Engine misfire.MGTC #TC9984

[tedjan]

Hello Group,
I am experiencing an engine misfire once engine reaches 90 to 95 decrees c.Misfire occurs when accelerating,and is more pronounced in 2nd and 3rd gears.Compression is a straight 160 across.New plugs,points and condenser,rotor,wires and cap.Engine runs perfectly while warming up.Also,new thermostat and flushed,renewed coolant.Cannot duplicate misfire at an idle.If engine is allowed to idle for more than 20 minutes,temp will reach 100 degrees c.but not boil over.Misfire feels like a bad sparkplug wire but wires were renewed and tested.Misfire was there before wire replacement.Engine will maintain the 90 to 95,as long as car is moving.
I did not have this problem last year and nothing was done to vehicle in between.Someone mentioned that I could have a cracked valve seat.I will pull cylinder head if necessary but am hoping someone could suggest an alternative fix.
I also replaced floats,needle and seats in carbs to avoid a flooding issue.Misfire existed before and after carb repair.Engine was renewed by previous owner.
Thank you for your concern.Ted

[Steve Simmons]

Just a thought, have you checked the timing? Retarded timing can cause overheating, and I wonder if it could cause a misfire should the fuel and combustion chamber get really hot and pre-ignite?

[Gene Gillam]

With your compression I doubt seriously you have a valve problem...concur with Steve irt timing. At the temp you're running the timing sounds severely retarded.

[tedjan]

With timing light,notch in crank pulley is aligned with pointer @ idle.Is this correct?Have manual but there are no specs for dynamic timing.

[Tom Lange, MGT Repair]

Static timing at TDC is a good beginning, but does not take into account the differences between 40's and modern fuels. Using a timing light with total advance is necessary; you want 32-35 degrees total advance at 3500RPM. If you see things hopping around with a dwell meter, you probably need to have the distributor rebuilt. In the US go to Jeff Schlemmer, Advanced Distributor; I have heard that the Distributor Doctor in the UK is pretty good, (not knowing where you are located).

Tom Lange

[stephen stierman]

You don't have a cracked valve seat.
Exchange the coil for a known entity and see if that helps.

[tedjan]

Great replies!!Thank you.Distributor had 8 degrees in dwell variation on acceleration due to worn shaft bush.Plus new condenser was intermittently defective.Fix was a Petronix ignition conversion plus a new coil.I bumped the timing up 10 degrees and car maintains a 90 to 95 temp as long as it doesn't have to idle for a long period.I think an auxiliary fan is the answer for that.
Love that Petronix!.
Ted

[Steve Simmons]

Glad it's running better, but installing a Pertronix is just a band-aid on a worn-out distributor. It should be rebuilt. Once that's done, regular points would work just as well as EI.

[Gene Gillam]

Congrats...glad it's running smoothly again!