Gearing down with blue smoke and back firing

[Mark Maras]

 I don't think there's anything to worry about. Valve seals in the future would be a good idea. So would checking RB's oil level a bit more frequently. Maybe the other red Z's owner is a Datsun mechanic. And as long as we're hoping maybe he likes to do valve seals.

[EuroDat]

I agree with Mark. Valve seals are not that big a deal. You will get carbon buidup around the inlet vavle head (on the manifold side), people behind you may comment at the occasional smoke plume and it might use a little more oil than normal. Leaking valve stem seals won't leave you standing on the side of the road waiting for road side service.

[ajmcforester]

From what you stated your burning oil and you are leaning out. Check for a gas smell from the oil cap and dip stick. If you smell gas you have some blow by and you might want to fix it. Old cars can burn oil for many reasons, the biggest problem would be the lean conditions. Also with the car running look for head, and exhaust leaks.

Next Check your carbs are balanced and the valves are adjusted properly. Also pull the plugs and see if one or more look different than the others. You might not be lean overall and be lean on one cylinder. If that look a good try a leak down test. I can keep going but that is wait to start.

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[Redwing]

Just now, EuroDat said:

I agree with Mark. Valve seals are not that big a deal. You will get carbon buidup around the inlet vavle head (on the manifold side), people behind you may comment at the occasional smoke plume and it might use a little more oil than normal. Leaking valve stem seals won't leave you standing on the side of the road waiting for road side service.

This sounds good, well, at least not bad.  Aha, you mention some oil use.  She has always used some oil.  Not much, a quart or two a year.  So along with what has been said about the backfiring, blue smoke, downshifting and coasting, this all may be something that has been going on for a while?  Brought to the forefront by the new muffler.  Think?  Hmmm...

Thanks,

Jai