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MG MGB Technical - Thoughts?

Took my 67 GT out for a 300 mile run. This is the longest run since the new rebuilt motor was installed (has about 400 miles on it).

The new power with the rebuild and an AP12 cam is impressive. zips right along.

Issue is that when I was cruising on the highway at 65 to 70, the car has a feel like the motor is missing but the tack is rock steady. I also noted a few times where the motor stared to stall (tach. dropped to near zero and then picked back up.)

I have new points, cap, rotor, wires and plugs and have checked the electrical connections for the coil and distributor. Also checked the wires under the cap to assure they were not being pinched.

I am thinking the dying is due to a bad wire and will redo the ends on the dist. to coil wires to assure they are making good contact.

Don't know where to start with the missing feeling while at high speed. Unsure if another system such as fuel would cause this feeling. Best I can describe is a back and forth rocking feeling (not caused by the road. I drove the car across the US last summer and did not notice this feeling.

The car has original dual SU's and pretty much is the same with the exception of the new motor.

Bruce TD4139 Cunha

Depending on what you have done to the engine, i.e., porting, over-boring, breathing etc. could be running weak at certain revs. Hence the needles may need "adjusting" to suit the new engine demands. But that would cause flat spots and a bit of 'hunting", usually on a trailing throttle, rather than a stall.
Allan Reeling

Bruce:

You may want to check your ignition switch. My 79 would do that and finally just quit.

Cheers

Gary
79 MGB:
gary hansen

"tach. dropped to near zero and then picked back up."

That at least does indicate a failure of the ignition LT circuit. If the ignition warning light works as it should, and that came on as well, then it is a loss of power from the ignition switch as Gary says. If it stayed out then the switch itself is OK, but there has been a break somewhere from the switch, through the tach, coil, points and distributor earth wire.

In my experience flat spots from a 'weak' needle with non-standard air filters and exhaust were evident not on a trailing throttle or steady cruising, but mild acceleration. Heavier acceleration, or pulling the choke a little, would overcome it, as did 'richer' needles of course.
Paul Hunt

Most appreciated. Ignition light does not come on.

Engine was bored 30 over and hotter cam is all that were changed. Head was rebuilt for valves and very lightly surfaced.

I will rebuild the wire from the dist. to the coil and also recheck the connections for power to the coil.

I think these are two different issues, but will start by working on the shut down issue. If I solve that, at least I will be a bit more comfortable in doing longer drives.
Bruce TD4139 Cunha

Also check that cotton covered wire in the distributor. If they fracture then you can't see the problem.

Herb
H J Adler

Bruce
When my ignition switch fail, the IGNITION light did not light up. The car just died - flat!!!
After a while it would start and run, until the next time. Then again it just quit....Fade to black as they say.

Cheers
Gary 79 MGB

PS. Let's see some pix of your TD when you can
gary hansen

Points are from Advanced Distributors and was the entire point, capacitor, rotor and plate. I will double check that there is not a potential intermittent grounding in there also.
Bruce TD4139 Cunha

"and was the entire point, capacitor, rotor and plate"

That would be very unusual, did you refit an earth wire when you fitted that? Without an earth wire the points plate can earth through springs underneath, but it is only a sliding contact, hence the earth wire. Many years ago I had a Scimitar GTE with a Ford Essex engine and that had the habit of spluttering and dying as I opened the throttle to pull away - disconcerting when pulling onto a main road. That distributor never had an earth wire by design, adding one cured the problem.
Paul Hunt

This thread was discussed between 18/10/2015 and 19/10/2015

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