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Discussion Starter #1
Hello folks,
Plugs carbon fouling, and I need some more smarts.
1600 GTV, stock cams/carbs/jets/tubes. Always use 98 octane. Has hardly missed a beat in 3 years. No equipment changes or fiddling before symptoms arose.
My car began to run poorly on steady throttle, tho still pulled like a train under accel.
Did a few things:
Checked: timing, carb balance, float height/droop, wiring to from dizzy & coil, coil resistance, plug gaps, points gap. Air cleaner (crossover, canister style) not clogged.
Points spring broke while I was fiddling, replaced with Hotspark module (3+ ohm coil required, which my existing Bosch black coil easily exceeded, as did another I swapped in later to cross-check, both 3.3+.
Changed coil HT lead. Replaced plugs (B7ES), which still quickly fouled. Changed to B6ES. Still fouling, tho not as quickly.
Winding mixture screws in slows/reduces fouling, but even at the point where revs start to hang and carbs start to pop (@ 1-1.25 turns out) they are still inclined to foul.
Some extra research tells me:
- Weak spark can cause fouling (but wouldn’t the car run poorly under load too?)
- Alfaparticle quote: “coil resistance tells you what coil you have, not what condition it’s in”.
So...should I try a new coil?
What else might be at play?
Thanks in advance...
 

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Richard Jemison
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What else might be at play?

You had a big clue. Leaning the fuel mixture reduces the wash happening on the liners & rings.
1- Oil is then included in the air/fuel mix. Oil is the carbon source. Rings weak...
2- Intake valve seals, and likely the guides (on both sides) allowing oil into the combustion. Old 1600 engines had no seal on the exhaust side. But on any rebuild of the head they should be used.
 

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Premium Member
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13,071 Posts
The symptoms of a weak or failing coil are misfiring under load and at high rpm. I doubt that is your problem.
 

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Points spring broke while I was fiddling, replaced with Hotspark module (3+ ohm coil required, which my existing Bosch black coil easily exceeded, as did another I swapped in later to cross-check, both 3.3+.
I once had a reliability issue with a brand new Hotspark, so you might try swapping back to points & condensor, just to make sure the Hotspark isn't the issue. In my opinion, Pertronix makes a better product for that application.
 

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Discussion Starter #6
Hmmm, thank you all,
- compression is a consistent 190-195, on a peppy, non-smoky motor. Forgot to mention that.
- The fouling looks very fuel/fluffy-black fouled, not oil-wet, but ill accept that oil fouling can still produce that. I wasn’t aware of the fuel wash thing.
- symptoms presented pre Hotspark installation.

One other factor I didn’t mention which has just occurred to me....I experimented with a 10w-xx oil in the recent winter (I’m Southern Hemisphere, remember).

I’ll stop/reverse the leaning-off and go back to 20w-50/60 as a starting point, and will report back.

(P.s. - a friend dug out a container of 20/50 BP Corse-Plus recently. Now there’s a blast from the past.)
 

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Discussion Starter #7
Righto...swapped 20/50 oil back in. A week or so in now, and the plug fouling has reduced dramatically, allowing me to get home without stuttering after a 20 minute drive, and badly fouled plugs.
I am still fiddling with (minor this time) idle mixture changes, but I won’t use the thin oil again...winter or not.
Thank you all, particularly Alfar7 for the lesson on oil burning.
 
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