Hi Kelvin,
The distributor is a 25D4, Model 41220. Vacuum is being taken off of the
rear HS4 at a small tube inseted into a hole in the carburetor just in front of
the mounting flange, so I guess it's ported vacuum. A big problem is that the
moveable plate in the 25D4 is badly worn at the the central hole where it
rotates about the center shaft. The effect is to cause very erratic ignition.
I suspect that it's causing an intermittent path to ground for the coil
primary. Do you know of a source of decent 25D4's ? Thanks.
Bud Krueger
Dodd, Kelvin wrote:
> Bud:
> It is important to make sure that all of the pieces work
> together. You will need to check the distributer number to make sure
> that it has the correct characteristics for the carbs. You can use
> either of the two distributers once you know what vac/cent.
> characteristics they have. With the HS4 carbs you can either plumb the
> vac. adv. to the ported fitting on the rear carb. Or you can pick up
> vacuum at the manifold. Either system works with the correct dist. The
> most documented layout would be the HS4 and an early (non-HIF) 25D.
> Once rebuilt with high comp. pistons and an early cam you would have
> specs similar to 62-67 cars. The factory designed this setup for the
> best balance of power for normal usage.
> Get me the dist. numbers and I will check to make sure they are
> suitable. Also check the dist. shafts for wear and vac. units for
> operation. To my mind the best bet for you would be a new 45D dist.
> suitable for the HS4 carbs. Pricey, but set and forget. There is a
> Pertronix conversion for this dist.
>
> Kelvin.
>
> -----Original Message-----
> From: Bud Krueger [mailto:bkrueger@ici.net]
> Sent: Wednesday, November 25, 1998 9:32 PM
> To: MG List
> Subject: 25D4 vs 45D4
>
> A bit of advice, please. My '77MGB has HS4's and an early twin downpipe
> exhaust
> system (once I get around to installing it). I will be using a
> Pertronix
> ignition system. My problem is this: I have a 25D4 and a 45D4
> available to
> me. Which one should I use? Why? TIA.
>
> Bud Krueger
> 52TD
> 77MGB
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