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100M engine: misfiring after ingition turned off

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356roadster

356roadster

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I made my first trip with my new 100 today. The car pulls strongly and does not miss a beat. The only thing is that after turning the ignition off the engine does not stop instantly but misfires heavily for some seconds. I am using fresh unleaded premium petrol with lead additive and new NGK BP6ES sparks. The engine has full Le Mans spec with high compression pistons. Does anybody know how to solve this problem???
Thank you for your answers, Wolfgang
 

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/bcforum/images/%%GRAEMLIN_URL%%/banana.gif When Dave Russell sees your post, I am sure he will cure your problem. My M, Agatha, gave me the same problem. After new plugs, carbuerator adjustments and 2 gallons of aviation fuel (100 Low Lead) every other fill-up, the problem seems to have resolved itself. Interestingly my opinion is that a replacement of one of the screw off thingies in the top of the carbuerator is what did the trick. Husband (I know I shouldn't say this) over-tightened the thingie (don't know what it is called) and it would just loosen up as he stripped the threads. I think this allowed it to suck air but then what do I know. Dave Russell knows.....
 
Oooops, I fear that my english is too bad. I did not understand exactly what you mean with thingies..... Do you mean the copper top of the carburettor screws (I do not know the exact english name, sorry....). I am really curious now as you seem to have had the same problem...... Did it really disappear totally?
 
Re: 100M engine: misfiring after ingition turned o

This is a problem that can "usually" be cured by a SLIGHT change in idle mixture, idle speed, or ignition timing. It is sometimes caused by a bit of glowing carbon in the combustion chambers. A good hard run will often remove the offending carbon (glow plug).

I occasionally have this problem, about one out of ten times,
with 10 to 1 compression ratio & 93 octane fuel.

As a last resort, when you shut off, have the transmission in gear, foot on the brake, & let the clutch out.

Wolfgang & Judow,
Very nice looking cars. If you have higher than original compression ratio of 7.5 to 1, Which the M spec has, you might need one range colder plugs such as BP7ES. Or possibly even colder BP8ES if you are at low altitude.
D
 
Re: 100M engine: misfiring after ingition turned o

I'm a last resort man as I get a touch of dieselling - as dave says, caused by the glowing carbon inthe chamber that ignites the mixture even after ignition is switched off.

When I am finished driving and still grinning like an idiot, I pull on the handbrake, slip the car into 3rd and slowly let the clutch out. When the revs drop to about 500, I turn off the ignition.

Never had a problem and this is my standard operating procedure.

Interestingly though, the screw-off thingies (damper caps) both come off on my BJ8 with every drive (mine are plastic). The threads are shot so I'm hoping replacement caps might help.
 
Re: 100M engine: misfiring after ingition turned o

/bcforum/images/%%GRAEMLIN_URL%%/thankyousign.gif making a note of that suggestion. And yes it is
the original higher compression engine. Mechanic confirmed this. We live at high altitude so I am going to take your suggestion in spite of the fact that there is no pre-ignition problem at the moment. I also think that temperature influences the problem. I may not be correct as husband thinks my discussions of the thingies and whatchamacallits are a tad confusing. Gee whiz I know what I'm talking about. lol

<u>To Kevin</u>: I looked up the schematic in Moss Motors showing the fuel system. The parts I am talking about are called:

Chamber and piston assembly, cap and damper assembly. My mechanic actually had just the chamber and it fit Agatha quite nicely. I had visions of having to have the original chamber rebored. Alas I couldn't locate one. If you go to Moss Motors and look at the schematic you will see that #5 for the 100M is not available.

See I told you Dave would know the answer.

<u>Dave</u>, thanks for the nice compliment given Agatha. I will tell her so she can blush!

/bcforum/images/%%GRAEMLIN_URL%%/banana.gif /bcforum/images/%%GRAEMLIN_URL%%/banana.gif
 
Re: 100M engine: misfiring after ingition turned o

I posted before I saw Rob's response. Rob thanks for helping me with the 'thingies.' I also tried to explain my use of the clutch. I, however, after getting Agatha in the garage wait about a minute or two, then I put her in first gear and shut her down. I always leave her in gear as I live of fear of someone accidently disengaging the emergency brake. I doubt that would ever happen but I think my logic as something to do with my learning to drive on a standard and Dad's 54 Ford's emergency brake was less than useful. Old habits die hard.
 
Re: 100M engine: misfiring after ingition turned o

Thank you for all the recommendations. I will try all the small adjustments first and it will be a pleasure to do a hard run within the next days (although we have a temperature of around +3 Celsius over here in the moment).
I will report whether I can solve the problem.......
Wolfgang
 
Re: 100M engine: misfiring after ingition turned o

/bcforum/images/%%GRAEMLIN_URL%%/thankyousign.gif I/we appreciate that information. I will pass the word on to others at our local Healey club meeting tonight. This is a company I was totally unaware of.
 
Re: 100M engine: misfiring after ingition turned o

for all the oldtimers out there who became addicted to all this stuff through the writing of Henry Manney, the trait of English cars to keep dieseling on prompted him to say: "There will always be an England because when the engine is turned off it will keep on running." Other Manney quote: "torque is just a figure of speech"
 
Re: 100M engine: misfiring after ingition turned o

Healeys in particular were prone to running-on. High octane petrol fixed it - Shell with the blue shell lamp on the pump, 105 octane. Good for 4- and 6-cylinder cars.
Slightly over-rich mixtures can help cause it, but on the whole, better over-rich than too weak. Less chance of a burned-out plug or melted hole in piston.
 
Re: 100M engine: misfiring after ingition turned o

I have tried to enrich the idle mixture and use NGK BP8ES plugs now; it seems to be a little bit better but there is still much room for improvement......

By the way: I can only get 93, 95 or 98 octane fuel in old germany....
 

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Re: 100M engine: misfiring after ingition turned o

Due to differences in octane rating methods, Your 98 should be equivalent to USA 93 octane. Using 98 "might" help a bit.

You didn't mention reducing idle speed setting, but this often cures the problem.

Try adjusting the timing a bit. Either advance or retard about two turns on the adjusting knob on the side of the distributor.
D
 
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