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Oil sample - fuel %

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bobct

Advanced Contributor
I sent samples from each engine to Blackstone Labs last week. For the past couple of seasons, I've noticed that my Port engine oil turns darker a lot faster than the Stb side. It also seems thinner and "drips" off of the dipstick. The did not detect a significant difference in the viscosity so it is more of a visual difference to me.

The fuel % on the engine in question is 3.8%, while the other is 0.8. I have no performance issues. In fact....

I was going to post this as a separate question but it's relevant to this post. Thanks to suggestions here, I rebuilt both my Q-Jets four seasons ago (250 hrs?.. I can check) and have literally not touched them since. The hot/cold start, idle, power up are perfect on both engines. How long have you guys gone on a rebuild and/or adjusting? Do you think a mixture adjustment should get this down?

Is the Stb engine maybe a bit too lean @ 0.8 ?

thanks
Bob
 
fastjeff said:
IF you're using a mechanical fuel pump. the diaphragm might be leaking gas into the engine.

Jeff
Click to expand...

Both mechanical pumps were replaced by me four years ago with new ones. I replaced the Tygon hose too. I guess it could be a small leak. The guy at Blackstone didn't think 3.8% was off the charts high but I'd like to track it down. Wish I did some troubleshooting before it was winterized.
 
Jeff makes a good point.
Depending on If/Where the diaphram ruptures, or even develops a small leak....., and in the right place, the expelled gasoline will end up in the crankcase.


Comments/Questions:

Is your Stbd engine REV RH rotation?
If so, was it built with the piston wrist pin offset orientation done correctly?

Were both engines built with the same specs being used?

Are both engine ignition systems offering the exact same progressive spark lead and total advance?
If this is off, it may perhaps explain a fuel burn difference between engines.

Are both engine's cylinder pressures up to snuff, and are they fairly equal to each other?

As for any Q-jet carburetor fuel metering changes, we can only adjust the low speed circuits externally.
There is an external adjustment/change for the secondary metering rods.
Anything past that would require disassembly.
You have twins, so swapping carburetors will allow you to see if a carburetor issue exists by seeing if the issue follows the carburetor.


.
 
Not likely to be the diaphragm....pulling the tygon will tell you if that's it. The idle air/fuel mixture is the only adjustment; the other systems require part changing....last Blackstone report I saw suggests you're about twice their "normal"....if you spent a lot of time at low speeds, that engine could be suffering from nozzle drip...and the engine will have to be running to determine this..sorry, return key won't let me separate paragraphs...as far as rebuilds/adjustments.....eight years is the best I've done though I know a few guys that claim as many as 12 years.
 
Mark,

There's something weird about this board, I have the same issue with "returns" on my windows laptop. I exchanged emails with Cliff Ruggles and he suggested swapping the carbs to see if the problem moves. His gut reaction - if the carb was that far out of adjustment I would have noticeable performance issues. I'll check the hose on the off chance there's a small leak. He thought it might be blow by and the carb swap would rule that in/out.

I don't do any trolling and both engines are always running so I can probably rule that out. Rick, these are bone stock 454's. The engine in question is reverse rotation. I guess all I can do for now is swap carbs, check the hose and dig into it in the spring.

Thanks
Bob
 
Sounds like a plan and I agree with Cliff...that said, nozzle drip isn't a malfunction but a by-product of the efficiency of the primary system. It occurs much more frequently than most realize, especially on big blocks. But we can address that in the springtime, if necessary.
 
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