Hey all! I have another (probably inexperience- and ignorance-related) issue that I'm having trouble pinning down. 1970 200 straight six with stock reman Carter YF My PCV valve has rattled for a couple years now, even after replacing it, but lately it has gotten worse and now the intake manifold is "rattling" from what I can tell. I had an issue where a bad power line to the alt caused burnout through the entire electrical system but I replaced everything and it as running well until a couple weeks ago, other than the PCV doing its thing. There's now a loud rattle coming from the intake manifold that's also coincided with a slight loss in power. Timing is top notch, carb is tuned pretty well and only a couple of years old, but either this is a spark knock or something is causing the carburetor to act... super funky and effect intake hardware as a whole? I'm kind of lost, honestly. And, in addition, in checking out the PCV thing, I found two things to be the case: 1. The PCV, when disconnected from the engine but attached on the other side to the carburetor vacuum port, still rattles. Which tells me the PCV itself is good but that... something else is the matter? (Ignorance! Also, it's disconnected in the picture below.) 2. The throttle shaft on the front is wet with gas/oil (pictured). It might help to get a good video to hear the sound, but I can't do that yet. In any case- I'm at a loss. And I realize my description might be a little vague, but any help or direction would be so awesome. I'll get a video to describe the sound soon, too. Thanks in advance!
Do you mean plug at the carb where the pcv line meets the manifold or at the crankcase side? I can check this out after work! It is barely audible when idling and the engine is fully warmed, but it's loudest under load. I took a video while driving but it's not that great. Will definitely get one from under the hood after work! (Excuses, excuses...)
At idle, you might be hearing the PCV operating correctly. If you are getting pinging sounds under load, I would be concerned about detonation. Is your timing correct? Is it running lean? I would look at the plugs, check for vacuum leaks and a clogged fuel filter? If auto trans, see if the vacuum line to the modulator is connected. Micah
A noise under load isn't going to be the PCV valve, it requires vacuum to operate and under load there is no vacuum...
In your initial post, you said this had been going on for a couple of years. Did this coincide with the purchase of your rebuilt carb? I'm wondering if you got the wrong carb. There is really nothing to adjust on these carbs. I had a similar issue several years ago when I went from a 170 to a 250. I had to replace the carb to the 250 model to fit under the hood. I had headers on the car. The carb was set up for an EGR which I did not have. It ran lean and I had detonation. Do you still have your original carb? Micah
I still have the body but it's missing some parts I commandeered or sold for one thing or another. The new one actually hasn't been running lean all this time- just the PCV has done that dance for a good long while. The new carb was reman'ed and is a twin-replica (exteriorly, anyway) of the old carb and hasn't given me any problems other than lately, if indeed it is the carb's fault at all. I imagine moving from the flatlands of Atlanta up to the mountains of Western North Carolina (double the elevation) might could play a lot in to timing adjustments, if not carb re-tuning, though. Am I right about that assumption?
An emissions carb would be jetted leaner. Higher elevation would necessitate a leaner mixture. Not sure that the elevation would cause any change in timing. Not really sure if you have a PCV issue as Tom mentioned previously. You indicate that it is running lean/pinging under load. Unless anyone has other ideas, I would look at the float level and for debris in the needle/seat or main jet. Are you sure you do not have a vacuum leak? You mention timing is good but what about dwell? Is there vacuum advance to the distributor? Are the distributor springs broken causing it not to advance? I didn't quite understand what transmission you have. Manual or auto? Micah
sounds to me like you have tuning issue related to swapped parts. Might be best to try to replicate the old carbs tune or swap back to an original style carb and rebuild it. Otherwise you need to learn how to tune ignition and fuel curves to better your aim towards the newly positioned bullseye. PS. not to try and make a mountain out of a molehill here.. but fluctuating manifold vacuum due to weak or downed cylinder/s pressure will also make an PCV valve flutter as well. Simple compression tests will tell you how healthy the engine is and should always be used as basic troubleshooting procedure to rule out bigger issues and baseline the overall condition. Course, as you get older and the school of hard knocks leaves you feeling more lumped up.. you tend to assume the worst and hope for the best. lol
You might try swapping the main jet and metering rod. You can do this without pulling the carb from the motor. Take a look on them to see if they are sized differently. Micah
Everything here noted- I had a reply but then somehow it got deleted so I will get back to that soon. One thing though- I was messing with my timing just a bit ago and for the first time (??? Inexperience showing) I unplugged the top of the two vac lines on the dizzy, and after I plugged said line, all stuttering, rattling noises basically vanished very nearly immediately. Does this mean I have a vac leak in the dizzy/vac advance module itself or would it always do this if you plug vac advance lines?
First off, if you are correctly setting the timing you need to unplug the vacuum advance from the distributor and plug the hose. If you have not, then your timing is not correct and this may be your problem. You could have a vacuum leak at either the hoses or the distributor. Replace the hoses. Remove your distributor cap and suck on the hoses. If you keep sucking and you cannot establish a vacuum, then the diaphragm is broken. If you build up vacuum, you should see the advance plates move. If not, your distributor is bad. Micah
