Holley - What size secondary jets?

[comeinhandy]

I am happy enough with 53 size primaty jets in my Holley carb and have the same size in the secondaries. However I am starting to see lean running on fuller throttle. I'm not sure if I should go for bigger secondary jets or if something is getting clogged up (the fuel flow into the secondary bowel is good and the float level is adjusted as high as possible, without overflow).

Has anyone experimented with secondary jet sizes? What size do people have in theirs?

- Jon

[Stagdad]

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Jon,

Have you changed the plate so you can swap secondary jets ?

Cheers Steve

[mjheathcote]

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I have 49's in the primary and 51's in the secondary (I modded for the secondary jet plate with screw in jets).

53's sound large to me?

I also have a wide band sensor in the exhaust and don't run lean. My heads are gas flowed with tubular manifolds etc so plenty of gas flow.

How do you know you have lean running, do you also have a wide band oxygen sensor?

[comeinhandy]

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Thanks for the feedback.

Hi Steve, yes I've got the plate that allows secondary jets sizes to be changed.

I have a narrow band O2 sensor (not as good as wide band I know, but good enough). I was investigating a slight lack of power and slight misfiring when at full throttle and so hooked up my meter again to the sensor. Previously I had though the O2 level was good enough but this time it showed a very lean mixture at full throttle when the secondaries open. Primary strength still seemed ok.

I suspected a fuel blockage but everything checks out ok. The needle valve was a bit sticky so I changed it but to no effect. The fuel can be made to flow quickly enough out of the secondary overflow if I set the needle valve too high so nothing seems blocked.

All very odd, which got me thinking about changing the jet size. Yet another carb strip down coming up I guess.

Could it be fuel vapourisation somehow? not sure how that would do it.

BTW by car is tubular manifolds, custom adaptor plate, rebuilt heads/engine.

regards - Jon

[alan230752]

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i concur with above comments

my holley is 51 front 49 rear (adjustable plate ) and wide band o2 sensor

personally i think 53 is a bit rich

alan