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MG MGA - Proper Needle for 1800 with H4 carbs

I am putting a 1800 3 main stock rebuilt engine in my MGA to replace the 1500. I plan to transplant the H4 carbs to the new engine. I couldn't find a real answer in the archives but which is the best needle for the H4's in there new assignment.

The "5", "6" or "MB" needles have all been recommended. This is a street/highway engine application and I am upgrading to a 5 speed and 3.9 rear at the same time. The "5" appears best to me but what is the experience of those of you that have run this modification.

Jim
Jim Ferguson

#5's as determined using an on-board rich-lean indicator. exhaust is the MGA manifold into a Falcon stainless steel, stock diameter MGA set sold by Moss.
D Sjostrom

Hi Jim mine had 6's with that same set up


gordon
g c pugh

Jim,
I'll add to the mix: I'm using MB needles and my setup is an 1800 3 main but with A parts all around including carbs, head, & exhaust manifold. I still have the 4 speed gearbox but have a 3.9 rear end.

It runs fine and I've put about 2600 miles on it since completing the rebuild over the winter.

Larry
LP Pittman

I guess they all work reasonably well. Maybe there are others who can add there experience to help form a consensus.

I have emailed Jimmy Hilton on the question but haven't heard back yet. John Twist said MB (from archives). Others say the 5 is better at higher RPM because it is a little richer than the MB. Others run the 6 without problems but I have seen reports of it being too rich.

I still don't know which way to go.

Jim
Jim Ferguson

Jim,
I dialed mine in on the road using an on board Rich/lean gauge. This has an oxygen sensor welded into the header pipe immediately after the cast iron mga manifold. I started with the MB's and went to the #5's based on actual road observations of the mixture. I get about 26 miles per US gallon and am quite satisfied with the performance throughout the range of operation. Engine is a five main 1800 over-bored. 040", stock camshaft with a Sierra five speed box.
D Sjostrom

To add a final note, I received the following from Jimmy Hilton who I consider an expert on SU's:

"My guess for the early H4 carbs would be to start with a #5 needle. If you feel that you are lacking a bit on the upper end, then give the #6 a shot. They both should provide a similar result to about 3600 rpm, and then the #6 should start to increase the fuel delivered."

I don't know that there is a clear consensus but I will probably start with the #5.

Thanks for all the input on this question.

Jim
Jim Ferguson

Jim

Any contact details for Mr Hilton?
dominic clancy

Email Jimmy Hilton at:

jimmy@batterypowered.com

You can check his member page at MG Experience at:

http://www.mgexperience.net/member/JimmyHilton

or Web page:

http://www.britcarfun.com/

He does not have a full time SU business but rebuilds them after his regular job. He may take a little time to respond to emails.

Jim
Jim Ferguson

This thread was discussed between 15/08/2008 and 21/08/2008

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