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MGB 77 MGB Rev Problem

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kyreb1862

kyreb1862

Jedi Knight
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I'm having a problem getting my 77 B to rev above 4000 rpm. At 4000 rpm the car just seems to bog and at the same time the tach needle starts to jump. Below 4000 rpm, no problems at all. The car is currently running a ZS carb with a K&N air filter on a Jet Hot coated Austin Marina intake/exhaust. The exhaust side of the manifold feeds into a custom 2 inch exhaust system. I modified the carb by removing the poppet valve throttle disc and installing a solid throttle disc. The car is equipped with the factory CEI ignition and is currently timed at 12 degrees at 1500 rpm, the plug wires check out good and the plugs are Champion R9NY's. The plugs are gapped at .035 they show a dark brown to black color with the front two plugs being a bit lighter than the back two plugs. Any ideas or suggestions would be appreciated.

Regards John
 
Hi John,
When our B had a very simular problem, it turned out to be the upper bushing in the distributor. Suggest you check yours for sideways play.
Cheers Ric
 
wrenchpuller said:
Hi John,
When our B had a very simular problem, it turned out to be the upper bushing in the distributor. Suggest you check yours for sideways play.
Cheers Ric
Click to expand...

Thanks Ric. I had a thought along the same lines. The book says the pickup gap should be .010 to .017. The gap was under .010 so I just got through opening it up to .016. Haven't had a chance to road test yet, but I'll post how it goes.

Regards John
 
John,
that was the problem with ours, although I had checked and set the air gap, at higher rpm's the shaft would start to occilate and mess the gap up. Tach went beserk and it almost felt like there was a govenor on the engine (not a real missfire as such, just would not make more rpm). I replaced the upper and lower bushings and all was well.
Cheers Ric
 
Ric, I believe you have hit the nail on the head. After setting the gap the car ran much more smoothly but still has the same problem above 4000 rpm, as you stated, it feels more like a governor than a miss. How difficult were the bushings to install and where did you source them?

Regards John
 
Hi John,
I contacted Jeff (Advanced Distributors) he was kind enough to mail me 2 used but zero wear bushings (I must confess I did turn 2 on my lathe from stainless to see if that was the prob) but fitted the correct alloy ones as soon as they arrived. You will need access to a small press or a really good vice to to remove and fit the replacements. But suggest you give Jeff a call, his rates are most reasonable, and he would check the curve as well.
Can you feel any sideways play on the shaft? It would be a waste of money and time if there is no play there. It does not take a lot to alter the air gap, but you should be able to feel it and see the deflection by eye.

Cheers Ric
 
Hi Ric
I can definitely feel some deflection when I push or pull against the distributor shaft. I think I will probably just pull the distributor and send it to Jeff. I have heard nothing but good things about his work. Many thanks for your input maybe I can return the favor some day.

Regards John
 
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