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 - Fuel Problems At High Ambient Temps

Hey All, I have been periodically having an issue with my '73 MGB with Dual SU's and believe it to either a carburator or fuel pump problem.

Problem:
At high Ambient Temps (Above 90) the car fells like it is misfiring or running on one cylinder. It usually occurs under load driving up a hill. I have no power at all. When I am experiencing the problem I have pulled to the side of the road, left it idling(idles great) and popped the hood and looked at the level of fuel in the filter and appears to be near empty. As I sit there idling it slowly fills back up again. The engine is running warm but is definitely not overheating. I have ruled out the ignition as well.

Other than this occasional problem the car runs great and starts great. I get to the top of the hill and all is fine.

I couldn't really find anything in the archives so am hoping for some advice.

I am thinking it is either a Fuel pump or possibly be that I might be seeing some vaporization in the float bowls? I rebuilt the carbs a couple of years ago and am thinking that I may have set the float level too low. Is it something else?

Help!
Thanks, Eric
Eric Willis

Eric,
It sounds very much like the fuel pump is just able to deliver the needed volume.
I would check that first for both pressure and volume and also for any blockages / restrictions / kinks in the fuel delivery line.

Pete.
Peter Thomas

Eric - Check that you are getting 2.4 pints per minute being pumped through the pump when it is operating wide open. To do this, disconnect the fuel line going to the carburetors and direct it into a quart jar, then turn the ignition on. The jar should fill in 50 seconds or less. If the fuel is pumping slow, see the article, Fuel Delivery Troubleshooting Guide in the SU Fuel Pump Articles section of my web site at: http://homepages.donobi.net/sufuelpumps/ Cheers - Dave
David DuBois

Sounds good, thanks for the advice..I'll check the fuel pump out first. Still a little stumped as to why it only occurs at high ambient temps and not all of the time. I have one of those aftermarket noisy fuel pumps which I installed about 10 yrs ago. Thanks, Eric
Eric Willis

Eric - It could be that the ten year old pump is getting tired. I had a Mazda pickup with a Facet pump in it that exhibited the same symptoms. since it wasn't a SU pump, I never suspected it for a long time. Just confirmation that the SU pumps are not the only nes that get old and fail. Cheers - Dave
David DuBois

The fuel filter not being completely full is not unusual. If it is a plastic filter keep an eye on it, they tend to crack in the area that is not filled with fuel.
John H

This thread was discussed between 11/06/2008 and 12/06/2008

MG MGB Technical index

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