carfreak6970
Well-Known Member
Hello,
So I inherited a 70 charger that I have been having some issues with and have posted about this car a couple times here on the forum. It is a 440 HP out of a 68 New yorker, with the 727 auto and an 8 ¾ rear end. I know the engine was bored, block decked, heads shaved, running XE274H-10 cam with the cast iron heads, cast iron four barrel intake, stock exhaust manifolds and a holley 750 cfm vacuum secondaries carb I got 3 years ago new.
While running the initial at 12 btdc I am only pulling 11-10 inHg at idle in gear. When I started down the path of trying to dial in the carb in This Thread I started to think something else may be causing some of my issues. It is even stated in that thread that the vacuum I am experiencing seems kind of low. I wouldnt know but I dont have much experience with non-stock engines. My issue is that cold start is beyond miserable. I set the choke (automatic) and start it and initially it starts right up fine, goes to about 1400-1600 rpms but then the engine rpms drop and it starts to smoke out the tail pipes. It will continue to stumble before it eventually dies. In order to get it past this issue you have to hold the throttle open more than the fast idle allows it to get it through this stumbling issue before the engine starts to smooth out and fast idle fine.
Now I attached a vacuum gauge to manifold vacuum during these episodes and during initial start up vacuum is as high as 15 inHg then drops to 8-5 inHg while stumbling and smoking. Once it gets past the stumbling vacuum goes back up to where it was and a little higher. Another test I ran is I increased how long the choke stays closed and stays on the fast idle cam. Once it gets past the stumbling the rpms increase to well over 2000 rpms. I verified that the fast idle cam did not move between the initial start and once it got past the stumbling.
My question is why is it doing this? I have a theory and would like your opinion on whether I am on the right path and how to check this out:
When installing the intake it was always a ***** to get all the bolt holes to line up. To the point that you can see where the bolts deformed the valley pan at the intake ports due to the bolts contacting where I believe they shouldnt be. I am only running the valley pan as a gasket because putting that other gasket material below and on the top of the valley pan just added more frustration. My theory is that when the block was decked and the heads shaved it moved that head/block mating surface lower and close together which almost moved the head to intake mating surface lower and closer together to the point that the intake isnt sitting where it should causing a vacuum leak there. I am guessing this vacuum leak is present when the engine is closed and mostly sealed up once the engine gets some heat to it. I do not know how much was shaved or decked, but I did need to get shorter pushrods. Now I tried to do the propane test (spraying propane around there to see if the rpms increased), but I did not get any increase in rpms. The plugs always looked very white and dont have a hint of tan or black on them which makes me think it is running a little lean, which would make sense if there is a vacuum leak.
Does any of this make sense? Is this something that could happen? there has to be some information out there that mentions the dimensions that the intake needs to be to fit on the engine, which would mean there would have to be something out there that says where the intake ports should be positioned on the engine in order to properly mate up with the intake. Is there a way to check that out? I guess I should mention that the engine the car was initially in was in a fire. Hot enough to melt the carb, but according the machine shop not enough to distort the engine. The machine shop did have the heads and block, but I can not say for certain if they had the intake.
Thank you for the help
So I inherited a 70 charger that I have been having some issues with and have posted about this car a couple times here on the forum. It is a 440 HP out of a 68 New yorker, with the 727 auto and an 8 ¾ rear end. I know the engine was bored, block decked, heads shaved, running XE274H-10 cam with the cast iron heads, cast iron four barrel intake, stock exhaust manifolds and a holley 750 cfm vacuum secondaries carb I got 3 years ago new.
While running the initial at 12 btdc I am only pulling 11-10 inHg at idle in gear. When I started down the path of trying to dial in the carb in This Thread I started to think something else may be causing some of my issues. It is even stated in that thread that the vacuum I am experiencing seems kind of low. I wouldnt know but I dont have much experience with non-stock engines. My issue is that cold start is beyond miserable. I set the choke (automatic) and start it and initially it starts right up fine, goes to about 1400-1600 rpms but then the engine rpms drop and it starts to smoke out the tail pipes. It will continue to stumble before it eventually dies. In order to get it past this issue you have to hold the throttle open more than the fast idle allows it to get it through this stumbling issue before the engine starts to smooth out and fast idle fine.
Now I attached a vacuum gauge to manifold vacuum during these episodes and during initial start up vacuum is as high as 15 inHg then drops to 8-5 inHg while stumbling and smoking. Once it gets past the stumbling vacuum goes back up to where it was and a little higher. Another test I ran is I increased how long the choke stays closed and stays on the fast idle cam. Once it gets past the stumbling the rpms increase to well over 2000 rpms. I verified that the fast idle cam did not move between the initial start and once it got past the stumbling.
My question is why is it doing this? I have a theory and would like your opinion on whether I am on the right path and how to check this out:
When installing the intake it was always a ***** to get all the bolt holes to line up. To the point that you can see where the bolts deformed the valley pan at the intake ports due to the bolts contacting where I believe they shouldnt be. I am only running the valley pan as a gasket because putting that other gasket material below and on the top of the valley pan just added more frustration. My theory is that when the block was decked and the heads shaved it moved that head/block mating surface lower and close together which almost moved the head to intake mating surface lower and closer together to the point that the intake isnt sitting where it should causing a vacuum leak there. I am guessing this vacuum leak is present when the engine is closed and mostly sealed up once the engine gets some heat to it. I do not know how much was shaved or decked, but I did need to get shorter pushrods. Now I tried to do the propane test (spraying propane around there to see if the rpms increased), but I did not get any increase in rpms. The plugs always looked very white and dont have a hint of tan or black on them which makes me think it is running a little lean, which would make sense if there is a vacuum leak.
Does any of this make sense? Is this something that could happen? there has to be some information out there that mentions the dimensions that the intake needs to be to fit on the engine, which would mean there would have to be something out there that says where the intake ports should be positioned on the engine in order to properly mate up with the intake. Is there a way to check that out? I guess I should mention that the engine the car was initially in was in a fire. Hot enough to melt the carb, but according the machine shop not enough to distort the engine. The machine shop did have the heads and block, but I can not say for certain if they had the intake.
Thank you for the help
