Fouled plugs questions

[adriaan pienaar]

I know this topic has been covered time and again, but I have searched around and still haven't found the answer I am looking for. The problem is that my Lolette buggy keep on fouling its plugs - standard 1600 twin port engine with single Solex carb. It seems to happen when the gas level gets low, giving me the idea it could be because of rust residue in the tank? I have since installed 2 x in line fuel filters, but this is what the brand new plugs looked like the weekend after covering about 300km (around 200miles) with them installed - has a funny brown residue, and the engine is running badly - stuttering and missing etc. If I clean the plugs with a wire brush, it runs good again for a while - any suggestions? Thanks!

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[EVfun]

It looks like a lot of dry black carbon on the insulator. Right off the bat I'd say the plugs are running to cold, perhaps because the engine isn't really warming up.
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[adriaan pienaar]

[lil-jinx]

this may help.
http://www.gnttype.org/techarea/engine/plugs.html

[LeeVW]

Here's the best chart I've seen. It shows the whole range of temperature conditions:

Could you be getting a weak spark? What is the condition of the rest of your ignition system? Points or points replacement module?

Lee

[adriaan pienaar]

Thanks everyone for the replies and suggestions. I have since replaced the plug wires, rotor, breaker points, condensor and coil with no success. Thought that it might be the choke giving problems, so I fixed the choke butterfly open permanently in the 'open' position - and so far, so good. I just can't understand why the carbon deposits on the plugs don't simply burn away?
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[Axitech]

Heat risers present and functional?
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[LeeVW]

I'm wondering if it's running uber-rich. What type of Solex carb do you have on there? When I upgraded from a 1600 to a 1776, my engine builder asked to see the carb (34PICT-3) so he could check the jets. He measured the jets and discovered that the main jet had been hogged out to 132.5, even though it had "127.5" stamped on it from the factory. No wonder the 1600 always seemed rich no matter what I did with the idle mixture screw! Turns out the 132.5 was perfect for the 1776. Live and learn.

It is a common practice to increase the size of the main jet and sometimes even the idle jet and accelerator pump when using a Solex 34PICT carb and a 009 distributor. Some folks even block the hole in the throttle plate in addition to all this. All of this masks the symptoms introduced by the lack of a vacuum advance on the distributor. The carb runs super rich all the time, and you get symptoms similar to what you've described. Even if you're running the proper distributor on your engine, chances are someone at some point messed with the carb.

So my suggestion is to disassemble the carb, give it a good cleaning, and measure the size of the jets with the proper gauges. Put it all back together with a rebuild kit, then set your idle mixture and speed. Also make sure the accelerator pump is delivering the correct amount of gas with each stroke. There is a spec in the service manual, but I don't know it off hand. Even if this doesn't fix the problem, at least you will know for sure what you have.

Lee