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Spark plugs look like a lean burn


arnulfo de l.a.

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My #1 and #3 spark plugs looked real lean no noticeable brown coloring. The rest looked perfect. I'm thinking I may have a intake manifold leak that may be located on the runners that feed these two cylinders. What do you men think? I believe these are the original intake manifold gaskets. Thinking of changing them. Anything I should beware of on this endeavor? 1965 rivi gs over well over 100k on odometer

Gracias

arnulfo

Edited by arnulfo de l.a.
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I thought that with today's fuel you couldn't really "read" spark plugs any more. Perhaps all the others are fouling. Terrible thought, I'm just rambling.

There are no certain runners that feed any particular cylinder. The plenums in the manifold are open. On most street driven type engines, the right side of the carb will feed the left bank and vice versa. This goes for the primary venturi and the secondary venturi as well. (The one primary venturi on the right side feeds all four cylinders on the left, the opposite is true for the left venturi. When the secondaries are opened, the same principle applies.)

You could find a gasket leak by spraying carb cleaner on the surface where the gasket it. If there's a leak, the carb cleaner will momentarily plug the leak and your engine will smooth out and run a little faster. If you had a gasket leak, I think you'd be experiencing other performance problems as well.

Ed

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you are right ed. what i meant is the intake manifold port that connects directly to the intake port on the head . although for the most part the car runs great, it does idle a bit rough once its at running temperature. im thinking that once it reaches running temps the expansion of the metals may be causing a small intake leak at the intake manifold gasket.will try the carb cleaner method with a fire extinguisher nearby of course. while the gas around here is crappy, i still am able to read the plugs on my old chevys , buick and harleys.

arnulfo

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.....will try the carb cleaner method with a fire extinguisher nearby of course. arnulfo

That's why I recommended carb cleaner rather than starting fluid or something else that's more flammable. Not to say that it's not flammable, but it's not AS flammable.

Ed

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Here is the distribution diagram from a factory manual:

post-46237-143142696131_thumb.jpg 1 and 3 are fed together. There may be a vacuum fitting in that area of the manifold. Be sure the hose is not cracked and the device at the end is air tight.

Bernie

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Hey, I need to retract my previous post about which venturi feeds which cylinders. Sorry for the wrong info.

After looking at the picture that Bernie posted, I can see that #1 and #4 on the front half of the engine are both fed by the lower plenum in the manifold. #2 and #3 are fed via the upper plenum. On the rear, #5 and #8 are fed from the upper plenum and #6 and #7 are fed by the lower plenum. If you find a picture of a two barrel manifold, you'll find the same distribution scheme. It appears from the picture that the left side of the carb feeds the upper plenum and the right side of the carb feeds the lower plenum.

What I said about primaries and secondaries is still true though - Primaries feed the entire engine until your right foot pushes the accelerator way down and the secondaries are opened.

Ed

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