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MG MGA - new vac unit - something you likely need!

This could change your life, and is a shameless plug for this manufacturer - but it is a personal endorsement which I stand behind. You probably need a new vac diaphragm on your car and don't even know it!

I met up today with Rob, the owner of British Vacuum Unit (www.britishvacuumunit.com) in Canterbury NH (really out in the woods). Rob invited me up to look at my car. He has been working on these cars forever, and I really wanted someone OTHER THAN ME to drive mine and give it a once-over. I felt that I had done the best I was able to do tuning and adjusting without having any point of comparison other than what I read here and elsewhere. Rob was nice enough to take it for a spin and give it a good shaking down.

I started talking to Rob because of his business at BVU. Right in his shop, Rob casts and manufactures exact replicas of the original Lucas vacuum advance units for the 25D distributor. The units are "authorized" and have the Lucas name on them, and come in original Lucas boxes, with original labeling and instructions.

He said that not many people realize how important having the vac unit work correctly is to the operation of our cars. I have been chasing my tail on carb and distributor adjustments, and decided to try it out. He put my dizzy and original vac unit on a test machine (pics to come later once I download them), and my vac unit was shot! The 25D should begin to advance at 7"HG, and top out at 14"HG. Mine didn't start to move until it got to 12" or 14" and didn't finish up until he got to 22" or 25"...the rubber was dried out and the whole thing was too stiff. Otherwise, my dizzy and points were good - which was encouraging.

With the new vac unit on the car, the whole engine was totally changed! I hadn't realized that before I really had no vac advance at higher RPM's. The car now seems to shift smoother (probably because the vac kicks in when you let off the gas at higher rpm's and it sort of "carries over"...sorry if that is not technically articulate, but it definitely runs better, is more responsive, and just smoother (there's that word again) all around. It felt soooo good on the 60 mile drive home, even though I thought it ran well enough on the way up, I was wrong.

I really really recommend trying this before you kill yourself adjusting your carbs, your timing, your dwell, etc. etc. etc. The unit only costs about $80. Definitely cheaper than buying a new dizzy and might keep you from from going to an ($$$) electronic ignition. It seems that if your vacuum advance is working, all the other niggling little adjustments aren't so critical as if it is not!

Rob also makes spare parts for the turn signal switches, and the carb overflow tubes. And, he machines nifty replacements for the little screws that go in the voltage regulator and dash switches! (He is now supplying these to SF and Moss.)

Rob was a great guy and took a lot of time to talk to me about my car and what I had done and what issues I still needed to sort out, etc. In general, I have found this is a great community (of MG and Brit car folks) and he is one of the ones that helps keep our cars going (though he doesn't really do the online forum thing much).

Contact Info (tell him I sent you!):

Rob Medynski
(603)783-0566
email: britishvacuumunit@isp.com

JIM in NH
AJ Mail

Distributor Doctor in the UK provides new vac units (NOS) for 22.50 + 7.50 shipping (sterling).
Art Pearse

I second that Jim. I ordered a new vacuum unit from British Vacuum last year and what a difference it made to the way the car runs. The unit was cheap enough but the shipping was a bit pricey once our tax people and Royal Mail got their claws into it, but still worth it. Just typical that a source pops up this side of the Atlantic after I've got one!
Lindsay Sampford

Went for another drive today. The biggest difference I can see/feel is that, with some actual advance at higher revs, my engine doesn't sound like it's so wound up at 4000+ rpm's and I am much more comfortable going up to 5000, or just running at 3800 without wanting a 5th gear to put it into. Also, the engine is now consistent throughout the rev range - again, "smooth" all up and down.

Money very well spent!

JIM in NH
AJ Mail

When I did the timing on my car recently I also got the impression that the vacuum advance does not work as it should.
I found that it took a lot of force to compress the spring/membrane. Is this normal?
Then I used the MityVac vacuum pump and I could not get it go move much. It would barely move if I kept pumping it. Should any air pass through or is the membrane broken?

Let me know what you think, if this is the case I am definitely going to purchase a new one.

Thanks!
Gonzalo
Gonzalo Ramos

Gonzalo, no air should pass through the unit, if it leaks it is shot! Make sure that it is not leaking at the joint washer behind the large hexagon nut on the front of the unit, but if it doesn't have the large hexagon your only option is replacement.
Lindsay Sampford

Gonzo, get one of these! You will have a changed car! Mine is running soooo much better!

JIM
AJ Mail

This thread was discussed between 27/08/2011 and 29/08/2011

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