FYI, engine is a '67 425 ci with 4bbl.

Idles perfectly when in park, but runs rough when idles when trans is in park with the brake pedal. It feel like it runs fine for 2 secs then does a big hesitation and then repeat. Not always exact frequency.

I see 3 vac hoses - one to pvc valve, one to distributor, and one to brake booster. Also battery is 6 - 1/2 years old. I have it on a trickle charger but realize it is past its life. I know the hose to pvc has a small tear by carb - I currently have duct tape around it and ordered a new one will come tomorrow.

I tried to tried to adjust idle mix screws. I noticed that when I turn both in all the way the engine still runs like nothing changed.

I remember taking this to a mechanic around 2 to 3 years ago to have the brake redone (including master cyclinder) and he could not figure it out. He said that he thought the stumble was due to the big 425 engine delivering differnet vacuum along with the 442 brake booster and would not never run smoothe.

Any ideals what it coulld be ? It is really frustrating. I have to have the idle speed high too so it does not stall at a red light.

Also I remember on another car when the idle mix screws did that it meant the carb was gunked up inside and needed cleaning - could be wrong.

 

Ok, you have a couple things going on.

The car is not "idling well in park and idling poorly in drive" it's idling well at the RPM it is in park, and it is not when the torque converter loads it up when in drive. This is the time to ask if you still have the switch pitch torque converter and is that switch working?

However, please do this. Run the car, warm it up, air cleaner off, and smack your hand over the primaries. Right on top of the choke. Seal it off. It should die immediately. It if doesn't you have confirmed the other thing that should kill the engine, which is turning the mixture screws all the way in. You have a massive vacuum leak somewhere, and your minimum throttle is turned up so high to make it not lean enough so it will idle that you are idling on more than the idle circuit (as in you may be running on the primaries.)

A 425 is a powerful engine, but it is traditionally a powerful engine with manners seen in the Toronado and the 98. What cam is in that engine? It should make great vacuum if the original cam. Please get a vacuum gauge and hook it up to manifold vacuum. Vacuum troubleshooting is fun, because all you have to do it cap **** off and look at the gauge.

Also, remember that 90% of carburetor problems are electrical. How're the points and dwell?

My money is on bad vacuum booster at the brakes.

 

The car is not "idling well in park and idling poorly in drive" it's idling well at the RPM it is in park, and it is not when the torque converter loads it up when in drive. This is the time to ask if you still have the switch pitch torque converter and is that switch working?

For clarification, when the car is in Park the car seems to runs smoothe and perfect at practically all RPMs. However, when I put the car in Drive, the car run rough at practically all speeds. Even if I crank the idle RPM screem up, the car runs less rough but still does not run smoothe like it is in Park. So for example, 500 RPM in Park is smoothe, 500 RPM in DRIVE runs rough or not as smoothe.

I have no idea about the torque converter working or not. Is there a way to tell that it is functional other than rough idle and poor acceleration?



However, please do this. Run the car, warm it up, air cleaner off, and smack your hand over the primaries. Right on top of the choke. Seal it off. It should die immediately. It if doesn't you have confirmed the other thing that should kill the engine, which is turning the mixture screws all the way in. You have a massive vacuum leak somewhere, and your minimum throttle is turned up so high to make it not lean enough so it will idle that you are idling on more than the idle circuit (as in you may be running on the primaries.)

Okay I plan doing covering the carb tomorrow.

You have a massive vacuum leak somewhere, and your minimum throttle is turned up so high to make it not lean enough so it will idle that you are idling on more than the idle circuit (as in you may be running on the primaries.)

I don't understand what you wrote in bold above.

A 425 is a powerful engine, but it is traditionally a powerful engine with manners seen in the Toronado and the 98. What cam is in that engine? It should make great vacuum if the original cam. Please get a vacuum gauge and hook it up to manifold vacuum. Vacuum troubleshooting is fun, because all you have to do it cap **** off and look at the gauge.

I plan on getting a vacuum gauge tomorrow. I don't about the cam, but I assume it is the original cam. You are right, the 425 should yield a lot of vacuum. Does anyone have a diagram where a 425 intake and 4 bbl vacuum hoses go? I have the Chassis Manual and don't see any pages where it is very clear. Like a said I have only 3 hoses right now, one from PVC valve, one from the brake booster, and one from the distributor. I know I have a bad hose from the PVC

Also, remember that 90% of carburetor problems are electrical. How're the points and dwell? Well this was checked several years ago and I put on less than 200 miles since. Can it go bad by just sitting in the garage and just starting and running it in the garage?

My money is on bad vacuum booster at the brakes.

My brakes were bad a mechanic installed a new master cylinder and brake booster a couple or years ago. When he installed the brake booster it didn't idle in park perfectly then either and the mechanic could not figure out how to run smoothely in drive at idle. It performs worse now. Older gas and older fuel filter doesn't help. I replaced the fuel filter with a type that is not paper - looks like thimble. It improved a little bit.

Thank you very much for your reply.

 

FYI, checked again there is another vaccum line that runs from the manifold to down to what appears to the transmission - the connection to the manifold seems tight.

I mentioned the vaccum house that runs from the front of the carb to the distributor on the vacuum advace. The connection to the vacuum advance is quite lose and no doubt there is some sort of leak there. I will tighten that up. Probably need a vacuum hose reducer.

There is also a short , small hose on the front of the carb - looks like its conncected to a round object and then a carb port . This connection is not super tight.

 

The first part of your reply seems to indicate either a torque converter problem or a modulator problem. You can temporarily remove the vacuum line to the modulator, it's on the transmission, that line you mentioned, and cross that off the list. Use a good vacuum cap over everything you temporarily remove. Or, a large vaccum leak is making you very lean and pissing your engine off whenever it has any load at all.

You can also remove the power brake hose and cap it off a to test that.

What I meant by the throttle is, the throttle is a shaft, with linkages to the secondary shaft. The throttle has an adjustable stop. This adjusts the idle. Vacuum leaks present as extra air into the system. If you have a vacuum leak bad enough, backing the mixture screws out all the way will not be enough fuel and it won't run. Thus, the idle speed screw has to be cranked way up to get it to idle at all. As the idle screw is cranked up, it moves the idle position of the throttle out of the idle circuit, to the off idle circuit, to the primaries. The idle mixture screws no longer matter as they are not in control. Thus, screwing them all the way in does not kill the engine as you are running on something else.

So, confirm all your vacuum connections, or even disconnect and cap them temporarily. When you find that leak, your idle should go way high and you'll have to back it down. The idle screws will then work.

 

Okay Thank you Koda makes sense. Well all I did yesterday is I adjusted the mixtures screws, changed the fuel filter from a paper type to that type that looks like a sparkly thimble, sprayed carb cleaner in the carb.

Now today I wanted to run it so I cna put my hand over the carg. When I try to start is when I touch the gas, I get a backfire in the tail pipe when it tries to turnover. I immediately shut it off. Ugh I was afraid I would cause more problems solving my problem. I tightened he screws one turn and did not seem to make a difference.

I never paid attention to the choke, but isn't it supposed to be closed? It's cold this morning and the front part is open and smells gasey - could be just me. When I use my finger to adjust the linkage for the choke to close it , it just opens again. I put a piece of paper to hold the choke closed and it still backfired when starting.

I think the first think is to put an paper fuel filter back in. What could be causing the backfire now - that never happened ? Thank you so much

 

You may have flooded it. Leave it alone for a few hours and try again.

 

By the what it was sitting for 12 hours. I only pumped the pedal 3 to 5 times and now it backfired already and it never backfired in 8 years. Ugh

By the way, isn't the choke valve suppoed to be closed? It is open and it is currently 45 F.

 

Yeah you flooded it.

Ok, little carbology here. When warm, car is started by slightly depressing pedal 25% and crank. When cold from running the day before, ONE pump to set choke, then depress to 25% and hold and crank. When cold and set for several weeks, a few pumps, foot off gas, crank, wait for bowl to fill, then throttle after start. The "cold but ran yesterday" start varies per car. One pump, maybe 2. Not five.

It will evaporate out. In a few hours, just put the pedal down 25% slowly, hold, then crank. If it still backfires, ease the pedal down and prop it so it stays floored and leave it like that for a while so it evaporates out.

Yes the choke should be closed.

 

Thanks. Good point. I rarely start it two days in a row, but I am surprised it flooded so bad with just a couple of pumps. Also the choke is open and should be closed

How this all started is I started the car earlier yesterday and after running fine for around 10 minutes it just stalled. I was not sure if there was problem or I ran out of gas. I did not think it was gas but never know. My fuel gauge is not perfect so I add a couple more gallons as a safety. It did start but there was a good amount of stumble when in Drive and that is how I proceeded.. I am attaching pics. Is there anything that sticks out out of place?

 

I just pulled a couple of spark plugs. Black and dripping with fuel. This must have been contributed to the idle mix screws and pouring a little sea foam and spraying some carb cleanerin the carb yesterday perhaps too.

 

Perhaps dumb question, I sprayed car cleaner around the outside of the carb last night? could that have affected the float adjustment and now causing more flooding?

 

In addition, I am really confused now. I don't see a thermostatic coil and rod that is supposed to control the choke according to the manual. I see the vacuum diaprhagm and linkages but not the coil location. Weird. I'm lost now.

 

I have a Quadrajet 7027156. Appears divorced choke. Anyone have something like that? I never really noticed how it performs when cold until this week. I typically have the air cleaner on. But how do you know the choke is adjusted right? It is not intuitive. I would think it should be closed and then slowly open. But mine appears to be always open.

 

Well now I know why I had to pump the pedal a lot in the winter to start it - I don't have a functional choke! My divorced choke is not connected to a choke thermostat. My carb is always open. What are my options for this? Wow. How weird.

This does not really solve why it runs rough at idle when warm but good to know.

 

Car won't stay running rough unless I constanlty pump the pedal but afraid it will backfire if still pump

 

You definitely do not have a choke setup. Your intake manifold looks to be an Edelbrock, can't quite make out lettering, without the divorced choke pocket to install the thermostatic spring and lever assembly. Check your overall engine vacuum with warm engine running with everything connected and make note. Use a vacuum tool to apply vacuum directly to each of the vacuum-controlled components to do a leak down test. Vacuume modulator on trans, vacuum brake booster, vacuum canister on firewall, and vacuum advance on distributor, making sure advance is operating smoothly and returning quickly when vacuum is released, in addition to leak down. My guess is the problem is likely at the distributor, maybe vacuum advance, points/condenser, or just a worn out distributor. That being said any of the above could be an issue. Oh, I will attach a pic of correct manifold with open pocket to receive choke thermostatic coil.

Good luck

 

Yeah, I have the 67 engine and carb, but an Edelbrock intake that does not have that bracket for the choke. My hunch is my only way is to convert it to electric choke.

Can my idle RPM screw cause flooding? I cranked up the idle RPM some and now I can't even get it to run . All the cylinders are flooded and seem to stay flooded. I did not touch the float adjustment other than to spray the outside and inside with cleaner

 

Increasing idle with the idle screw should not cause it to flood, just should increase RPM. Spraying carb cleaner inside and out should be ok but i suppose it is possible that some trash washed off and got stuck in the needle and seat, causing the flooding condition. Try lightly tapping on the top of the carb with a brass hammer or the like to try and unstick the needle and seat if that is in fact why it's flooding. Not too hard of course. To be clear, this flooding condition was not there originally but happened after you sprayed down the carb correct?

 

----_------------------

I had the car for around 8 years - never flooded until this morning . Yesterday I did the following to get rid of stumble at idle in drive although it was not bad was not perfect like in Park.
​​​​​​
Yesterday I did the following :

Increased idle rpm screw (this did work increase rpm)
Adjusted the mixture up and down ( didn't seem to have an effect)
Sprayed carb cleaner in inside and outside
Poured a little of sea foam in carb
_
This morning tried to start it after hit pedal a couple of times and has several backfires ( that never happened either). Won't stay running unless I keep hitting gas pedal and then wants to die after that. Too much pedal and backfires. Pullled 3 spark plugs and they are well and black. Tuned car in a piece of garbage overnight.

 

I bought a vacuum pressure gauge and some new hoses and clamps. I know there are 2 vac leaks. - dont know if it will solve problem but still need to do once running close to at least before

 

1. 7027156 is the correct number Quadrajet carburetor for your 1967 425 motor.
2. The 1967 Chassis Service Manual (CSM) has a 20 page section dedicated to the Quadrajet carburetor. Everything you need to know about servicing, troubleshooting, and understanding the various circuits of that carburetor are explained there.
3. It is possible that your distributor needs attention also as mentioned above. The CSM also provides great information in that area.
4. I have seen online two basic types of electric choke conversions for the Quadrajet offered by various carburetor shops. One type attaches directly to the choke well of the stock factory intake which you obviously do not have. The other type attaches directly to the carburetor. I do not know if there is a conversion kit specifically for the early Oldsmobile Quadrajet but the one listed for the Pontiac carburetor of that same year grouping may work. Maybe one of our forum members has more info on that and can contribute.

 

As Jim said, that's a correct carb. The intake doesn't work with it. Does that intake work with the onboard choke of later years? Getting another carb might be the least expensive thing to do. You may even set the choke up as manual for now. You'd need a cable.

You may need to rebuild the carb. They're not hard, just be meticulous.

 

===================================
Update: Short story is car started easily and runs great in Park and Drive Now!

Longer story below:

The service manual is entirely clear to me regarding divorced choke. I spent hours reading about it, and took longer as didn't know at first I had the incorrect intake, but figure out that I don't have the correct intake and don't have a functional choke. Who knew. If I want a real choke, I would think I could convert the divorced choke to an electric choke. I would like to keep my carb if I can as it is the correct carb.

But so far I have wonderful news. In addition to what I already did regarding spraying inside the carb and a little sea foam while running it. As a recap the car would not run the next day. It backfired (which it never did before).

I checked the plugs and they were flooded and corroded. Time flew by, I thought the plugs were not that old, but realized they were 7 years old and didn't look good. Also my battery was 6-1/2 years old and wasn't holding a charge without the trickle charger. Don't know if the battery could affect the idle problem but realized there was no use trying to ride with that old of a battery.

So I went ahead and splurged and bought and installed new Iradium spark plugs and battery. The prior plugs were AC Delco which worked very good when they were new but wanted to try something different. I typically want to keep it original with GM parts, but I was desperate to try something new. I don't know what y'll think of Iradium plugs. They came gapped around 0.036". I know the book says 0.030, but I read one posted gapped his to .045" so I left it at that at the start.

I went got a new a hose that goes to the PVC valve and for every vacuum hose (PVC hose, distributor advance hose, brake booster, and choke hose) I installed hose clamps around each vacuum hose connection. I could tell before I did this the PVC hose had a small hole, the distributor advance hose was loose at the distributor, and the brake booster hose was not that snug. Now each vacuum hose is iron tight.

I let the car sit for 2 days and ran a fan over night to circulate around the help dry out the car and evaporate any flooding. For most of the cylinders I took the spark plugs out. I turned the idle mixture screws in and out 2-1/2 turns.

As you can see, technically I really don't have a functioning choke. A normal choke is supposed to operate 70 F or below. It's 50 F so I know it was not ideal conditions, but I thought I would start it tonight to see what it would do. Well, it started right away with just a light touch of the gas pedal and it idles smoothe in Park AND Drive!!!! It runs better than it ever did even after I had two mechanics work on it 7 years ago. Some of it was not their fault but I can tell they did not do a meticulous job sealing all of the vacuum hoses.

One of the reasons why I did not drive it much because it never ran great at idle in drive like when stopped at a red light. Tonight it was smoothe and no stumbling and hesitation. I used to feel like I was handling a bull at a rodeo a little. So knock on wood. Real test is to drive it around town but the garage I love it so far. Thank you guys for your help!! It's like a brand new car!

P.S. I did get a vacuum gauge but so far I didn't use it. I don't know if the idle screw 2-1/2 turns out is ideal but so far it's running better than it ever did so I don't want to disconnect anything at least for now although I am curious what the manifold vacuum reading is.

 

Good. You are running mad rich, so that's why you are not needing a choke. Normal is 1.5 turns out on idle.

Read up on how to tune with a tach, dwell meter, timing light, and vacuum gauge. The short version is to get the dwell right and adjust the idle mixture for the most vacuum, then use the rpm screw to set the rpm where you want it. This will make the car run badly until warmed up, but will get you cleaner hot idle and better mileage. By adjusting for most vacuum, you:

1. Write down where the mixture screws are now.
2. When engine is warm, adjust them both the same, one then the other.
3. With engine off, put them all the way in (and write down how many turns it took, that's #1.)
4. Set them to 1.5 turns out.
5. Start engine, observe manifold vacuum, write it down.
6. back them out 1/4 turn at a time, write that down. Observe vacuum, write that down.
7. Vacuum will either peak, or just keep dropping. Once it starts dropping, you are too rich.
8. Go the other way (in), past the peak, and it will start dropping again.
9. Go back to peak vacuum mix, write that down. Then go in 1/4 turn. Write that down. That is your setting.

Adjust RPM for what you want in park. Now, the idle mix and rpm is dialed in for warm operation.

Choke is as much a function of humidity as it is temperature. Gasoline does not care about it being cold if it is dry, the reason chokes are there is because cold and humid conditions result in worse atomization. In other words, doing it in your garage might not be the same as leaving it outside overnight in the rain.

The choke system has the butterfly plate and the fast idle, both of which give the engine a richer mixture until it warms up.

https://www.everyday-performance.com...kit/p/60306004

This is for a Pontiac but might be a 100 dollar bolt on choke solution.

 

If you flood the car again, hold the gas pedal on the floor while you crank the engine. Just hold it there until it starts. Resist the temptation to pat the gas pedal. I have done this for many many years.

 

Thank you Koda, you are right. The last time I did a timing was in auto shop in high school decades ago. Would like learn ago Have everything except dwell meter.

Appreciate the detailed tuning procedure.You are right about the mixture screw too far and good procedure on tuninng. I started out at 2-1/2 turns as not to starve the engine. Yesterday I started it cold and just let it run to operating temp and shut if off at idle in the garage. It probably was fine as it was cold last night.

However today in the high 60sF, I started it a drove it around town several miles this time engine at max temp in traffic. At stop I noticed and it was a little bouncy and even before I read your email, I tighted each screw around a turn and it runs awesome. What an amazing difference. It used to run like with varying levels of stumble. The car now runs better than it ever did - thank you so much cannot thank y'll enough!! To get it perfect I would need to hook up equipment like you mentioned.

Moist air does negatively impact combustion due to increasing the volume of water vapor in the air. Humidity also can impact old electrical components. However, fuel vapor pressure is a correlated to temperature and the engine block is closer to operating temperature on warm days than when it is colder. Cold Temp also affects the battery and starter. So the worst is cold and humid. I typically have an easier time starting on warm wet days than very cold dry days (with other carburetor vehicles with a choke including motorcycyles), but I can see others have differing experiences. But the reason why I mentioned the outdoor temperature is choke operation is based on temperature of the choke element. I believe the service manual says the stock choke operates when air temp is below 70 F.

Thank you for the link to the conversion kit - that is what I need. I take it the one I need is for the Pontiac as Old is not mentioned. Why did you mention the butterfly valve is included? I already have a choke butterfly valve on my Rochester carb. I thought the choke conversion kit is just the electrical choke element that move the choke open and closed and not carb components? Perhaps I am misunderstanding.

Has anyone done the conversion and is not too painful?

 

What really scared me is that when I tried to start it (a couple of days ago before the plugs and hose work), granted I did tap the pedal once or twice, it backfired in the tail pipe a few time very violently and it never did that before. I realized that opening up the throttle increases the air in the mixture but goodness it is terrifying to lay down the pedal when you car is backfiring. Thank you - will try it next time if needed.

 

.....Let me stick my neck out here a bit and provide some thoughts and experience.
1. A choke in the older Rochester's responded to air temperature. There were no sensors for humidity. Expansion of the Bi-metal spring in the choke housing controls the choke.
2. Gasoline does care about the temperature because it atomizes at an approximate temperature. During winter, additives are mixed in gasoline to aid atomization at lower temps.
3. "Air" is more dense at cooler temps (more oxygen molecules per volume) than at warm/hot summer temps.
4. Water molecules is not entirely a bad thing. It does displace some oxygen molecules but it can have benefits. Example 1: Water injection was added to combat airplane (fighters) for a short, quick burst of extra power. Example 2: Jetfire "Rocket Fluid" was a mixture of Methanol and water that was injected into the airstream when needed. Example 3: I was told by an "Oldsmobile Big Dog" (Berijik Olds mechanic) to spray a mist of water in the air scoops of my '68 Hurst/Olds. I also sprayed the inside of my '70 W-30 scoops later. There was also an aftermarket company selling some crude type "water injection system". I didn't spray on hot, humid days.

The same spray can with water was used to "mist" the tires before a short burn out before staging. This was long before the word "Bleach box" was invented. The spray can was used to spray the radiator to help cool it down between rounds.

 

Thanks Ralph, A splash of water temporarily cools and cleans an exisiting running engine and temporality cools the incoming air which as said increases the air density. Having that said, typically, when a car engine is colder and sat for more than 5 hours, a car sitting outside in Arizona is going to start easier than out in the winter in Seattle.

From my experience in NC, it's typically relatively on the more humid side most of the year, but what fluctuates for me more is air temperature and when temperatures are warmer my carb engines start much easier. For me, my carb engines start up right away from Jun to Sep. I typically don't enjoy starting in Jan and Feb. Another thing for me is even though it may be humid outside, I typically dont leave it outside in the rain where there could be extensive water droplets inside the engine bay. But on the times when I did, I had an easier time starting in rainy July's then freezing Januarys. It's seems like its a bit complicated and could depend on the state of the each vehicle.

 

Glad you’re getting sorted out. That PCV valve with the duct tape caught my eye. Took me years to suspect brake boosters, easy to check once you think about it. Same for transmission modulators.

The vacuum port it’s hooked to on the throttle plate is one of the largest on the carb - it has to be sealed or you’ll have a vacuum leak like you describe. As you zero in on the best metering, you might want to be sure your PCV valve is working. I believe the traditional fix is to remove from the car and shake it - if it rattles, it’s o.k., if not, replace it.

I’ve gone electric chokes on my carbs long ago with Joe P.’s instructions from here for the fused power supply running through the oil pressure switch.

if you really want to dial that carb in, consider an oxygen sensor on the exhaust to show your air/fuel ratio or lambda if you like that scale better.

Hope you enjoy the car more now.

Chris

 

What I was referring to in my previous post is that a damp environment, with a humidity soaked engine, will cause a longer, and rougher, warmup than being in a cold, but dry, garage. This is exceptionally noticeable if the heat crossover, and, in later years, the temperature controlled warm intake air mechanism, don't work. Thus, an engine performs worse while warming up if it's been left outside. I am aware how chokes are regulated.

 

Thanks Koda and I agree. Thanks for clarification. I think the miscommunication was due to one little quote, where the topic was related to choke operation, where you said "fuel doesn't care about temperature"..... Anyway, I gotcha.

 

I have a question on the correct type of vacuum hose to use. I bought a two type of 3/8" hoses to run from the PCV valve to the carb.

The type of hose that was on the car since I bought it was a thicker, more ridged, oil pressure type hose rated for over 100 psig. I first purchased this from Amazon.

While I was waiting for the oil hose to arrive, I purchased a 3/8" vacuum hose from Autozone which was more of the softer, thinner, flimsy type. I installed this one right away and the cars great and smoothe at idle.

However, yesterday even though it was running great, I looked underneathe the hood while it was running, I noticed that the vacuum on the PCV Valve was so strong that it was sucking the hose practically together and looked like it was struggling to decent air flow (essentially the vacuum was so strong it was contracting the hose almost entirely together). So at that point, I realized, that is why I must have had the more rigid type of hose to ensure the hose didn't contract and allow the max air flow.

So I swapped out the flimsy vacuum hose with the more rigid hose, tightened up connections and now even though it I have max vacuum flow the car idles a little rougher. Perhaps allowing the max vacuum flow required adjusting the idle mix screws again? I would assume that would be recommended versus have a hose that is starving flow, correct? Quite frankly I was shocked to put a hose on there that did not contract where air low would be unhindered and it ran rougher. Interesting on thoughts of what is the proper vacuum hose type. Perhaps it's me and minor difference.

FYI the car appeared to be running well at acceleration and faster speeds equally.

 

I'm no expert on hoses, but mainly you want manifold vacuum being fed to the PCV valve so the crankcase gases get sucked back in to keep the environment just a little cleaner. If your thinner hose collapses under manifold vacuum, it's too thin.

Having said that you're now into the world of PCV valves. I warmly recommend that you be sure you've got the right one. It took me a long time to learn that they're not all the same. Not only do the vacuum nipple locations and shapes change, but inside there are springs and other components which can differ from valve to valve.

If they're still cheap, begin with the factory correct one for your car, but get a couple of others too in case they work better with any modifications you may have done like cam, carburetor, distributor, compression etc. It'll be a fun experiment to test drive with each and see which you like best.

Let us know where you land with part numbers and what not so the rest of us can learn from your experience.

Cheers
Chris

 

Thanks, I agree restricting flow cannot be good but surprisingly it idled better with the current settings.

I bought and have this PCV valve that I bought last year from Amazon. This is the model recommended by Rock Auto for this model. FYI, I have 425 engine and the PCV model number didn't change. Barely has any miles on it.

ACDelco Professional 19310783 Positive Crankcase Ventilation (PCV) Valve

 

You have to tune the car's mixture settings to match the air coming in. PCV working right means more air, thus you will need a vacuum gauge. All this is in the chassis service manual, engine tune up section. Does the PCV valve rattle when you shake it?

 

Thank you Koda - that makes sense. I would then be running leaner with more air flow. Yes the PCV valve shakes and rattles fine. It's pretty new. Bought it a year ago and rarely used. I shook it again as a double check. I'm going to buy another one as a double check too.