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Unread 10-07-2013, 11:54 PM   #1
JimRico
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1976 CJ7 
 
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Does temp affect jetting?

I have a 304 with #52 jets on a MC2150 carb that worked great in the heat of the summer, Both running and on the wideband. With the temps dropping do I need to re-jet. It still runs good but seems down on power. I had to give my buddy his wideband back cause someone else needed it.

I'm heading to Moab which is about the same elevation as where I live and these jets did fine on Logan's peak so elevation shouldn't be an issue.

Any thoughts or ideas?

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Unread 10-08-2013, 12:46 AM   #2
Spieg8
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Short answer is Yes - temperature and altitude both affect your fuel/air mix. Dropping temps will usually make you run a little on the lean side.

Longer answer is Maybe - temperature usually has a lesser affect on performance than altitude does. If you're running a stock air intake, then some of the heat from the exhaust manifold is used to warm the intake to the carburetor. If the intake is working properly, this can offset a lot of changes due to temperature. Running a bare air filter is another story and will frequently require re-jetting to suit the existing conditions.

Only you can decide if or how much your performance is suffering. Re-jetting is not that difficult if you've done it a few times. It can't hurt to experiment a little... worst case, you just set it back the way it was.
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Unread 10-08-2013, 05:00 AM   #3
86cj74.2L
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Every 20 degrees change in temp I was rejetting my road racer 1993 Kawasaki ZX7r and my dirt bike 1995 CR500

Once you know what proper jetting feels like you will notice the temp change. You will need to have a jet for summer, one for winter, one for spring and fall other than that its find the jet that's in the middle. )A little rich in summer a little lean when its 25 outside. )
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Unread 10-08-2013, 05:41 AM   #4
Matt1981CJ7
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JIm,

I recall reading that a good rule-of-thumb is to increase one jet size for every 40* F drop in ambient air temps, all else being equal. I think that info came from Holley.

Let us know what you figure out.

Matt
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Unread 10-08-2013, 08:21 AM   #5
strvger01
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you might consider adjusting your air/fuel mixture a little before the jet swap. here is an article that should help your situation: http://www.hotrod.com/techarticles/e...g/viewall.html
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Unread 10-08-2013, 02:23 PM   #6
JimRico
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Thanks guys. I was a hair on the rich side so I figure on the cold mornings I may be a lil lean. I'll have to order a size or 2 bigger cause my #52's are the biggest I have but will do.

I am running the stock air intake but headers so the tube and intake to the intake are blocked off at the moment. I may be able to do something with that.

Thanks, Jim
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