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Carbon on Intake Valves-in Carbureted Engine? #5452446 06/12/20 09:14 PM
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bunnspecial Offline OP
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I have some serious engine problems in my MG, starting with my head and working down. The short answer now is that I'm waiting both for a replacement head to replace the boat anchor(visibly cracked) on it as well as for a machine shop to bore it.

In any case, though, we hear a lot now of carbon on GDI engines, but I was always under the impression that gasoline washing over the intakes kept them relatively clean.

This cylinder head was redone about 5K miles ago. The original intake valves were reused, but were spotlessly clean and were lapped to the re-cut seats. I think there were some issues with how the work was done, but that's another topic and something I'm discussing with some MG guys. I'm doing a "post mortem" on the head, and pulled one set of valves.

I'm a bit surprised at the amount of carbon on this intake valve(on the right in the below photo) especially given 5K miles. Any thoughts on what could have caused this? I did have a fair bit of blow-by, but ran both a cleaned/refurbished factory oil-air separator and a catch can(that didn't catch a ton) so don't think I had much if any oil going into the carburetors. It's always run on 92/93 Octane gas, and usually Shell V-Power. I do Berryman's B-12 once a year or so. Every tank also gets Sta-Bil, more because I don't know if I'll run it out in a week or in 3 months.

_DSC4792.JPG

2010 Lincoln MKZ-Mobil 1 5W-30
1970 MG MGB Roadster-Valvoline VR-1 20W-50
1974 Austin Marina GT VR-1 20W-50
Re: Carbon on Intake Valves-in Carbureted Engine? [Re: bunnspecial] #5452468 06/12/20 10:01 PM
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andyd Offline
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Were the valve guides/seals replaced when head was refreshed? Running rich or maybe just leaky valve seals? Just guessing. grin2


'16 Camry LE STP synth 0w20 and STP filter. the Fridge

1994 Ranger ,the Rat, 5w30 dino, STP filter

'16 Camry SE, Valvoline HM 0w20 and OEM filter
Thick oil is better grin2
Re: Carbon on Intake Valves-in Carbureted Engine? [Re: bunnspecial] #5452472 06/12/20 10:19 PM
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bunnspecial Offline OP
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New cast iron guides with "umbrella" type oil seals.

I can't deny the occasional period of rich running, but the last tune-up I did had the plugs a nice light tan color so it wasn't overly rich.


2010 Lincoln MKZ-Mobil 1 5W-30
1970 MG MGB Roadster-Valvoline VR-1 20W-50
1974 Austin Marina GT VR-1 20W-50
Re: Carbon on Intake Valves-in Carbureted Engine? [Re: bunnspecial] #5452479 06/12/20 10:55 PM
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Silk Offline
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Carbon on intake valves was seen sometimes back in the day, sometimes to the extreme and cutting power like a blocked exhaust...we used to chip it off the valves in place if need be. But it was not common on BMC engines...although what you show would be considered ''normal.'' At the time we put it to oil running down the inlet guide.


1987 BMW R65 - Penrite VTwin 20-50
2005 Nissan Expert - 5W-30 Castrol Edge
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Re: Carbon on Intake Valves-in Carbureted Engine? [Re: bunnspecial] #5452487 06/12/20 11:10 PM
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Linctex Offline
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Sloppy valve guide reaming at the machine shop.

That's definitely from oil running down the guides.

Good luck - - I have butted heads with machine shops over the exact same issue - only 10,000 miles and even worse carbon than that!


"The evidence demands a verdict".
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Re: Carbon on Intake Valves-in Carbureted Engine? [Re: bunnspecial] #5452508 06/13/20 12:05 AM
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oldhp Offline
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I agree with oil on the valves. New guides/seals are fine "if' they installed correctly.


"None of us are getting out here alive...drink that beer...eat that pizza...drive that Hot Rod"
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Re: Carbon on Intake Valves-in Carbureted Engine? [Re: Linctex] #5452660 06/13/20 08:26 AM
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bunnspecial Offline OP
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Originally Posted by Linctex
Sloppy valve guide reaming at the machine shop.

That's definitely from oil running down the guides.

Good luck - - I have butted heads with machine shops over the exact same issue - only 10,000 miles and even worse carbon than that!


Thanks!

Unfortunately, I'm not dealing directly with a machine shop on this.

I bought the head prepped and supposedly ready to bolt on from someone who "worked part time at the machine shop" and claimed to have done dozens of MGB heads. He's an MGB owner himself.

The carbon unfortunately is the least of my problems on this boat anchor...


2010 Lincoln MKZ-Mobil 1 5W-30
1970 MG MGB Roadster-Valvoline VR-1 20W-50
1974 Austin Marina GT VR-1 20W-50
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