What you get with jets too big

[Old Henry]

Just removed the pistons from my engine to replace with new because one blew apart. Here's what the tops of the pistons looked like after just 30,000 miles.



Then just checked the jets in my carburetor to see if they were too big and, sure enough, the carburetor had come with 51's which I've been driving on for at least a year at elevations generally over 5,000 feet when the specifications for my altitude are 46's. Plugs were never dark like this piston head but obviously the jets are too big. Just ordered smaller ones from ken ct to put in. Not going clear down to 46 but probably will try 47's. Hopefully will help my gas mileage too.

[TStiles]

Thanks, Professor for knowledge-sharing. Learning through others' experiences is one of the many great values of the Barn.

[Ol' Ron]

I think the use of an AF meter would help with the tuning of these engines, especially with the price of gas ans the fact that a rich mixture is bad for the rings.

[Old Henry]

Originally Posted by Ol' Ron

I think the use of an AF meter would help with the tuning of these engines, especially with the price of gas ans the fact that a rich mixture is bad for the rings.

Tell us about an AF meter, what it is, what it does, and how to use it.

[Talkwrench]

Air /Fuel ratio meter. Best to get a broad band meter, it reads your fuel mixture [ratio] via a sensor that you attach to your exhaust pipe , usually you weld a bung in the exhaust close to the motor but some you can put the sensor up the tail pipe. See the meter as you drive, alot connect to a laptop you download and look how your car has been driving.

[richard crow]

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dident so one say check your jets i wonder who that was

[john in illinois]

I bought an air fuel meter and found that my model A with a 97 was running too lean. I welded a bung in the exhaust pipe just after the manifold.It sure takes the guess work out. I will also use it on my AV8 to jet 2 97's when I get to that point.

Cheapest price was at Amazon

http://www.amazon.com/Innovate-Motor...r%2Ffuel+meter

Here is an article about it.
http://www.carcraft.com/techarticles...l_ratio_meter/

John

[Old Henry]

Originally Posted by richard crow

dident so one say check your jets i wonder who that was

That's why I did it. Good idea and valuable suggestion.

[Richard in Florida]

Originally Posted by john in illinois

Cheapest price was at Amazon

This is the one we use, also available at Amazon. It is a wonderful thing, especially coupled to a camcorder.

http://www.amazon.com/Innovate-Motor...&keywords=3844

[JWL]

There is NO WAY to look at those pistons and determine there is a problem with jet sizes. Period.

[BUBBAS IGNITION]

Originally Posted by JWL

There is NO WAY to look at those pistons and determine there is a problem with jet sizes. Period.

JWL you got my vote as well. Carbon like that seldom comes from fuel and air fuel mixture. I believe oil control made that coating.....

[AlDeBear]

Old Henry, paraphrased, with respect, "........uses a quart of oil every 1000 miles....." ???? Maybe some got up on those piston? (Boy I hope I don't have CRS this morning!)

[bluardun]

JWL is on the right trail. Today we buy formulated fuel, not gas as we use to know it.
They have removed the lead (to protect us). I believe in leads place, part of the formula has added some chemical to "soften" the explosion upon combustion. Modern engines burn much hotter, and digest the gases.

[Old Henry]

Originally Posted by JWL

There is NO WAY to look at those pistons and determine there is a problem with jet sizes. Period.

Could we just move a little beyond period and get your take on the heavy carbon build up? Is it normal? If not, what do you attribute it to?

[DICK SPADARO]

I saw this post yesterday so after much consideration I dont think that the carbon build up led to your piston failure. If this is a 30,000 mile engine, this is more like a normal carbon deposit from the oil consumption not excessive fuel. I dont think reducing the jet size will cure you issue as I think it is necessary to increase the jet size using the new ethanol enhanced fuels so your 51's would be ok even in high elevations. The tell tale would be a slight soot smoke out the exhaust for a too rich mixture. Most problems I have had with cracked or broken pistons have come from incorrect spark timing that produces detonation. I'd be checking the timing first especially with the junk gas.

[Ross F-1]

Is this an 8BA? Where did you see that #46 is appropriate for your altitude? I am also at mile-high elevation and do not find that a drastic jet size change as that is needed.

[Old Henry]

Originally Posted by Ross F-1

Is this an 8BA? Where did you see that #46 is appropriate for your altitude?

It's a 59A-B. Here are the carb specs for the Holley 94: http://www.flatheadv8.org/holley94.htm