the belt tension adjustment screw can be slackened off, but not more than ½"! Do not remove the belt just yet, using a suitable nail or drill bit that is roughly 4mm in diameter (5/32") as a locking pin for the spring loaded tensioner, push down on the belt thus pushing the tensioner back and insert your locking pin in the small hole provided in the body of the tensioner. Now the belt is free to be removed from the pulleys.

Now the cams can be timed. On early 907s the blue dots were aligned on U.S. cars. On later 907s the blue dot on the intake and the red dot on the exhaust cam were aligned on U.S. cars. On early 907s remove the intake pulley and flip it over so that the dimple faces into the engine. Note each cam will have a dimple only on one side allow its outer edge. On the exhaust pulley likewise flip it, but the dimple will face out. Now both cams will require slight adjustments to align the red dots. Do not attempt to tighten the retaining bolts unless you have locked the cams in place (it's easy to turn a cam too far, pushing valves into pistons and bending those valves while excuting the tightening). Later 907s do likewise except align the yellow dots.

Now the jacksaft will require retiming. This is done by lining up the red dot (adjecent to the dimple) in line with the centers of the crank and the jackshaft. You can now replace the timing belt. If you do not have access to a belt tension gauge I recommend counting the number of turns that you loosened the tensioneer and additionally measure the deflection in the belt BEFORE having removed the belt. In this way you can refit the belt back to the original settings. Check the belt tension after turning the engine by hand at least one full turn. Replace V-belt, alternator, air box, etc. The ignition will have to be retimed to specs, but more on the next.

Spread sheet with cam data

http://users.ox.ac.uk/~ohare/Cam_Data9XX.xls

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Many thanks for the info Steve and Gavin. Its nice to get all the info together before I make a decision.

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