how fast should it go (SORTED)

[hotrodder13]

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

[linearaudio]

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!

[hotrodder13]

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

[linearaudio]

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!

[bmcecosse]

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.

[linearaudio]

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

Not even on a full road race cam?

[hotrodder13]

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

[bmcecosse]

Oh well - you obviously know best!

[Roni]

Fuel pump?

[hotrodder13]

the fuel pump just ticks away,

[hotrodder13]

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

[bmcecosse]

Great success - i'm not often wrong

[hotrodder13]

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

[Alec]

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

[bmcecosse]

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.

[hotrodder13]

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

[bmcecosse]

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

[hotrodder13]

well done quiet a bit of driving and no flooding yet