Morris Minor Owners Club

well changed the needle on the card and it sorted one problem but another has come up, it has started to backfire a bit and when it gets up to about 70 its just seems to die, slow down, carry on then dies a bit again, is that my top speed or is someting wrong

thanks tom

Sounds like your needle is too weak around the halfway mark. Unless you can find out what cam you have fitted to give a clue, it will be a matter of finding someone well aquainted with sorting SU needles!

To see if it is the mixture, try pulling the choke right out as you enter the problematic speed- if there is an improvement then its your mixture, which could also explain the backfiring!

Whatever you do, don't keep on with it as it is unless you want a burnt exhaust valve or worse to post about!

Oh- and in reply to the opening statement- a lot better than 70!

kk found someone to do a temp set up on a c02 machine (for mixture) then im gona try gettin it rolling roaded

Hope this person knows what CO2 readings a warmed up 1275 A Series should have all the way through the rev band! Sounds like rolling road territory already!

Sounds like fuel starvation to me. There's no way a BDL needle will be weak! However - back fire suggest an ignition failure of some kind - but could simply be 'running out of fuel' syndrom.

bmcecosse wrote:Sounds like fuel starvation to me. There's no way a BDL needle will be weak! .............

Not even on a full road race cam?

had half a tank, so dont think it could be that might just go stright for the rolling road then

Oh well - you obviously know best!

Fuel pump?

the fuel pump just ticks away,

bmcecosse wrote:Sounds like fuel starvation to me. There's no way a BDL needle will be weak! However - back fire suggest an ignition failure of some kind - but could simply be 'running out of fuel' syndrom.

well you was right again changed the fuel pump for a modern day one and its does go that bit quicker and dosnt die, this one puts out 4-7 psi

Great success - i'm not often wrong

i know
should a marina 1275 have a diffrent pump anyway can i ask,

Hello HR,

glad you found the problem, but "this one puts out 4-7 psi", which is too high for S.U carburettors. You can get a pressure regulator to bring it down. I forget the correct pressure but somewhere in the 2 psi. mark. Too much pressure can cause flooding.

Alec

Marina and Mini 1275 engines had mechanical fuel pumps - and no problem with fuel flow. Your original SU pump should have been fine - may be the filter is blocked or the stroke is set too short. As Alec points out - the pressure you state (how do you know ??) is a bit high for an SU - although the HIFs can cope better than earlier carbs.

kk ill try getting one and i know it puts out that cause it says it on the side

If there is no problem with flooding - don't bother doing anything!

well done quiet a bit of driving and no flooding yet