Morris Minor Owners Club

hello folks, now, some of you may remember my questions about my dads engine a few months ago.
a recap...
a +30 rebored 1098
940 big valve head
1.75 SU
LCB exhaust
longer duration cam(270 i believe)

right, he rebuilt the thing himself, and is currently breaking it in. but there is a real noticable drag at low revs, and as he is breaking it in, isn't taking it above 3000 revs(ish).
i went out with him as he was a bit miffed(he had a 1275 in there before). i agree that there is a problem low down, but once it gets to 2500ish revs you really do feel the power kick in a bit.
so my thoughts, he is adament that the timing is set right, but i am not sure. it doesn't feel like a mechanical issue low down, but more if a timing problem, does anyone have any ideas what it should be set to?
also the carb came straight off the 1275 A+ engine, so is there likely to much jetting issues? bearing in mind the head used on this 1098 now.
any help would be great as he is being a bit precious about it all and it's beginning to wind me up quite a bit!!

I would say it's down on low down torque because of the cam and large inlet. Having owned a 1043cc Polo I can say with confidence that the standard 1098 BMC engine has excellent torque low down. As with any engine mods, a rolling road sesh can work wonders, but a standard cam may be the only answer.

hmm, interesting, and unfortunate if true!

Bible, page 312(cam duration): "small displacement big valve engines rapidly loose (sic) low end output...... if you are using a smaller verion of engine then you have to be more conservative with duration". As the power is kicking in sharply, it certainly sounds cammy.

But.... I had a similar flat bottom with my hif carb, stretching the damper spring cured it by keeping the airflow speed up in the carb at lower revs. Worth a try!

I reckon it would be better with a 1.5" carb!

Yes -the cam and the largish carb may be working against it. But also make sure the vacuum advance is working properly - and advance the ignition timing till it pinks - then back it off slightly.
Is the head 'big valve' or standard valve vesrion ? I reckon when set up properly it will fly above 2500 rpm - that's about when a 270 cam is supposed to kick in!

Ok, well dad has a couple of carbs that he can use, not sure if theres a 1.5 though. Nikki, downdraught weber, the norms!
It certainly does feel like it 'turns on' once it gets going. So if we get a 1.5 do we think it could negate the needto remove the cam?

Oh, the vac adv. Is working and it is a big valve 940 head.

Well my warmed 1275cc runs fine with an 1 1/2 carb but it needed both the spring and needle changed when set up on a rolling road, which is the only way to make sure the set-up is correct..

I hear you kevin, but daddy's a bit of a penny pincher(he was born in glasgow!!) so i think a rolling road will be done as a last resort. Bless him!

The 'big valve head' answers your question! With that cam he has built a flyer - it will be fine! Don't bother changing the carb - that's the beauty of SUs -the variable throat is self regulating to the airflow. May be worth fiddling with the spring though - as LA suggests, but DO try tweaking up the timing. The needle will have to be optimised later - just go with plug checks at the moment to make sure it's not running too weak.

Well so is a large part of my family and its not called penny pinching just cautious

You won't get anyone more 'cautious' than me!

So smaller carb and we will see. Excellent. Ill keep you posted!

Sorry roy, only just saw the rest of the post. Ill get dad to do as you and la say. Cheers.