Lotus Elan

Balancing carbs

PostPost by: rdssdi » Sun Sep 09, 2012 10:41 pm

I wish to adjust my CD175 carbs. I have a new Uni-Syn.

Any suggestions? All the emissions paraphernalia has been removed.

Thanks

Bob
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PostPost by: elanern » Sun Sep 09, 2012 11:41 pm

Bob, I have the same carbs on my S4. There's lots of info on the internet, and probably here (I did not do a search first). Here's what I do. I am assuming you have non-adjustable needles.

Make sure it is timed properly. It's been said that many carb issues can be traced to improper timing.

I warm my engine up to operating temperature. Adjust the idle speed so that it is where you want it.

Remove the air cleaner. I have to remove the throttle return spring to do this, remember it is off as you get into the balancing act, you do not want the engine to race unexpectedly and possibly detrimentally.

Loosen one of the links between the carbs so that each carb operates independently of the other.

Start the engine and put the uni-syn on one of the carbs. I usually start with the front, not sure if it makes a difference. I try to ensure the sight glass is vertical. Note where the float is in the sight glass. I use the adjuster on the uni-syn to line up the float with one of the lines. Keep the same adjustment for both carbs.

Then move to the other carb, and adjust the idle screw until the float is in the same position as the other carb. You want both carbs to be drawing the same amount of air. You might have to fiddle with each carb a couple of times to ensure you have the right idle speed and same float height. Throughout this process I will "blip" each throttle a couple of times after adjustment to ensure it idles down to the same speed/float height. Remember the return spring is disconnected.

Once the carbs are balanced I reconnect the two carbs and double check the float height again. Should be spot on, if not you might have to loosen the connector and try again.

Let us know how you make out.
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PostPost by: oldelanman » Mon Sep 10, 2012 7:26 am

On the Stomberg the float chamber vent, diaphragm chamber vent and the temperature compensator air way drillings are all on the intake face of the carb and some of the synchonisers will cover these ports (not sure if this applies to the Uni-Syn). Does this matter ? I struggled to get consistant results with this type of synchroniser and wondered if this may be why.
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PostPost by: elanern » Mon Sep 10, 2012 1:50 pm

Short answer is "yes", the uni-syn covers the float chamber vent, diaphragm chamber vent and the temperature compensator air way drillings. The outer diameter of the uni-syn's foam seal is 3", and the foam is 1" wide, resulting in a 1" hole in the center for the air to pass through.
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