Lotus Elan

Carburator Tuning

PostPost by: heinrichgoldmann » Sun Jul 25, 2004 6:41 pm

Hi,
I have a new engine installed and fitted the 40 DCOE 32 which cam with the engine, it is a big-valve with C-type cam and 43 D 4.
The carburator is main 120, air 170, pump 45, F 11, 50 F9., choke 32, K+ N,
It runs at idle but if one give throttle it roarssss and then it goes up. have fitted 45 F9, 50 F8, less and more than 10-12 ignition, but can?t sort it out where the mistake is. Use Shell 100 oktan, after 3000 it goes like turbo charged.
Any idea, never have had this problen on many engines of mine, what did I make wrong?
Thanks
Heinrich :o :unsure: :rolleyes:
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PostPost by: john.p.clegg » Tue Jul 27, 2004 5:41 am

Heinrich
Looks like you've drawn a blank on this one,maybe the best bet is taking it to your local tuner and let him have a go
"nothing ventured,nothing gained"
John
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PostPost by: types26/36 » Tue Jul 27, 2004 7:20 am

Heinrich,
Dont really understand what "roarssss" means? :huh: but if you mean it has a flat spot (hesitates) .....does not rev up quickly then I would check that the pump jets are spraying (not blocked and pump diaphrams are O.K.) then recheck the ign timing.
Also make sure the distributor centrifugal advance is working O.K.
As you say it is a new engine, are you sure the cam timing is correct? it may be worth taking off the cam cover to check the cam timing.
Brian
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PostPost by: heinrichgoldmann » Tue Jul 27, 2004 8:48 pm

Dear Brian,
thanks for help.
I tried pump jets from 35 to 45, same problem.
I tried ignition timing from 10 degrees and more, same problem.
Have not checked the valve timing yet, but because the distributor worked before in my other engine with c-type cam perfect and without " a minute" from idle between 700 and 1000. If I idle the engine to about 1500/2000 and give throttle then it works right up in an hurry!
Before I tried a 23 D 4 one, same problem!
Also with open trumpets - without air filter cover, same problem, may be that the
carburator delivers to much fuel and the engine could not work with so much at this moment.
Heinrich
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PostPost by: type26owner » Wed Jul 28, 2004 12:50 am

Heinrich,
I've posted lots of info on tuning Webers on this forum. Suggest you burrow back in time and read that stuff and you might just find the bit of info you're looking for....
Good Luck,
-Keith
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PostPost by: type26owner » Tue Aug 03, 2004 4:46 am

Heinrich,
One dead give away that the throttle spindles seals are leaking in air through the bearings pockets is on a properly sealed and tuned pair of carburetors the engine can be forced to quit running by just backing off the idle speed screw slowly. It will quit running below about 400 rpm if all is well. If the idle speed screw is already backed off and it idles on the air leaks alone then the throttle plates are closed enough from the correct positioning so it will likely have a lean stumble ('it roarssss') because they are rotated away from the first progressive hole. Worst case is they installed the wrong angled plates altogether to save on the tuning costs.

If the C-type cam is a performance cam you've probably made the effect of regression worst and impacted the vacuum level of the induction system. The DCOE works normally with an extremely small potentional vacuum energy so by making the induction system less efficient you've cut the margin for error to expect them to work well at low rpms. They are tricky if not understood but if examined carefully and the problem signs recognized then the repairs are not too tough to do and the state of tune can be improved significantly.
Regards,
-Keith
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PostPost by: twincamman » Wed Aug 18, 2004 12:37 pm

by roars im assuming the engine speed stays up too long----this may mean your not on the idle circuit if the idle mix and idle screw are set too high this occurrs try to ldle at around 900 rpm smoothly --or your balance is off carb to carb ed law
dont close your eyes --you will miss the crash
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