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MG TD TF 1500 - S/C carb needle

Thanks to Kaz Belinski, XPAG S/C ( With my S/C roller cam), : Thanks Len, I replaced the RA needle with the RB needle, it makes a nice difference, engine is now pulling better at all RPM's" Jim Neel ( at sea level)
Len Fanelli

Len etc, my TF 1250 with blower and the standard 1 1/2 inch SU has been thru several needles, and wound up with an SY. Looks ridiculously rich, but works well. I'm at sea level, too. The car has 8.5:1 compression, larger valves and a fast road cam. We changed from the RA because it was way too rich low down, if you set it up at high power.

My expert used to use this needle in an MGB running 15 pounds of boost!

David
DavePro

Thanks!
Len Fanelli

http://www.mintylamb.co.uk/suneedle/
Len Fanelli

When opening up my last post, then clicking on the .100 needle selection it shows the graph of RA VS RB.
This shows all 3 needles on a graph. http://www.mintylamb.co.uk/suneedle/
Len Fanelli

From an older BBS post Ben Travato stated either a RA or RH needle, any comments on the RH needle.
So we have RA, RB, RH, SY
Recommendations at sea level & higher altitudes?
Len Fanelli

RH is the leanest overall and at speed, and should be a good starter for higher altitudes.

SY starts out lean like the RH, then richens up to about the same as the RB at speed.

RA starts out richer than the RB, but then leans out, but not nearly as lean as the RH. The RA is the base needle I supply.

For my tastes the RH is too lean except for high altitudes, the RA the best middleground, and the RB is good if a slightly richer needle is needed at speed.

The very WORST thing you can do is to run lean, as you are likely to burn a piston; this is also why timing is critical, and I insist that the distributor be recently rebuilt by Jeff Schlemmer. It is all too easy to get a car running great at idle, but then run lean at speed due to distributor wear and sticking weights.

This exercise is EXACTLY why I so strongly urge a dyno tune after all has settled in. On a dyno small adjustments to the needles, mixture, and timing can be compared. I have seen an average of a 10% gain in HP by paying close attention to the dyno results and changes.

The mintylamb.co.uk comparison guide is invaluable for needle comparison - click on .100 jet, enter the needles you want to compare, then watch the colors.

Tom Lange
MGT Repair
t lange

Thanks Tom, Running lean will melt pistons, normally aspirated or supercharged. This can be due to needle selection or float level too low.
To help prevent burned / melted pistons I always Ceramic (Thermal) coat the piston crowns, & dry film coat the skirts to prevent scuffing.

Len Fanelli

This thread was discussed between 13/05/2016 and 16/05/2016

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