Couple questions about new YJ and engine code

Ncman

New Member
Joined
Feb 13, 2021
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17
Location
Morganton, NC
Hello,
87 Wrangler 4x4 5 speed
Has wagoneer Dana 44 axles
4" Currie lift and 1" body lift
35" tires
258(?) with offenhauser intake
Edelbrock 1406 600cfm
Header
Ok, so I bought this and immediately started changing fluids as I always do. I got to the oil and filter and filter for 87 258 did not fit. It ended up being the 11/16 filter (Napa gold 1626). It should have been the filter with M20x 1.5. Has engine been replaced? Machined number on passenger side of block is 307C21. Can anyone decipher this code?
Next question is about carb. It runs good with more pep than others I've had in the past. My question is should I remove it and install a MC 2100 with the 1.08 Venturi? I've read that the 600 CFM I have is overkill and I could wash the rings with fuel and all sorts of stuff. It has a good response from 1st-5th. What say y'all?

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I have no idea about the carbs or switching them and also don't know what to say about the engine number. I think if the carb is too big you'll lose torque.

Is that an open hole in the side of the valve cover?
 
My 1990 4.2L YJ has this factory sticker mounted under the hood in front of the radiator (see photo) - the M20x1.5 is the correct oil
filter.


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Yeah, as mentioned in my OP it should take m20x 1.5 but doesn't. That led me to ask about code on side of engine because I think engine might have been replaced. Thanks for the pic and trying to help
 
Carburetor... if it ain't broke, don't fix it. 600 CFM is the capability, but the engine won't draw more airflow than it needs. As for piston ring wash, well, for that to happen the fuel system would have to be operating amazingly rich. It's possible... I've seen engines running so rich that there was a little flame at the tailpipe. In fact, I used to be able to induce that phenomenon by applying manual choke while driving down the road. BUT, if you were running that rich, there is no way you could make statements like "It runs good with more pep than others I've had in the past". Your spark plugs and tailpipe would show over-rich carbon residue. The Jeep would run terrible and your fuel mileage would be way down. I'm sure there are adjustments to optimize your fuel/air ratio if required.

It looks like you have an electric automatic choke... if your cold starts are good and the choke fully opens when the engine is warm, you are likely good to go with your current set-up.
 
Follow-up to the oil filter issue. I have had engine changes which affected the filter threads. The male threaded adapter on the engine block is removable. We had to make sure that old adapter was transferred to the new block before sending the old core back in. These threaded adapters are easily available. I'll bet someone swapped the original metric for an SAE version.
 
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I hope it's original but with engine code staring with a "3" it should be a 83. Another forum helped me identify it as it could be a 61,70,79,83, or 93.

Block has a C in the code which means 258....sometimes and 232 other times