Distributors are pretty simple things really, they "distribute" the spark from the coil across the four spark plugs. You'd think that there wasn't much more to it, but it turns out that there is a whole dark art to distributors - and it lies in understanding "advance". The basic idea is that as the engine revs faster, you want to the spark to be a little earlier in the combustion cycle. But how? Well distributors have springs in them that cause the rate of advance to change as they spin faster. This can also be augmented by vacuum from the carb manifold. As the engine runs faster - there is more vac - and more advance. Great stuff!
What happens if your distributor is old and tired and has worn springs and perhaps the vac advance is not working too well? In this case the engine won't get the advanced ignition that it needs at higher rpms and the power will decline. The engine will feel "bogged down" at high rpms.
Ok, so back to my car... I have noticed that at 4000rpm the engine does bog, it basically doesn't really want to rev higher. This is despite the dual barrel weber where the second barrel kicks in at higher throttle. I think these symptoms are consistent with a worn distributor. So I ordered a new (rebuilt) one from Jeff at advance distributors.
Let me say something about Jeff. Here is a guy who knows distributors - the guy is an expert and frequently posts on mgexperience.net. He rebuilds and, very importantly, recurves distributors. Recurve???? This is the process of putting in new springs and advance mechanics to make sure that the advance works as it should and also that the advance works for your specific engine set up. When you order a distributor from Jeff, you have to give him full details about your engine, carb, exhaust and other mods, so that he can set the advance just right for your set up. Its really tailor made and better than the factory set up or any that you could get from a large retailer of parts.
Back to my car, again. I also ordered Pertronix electronic ignition and a higher power Flame Thrower coil. Electronic ignition removes the need for points and is virtually maintenance free and more reliable. The Pertronix set up also gives you more consistent sparks and more steady sparks.
Swapping out a distributor is not too hard. I removed the old one after noting the position of the rotor arm (very important). I put in the new coil, and put in the new distributor and wired it all up. The little mounting bracket is a little tricky as you have to loosen it enough to get the distributor out. I ended up removing the bracket - and loosening it. The main thing is to try and put the new one back in in roughly the same angle as the old one.
When the engine was fired up - it started and I adjusted the timing to 14 BTDC. I took it for a drive and WOW!!! First of all - no bogging down. The car would red line if I let it - and this is on the highway not when parked. Second the performance, particularly at higher revs was much better (this is consistent with the old unit having tired advance).
Setting the timing is pretty easy with a timing light. Mine is a dial back type that allows you to put in the amount of advance and then you adjust the timing so that the marks are a TDC. It makes it very easy. Jeff includes his recommended timing settings for the unit when he sends it to you, so it really takes out the guess work.
He has a great article written on timing. Here is the link...
Read this before you start messing with your timing.
http://www.mgexperience.net/journal/B-racer/1818Anyhow, all in all, a nice upgrade that without a doubt bought me some extra HP. And as most folks know, HP is not cheap. In fact, with the new exhaust, carb, and distributor, I have probably bought all the cheap HP I can.
Jeff's website is here...
http://www.advanceddistributors.com/
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