Lotus Elan

Tuning Webers

PostPost by: carrierdave » Sun Feb 15, 2009 9:11 pm

Good evening,
I have been trying to set up my weber cars today using the procedures laid down in a copy of a Haynes manual for overhauling and servicing weber carbs.

The initial set up description states that you back off the throttle adjusting screw so that it is just touching the arm ? then turn the screw through 180 degrees.

It then states that you screw the idle mixture screws in until the hit there seat; then back them out by 270 deg (3/4 of a turn).

It then states that you should start the car and run until warm. Once warm then turn each screw out until you hear a pickup in engine tone/speed.

Finally adjust the accelerator screw to achieve the right tick over.

The problem I have is that it is only when I screw the mixture screws in do I see a pick up and better running condition of the engine; Which appears to be the reverse of what they suggest!!!

When I unscrew the idle mixture screws the engine becomes lumpy and the exhaust more sooty ? Am I doing it wrong?

Any help and assistance would be most helpful
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PostPost by: neilsjuke » Mon Feb 16, 2009 9:32 am

http://7faq.com/owbase/ow.asp?HowDoI%2F ... rburettors

I balance the carbs then use 4 colour tunes + rev counter

Neil
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PostPost by: dusty » Mon Feb 16, 2009 10:16 am

carrierdave wrote:Good evening,
I have been trying to set up my weber cars today using the procedures laid down in a copy of a Haynes manual for overhauling and servicing weber carbs.

The initial set up description states that you back off the throttle adjusting screw so that it is just touching the arm ? then turn the screw through 180 degrees.

It then states that you screw the idle mixture screws in until the hit there seat; then back them out by 270 deg (3/4 of a turn).

It then states that you should start the car and run until warm. Once warm then turn each screw out until you hear a pickup in engine tone/speed.

Finally adjust the accelerator screw to achieve the right tick over.

The problem I have is that it is only when I screw the mixture screws in do I see a pick up and better running condition of the engine; Which appears to be the reverse of what they suggest!!!

When I unscrew the idle mixture screws the engine becomes lumpy and the exhaust more sooty ? Am I doing it wrong?

Any help and assistance would be most helpful


That suggests your car is running rich at idle with the default settings. Have you also checked the float heights? The procedure should also be in the manual. whilst you're at it check that the floats have not leaked and taken in petrol, they should be empty.

Cheers
Jon
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PostPost by: denicholls2 » Tue Feb 17, 2009 4:36 pm

dusty wrote:
carrierdave wrote:That suggests your car is running rich at idle with the default settings. Have you also checked the float heights? The procedure should also be in the manual. whilst you're at it check that the floats have not leaked and taken in petrol, they should be empty.


Yes. So it would be quite useful to know what your idle jets are. It seems to be common when tuning Webers (I ran in that direction myself) to correct an overlean condition at the transition from idle to main (3000 to 4000 RPM) with a richer main jet. While it solves the problem at hand, the engine generally runs richer and therefore burns more fuel and fouls plugs easier. A potentially better solution is to enrich the mixture slightly via different air correction.

The Weber is wonderfully tunable, but this results in multiple options to address the same general conditions, some of which turn out to be sub-optimal.

It doesn't sound like this is your issue, but note also that there are two different mixture screw designs used on the DCOE and the "default" setting is much different for the second type than what's in your manual. This tidbit also catches the instruction follower out on occasion.
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PostPost by: twincamman » Tue Feb 17, 2009 6:49 pm

I back the screws out one and thee quarters ---then turn them in ------works far better -----ed
dont close your eyes --you will miss the crash
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PostPost by: msd1107 » Tue Feb 17, 2009 7:38 pm

There is another group, Sidedraft Central, that covers virtually anything you want to know about Webers.

http://autos.groups.yahoo.com/group/sidedraft_central/

David
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PostPost by: carrierdave » Tue Feb 17, 2009 8:38 pm

Hi all,
Thanks for your comments. I will check the float positions and adjust if required. Just for reference my idle jets are 50 F.8 as per the details for the s130 in my manual.
Thanks

Dave
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