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Author Topic: Engine Misfiring  (Read 1243 times)

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  • Message Board Member not current AMGBA Club Member
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  • Posts: 13
Engine Misfiring
« on: December 19, 2017, 05:49:31 PM »
I hope you can help with a problem I'm having with my 1967 MGB. The engine starts easy. At idle and cruising revs the engine runs fine but under acceleration it misses.

The car has a Pertronix ignition with red rotor. The distributor was rebuilt last Winter by Advanced Distributors. The timing was set by you this Summer at Louisville. Carb sync and fuel adjustments have been checked by Roger Deacon. I have replaced the plugs, plug wires,distributor cap, and choke return spring. The fuel filter appears clear.

Any suggestions for the solution of this problem will be greatly appreciated?

Thanking you in advance,
Bob Kerstetter


  • AMGBA Club Tech Staff
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  • Posts: 73
    • University Motors
Re: Engine Misfiring
« Reply #1 on: December 19, 2017, 06:04:43 PM »
This miss might be caused from being too lean Ė or from being too rich. 

I am a fan of 90 weight gear oil in the carbs.  Now the engineers will tell you that the viscosity of 20/50 engine oil and that of 90 weight gear lube is the same, but to me, the gear lube is thicker.  Thatís why I use it.  The thicker oil makes up for the wear on the damper and on the inside diameter of the dashpot.  Perhaps the oil isnít thick enough.  Perhaps the oil is too thick.
Try this:  Drive the car and just as you begin to accelerate, pull out the choke, which enormously enrichens the mixture.  Does it run better or worse?  If better, then it was too lean or the oil is too thin.  If it accelerates worse (more missing) then itís too rich or the oil is too thick.

Remember that most carb problems are timing problems.  Double check that timing at 32 BTDC at full mechanical advance (about 3-4000 rpm), vac disconnected.

Hope this helps.
John H Twist
John H Twist
University Motors Online
100 East Beltline Avenue SE
Grand Rapids, MI  49506


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