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MG MGB Technical - tuning engine

It was the best of times, it was the worst of times.

I'm trying to tune my new mgb 18ga engine. I did some grinding on the head, matched the carbs to the ports, major removal of exh guide boss. Polished exh ports and roughed-up intake ports. I made the exh funnel out and the intake funnel in just a bit. It's got a 3 angle grind, h4 carbs(it's an mga).
25D dizzy with pertronix.
new platinum plugs at .025(or whatever is recommended in the mgb book)

The best gas we can get is 93 octane with 10% something or other added. I have a

I broke it in per usual advise and now with over 1000 miles here is the story. At first it didn't want to rev over 4k and I really didn't try, but now it seems to run out of power at 4500rpms and barely can hit 5000. Enter the nifty timing light with dial.

The engine had also been pinning. Initial check found I was running at...
with vacuum connected
600rpm 21
w/o vac
600 20
1500 30

So, new settings with vac per spec..
600 14
900 18
1600 25
2200 30

Took it out and still had pinningunder load, but not quite so much, and still doesn't have any power or want to rev over 4500rpm. Brought it in for check and it still had the same settings. Here I finally checked the vernier dial on the dizzy. Using the light, I moved it 44 clicks either way and it had no effect. Thought so.

Synchronized carbs with wire kit and ear. Set jets equally to .080" because this is where the pin lift test indicated it's not too lean or rich.

I retarded it to get rid of pinning. New settings..
600 8
900 10
1600 16
2200 20

Took her out and still pings under load, but a little less and still no desire over 4500rpms.. Also runs-on again which surprised me.

My thoughts...
It seems to run rougher than when new this spring

when I use the light the timing mark jumps about 10degrees back and forth, but when I change the dial setting so it appears to be retarded, the jumping stops and it's rock steady???

A friend who races scca mgbs said to take about 4 degrees worth of metal off the advance curve plate in the dizzy. Too much advance at high rpms -where I'm not checking with the light

worn advance springs

mga needles not supplying enough fuel

fuel pump on last legs(it doesn't stop clicking, and I checked ALL the fittings, or pump filter.

Can't think anymore....eyes hurt...soooo tired.. must get back to garage..mustn't sleep

Oh yeah, I'm not the same Fred Horstmeyer that was dissing MGBs and whining about engine swaps, in an earlier thread. That was someone else. Really!




Fred Horstmeyer

Surfed over from MGA land. You will need new needles according to John Twist of University Motors. "MB" I believe. I'm doing exactly the same conversion, also with the MGA stock carbs re-needled for the 1800 mill.

The head work may necessitate even richer needles.

Did you Check your Camshaft timing?

Let us know how it goes.
Doug S.
D Sjostrom

Doug, thank you! Cam is stock. Do you mean to check the specs or dial it in? I'm not sure what you mean. I've read about dialing in a cam with a wheel, but I thought timing took care of that??

I haven't heard of mb needles, but it was suggested that I try #5 or #6 mgb needles.

I guess I'll roam over to the Univ motors site.Thanks again for the input.
Fred Horstmeyer

Fred,
I meant dialing it in. Reground/repro cams can and sometimes do exhibit errors in timing that can influence performance. Offset timing sprocket keys are made to compensate.
I highly recommend the technical manual available from University Motors, It's loaded with great information on just your type of problems.

Assuming the tuning basics are OK, I'd focus on fuel delivery/mixture.

I'm strongly considering installing a Holley Rich / Lean Indicator in my exhaust system to assist in establishing and maintaining proper fuel/air mixture.
Doug

D Sjostrom

Thanks. I just read that other than being too advanced, too lean a mixture will also cause pinging. I'm digging around for s useable chart for needles in my set-up, or I'll just order a set of #5 needles. My engine is std. bore. Do hs4 needles fit in h4 carbs?
Fred Horstmeyer

Fred, YOu can see a needle chart at;
http://www.teglerizer.com/suneedledb/index.html
Click on, View entire ordered list, and over 300 needles will be shown. Hope this helps, Clifton
Clifton Gordon

Fred,
I just checked and the "MB" needles fit the Standard MGA SU's with fixed jets. These are the ones recommended by John Twist for running the MGB 1800 on stock MGA SU's.
Doug
D Sjostrom

This thread was discussed between 03/06/2003 and 04/06/2003

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