Lotus Elan

Dellorto Trouble

PostPost by: tdafforn » Fri Aug 13, 2004 7:41 pm

Hi all,
Finished sorting out the suspension on the +2 and am now moving onto the Carbs...
Have been suffering from rough running at idle, the engine coming on song at 2K rpm.
The carbs are balanced and the buttlerflies seem to be in the same place on the progression holes. A quick look with a colourtune shows the rear carb is running relatively rich, with on carb throat seeming to run rich EVEN with the screw screwed right in! The front carb is running lean, and doesn't seem to respond to undoing the mixture screws at all. The plugs are black/brown on all cylinders. At WOT the burn looks good on all cylinders, and power delivery is smooth...
Now, does anyone have any ideas?
Cheers
Tim
1972 +2S130
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PostPost by: rgh0 » Sat Aug 14, 2004 12:11 am

I assume you are confident that the ignition is OK and working properly and that fuel supply is sufficient and at the right pressure.

If the above was correct and I was confident it was actually a carb problem which is always the last place I work on I would check the following things

1. Air leaks at o rings or throttle shafts

2. Float level and float valves, check that the valves are sealing off and not leaking and that the floats are set at the same level in each carb and are pivoting freely and not jamming. Ensure the floats and valves are the same in each carb.

3. Ensure all the jets are properly seated in there housings and are identical and have not been modified or drilled out versus their nominal specifications

4. Check over the rest of the carbs looking for any differences or blockages in any of the passages.

Rohan
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PostPost by: twincamman » Sat Aug 14, 2004 12:33 am

only try to set the carbs after 'brisk' motoring ----just setting up at idling brings nothing but grief ---------assuming everything else is good they will jump into tune ed law
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PostPost by: types26/36 » Sat Aug 14, 2004 7:52 am

Tim,
I agree with all the above but would like to add you say the butterflys "seem to be in same place" does that mean you have checked the air flow (suction) on the carbs with a meter or are you assuming they are the same? if so get a meter although some like to listen with a tube (me included)
Rgds Brian.
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PostPost by: gjz30075 » Sat Aug 14, 2004 12:10 pm

Tim, after all above is checked, is it possible that someone drilled open the holes in the idle jets, so that it says one thing but is really richer? Get a good, known jet to compare, I suppose.

I would certainly get a more precise way of knowing that your butterflies are sync'ed up and check that the idle screws don't have ridges on the tapered part from DPOs screwing them down too hard.

Greg Z.
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PostPost by: tdafforn » Sat Aug 14, 2004 8:21 pm

Hi Guys,
Thanks for the info...
Particularly the possibility that there is a secondary adjustment for the mixture..
The carbs were balanced 6 months ago before the car was laid up, but i'll check again.
Jets were new, bought by me, so should be fine, also checked they were seated, and they were..
looking down the jet tubes it looks as though the levels are close, although of course I'll check..
air leak could be it I guess..
Took the car for a 100 mile test run and checked the plugs afterwards, and they were a nice biscuit colour, so the mixture at speed looks spot on!
Cheers
Tim
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