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Unread 10-11-2010, 07:45 PM   #1
Corpus89YJ
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Intake vs Carb vs Cam

I have an 89 YJ 4.2 6cyl. I have been reading a lot on here about replacing the stock 4.2 carb with a Weber 2 barrel, however there is not much about aftermarket intakes except maybe putting a 4.0 intake on my 4.2. My question is do y'all think it would be better to go with an aftermarket Weber (WK551-34 34 DGEC) on the factory intake or the factory carb on an aftermarket intake (I havent decided on one yet)? I am not completely sold on the above listed Weber either so suggestions on that would be appreciated as well. The reason I am going to do this is the engine is coming out for a re-ring in the next couple of weeks due to excessive blow-by and if I have to have it out I would like to make at least one significant upgrade while Im spending money, I guess as far as that goes, maybe a new aftermarket cam might come in to the equation.

Anyway, any suggestions would be very much appreciated.

Thanks for helping out the new guy.

Keith

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Unread 10-11-2010, 07:52 PM   #2
gbeltran
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The 4.0 intake will only work if you are going to go with fuel injection. All of the other aftermarket intakes, usually made by clifford or offenhauser, are made for a 4 barrel carb. The weber is a good choice, lots of people also like adapting a motocraft 2 barrel to the stock intake.
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Unread 10-11-2010, 08:00 PM   #3
4.7stroker
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Quote:
Originally Posted by gbeltran View Post
The 4.0 intake will only work if you are going to go with fuel injection. .
Not true. I have adapted a 99 n up intake to take a Motorcraft MC2150.
True that the 4.0 intake is fuel injected but almost anything can be modified.
There is a series of pics in my gallery showing how I made the adaptor using phenolic and common wood working tools. Took me about 4 hrs to make.
I prefer the Motorcraft over the Weber.
If you need to take the head off then putting in a Comp cam/lifters is a great way to get a boost. Installing a 4.0 head is also worth the time money and effort.

Dwayne
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Unread 10-11-2010, 08:04 PM   #4
gbeltran
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Very nice work. I stand corrected. Most folks dont have those skills though, and nothing is commercially available for that application. I agree just about anything can be done, just takes time or money or both.
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Unread 10-11-2010, 08:05 PM   #5
Old4X
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Stick a 4.0 head on it when you pull the engine down. The later head flows a lot better than the 4.2, and it will work with the stock 4.2 intake and the carb of your choice. (you will have to use 4.0 exhaust manifold, though).

Save your pennies and add fuel injection later as budget permits.
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Unread 10-11-2010, 08:07 PM   #6
jsawduste
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Offy Intake and an Edlebrock. Runs well and works good.

http://www.jeepforum.com/forum/f12/j...-carbs-933880/
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Unread 10-11-2010, 08:27 PM   #7
Corpus89YJ
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I pulled the head off this past weekend, I blew the headgasket out at the #1 cylinder right under the exhaust port, I will have to post pictures later. Anyway, the head was just rebuilt so I will be staying with the 4.2 head for the time being. The head and the pistons all look brand new and you can still see the cross hatching in the cylinders. I bought the Jeep from a guy that used it as a hunting vehicle and I talked with his mechanic and they estimate that the motor has roughly 30,000 on it. Like I said, everything looks brand new, but I am getting very bad blow by and I dont know what else to do to stop this. I think it has gotten so bad that the rear main is now gone and my thoughts are if I have to do major work to replace the rear main I might as well pull the motor and re-ring it. Would y'all suggest the carb stated above as a good replacement for the factory one? If so, what do you do with all the vacuum that is hooked up to the factory air cleaner?

For the record, engine rebuild is nothing new to me, but it is the first Jeep I have ever had the pleasure of owning or working on to any extent.
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Unread 10-11-2010, 08:34 PM   #8
Old4X
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Blow by is often mis diagnosed. Make sure it isn't a bad PVC system coupled with mis tuned engine resulting in low vacuum at idle.
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Unread 10-11-2010, 08:45 PM   #9
zeus87gn
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Shoddy valve work or worn out guides will create blow by as well.

To answer the original question, I prefer the Holley. Mine's on the fcty manifold and works just fine. I've never preferred Weber and never tried the Motorcraft. The aftermarket manifolds look like they would flow enough air, but I have yet to try one.
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Unread 10-11-2010, 08:51 PM   #10
vicker
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i have the weber 38 dges and i love it never had tuning problems with it and its a simple design but i would recommend removing the stock needle and seat and replacing it with one made of viton. helps to control your fuel flow so well that i never even needed to add a fuel regulator.
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Unread 10-11-2010, 08:58 PM   #11
Corpus89YJ
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Blow by is often mis diagnosed. Make sure it isn't a bad PVC system coupled with mis tuned engine resulting in low vacuum at idle.

PVC system is in good shape (unfortunately) it would be easy enough to check vacuum at idle, I will have to find the vacuum gauge and give that a try. The valve seals are new and the valves themselves look good as well. I just cleaned them up. It is so bad that immediately after start up there is already oil being pushed out the fill hole. If you have the oil cap off, as soon as it is started you can see smoke coming out the fill hole. As far as tuning goes, it might not be perfect, but I have never had any issues with timing or tuning.
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Unread 10-11-2010, 09:22 PM   #12
Old4X
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Is the head still off?
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Unread 10-11-2010, 09:27 PM   #13
Corpus89YJ
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No. I put it back on this past weekend. Why do you ask?
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Unread 10-11-2010, 09:33 PM   #14
Corpus89YJ
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If you can give me some quick direction on uploading pictures I will add a picture of the head gasket as well as a picture of the block
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Unread 10-11-2010, 10:06 PM   #15
Old4X
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Quote:
Originally Posted by Corpus89YJ View Post
No. I put it back on this past weekend. Why do you ask?
I was confused by your posts. It sounded like the blow-by was occurring before you removed the head.

I was going to suggest pulling a couple pistons to check the ring grooves for gunk and possibly see why they wern't sealing.

30,000 miles is nothing on these engines, the kind of blow-by you describe is unusual, even for a 200,000 mile (maintained) engine.

As you are up and running again, try some high detergent oil (oils intended for diesels have the best additive packages for carbed motors now) and change the oil several times to see if you can free the rings and get them to seal up.

Otherwise, stick it on the engine stand and freshen it up.
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camshaft , carburator , intake manifold

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