Idle Speed Fluctuates

[1965-Mustang]

I have a Speed Demon 575 on my 65 and have been trying to get it running correctly for a while. Right now my engine idle speed will either be really low and will die or it will go up to 1500-2000 rpms. I think it is my PCV valve though as this is something I had changed recently. I am also pretty sure it is incorrect as I did not know which one to buy. Is there a way to find out which pcv you need or something? I have a breather on the other side which has smoke coming out of it also. I have tried adjusting al the idle mixture screws and idle speed screws only to have it go to the extremes of dying or idling at 1500-2000 rpms.
Would reallly appreciate any help....Thanks

 

[tos]

Did you just install the carb? What did you do before this showed up? It sounds like a vacuum leak to me. Check all your hoses including the pcv hose. Check the carb and intake for opened vac ports or cracks in the base. While the car is idleing move the hoses around and listen for rpm changes and feel for leaks. Pull the hose off the distributor and plug it to see if that makes a difference. Does it get better or go away if you increase rpm? The wrong pcv valve wont make much difference if it fits tight to your hose and in the valve cover.

 

[66HertzClone]

The wrong PCV valve will give you an erratic idle. The PCV valve is actually a "controlled" vacuum leak, if the valve you are using allows too much air it could effect the idle.

Go to a local parts store where someone has some knowledge, typically this will be a store that supplies the local garages. A Napa store or the like, ask the counter-person for some help getting the correct PCV valve. Forget about telling him that you have modified the engine, tell him year, make, model, and engine size. This should give you a valve that will meter correctly, the one in mine does.......

 

[Kriek]

Ive been told that symptoms of a faulty PCV valve are poor idle and excessive pressure in the crankcase. Which makes sense, because the valve uses vacuum from the intake manifold to draw the fumes from the crankcase, right? PCV (positive crankcase ventilation).

 

[tos]

Ive been told that symptoms of a faulty PCV valve are poor idle and excessive pressure in the crankcase. Which makes sense, because the valve uses vacuum from the intake manifold to draw the fumes from the crankcase, right? PCV (positive crankcase ventilation).

A Faulty pcv valve yes but a new one I doubt it. pcv valves were still kinda new on these motors and were all made to maintain pretty much the same vacuum and crankcase vent. The main difference was hose and grommet sizes. Some early stangs didnt have them. my first was a 64 !/2 (titled that way too) vented the crankcase through a metal tube straight out the bottom of the engine compartment.

I'm still curious about the circumstances before this happened. Did you just buy the car and it was running that way? Replaced the carb? Added the pcv yourself?

Were is your pcv routed to?

The easiest way to tell if it is in that pcv system or hose is take the hose off and plug it up. If your problem goes away them you know. Dont waist time and money changing pcv valves till you doe this.

And again-check for leaks elswhere, cracked hose etc...

 

[1965-Mustang]

I did not just buy the car. I have had it for 2 years now. Ran it back and forth from highschool for a year then the engine seized on me because of loss of oil pressure and no oil pressure gauge. Since then have purchased a 66 block 289 got it all running using a lot of parts swapped from other engine. For a year now I have been trying to get it roadworthy. Since I have not had the engine running a lot I am not sure when the problem started and I have messed with a lot of stuff since, but I am pretty sure it is carb settings+pcv+crankase pressure. I had taken it to my shop guy and he said I had too much crankase pressure, and the pressure was forcing oil into the distributor cap as the seal on the distributor is shot. So he said I needed a breather intead of my plug on the valve cover. While at the auto parts store buying a breather I also figured I would replace the pcv as it was the same one I had on my old engine just swapped it over, but me not knowing any better just grabbed a pcv valve off the shelf. I had also played with the carb settings including the idle speed screw :/ , idle mixture, and my idle-eze thing. All I could get was either too high of an idle or it would die. Shop said this was also because the of the oil in the distributror cap. So now I put on a breather and new pcv. Smoke then came out of the breather and I am not sure why? And I still could not get it to idle right, but I still have not changed the distributor seal.

Since all this I have just put the old pcv in and I think there is now less smoke out of the breather and I think it is idling better, however I cannot tune this demon myself so I know for a fact the settings are off. But I am not sure if I solved anything yet because what do ye know I test drove it down the road and my universal joint broke and my drive shaft fell off.

Also as a side note; I noticed it would seem to idle fine before until I brought the engine up to about 3000 rpms, then it would stay idling at 1500 rpms. I have sprayed all around the carb and intake with carb cleaner to check for vacuum leaks but did not notice anything. But I have never looked for a vacuum leak before so I dunno.. .

So bascially I think I have wrapped myself in a huge mess. And sorry for the long post. . .I am just gonna take this one step at a time now then take the carb to a garage I know that deals with old cars a lot.

Edit: The pcv is on the passenger side and the breather is on drivers side. The hose from the breather goes into the back of the carb like my old setup, I think.

 

[oz]

I had some idle issues as well and some 'sucking of oil' into the carb through the PCV hose on my newly rebuilt and modified '69 302 so I got rid of the PCV all together. Instead I have a closed system breather (with a hose outlet) that goes directly to my carb from an earlier Mustang. The breather just had a tab inside that was punched to allow air to flow. I pinched it down to restrict air flow a bit. The valve cover on the other side has the (closed) oil cap in it. My idle is much more stable and I don't burn oil any more. I kind of figure the vacuum that is applied to the crank case keeps any blowby pressure from building up but does not allow mass quantities of oil vapor to get sucked in to the carb (like an open breather on the other side would).... It may not be a text book setup but it has worked for me so far.
I got all the parts at National Parts Depot so send me a PM if you're interested in part numbers, detail, etc...

 

[66bluepony]

Does your carb have a power valve, could be opening causing more fuel flow, what is the vaccum readings.

 

[Ramrod48]

just curious what kinda ( how much ) oil pressure you running ?, If the engines not fully broke in you will get a lil blow by till everything seats ., On a side note a buddy of mine just did his first rebuild , Thing had a shi##Y idle an kept pumping oil in the bottom of the oil breather , I kept telling him he broke some rings on the install for this to happen , He refused to buy that as the answer,After about 400 miles he pulled it back down, Guess what ??? 5 outta 8 pistons had broken rings !!!!!!