What code needle would be needed for a 1.75" SU fitted to a 1275 for the best every day running. Currently it has a very flat spot at low revs when under load but takes off like a rocket when above 1500 RPM. It has a non standard cam but what profile, I have no idea. Ignition timing is set to 5 degrees BTDC. The distributor is from a honda, again type unknown so I don't know its tech specs for advance curves for vacuum and mechanical. It appears to have around 30 degrees advance on a quick check. Any advice welcomed.

With all those unknowns....take it to a Mini-friendly dude with a dynomometer and mention the SU needle selection program (if they don't already know) and get them to tiddly up your tune

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"Show me the Mini!"

Hi David,

What oil are you using in the dashpot? Is it at the correct level? Have you checked the idle mixture with the colortune? What profile is the needle? (should be stamped into it's base (take it out of the piston). I know you know this, it may help other's reading this topic though.)

Have you checked the cam timing?

Cheers
Matt

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68 Deluxe.... it's shiny..... I like shiny!!

Thanks Matt for the use of the colourtone. Tried it out today after fixing an ignition fault first. Will get it back to you now that I've found your address.

The current needle in the carb is a BCJ and the colourtune shows that at idle, it is running rich but once up in the higher rev range, it settles down to a good mixture.

Also checked what advance the vacuum advance unit gave. 7 degrees max. Mechanical advance appears to be around the 30 degree mark. This would seem to be a compatable ignition system however the real proof would be to map the advance curves.

As to the cam timing, not having any problems in the past means I'm no guru in checking it. To my way of thinking, that can only really be checked out of the car using vernier dial gauges to identify at what point the valves are operating. I think I will have to ask the previous owner if he knows what profile the cam is.

Hi David,

Keep the colortune as long as you need it. I'll let you know when I need it back.

As for the cam timing; I know you have a workshop manual! The idea is to simply note the position of the flywheel timing marks as no 1 is on compression (TDC), and note at what point the valves of no 4 start to rock. I think, my memory is dodgy on the specifics. It will let you see if you are more than a few degrees out, not an exact science, but this way you only have to remove the rocker cover.

Can also get some idea of the lift of the cam with a dial gauge and magnetic base, but checking (close approximating) the profile would require analysis with the motor out AFAIK. If the PO knows, this is easier, but he still may have installed the timing gears out a few degrees? Is there a timing chain rattle? Could be loose chain too?

Is it really poor down low? Worse than a stock 1275 in good condition? Could it be the profile of the cam means low running is poor (too much overlap) and that when it gets to a higher rev range it works better so ZOOM?

Some thoughts,

Matt

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68 Deluxe.... it's shiny..... I like shiny!!