| Re: [GMCnet] what a difference a spring makes [message #325394 is a reply to message #325388] |
Tue, 24 October 2017 17:15   |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
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Keith V wrote on Tue, 24 October 2017 14:37Last night I was reading about carb tuning and one thing I kept seeing is people saying you cannot read spark plugs anymore with reformulated gas as they are always white.
So I guess I'd be careful about that.
I was also looking at power vs economy curves for AFR and it looks like I might still be a bit lean. I just know that the next fatter jets will put my cruise AFR into the 13:1 range and I'd rather stay out of there during cruise.
I wonder how accurate Jets are, should I try another set of 69's?
Kieth and Carl,
I fear I have to jump in here and still not try to muddy things up.
Kieth, the reason you read that you cannot read spark plugs anymore is two-fold and sort of correct.
There are two issues here: One is that crapahol makes an engine look like it is running lean, and the other is that part of the color we used to see was the lead in the fuel.
The jets used in old carburetors were very precise. The chance of you finding jets of the same nimber that make different flows for the same condition is very remote. (About a hundred years ago - honestly over 40 - I did have a problem with a carburetor that turned out to be a big Fing burr in the jet as manufactured.)
BUT Rochesters do have other parts that can make a difference and any part can be damaged or worn. I have seen main jets and needles that were worn, but this was at the end of a very long durability run. If it can happen there, it can happen in the real world - it is just less likely. There is a spring on the power piston that can make a difference too.
Without very expensive collection of test stands, there isn't much more you can do.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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