Rebuild has carbon on all valves except first 3.

[D7]

Finished my last rebuild 1500/1775 and I ran the motor for about 50 minutes when it started running a little rough.Could not find any apparent problem, the valve settings were correct as were the carb settings, timing and points, so I removed the heads.

All the valves had thick carbon except the first 3 valves, both on #1 and the intake first (intake)valve on # 2 cylinder.Anyone have an idea on the cause of this? I am building a new engine with a new case from Aircooled and would like to know where I could have gone wrong so I don't make the same mistake whatever it was.

[sagaboy]

Isn't it extreme to remove the heads just to check for carbon?

[D7]

I did not remove the heads to "check for carbon" As I had exhausted all other possibilities that I thought it may. be, I removed them to see if there was anything going on under the heads, and there was.

[Jim Ed]

Using Marvel Mystery Oil in the gas tank will keep that carbon build up to a minimum.
I had no carbon build up on the spark plugs after using M.M.O.

[D7]

Yeah thanks Jim Ed, unfortunately we can't buy Marvel mystery oil here in Oz and the airlines probably won't ship it.Not absolutely sure on that point though.
The fact that the motor only ran from rebuild for about 50 minutes and had such a huge quantity of carbon, I don't think the MMO could actually handle that amount of carbon. The mystery part to me is why the first 3 valves were spotless and the other 5 were so heavily caked with soot.

[sideshow]

What is you induction? And how cold are you running?

MMO is nearly automatic transmission fluid, I don't think it is airline unsafe. I use MMO on occasion and do notice subtle deposits on the spark plugs, and no bad effects.

[sagaboy]

...The fact that the motor only ran from rebuild for about 50 minutes and had such a huge quantity of carbon, I don't think the MMO could actually handle that amount of carbon. The mystery part to me is why the first 3 valves were spotless and the other 5 were so heavily caked with soot.

50 minutes for large amount of carbon is nothing, just drive round the block with too-rich-fuel-mix and your spark plugs are foul-up with carbon. Unburned fuel are the main cause of carbon--what is your plugs gap? Have you check the colour of your sparks? Are you sure the coil produces spark voltage required? Have you check the voltage supplied to the coil? What spark plug range are you using? Are you assuming your plugs cables are OK or are you using silicon type coil with built-in resistance? The first 3 valves are spotless--could be due to valves settings, check all valves settings again.

[D7]

I have single 34/3 carb. All settings are good and the motor was in the correct heat range.All plugs are new and were clean and almost new coil.Valve settings were correct.To make it simple all of items were taken off the same motor before it was rebuilt which was running well but it was time for a complete rebuild before the summer.

Almost finished my new rebuild but I have to do a leaking axle job which as it is a 62 necessitates the motor being out and which I am not exactly looking forward to.
Anyway I guess I will never know now what was the problem was.Thanks all-till next time.