84 258 w/ Weber: Blow-by?

[cairo10]

Hey,
I am re-entering the CJ phase after not having one for close to 10 years - every spring I sulked over selling my 76 CJ7. Finally, we purchased a CJ7 (84) this summer. It has a terrific ride!

Bought it knowing that I'd have engine fun coming. The engine has considerable blow-by. I'm new to the 258 & its quirks. I love the "stoutness" of the 4.0 in my previous Cherokees, so I look forward to working on this earlier model straight six.

I welcome hints or ideas for dealing with the Weber Carb. I'm not yet sure which one it is. However, I have a few emission tubes that sit in the engine bay ... I assume from the original carb. I think one leads to the exhaust manifold & the other is a return from the catalytic converter ... actually it just came off at the CC and I pulled it out.

I'm going to try to post a few pics of the hoses.

I've been told that the Weber really needs to breathe and that the vacuum leak could cause the blow-by. Does this seem to be the case here? Originally, I planned an engine rebuild because I thought the blow-by was an internal issue.

Any ideas? Thanks.
Byron

 

[wm69]

uhh, you should have a PCV valve going from one of the ports on the top of the valve cover, and either a breather valve or a hose running to the air cleaner (for air being sucked INTO the crankcase). Almost looks like the back port is plugged on your valve cover.

 

[Collin the Hen]

uhh, you should have a PCV valve going from one of the ports on the top of the valve cover, and either a breather valve or a hose running to the air cleaner (for air being sucked INTO the crankcase). Almost looks like the back port is plugged on your valve cover.

:agree: On my 258, there's a little breather on the rear hole, and the front hole has an elbow that goes straight into the manifold vacuum port (below the carb). I have a motorcraft 2100 and it's been nuttered, so that may make a difference.

 

[ursman]

Hey,
I am re-entering the CJ phase after not having one for close to 10 years - every spring I sulked over selling my 76 CJ7. Finally, we purchased a CJ7 (84) this summer. It has a terrific ride!

Bought it knowing that I'd have engine fun coming. The engine has considerable blow-by. I'm new to the 258 & its quirks. I love the "stoutness" of the 4.0 in my previous Cherokees, so I look forward to working on this earlier model straight six.

I welcome hints or ideas for dealing with the Weber Carb. I'm not yet sure which one it is. However, I have a few emission tubes that sit in the engine bay ... I assume from the original carb. I think one leads to the exhaust manifold & the other is a return from the catalytic converter ... actually it just came off at the CC and I pulled it out.

I'm going to try to post a few pics of the hoses.

I've been told that the Weber really needs to breathe and that the vacuum leak could cause the blow-by. Does this seem to be the case here? Originally, I planned an engine rebuild because I thought the blow-by was an internal issue.

Any ideas? Thanks.
Byron

As for the tubes attached to the cat and e-manifold, those are smog pipes and aren't mandatory for the Weber application. They should either be removed and exhaust taps plugged/welded up. Having them dangle around free in the engine bay isn't a huge problem but it will give you less back pressure and bring a significant amount of unnecessary/unwanted heat in there. If you need them to stay because of smog nazis etc, I suggest to just plug the hoses up with a large rubber cap.

As far as the PCV goes, the other posters are absolutely right. The PCV should go to the manifold vac port (on the front of the carb adaptor). I had my EGR/CTO tee-d off to ported vacuum along with the dist. advance. That's really all you need. Make sure that the CCV hose (the one on the rear of the valve cover) is receiving filtered air from either the provided elbow that goes under the air cleaner or just get a stubby a/f from any auto parts store.

One last little bit of advice, periodically check the carb's base plates for looseness. I don't know why but mine got loose on a couple of occasions so I used some med strength loc-tite on the bolts and problem was solved. You shouldn't have to mess with the idle or mix. If it's running rough, make sure the mixture screw is 1 1/2~2 turns out and idle about 850rpm or so. You might also want to double check your timing. Hope this helps some! :mrgreen: