Technical advice - running rich

[Larry T.]

Re: Technical advice - running rich

every new BBC i ever owned and i owned 5 never got more that 600 miles per quart when new. they used oil but the exhaust systems never rusted from the inside.

I re-checked mine and it looks like I have used just over 1/3 of a quart in 250 miles. So I may be pushing closer to 700 miles. Whatever the case, 500 or 700 miles, or somewhere in between, should I just live with it until it starts using more? I do not want to be premature in pulling it apart and trying to remedy the problem. Clearly there is oil on the plug threads that seems like it may be a bit excessive. But it runs great. If I can lessen the heavy fuel smell I would feel very good about things.

I guess at the very least I should pull compression readings. What range should I be hoping for?

[Ronald L.]

Re: Technical advice - running rich

Larry, jm2 cents, gas and oil smell different. If you are burning oil, and easy if a side pipe car put your hand in the exhaust, what does it smell like after 30 seconds?

Rev it up hold it at 3000 for a minute, let off the gas and watch the side pipe - any change? a puff?

Who restored the carb?

Check that main gasket and if there is a heat shield for the 425HP.

Have you looked at all eight plugs & all are as the three you posted?

Exactly the same?

[Larry T.]

Re: Technical advice - running rich

Ronald,

I do not find it smells like oil myself, more so fuel.

Carb was done by Eric at Vintage Musclecar Parts. He has a very strong reputation for quality.

Which gasket and heat shield are you talking about?

Those four plugs (1,2,4 and 5) were randomly selected based on ease of removal. The others could be different.

Thanks,

Larry

[Joe C.]

Re: Technical advice - running rich

Those plugs look excellent to me; a bit on the lean side, though. The substance on the threads might be varnish (residue) from the fuel, and not oil. If they were oil fouled, then the insulators and electrodes would be black and wet with scaly deposits on them.

Fuel odor out the tailpipe is also an indicator of a lean condition. If the engine goes into lean misfire, then the HC levels out the tailpipe increases. A wideband O2 sensor will be fooled during a lean misfire, as it will "see" all of the excess oxygen and HC out the tailpipe as an overly lean condition. It does not "see" the unburned HC. It only "sees" the free oxygen which has not combined with the HC to produce CO and CO2.

If that engine has ever been rebuilt, then 1 quart per 700 miles is excessive. If it was done properly, using decent rings, then it should not be consuming more than about a quart per 2000 miles.

Assuming that it is an original build with (nominal) 11.0:1 SCR, then the engine, when warm will probably develop (around) 170 psig at sea level. Certainly no more than 190 psig. There are a LOT of variables involved in learning anything from cranking pressure, per se. Two of which are cranking speed and air temperature. Cranking pressures are useful as a diagnostic tool only whan RELATIVE pressures are considered. Pressures should not vary by more than (about) 20 per-cent from one cylinder to the other. A better indicator of engine health is a leak-down test.

I don't know the IVC (@ J604d) event timing for your camshaft, and if it can be provided, then plug it in to this equation for a ballpark number:

http://www.not2fast.com/turbo/compression/cranking_pressure.shtml