Lotus Elan

Compression Test - Need to Isolate Fuel?

PostPost by: Stevie-Heathie » Thu Jan 04, 2018 1:17 pm

Happy new year, Lotus lovers!

I?m about to run a compression test on my ?67 S3. Obviously i?ll pull the cable to the coil to eliminate sparks but do I need to do anything to isolate the fuel? I?m running Webers with a mechanical fuel pump.

Thanks in advance
Steve
1967 S3 SE DHC
1970 +2S (RIP - went out in a blaze of glory in 2001)
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PostPost by: nmauduit » Thu Jan 04, 2018 3:14 pm

I would disconnect an electrical fuel pump, then on a mechanical pump you may be able to plug or pinch the incoming hose to the first carb depending on your setup and what nipples etc. you may have at hand, but no big deal in my opinion : the pressure is reached within a few turns (typ. 3-5 I would say) for each cylinder, plus if you tie wide open your throttles (blocking them wide opened in case of Strombergs) you only pump extra fuel in once, so cylinders do not get washed out significantly more than when having a hard time to start. If your engine runs then you can always runs it afterwards so as not to worry in case of a long storage.
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PostPost by: MarkDa » Thu Jan 04, 2018 5:19 pm

No problem with a mechanical al fuel pump the float valves are designed to stop fuel flowing when not needed!
However as Steve says a compression test should be done with all the plugs out and the throttles open so jam open and only have one pump. The air going in and of of the cylinders would quickly disperse anyway.
In the day one could just press the solenoid button to crank the engine and that avoided energizing the ignition.
Without that option you'll need to disconnect the ignition low voltage supply as well.
My electronic ignition managed to jump from the coil to a nearby earth when I tried just pulling the HT lead!
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PostPost by: vincereynard » Thu Jan 04, 2018 6:02 pm

Jump a couple of wires across the solenoid through a switch. (Battery terminal to column starter connection.)

Then you don't need the ignition on to spin the engine.
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PostPost by: Stevie-Heathie » Thu Jan 04, 2018 6:11 pm

Thanks all.

If I don?t post again in the next few days it means my compression test indicated that all was well :-)

Best Steve
1967 S3 SE DHC
1970 +2S (RIP - went out in a blaze of glory in 2001)
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