Lotus Elan

loose auxilary venturi

PostPost by: seniorchristo » Thu Jul 21, 2016 12:32 am

While looking for an air leak in the progressive stage of my carbs I noticed all the auxiliary venturis are loose and also there is about 1/4" of fore and aft play in these venturis. I have a spare set of carbs that don't have this issue and when I swapped venturis between the two they move the same fore and aft. Any body else had this issue?
Thanks,
Chris :)
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PostPost by: prezoom » Thu Jul 21, 2016 2:04 pm

When I first go my S2, I had the same problem. I wound up expanding the loop in the flat P spring, then used an appropriate sized hole punch to cut out a piece of rubber from a Viton sheet. Inserted the rubber disc in the loop and reinstalled the aux venturis. They are still very tight in the bore, after 10 years, and seal quite nicely against the transfer port. A section cut from an O ring would also work. I also cut a strip from the sheet and inserted it in the groove that reaches from the P spring to the front of the carb, and used a thin O ring between the air horn and the venturi. Have not had any fuel leakage since this work was done.
Rob Walker
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PostPost by: seniorchristo » Thu Jul 21, 2016 3:48 pm

Thanks Prezoom. I still have a 1/4" gap in the stack of main Venturi, Aux Venturi and velocity stack. Were there ever different lengths of these items. I don't have this problem in my spare carbs with identically sized pieces.
Thanks
Chris :)
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PostPost by: prezoom » Thu Jul 21, 2016 4:26 pm

The only differences in aux venturis I have noticed are the ones that do not have the air horn slip down the outside of the aux venturi. These seem to be used in Alfa's that have the cast aluminum air box attached to the carbs, with no air horns, and are larger in diameter to fit snugly in the carb bore. They come out to the front face of the carb and the air box locates them in the carb. Where the aux venturis on my sets of carbs are located by the air horn. At one time, I turned down some of the Alfa style venturis to work with the air horns. The Alfa style are also longer, as they have to reach the front face. The ones used in my DCOE 31's are shorter and only reach to the lower edge of the recess cut in the face of the carb to locate the air horn.
Rob Walker
26-4889
50-0315N
1964 Sabra GT
1964 Elva Mk4T Coupe (awaiting restoration)
1965 Ford Falcon Ranchero, 302,AOD,9",rack and pinion,disc,etc,etc,etc
1954 Nash Healey LeMans Coupe

Owning a Lotus will get you off the couch
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PostPost by: seniorchristo » Fri Jul 22, 2016 12:05 am

Thanks Prezoom. I'm going to compare parts from both sets of carbs including the carb body stops which locate the main Venturi (choke) to try and identify the problem.
Chris :)
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PostPost by: seniorchristo » Sat Jul 23, 2016 12:17 am

The problem turned out to be the gasket between carb and airbox was not allowing the velocity stack to to seat against auxiliary venture and allowing everything to slide fore and aft. By enlarging the holes, the problem was solved. Unfortunately one of the velocity stack nuts worked loose and the engine swallowed a lock washer. I was able to fish it out of cylinder number 3 but I fear the worst. I'll check it out tomorrow.
Chris :( .
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