Issues after cam swap
Thread Starter
Racer
Joined: Mar 2007
Posts: 377
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From: Holmen Wisconsin
Issues after cam swap
I just got done with a cam swap in my 80. I am having some low rpm driveability issues. The car has an Edelbrock 650 carb that I just put the rods back to "stock" on to see if that was the issues. The car wants to chug or sputter a little when taking off. My brother and I set the timing today and that is set at 36 all in, just like I had it before. The only other thing I did besides the cam swap was to shim the distributor to .010-.011. Any ideas, or should I keep playing with the carb to try and iron things out?
Here is the cam and I am running the Summit heads with Comp 981 springs.
http://www.summitracing.com/parts/CCA-12-238-2/
Here is the cam and I am running the Summit heads with Comp 981 springs.
http://www.summitracing.com/parts/CCA-12-238-2/
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
If this is right after the cam swap, the very first thing to do is double, double check the firing order. Sounds simple, but run each wire all the way just to make sure something didn't get swapped around.
Thread Starter
Racer
Joined: Mar 2007
Posts: 377
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From: Holmen Wisconsin
Just checked the wires and they are correct. This was my first time adjusting valves and I used my service manual as a guide and it seems fine at WOT. I couldn't have gotten a rocker arm too tight? I did 1 turn from zero lash. I'm just trying to think of everything.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
Good job on running them down - seems like make-work, but it's an issue more often than not.
The next two obvious issues are a vacuum leak - usually at the front or back of the intake and yes...the valve adjustment.
Vaccum leaks can be found by spraying a LITTLE carb cleaner or starting fluid around the edges of the intake. If you get an increase in RPM...check more closely in those spots.
For the valve adjustment, key issues are positioning the engine and finding zero lash...are you 100% comfortable that those two were right? How exactly did you do it?
The next two obvious issues are a vacuum leak - usually at the front or back of the intake and yes...the valve adjustment.
Vaccum leaks can be found by spraying a LITTLE carb cleaner or starting fluid around the edges of the intake. If you get an increase in RPM...check more closely in those spots.
For the valve adjustment, key issues are positioning the engine and finding zero lash...are you 100% comfortable that those two were right? How exactly did you do it?
Thread Starter
Racer
Joined: Mar 2007
Posts: 377
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From: Holmen Wisconsin
After the cam swap I took it for a run and when I got back I had a lot of oil on the back of the motor and thought it was coming from the distributor because the clamp was not in the right spot. Tried that with no luck and then replaced the gasket with the same result. So, pulled the intake and replaced the gasket again. Now, no more oil leak, but now I have the other issue stated above. I have done the intake on my car two other times with no issues.
As far as valve adjustment, I followed the book. I had the timing cover off for this and had the dot straight up for TDC and dot to dot for #6 at TDC. I really got a feel for the zero lash after the first few. I feel pretty good about it.
I did not notice the issue I'm asking about after the cam swap initally. This started (as far as I know) after the second intake gasket and shimming the distributor.
I will check for a Vaccum leak tomorrow. That made me want to add that my idle seems a little eratic. I know with the 110 LSA I will not have a smooth idle, but it seems to jump up and down a few hunderd RPM. I really hope I don't have to do the intake a third time, but I do want the issue resolved.
As far as valve adjustment, I followed the book. I had the timing cover off for this and had the dot straight up for TDC and dot to dot for #6 at TDC. I really got a feel for the zero lash after the first few. I feel pretty good about it.
I did not notice the issue I'm asking about after the cam swap initally. This started (as far as I know) after the second intake gasket and shimming the distributor.
I will check for a Vaccum leak tomorrow. That made me want to add that my idle seems a little eratic. I know with the 110 LSA I will not have a smooth idle, but it seems to jump up and down a few hunderd RPM. I really hope I don't have to do the intake a third time, but I do want the issue resolved.
Last edited by Camss57; Jun 6, 2012 at 11:14 PM. Reason: More info...
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
I just had a brand new Holley 650 vac secondary do the stutter , ya go to take off and it falls flat then kicks in and your off . On the one I dealt with the acceleration pump linkage was binding , it would stick applied so it never worked after the first use !!
Let me tell ya it was not easy to spot and what made it even harder was it was a new in the box carb ,, which made me not even suspect it matter of fact being new made me think the carb could NOT be our issue, Check yours out ..
Let me tell ya it was not easy to spot and what made it even harder was it was a new in the box carb ,, which made me not even suspect it matter of fact being new made me think the carb could NOT be our issue, Check yours out ..
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
If you're using the cam valley gaskets at the front and back of the intake, they virtually always press out and leak. Don't use the gaskets, just a bead of RTV.
"The book" can mean different things to different people. If you were using the companion cylinder method (http://forums.corvetteforum.com/1580029245-post6.html) then keep in mind that when the timing marks are aligned with the cam pin at 3:00 and the crank key at 2:00 the engine is at TDC compression #6, not #1.
My gut says huge vacuum leak at the front or back of the intake due to the rubber gaskets pushing out.
"The book" can mean different things to different people. If you were using the companion cylinder method (http://forums.corvetteforum.com/1580029245-post6.html) then keep in mind that when the timing marks are aligned with the cam pin at 3:00 and the crank key at 2:00 the engine is at TDC compression #6, not #1.
My gut says huge vacuum leak at the front or back of the intake due to the rubber gaskets pushing out.
Race Director
Joined: May 2005
Posts: 10,674
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From: Millington Illinois
St. Jude Donor '08-'09
Intake gasket leaking at the front or rear valley will not cause a vacuum leak, just an oil leak. Intake gasket leaking at either side will cause the issues you are having. Since it didn't do it after the first install but did after the second I think you will be doing it a third time. Should be getting pretty good at it by now.
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Burning Brakes
Joined: May 2009
Posts: 1,232
Likes: 6
From: Tucson AZ
St. Jude Donor '12
I've had a similar problem. Richening the carb idle circuit cured most of it, increasing the idle rpms a little helped too.
Start out with it idling a little too rich and work back from there.
Start out with it idling a little too rich and work back from there.
Melting Slicks
Joined: Jun 2002
Posts: 2,844
Likes: 99
From: Orrtanna Pa.
If it didn't have the idle issue initially,..I'd pull the valve covers and recheck the lash. One cam lobe going south would cause the idle issue.
My first Comp Cam XE-274 lasted less than a month before I pulled the engine to replace the cam.
My first Comp Cam XE-274 lasted less than a month before I pulled the engine to replace the cam.
Le Mans Master
Joined: Aug 2010
Posts: 9,272
Likes: 17
Intake gasket leaking at the front or rear valley will not cause a vacuum leak, just an oil leak. Intake gasket leaking at either side will cause the issues you are having. Since it didn't do it after the first install but did after the second I think you will be doing it a third time. Should be getting pretty good at it by now.
Burning Brakes
Joined: Dec 2008
Posts: 971
Likes: 45
From: Middlesex NJ
I went to summits site and read the instructions for your cam it says to go 0 lash then go 1/2 turn.
http://static.summitracing.com/globa...a-12-238-2.pdf
You may have some tight valves depending on what lifters you used. I have pro-magnums and you can only go 0 lash on them.
http://static.summitracing.com/globa...a-12-238-2.pdf
You may have some tight valves depending on what lifters you used. I have pro-magnums and you can only go 0 lash on them.
Race Director
Joined: May 2005
Posts: 10,674
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From: Millington Illinois
St. Jude Donor '08-'09
Le Mans Master
Joined: Jun 2004
Posts: 6,231
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From: Seattle WA
St. Jude Donor '14
...but if this all happened after the 2nd intake R&R, then that would seem to be the place to focus on and not touch anything else.
Thread Starter
Racer
Joined: Mar 2007
Posts: 377
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From: Holmen Wisconsin
Alright, just sprayed carb spray all around the manifold and no RPM changes. I'm gonna take it around the block again and see how it acts.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
