Does temp affect jetting? -
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back > Models > Jeep CJ Forum > Does temp affect jetting?

Stainless Steel Door Hinge PinsPoly Door Hinge BushingsDual Color LED Light Bars White/Amber

Unread 10-07-2013, 11:54 PM   #1
Registered User
1976 CJ7 
Join Date: Jun 2013
Location: Tooele, UT
Posts: 29
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?

Half the lies they tell about me aren't true.
JimRico is offline   Reply With Quote
Unread 10-08-2013, 12:46 AM   #2
Registered User
1984 CJ8 
Join Date: Jun 2013
Location: Denver, CO
Posts: 1,028
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.
Spieg8 is offline   Reply With Quote
Unread 10-08-2013, 05:00 AM   #3
Web Wheeler
86cj74.2L's Avatar
2004 WJ 
Join Date: Jul 2006
Location: Stouchsburg, PA
Posts: 6,314
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. )
86cj74.2L is online now   Reply With Quote
Unread 10-08-2013, 05:41 AM   #4
Web Wheeler
Matt1981CJ7's Avatar
1981 CJ7 
Join Date: May 2011
Location: Elbert, CO
Posts: 9,882

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.

Matt1981CJ7 is offline   Reply With Quote
Unread 10-08-2013, 08:21 AM   #5
Registered User
1966 CJ5 
Join Date: Oct 2012
Location: Two Harbors, Minnesota
Posts: 1,099
you might consider adjusting your air/fuel mixture a little before the jet swap. here is an article that should help your situation:
1966 CJ5A, mods are coming
1966 Wagoneer, bone stock
strvger01 is offline   Reply With Quote
Unread 10-08-2013, 02:23 PM   #6
Registered User
1976 CJ7 
Join Date: Jun 2013
Location: Tooele, UT
Posts: 29
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
Half the lies they tell about me aren't true.
JimRico is offline   Reply With Quote

Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. is not in any way associated with Jeep or the Chrysler Corp.