Dellortos not idlling

**Voltaire** · 19th January 2012, 22:14

Got a set of S/H 36mm Dells on a fresh R90 BMW rebuild. I rebuilt the carbs with new seals, needle and main jet....the rest looked ok.
Motor has a sports cam ( 336), 1 mm off the heads and an electronic ignition.
Ignition is timed as per manual.
Has a 2 into one fitted.
Engine starts only on full choke, seems to run ok on the throttle but wont idle or idles high.
The mixture screw does not seem to have any effect.

Anyone had anything similar....anyone remember carbs?

Pulled the plugs and they look a bit sooty...but not too bad.

cheers

**Grumph** · 20th January 2012, 05:36

Couple of possibilities...if you're not running filters, the carb bodies could be worn allowing air leakage past the slides.

If you are running filters then you have an air leak somewhere.

Are the carbs spigot fitting or bolt up flange ? Either way, check the manifold to head joints.
Worth checking float heights too - and float weights if they've been bought secondhand, there are some odd ones about.

**Voltaire** · 20th January 2012, 05:51

Good points, I hadn't given much thought to air passing the slides...the carbs are well used.
Float weights...hmmmm. I measured the fuel level two ways, the 17mm cut off and the quantity in the bowl...55mls in both exactly.
I found that the inlet stubs were leaking so have sealed them, might try a quick loud start before going to work.....
cheers

**Motu** · 20th January 2012, 14:57

You generally need more advance at low speed with a lumpy cam - try locking the advance as an experiment, if it runs better that could be the way to go. Mind you, a lumpy BMW cam is similar to a Briggs & Stratton grind....try a carb off your lawnmower.