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Why does the ZX-11 D have two different sizes of main jets? Example, 162-158-158-162, etc. Is it for a performance gain, emissions compliance, controlling combustion temps, compensate for ignition advance of the #1/4 or #2/3 cylinders? What? My 1997 ZX-11D is used purely for drag racing and I am currently running 150 DJ jets all the way across and my carbs have been completely rebuilt and Dynojet kits installed, including drilling the slides. I run at 4400 ft elevation and use a wideband to check air fuel ratio. I think I am gonna richen them a tad but should I change all four the same or run richer on outer two? The bike runs pretty solid now.. just tweaking for top end performance. It seems just a little lean on the top end since I installed the full RAM air system.

Any ideas would be great! Thanks in advance,
 

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I believe the two inner jets are smaller since those cylinders will run a bit hotter and thus potentially richer if the jets were all the same size (warmer air being less dense and thus providing reduced oxygen for combustion). If you are drag racing it then I not sure if having them all the same would be a big issue or not?
 

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I believe the two inner jets are smaller since those cylinders will run a bit hotter and thus potentially richer if the jets were all the same size (warmer air being less dense and thus providing reduced oxygen for combustion)...
That's also my opinion. They probably did so for EPA emission purpose too. I would not care about this for racing.
 

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Discussion Starter · #4 · (Edited)
I believe the two inner jets are smaller since those cylinders will run a bit hotter and thus potentially richer if the jets were all the same size (warmer air being less dense and thus providing reduced oxygen for combustion). If you are drag racing it then I not sure if having them all the same would be a big issue or not?
You've got the cart in front of the horse on this one I think. Leaner runs hotter. Not "hotter and thus potentially richer". The air coming into the airbox comes in on either the left or right RAM inlet and is the same temp for all cylinders as it enters. Cylinder temps have more to do with scavenging and heat removal after the combustion takes place. It could be close to what you suggest though... well exactly opposite but possibly you are on the right road just in the wrong lane. The outside cylinders could actually be the hotter cylinders and therefore they run them richer to reduce risk of pre-detonation (PINGING) and keep them cooler. This could be because the outer cylinders don't have as many water jackets as the inner cylinders which would have water jackets on both sides. A complete guess as I have never taken this engine apart and can't remember from any pictures I have seen.. so I don't know for sure. Another scenario is that the timing advance is greater for the outer cylinders.. yet another reason to need to reduce heat... but what would the point be to advance #1 & 4 more than 2 & 3?

I was hoping for a definitive answer... but I appreciate the input.

I am inclined to agree with you though about it not being an issue for drag racing. I only warm the engine enough to have normal temperature oil and then shut it down as soon as I am back to the pit area. I rarely warm it enough to even get a fan on.

Thanks,
 
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