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Misfire diagnosis
#1
Hi All,

As a newbie to Sevens I need a bit of help. My car shipped to the US over Christmas and I've sorted a few things out, but only had the opportunity to start it on Sunday,  a nice warm(70 F.) day. I put in fresh 87 octane non ethanol fuel. It wouldn't start so I looked at the obvious. I tickled the carb to make sure I had fuel(it is a Solex 30 MOV). I pulled the dizzy cap and found the rotor had a bit of burning so I cleaned that up. There were also some brass flakes in the dizzy which I blew out. The points looked good. It still wouldn't start so I pulled the plugs(two NGKs and two French Champions). They were all sooty. So I changed to a new set of Champions. The engine started easily but was running running rough, hunting. I drove it for about 15 minutes and the car had no power and wouldn't rev past 3500. When I got back, I pulled the plug wires and confirmed I was getting spark on each. No. 1 wire came loose from the blade connector when I pulled it, so I will resolder. My inclination is that there are two issues. One may be the No. 1 plug wire which may be causing the misfire. But the sooty plugs on 1 through 4 would seem to indicate a rich mixture. The car was apparently running fine in the UK in December so I'm at a loss as to what might or might not have changed.
I'll check the carb main jet to see if it is seated well. I also ordered new plug wire and blade connectors to make sure that isn't the issue. Rotor, condenser? In past engine experience a bad condenser would manifest on load, but not at idle. All this, including the sooty plugs, would seem to indicate a mixture which is too rich. A sunken float perhaps?

Any help is greatly appreciated. (Sorry for the long post)

Erich in Seattle
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#2
Normal fuel available in UK is 95 RON or 97/98 for super - would that explain at least part of the problem?
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#3
Nick, I had thought of that, but the sooty plugs came from the UK. I may be running rich now and will know when I look at the plugs. Here in the US, farm co-ops sell non ethanol fuel. Better mileage, more power. Less pollution? I don't know.

Erich in Seattle
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#4
Hi Erich, 

All I can meaningfully contribute is that whenever I experience poor running the first thing I do is replace the points. Usually cures it. The state of your ignition system doesn't sound great so I would suggest replacing anything which is less than perfect anyway. 

Hard for me to comment usefully about mixture - I use an SU and it never gives me trouble. 

I doubt petrol is the problem. I've used all sorts over the years, including paraffin when I was much younger! But never experienced the sort of trouble you describe.
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#5
Hi Erich like you I think sooty plugs to rich a mixture.The loose plug lead I think may well be the cause of the misfire. Try letting it idle when only 3 plus leads are connected and see what is sounds like. Also try cleaning the contact breakers (points) and reset the gap.
I am am sure you are familiar with British words but for otherefore the American readers petrol -gasoline. paffafin - kerosine.

John Mason
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#6
Hi John, I did try it with No 1 disconnected and it seemed not to change, though hunting. I was getting good spark at all plugs initially. Your mention takes me back many, many years when I had a Mamod steam model. There was a part, as I recall, which needed periodic cleaning in paraffin. I asked my mother for some and was handed a block of wax. Needless to say, I didn't get very far melting the paraffin, before I was corrected in the nomenclature.

Thank you for the help.

Erich in Seattle
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#7
KAbout the word petrol which is a British word used for what is known in the USA as gasoline. In the early days of motoring in the uk before petrol stations it was known as motor spirit and sold in gallon cans such as you see sometimes mounted on running boards of early 20th century cars. Petrol was the trade name of a company that supplied motor spirit and over time people referred to motor spirit as petrol until it became universally known as petrol in the uk.
This is just a bit of useless knowledge that may interest readers  however it does not help Erich with his misfiring engine.

John Mason.
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#8
...and 'Bowser' was a brand name for petrol pumps and associated equipment before it became associated with bowsers. OK, I will now go and do some hoovering.
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#9
Have you done a compression test to exclude sticky valves or bad rings? If the engine has sat doing nothing for some time (like my recently acquired one) I have found things tend to get gummed up.
Edit to add apologies, your post says running ok in December, but maybe worth testing anyway - one person's "running OK" being another's "dog rough" (that's English for c**p).
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