Lunati 60402 Cam Question

[cwestra]

are 5 & 8 tied into the runner that feeds the brake booster sometimes it is 6&7
anyway my guess is a leak into the brake booster , try plugging the hose & see if the cylinders respond better , could be a vacuum leak under the intake also .
On a dual plane intake 5&8 also 6&7 are fed by the same runner so you have a leak into those runners somewhere

It almost has to be something in that runner then.  On my car the brake booster does tap into 5 & 8 but I blocked it off and still did not see an improvement.  I also tried spraying carb cleaner along the point where the intake meets the head when it was running.  I did notice an increase in smoothness but it was not conclusive.  This morning I pulled the intake and will be replacing the gasket.  The ones that were on there appeared to have oil seepage into the gasket from the bottom.  I don't know if that suggests a bad seal or not.  Laying a straightedge across the intake surface shows that it is flat.

Would the casting roughness be enough to cause leaking?

Is there a sealer that I can or should use in addition to the gasket when I reinstall it or will just gasket be okay between the head and intake?

Is there anything else I should be checking for that could be the source of leak while I have it off?

[Chryco Psycho]

generally I use the Fel Pro gaskets & you shouldn't need sealer , Right stuff sealer is expensive but is the best sealer I have found . Oil seepage from the bottom is definatly a leak from below , I had a similar problem with a Ramcharger several years ago , I installed a 340 intake & 4 bbl on a 360 & it always used some oil , when I sold the truck I kept the intake & carb & re-installed the 2 bbl Holley , when I pulled the intake the gasket below a pair of runners had slid down & was allowing oil into the pair of runners , no wonder it always ran a bit rough 
 using a bead of sealer along the bottom edge of the gasket won't hurt , possibly the intake is planed a bit off angle & could be a loose fit at the bottom

[cwestra]

generally I use the Fel Pro gaskets & you shouldn't need sealer , Right stuff sealer is expensive but is the best sealer I have found . Oil seepage from the bottom is definatly a leak from below , I had a similar problem with a Ramcharger several years ago , I installed a 340 intake & 4 bbl on a 360 & it always used some oil , when I sold the truck I kept the intake & carb & re-installed the 2 bbl Holley , when I pulled the intake the gasket below a pair of runners had slid down & was allowing oil into the pair of runners , no wonder it always ran a bit rough 
 using a bead of sealer along the bottom edge of the gasket won't hurt , possibly the intake is planed a bit off angle & could be a loose fit at the bottom

Thanks.  I think that may be the case with mine too.  I just changed gaskets and still have the exact same problem.  Funny that it's 5 & 8 only though.  All other cylinders seem to be hitting fine.  I'm just wondering if maybe a crack in the manifold could cause it.  Or could it just not be getting fuel through those runners?

If I remove the manifold and add a bead of Permatex do you think I'd be able to re-use the gaskets?

[Chryco Psycho]

the gaskets are only hours old so I would think you could re-use them , sucks that the problem still exists after all that work , did you try to adjust the mixture screws in the base of the rear carb , , they should be about 1/2 - 3/4 of a turn out from bottomed out

[cwestra]

the gaskets are only hours old so I would think you could re-use them , sucks that the problem still exists after all that work , did you try to adjust the mixture screws in the base of the rear carb , , they should be about 1/2 - 3/4 of a turn out from bottomed out

Yeah, I know.  I was really hoping that would solve it.  I could try looking at the idle screws.  That's easy enough.  I know I've played around with them in the past but don't know how they were adjusted to.

The characteristics of the problem do seem to suggest the vacuum leak in the manifold, mainly by the link to 5 & 8 and the oil soaked gaskets.  I'll admit though, I was surprised when I found out that I was losing 2 cylinders at idle when I checked them by pulling plug wires.  I always used to be able to pick up on the sound of an engine missing (like when a plug wire is off).  Now I essentially have 2 cylinders not working and I wasn't able to pick up on it.

I suppose if it is vacuum related the problem should lessen as the throttle opens and manifold vacuum decreases, which is what seems to happen (although I think it should be even smoother than it is when I accelerate).  That might explain why it doesn't have the characteristic "miss" sound and feel when I accelerate.  But I suppose that could point to the idle mix screw adjustments, as well.  I'll have to try and eliminate that as a possibility.

Well, at least I feel like I'm getting closer to pinpointing the source, thanks to guys like you.

[cwestra]

the gaskets are only hours old so I would think you could re-use them , sucks that the problem still exists after all that work , did you try to adjust the mixture screws in the base of the rear carb , , they should be about 1/2 - 3/4 of a turn out from bottomed out

I just pulled the rear carb.  Adjusters are locked in tight, won't budge.  So I have no idea what they are set at.  The front ones I am able to adjust, so I swapped front and rear carbs with the front one (now in the rear) adjusted to 3/4 turns.  The missing problem is no longer on 5 & 8 but on 2 & 3.  It followed the carb.  So I am assuming the problem is in the idle circuit of the rear carb (now in the front). 

[Chryco Psycho]

Awesome ...sort of , at least you know where the problem is & do not have to pull the intake yet again , start soaking the mixture screws in Penetrating fluid & see if you can work them loose, probably go through the carb again as well

[cwestra]

Awesome ...sort of , at least you know where the problem is & do not have to pull the intake yet again , start soaking the mixture screws in Penetrating fluid & see if you can work them loose, probably go through the carb again as well

Yes.  You have to locate the problem before you can fix it.  Now I am at the "fix it" point.  I'll see if I can get the screws loose by soaking.  Thanks.