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MG MGA - Judson Update

As reported in a previous thread, after installing my Judson I had a problem with pinging when accelerating in high gear. I had my distributor recurved by Jeff Schlemmer at Advanced Distributors for use with the supercharger. Jeff advised to set initial advance at 18-20 degrees BTDC with vacuum disconnected and then connect the vacuum advance to manifold vacuum. I did this but still found I had much pinging on acceleration in high gears. I dialed the initial advance back as far as 13 BTDC which was better, but still getting pinging in 5th, 4th, and sometimes even 3rd gear.

Problem #2, according to my cheap Sunpro vacuum/boost guage, I was getting only about 1.5-2 psi of boost on hard acceleration. My first thought was "vacuum leak", but the guage was showing good vacuum of roughly 20" hg at idle. When George rebuilt the kit for me, he supplied a 5" crank pulley and 4" blower pulley. That should be over driving the blower by about 25% which George thought should compensate for the roughly 20% increase in volume of an 1800 engine over the MGA 1500.

With summer being so short, I was begining to feel pressured to get the car running so as not to miss any more activities with the local MG club. I'have temporarily removed the Judson from my car and put the SUs back on. In a month or two when I have a bit more time, I intend to have another go at it. In the mean-time, I'd like to try and get a good handle on what might be causing these problems.
Andy Bounsall

One of the first things I think I need to establish is whether the air/fuel mixture is correct. I understand that either too rich or too lean can increase the potential for detonation. I have 2 carbs, both were rebuilt by IHOnly North, so I'm quite confident that they are in good shape. Both are currently fitted with #62 main jets. I'm fairly sure that these are not too rich, but I'm not sure if they might be too lean. Which main jet are others using on their Judson installations?
Andy Bounsall

Andy,
Not running a super, but installed an Edlebrock Rich / Lean O2 sensor based meter and was able to dial in precisely the correct SU needles for an 1800/ 5 Speed conversion...Sweet!
D Sjostrom

1. Try running 98 octane, reduces pinking a lot.
2. Check the Jet, sounds if you are running too lean and need a richer jet. Would be interested to know what you have now, and also what you end up with. the guys at IHOnly North suggest around a 62 jet on a 1622, so for yours you may need more again.
3. Carl Heidemann also suggests around 20 BTDC for a Judson.
dominic clancy

Dominic, as stated, my carbs currently have #62 jets. Is that what you are using on your 1622?

Re octane rating. If I remember correctly there is a difference of about 4 or 5 points between the way octane is rated in Europe and North America. So your 98 octane rating would be about 93 or 94 here (I think). 91 is available everywhere and is what I had been using. As far as I know, only one company (Petro Canada) carries a 94 octane fuel and it's only available at a few places locally. I will put that on my list of things to try though.
Andy Bounsall


Hi Dominic,

As your the judson guy, I sugest you put a similar spreadsheet to this on your web site and build it over the years:

http://myweb.tiscali.co.uk/hesterracing/Technical/Typical_MGA_Twin_Cam_Webber_Settings.doc

Cheers
Mark
Mark Hester

This thread was discussed between 21/06/2011 and 23/06/2011

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This thread is from the archive. The Live MG MGA BBS is active now.