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Discussion Starter · #1 ·
Well, finally got the old Jeepster to pass the smog out here in NV. It was such a little thing causing the problem I'm embarrassed to mention it, but...

It appears that a few years back for some reason I hooked the PCV valve directly to the manifold instead of the rear of the carburerator like it was in the first place. Stupid me....

Anyway the HO% dropped to under 80 and the CO% is at 1.80 at idle and .74 at 2400 rpm. Now I can enjoy the great gas mileage that I used have before I messed with the PCV valve. Just in time to combat these new gas prices. Live and learn.

Time to relax and do some four wheeling out here now. Hopefully I won't screw
that up.

Mike, '70 Pick-up
Las Vegas, NV
 

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Congratulations.

Interesting -- Apparently the added air going into the manifold fitting was diluting the rear cylinders mostly and not affecting the front much. Possibly accentuated by the single plane manifold and relatively small displacement engine. The big manifold chamber is one big empty can with low velocity. Feeding it to the carb base distributes it better, dumps it right into the airstream. Theoretically it's the same, manifold vacuum, but obviously different as far as distribution goes.

When you'd lean it down till the stumble point, the rear was right, but the front ones were still too rich. If you leaned it further, the rear would be too lean, kicking up HC. Can't win for losing on that.

I'll have to experiment with how much that affects it with an exhaust analyzer.

It's definatly something to remember, run the PCV to the carb base, not the manifold. It can/will affect both emissions and mileage.

I'd suggest anybody (including me) that has it routed to the manifold re-route it, and then readjust the carb, especially now that gas is $2 .

Thanks



98% is Understanding it
"Don't Fix Unless Broke"
 

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Discussion Starter · #3 ·
Rich,

Thought that I was the only one who had done that switch with the PCV valve to the manifold. You'll see what I mean once you get it on the engine analyzer. The HC really shoot up at idle. You can bring them down with a carb adjustment bu the CO sky rockets. Like you said can't win for losing and I spent a lot of time playing around with it. Anyway I can't take all the credit for finding the PCV Problem. It was Rick at Carbuerator Exchange in LV. He was stumped for about an hour, pulling plugs (seeing how clean they were), adjusting the carb, playing with the timing, then he said let's see if the PCV is plugged. Hey's here's the problem etc.

Runs the best it has in years. Engine's quite and sometimes it's been getting away from me on the freeways here. RPM's are about 200 lower at 70 mph then before and it's running cooler. Excellent vehicle again.



Mike, '70 Pick-up
Las Vegas, NV
 

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Mike,
Just in case I decide to perpetuate your mistake, could you fine tune your fix for me? My PCV valve is connected to a 1/4" pipe nipple screwed into the back of the carb base. Is this where you attached yours to bring things around? I wondered about the "manifold" connection, but all I have is a small 1/8" barb (plugged with piece of hose w/ screw in it) between cylinders 4 & 6. Is this where you had connected it originally?

Caver Dave
'68 Jeepster Wagon
225, 3spd, & road salt A/C
Vintage Jeeps(ters) have Character,
new Jeeps just have payments.
 

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Glad it works better.
Haven't been to where mine is about 150 miles from me now, but I'll play with it. But I've been thinking about it quite a bit, I should have known better. My apologies.

Air flows down the carb, turns in the plenum chamber, then flows down the ports in the manifold. By the time it gets under the vacuum tree behind the carb it's already separated to each cylinder. The air coming from the PCV has oxygen in it, so it dilutes the mixture in that runner, which I believe is #5, left rear. Being a single plane manifold means the air is moving slower, the area of the passages are bigger, so there's much less mixing with other cylinders, which would dilute the affects of the extra air more.

Feeding it into the carb base, it mixes with all the mixture and gets more evenly spread throughout the engine. All the cylinders get some.

When you screwed the mixture screws in, clockwise, looking for the lean stumble, that #5 leaned way before the rest did, you felt the stumble, then richened it a tad till the stumble went away again. That's the correct procedure. But, the stumble was only #5 lean, the others were still too rich. That made the CO too high overall. At that setting #5 was perfect, but all 5 of the others were still making way too much CO.
If you leaned it further slightly, the #5 lean misfired and HC kicked up.

I had sort of a similar situation today. I stopped by a friend's Mobil station, he does lots of smogs. (I'm retired but can't seem to stay away.) He had a Toyota that was doing similarv to yours. When we got the CO down where it should be, both HC and NOX kicked up. I first suspected a small vacuum leak, but propane tests found nothing. Even told him about yours. Everything seemed to check out fine ignition wise, and timing was OK. PCV was hard piped in the right place, so that wasn't it.
Someone else had already replaced the carburetor, EGR Valve, and ignition parts. The poor customer had already spent close to $1000 on it and it still wouldn't pass. ---- A challenge!
Seeing NOX go high when CO was down where it should be had me going. It was telling me I was losing a cylinder. I was about to do a cylinder balance with gasses test when I started thinking about compression, then realized one cyl was hot causing the NOX to go high.
Sure enough, a block check chemical test showed a leaking head gasket - just a small leak. Combustion gasses were getting in the water jacket, causing that end to run hot.
Just to prove it, I put in a couple of Solder Seal tins and ran it a few minutes. Block Check no longer turned yellow - it sealed the leak.
Passed with flying colors.
John is doing the head gasket tomorrow and flushing that stickey stuff from the radiator. But it passed!

There's always a reason something happens, all we mortals have to do is figure it out.
My Jeepster's PCV Valve hose is on the manifold vacuum tree too I think, but we don't have to smog them here, too old. I think I had it on the carb base when I did all the dyno testing to curve the dist and jet the carb, but don't remember for sure.



98% is Understanding it
"Don't Fix Unless Broke"
 

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I'm with Caver! Sometimes a pic. is worth a lot of words! Could someone do a drawing so the few of us with low comprehension of the written word could connect all the dots to a proper PCV hook-up? Mines a 231 w/Q-Jet.

 

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Discussion Starter · #7 ·
Carver,

It sounds like yours is hooked up right. The PCV should be connected to the base of the carbuerator in the rear. I wouldn't mess with it since it's hooked up right.

I don't know why I went to the manifold connection. I think the hose broke and with the shorter hose that's the only place it would fit. I haven't hooked it back up yet. We just plugged the manifold nipple and left the PVC disconnected. I'll be putting it back together right the weekend after I get the right connector for the base of the carb.

Rich,

I had the PCV connected to the plug on the driver's right of the manifold. That's why my #6 plug was always clean while the other's would tend to foul if I just drove around town. With me driving on the freeway everyday to work now it was keeping the plugs clean making it harder to trouble shoot. Hopefully we can help sone avoid the mistake that I made. By the way I double checked my tach today on the way home and it looks likes it running 400 rpm lower while cruising at 70 mph. Before it was hitting 3000rpm and now it's only 2600 at 70 mph. I like it... Oh yeah the vacumm always looked good with the guage hooked up because I would disconnect the PCV and use that nipple to hook up my gauge. Just couldn't win troubleshooting that way...


Mike, '70 Pick-up
Las Vegas, NV
 

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I'll probably be with mine this weekend, I'll play with it.

Something I don't understand at all, the lower RPM. It shouldn't have changed it at all. That's a function of gear/tire ratios. That's saying the tranny was slipping before, it shouldn't have, even if the vacuum was disconnected to it. That would make a difference in the shift points, but not make it slip. Something's changed, what I don't know.

Yup, everyone needs to take a look at theirs to make sure it's right.
I've made a couple of drawings to post about how the PCV should be routerd, but for some reason I can't shrink them small enough to post. I'll keep trying.

Glad it's working right.
Rich




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"Don't Fix Unless Broke"
 
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