MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - idle issues

What could cause this. After the final step of balancing the carbs, idle set at 1000 and running well, air cleaners put back on and idle drops to 500. I checked the air cleaners, and they're put back correctly, gasket aligns with holes in both the carbs and air cleaners. Any ideas?
Keith Yarbrough(TD 1275)

Dirty air cleaners? Remove them and just put the housings in place for a check. Cheers - Dave
DW DuBois

only a theoretically perfect airfilter will filter whilst offering no resistance to airflow. however, idle is not very demanding in terms of flow. are you using pancake filters? they have the smallest surface area of suitable filters so would offer the greater resistance - and foam ones are not great at the job.
if you are getting resistance to flow, the mix will be enrichened when filters are replaced and rpm will drop.
G
Graham Moore

On the MGB at least the air cleaner bases have two offset holes that allow part of the carb body to remain at atmospheric pressure, so the piston operates correctly. Original gaskets also had two offset holes, so could be fitted the wrong way round and block them. Later types had holes in both positions so that couldn't happen, but the bases themselves can still be fitted upside down.
paulh4

Paulh4, gaskets are fitted correctly. Dave, These are stock, new air filters.However, as many times as I've had these on and off to figure this out, I could have inadvertly put them back correctly this last time. Just waiting for a little "dry" time to take her out and shake her down. We're pretty wet here in Sacramento. Thank you for all the advice. It is all much appreciated from this rookie.
Keith Yarbrough(TD 1275)

That same thing will happen when the throttle spindles need replacement or rebush and oversize spindles.
D Peltier

"That same thing will happen when the throttle spindles need replacement or rebush and oversize spindles."

Running problems yes, but I can't see why that should make such a big difference at idle between filters fitted and filters not fitted. Unless the filters are ridiculously restrictive at 3-4k they won't be having a measurable effect at idle.
paulh4

This thread was discussed between 08/02/2017 and 10/02/2017

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.