what would be your diagnosis?????

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Also, I notice your gauge bouncing a bit. There is a good vid on youtube about this but I can only find part of it. Try tracking this down.

[ame="https://www.youtube.com/watch?v=NrnzD7PgoHI"]How To Diagnose Common Engine Problems With A Vacuum Gauge - YouTube[/ame]
 
AJ/FormS said:
Ok, so, the intake is off we have to wait. I get that. I also get that you have been fairly systematic and thorough.This points to you either having a lot of help, or that you are fairly knowledgeable to start with.And you have tools.So my guess is you have been down this road a time or two already. And I know it can be frustrating to keep hearing the same thing post after post.
But here it comes again; since the carb is off, get after the T-port sync. It is so easy to do, you'll wonder why such a little thing could be such a big deal. If you need help with this, it's easy to explain, and every cam bigger than about 210@050 needs this addressed to some degree or another. Your cam is not that big, so a minor change can make a big improvement.

Ok, it's Sunday. Sunday is family day,but the kids were home last week, so, I got all day, and so, I'll just jump in here.

-Put the throttle control on the curb-idle stop, and keep it there making sure the choke mechanism cannot interfere. Flip it over,upside down. Get eyes on the transfer ports. They should appear as little square openings, to, in your case, perhaps a teensy bit taller than wide. Use the curb idle screw to make it so. Now, counting the turns, back out that same screw until the screw just comes off the stop, indicating that the primaries are fully closed. Eyeball them and prove it! Write that number down.
-Next, move to the secondary side. With the primaries still fully closed check to see that the secondaries are also fully closed, that the linkage is not holding it open. Then find the secondary cracking screw. Screw it out until the secondary throttle blades just barely stick to the borewalls.Then open them 3/4 turn.
-Now, flip it back right-side up, and turn the idle-speed screw back in the same number of turns that you previously backed it out (you did right it down, right?).
-Finally readjust the mixture screws to the base setting, which for Holley-types is 3/4 turn out, and for most others is 1.5 turns out.Now this is the really,really,really,important part. This is your baseline. If you get lost after this,return to the baseline.This is why you write stuff down;so you won't have to pull the carb off again.

And finally the quadruple-really important part; from here on you will not be touching the idle speed screw again.Unless I, or somebody smarter than me,(and there are lots of those guys) says so. You will be setting the idle speed with idle-air bypass (PCV leakage or secondary cracking screw), or idle timing;NOT with the idle speed screw.

When you get it back together,your target idlespeed will be 700 rpm.Your target idle timing will be 16* to 18*, +/- 2*. For a streeter I like the lower numbers, cuz I have an easier time tuning the Vacuum advance later. And a streeter quadruple-really needs the V-can working.
-If you cannot achieve the 700 in Neutral/Park, with the outlined method, something else is wrong. Either she is sucking air/fuel somewhere or the timing is out too lunch.
-Your mixture screws should now be working.If not, that's the very first thing I wanna know. Nothing moves forward until the mixture screws work and work best at between 1T and 2T.

To be continued; after you are up and running.
Click to expand...

I will look into this.
 
duster360 said:
Yes.
Click to expand...

Lol, it's good to check it multiple times, it's real easy to cross 5 and 7. I did it once and had a miss and was just at a loss. My buddy came over, looked at it for about 30 seconds and switched them around. Doh!
 
duster360 said:
Vacuum gauge shows 8 to 10 Hg.
Click to expand...



Nothing to write home about but I have seen worse......

A few questions.

Does the problem change from a cold motor to operating temps?

Does the miss get worse as it gets to operating temp?

You said not really smoking. Be specific. Yes or no to smoke and if yes put in your best words when it does smoke the load on the motor (accel, decel, etc?)

Does the motor fire right off or does it take a whole bunch of effort?

Based on what I am reading the oil contamination on the Valves is where my laser beam is pointing to right now but need more info....

JW
 
SLOPAR72 said:
Nothing to write home about but I have seen worse......

A few questions.

Does the problem change from a cold motor to operating temps?

Does the miss get worse as it gets to operating temp?

You said not really smoking. Be specific. Yes or no to smoke and if yes put in your best words when it does smoke the load on the motor (accel, decel, etc?)

Does the motor fire right off or does it take a whole bunch of effort?

Based on what I am reading the oil contamination on the Valves is where my laser beam is pointing to right now but need more info....

JW
Click to expand...

Engine runs the same cold or hot. Doesn't smoke. I saw a little something coming out the tailpipe once but it may have been some condensation. It disappeared within 4 inches of the pipe. Engine will fire right off. Even when it is hot I can reach in through the window, turn the key and it will fire immediately.
 
AJ/FormS said:
I have found that cams of this size, once the T-port sync is set and the timing is optimized,idle-vacuum comes up to where the PCV leakage actually helps with the idle-air bypass. SO FAR, in my experience,the "leaky" PCV can easily be compensated for with the secondary cracking screw. If however the PCV is directly sent into the intake,into the booster tap between runners 7 and 8, that makes trouble. The PCV has to be sent to the carb base for some semblance of reasonable mixture distribution.
As the OP describes the way his is working, is exactly the way I have experienced, and have always been able to make it work, SO FAR.And with any common sbm type 90* PCV. In fact, I use that PCV circuit to help establish the initial amount of secondary cracking, that I will dial in on the upside-down carb on my bench.
Now, I will say that on some combos, and without 4-corner idle,I have run into idle issues with the back running lean from the secondary cracking. And in those cases I sent a little air directly in through the primary plates. Nobody wants to hear that, but I do what I gotta do, to make the engine happy.Some guys compensate with excessive idle timing. That works, but for a streeter,IMO is a poor solution and causes other issues.
So, nm9, I'm not trying to minimize your experiences, only adding mine.

So how about that T-port sync?
Click to expand...
Roger all of that, AJ. It just bothers me to see the PCV used as an 'air compensation' mechanism. The are not calibrated, who who knows what will change hot to cold or when the PCV is changed. IMHO, get it out of the equation. Drilling holes in the throttle plates seems like a lot more stable solution. (And I don't like that either! LOL) As said, excess air leakage makes the idle mixture screws lose their authority....which looks to be a symptom set here.

And yes, on the secondary stop being set wrong and have the front or rear 4 cylinders' mixture off; we found that off the bat on my son's 340 with the Avenger 670.
 
duster360 said:
Engine runs the same cold or hot. Doesn't smoke. I saw a little something coming out the tailpipe once but it may have been some condensation. It disappeared within 4 inches of the pipe. Engine will fire right off. Even when it is hot I can reach in through the window, turn the key and it will fire immediately.
Click to expand...


Has anyone been behind you driving it to verify no smoke? You have oil around the valves.... That oil is ending up in the Combustion Chamber and will burn. Just trying to make sure I am asking the right questions.

If it fires right off no problem you can't be far off on timing....

JW
 
duster360 said:
1.They look like Teflon seals. They are white with the clamp around them. I will try and get a picture. I don't think he turned the guides. He just opened up the seat ( very little cutting ) to accommodate the spring cups. He did remove them to get in and cut the seats though. .
2. Have not adjusted the secondary screw yet. Have to get the intake reinstalled.
3. I haven't changed the PCV. It idles up when I remove the hose from the PCV and let it pull air freely.
Click to expand...
OK. You just need to work through the tuning adjustments (like 2 and 3 above) one at a time. There is likely a few contributors to the issue, and you have to cumulatively fix and adjust each one. And sometimes you need to go back and revisit something you have adjusted earlier after fixing other things; like the secondary stop screw. This is what tuning is about; it is often a lot of iteration.

My comment on the seals is based on that: they could be the wrong or marginal part; or being teflon, they have been known to not seal so well. My take is that the teflon is great versus hot valve stems but nothing special in the sealing department. There is a reason that the good old Viton seals keep on being used. (BTW, I used Teflons on a Ford once, they sealed fine in that case.)
 
duster360 said:
Even when it is hot I can reach in through the window, turn the key and it will fire immediately.
Click to expand...
The last is a good sign of a denect spark system. Having said that, and HEI will out-spark an MSD. MSD just uses a capacitive discharge system with a the feature of multiple firings at low RPM's. But the Blaster 2 coil you are using limits the charging current to about half of that in an HEI coil, and so the spark will consequently have less energy. This WILL make a difference in certain firing conditions; higher compression ratio will make the spark energy more critical to get a good spark kernal started.
 
Man. That video might as well have been shot under my hood this weekend. Idle. Vacuum gauge. You name it. My uncle had told me in the beginning of my diagnostic that I had to flop the carb and make previously mentioned adjustment so that I have idle air adjustment before tuning my engine. The other two guys that helped me from that point on called BS on that idea so the rest of my story goes a lot like yours. Took it to the track Saturday. Had the same bog under acceleration. Motor is 360. 284/292 hydraulic cam. 241/[email protected]. 11.1 compression. Installed at 104 with 108 LSA. Summit racing vacuum secondaries 750 carb. Other buddies kept telling me "you've never had a poppy cam before". It still shouldn't be idle that rough or behave that way. I didn't want to argue but my 440 has a similar 292 cam with a lot higher valve lift and does not act like it wants to jump out of my car. I am not familiar with Holley style carbs (q pukes, t quads, edelbrocks past cars). If I get to previously mentioned carb adjustment before you do I will post results. If you get this problem figured out please post what you had to do so I can try it on mine. Good luck and happy hotrodding
 
Looks like a case of carburetor-itis to me. Do you have access to a wideband air/fuel meter. Without a doubt one of the best tools for tracking down these kind of issues.
Another thing to try is checking the temp at the header pipe just off the head with an infrared thermometer gun. Will give you an indication if the cylinder is working properly. Cold pipe = dead hole.
 
If you run a PCV, and most streeters should, I think one doesn't have a choice but to treat it as a controlled leak. As long as it the engine has enough vacuum to properly seat the valve in its minimum position, you are good to go.And I've never had a problem with one on cams of 250* or less, and typical street cams like this, even down to 600 or sometimes 500 rpm, with the vacuum falling to 8 or 7 on my gauge. But then I typically tune that area a little fat, for easy cold light off.Now I know that can cause issues with hot starts, in hot weather; but up here in igloo-country we only have a few summer days where the temp might crack 90*F. Mostly we are in the high 70s/low 80s.So for us, a hair fat is where it's at.
I know some fellows have mentioned problems with PCVs but I just have never seen it..
Even my personal engine with a 230@050,and a 750DP, will pull itself on hard ground, down to 600/500, with a starter gear of 11/1(4-spd). It will be pretty smooth right until it pukes, or I pedal the clutch.This tells me that the 50 year old PCV, and the 17 year old power valve, are functioning near perfect. At this time, just before stall, I can vary the timing plus or minus 7 degrees, from the cab, with my dash-mounted,dial-back,adjustable timing tool, and the engine doesn't seem to care too much about it.It often responds to a little retard from the 14 or 16 initial I might be running.I have had to conclude, that my engine might even like more air as the rpm drops, perhaps in response to a power valve that may be starting to open.I really have a hard time imagining the PV circuit dribbling at such a low rpm/airflow. IDK. And mostly I don't care, cuz it is still pulling. And smoothly.And she rarely gets into this situation.
I think if a guy listens real hard to his street engine, he can probably get to 80/90% pretty quick. But that last stretch seems to take forever. I don't mind her being a little fat on the low-speed circuits.She doesn't do long hauls anymore, and I have a 600 for that, if I ever need it again.
So IDK. For me PCVs are a non-issue. I just plug one in and never think about it again. Well except for one thing; those cheap plastic bodied ones are prone to break after a few tugs.And you know how they run then.I try to stay away from those.
I also stay away from plastic or glass fuel filters,rubber fuel lines,used gearclamps,KnN filters,sealed beam headlamps, electric fans,cork gaskets, cigarettes, alcohol, beaches, and bars.WhadImiss? Oh yeah; trouble!
 
Classic intake manifold vacuum leak symptoms. Low manifold vacuum at idle. Oil in the intake ports. Rough idle. Hesitation. The intake is not sealing on the bottom sides of the ports. It's sucking engine oil into the ports. There's your proof. Check the angle between the intake and heads. You will likely find a mismatch.
 
^^^ What he said. Before you bolt that intake on, measure the head and intake flange angles with a digital protractor. A few tenths of a degree can cause a leak.
 
WA71swinger said:
Man. That video might as well have been shot under my hood this weekend. Idle. Vacuum gauge. You name it. My uncle had told me in the beginning of my diagnostic that I had to flop the carb and make previously mentioned adjustment so that I have idle air adjustment before tuning my engine. The other two guys that helped me from that point on called BS on that idea so the rest of my story goes a lot like yours. Took it to the track Saturday. Had the same bog under acceleration. Motor is 360. 284/292 hydraulic cam. 241/[email protected]. 11.1 compression. Installed at 104 with 108 LSA. Summit racing vacuum secondaries 750 carb. Other buddies kept telling me "you've never had a poppy cam before". It still shouldn't be idle that rough or behave that way. I didn't want to argue but my 440 has a similar 292 cam with a lot higher valve lift and does not act like it wants to jump out of my car. I am not familiar with Holley style carbs (q pukes, t quads, edelbrocks past cars). If I get to previously mentioned carb adjustment before you do I will post results. If you get this problem figured out please post what you had to do so I can try it on mine. Good luck and happy hotrodding
Click to expand...

Will do.
 
RustyRatRod said:
Classic intake manifold vacuum leak symptoms. Low manifold vacuum at idle. Oil in the intake ports. Rough idle. Hesitation. The intake is not sealing on the bottom sides of the ports. It's sucking engine oil into the ports. There's your proof. Check the angle between the intake and heads. You will likely find a mismatch.
Click to expand...

Intake was machined to fit because of the block being decked. Last time I checked the intake it had a .005" taper top to bottom. The bottom being tighter than the top. But I have it off again at the moment so I could check other things in the engine. Since it is off I will be looking at it again before reinstall.
 
If it turns out to be intake issue, I resolved a similar issue by removing the heads, bolting intake to the heads, with proper gaskets, checking angle between heads and bottom of intake. compare to the deck surface and the china walls. You will get a good indication of clearance.
 
duster360 said:
I take was machined to fit because of the block being decked. Last time I checked the intake it had a .005" taper top to bottom. The bottom being tighter than the top. But I have it off again at the moment so I could check other things in the engine. Since it is off I will be looking at it again before reinstall.
Click to expand...

Pretend for a moment, that either you have not done it, or possibly measure incorrectly. It's not difficult to make a mistake there. I would double and triple check those angles, especially since the intake is off. It sounds to me like that's where the trouble is.

Also, which intake gaskets are you using?
 
I have used the Edelbrock gaskets and the Felpro printo-seal. I will definitely be checking it again just to be sure.
 
duster360 said:
I have used the Edelbrock gaskets and the Felpro printo-seal. I will definitely be checking it again just to be sure.
Click to expand...

They are Edelbrock heads, right? Do they recommend a particular intake gasket, I wonder? Would not hurt to check into that as well.

Try to cover all your bases, cause you don't want to do it again......and I know you want the thAng fixed. lol
 
RustyRatRod said:
They are Edelbrock heads, right? Do they recommend a particular intake gasket, I wonder? Would not hurt to check into that as well.

Try to cover all your bases, cause you don't want to do it again......and I know you want the thAng fixed. lol
Click to expand...

Oil in the ports...... It is a vacuum cleaner sucking oil into that port..... So when I was fresh out of highschool and had a problem similar to yours I watched a man who passed 20 years ago that was a Cylinder Specialist for a big Nascar engine builder use Cash Register Receipt paper to verify an intake was sealed for me..... I use this method today for Maintenance in Manufacturing in many applications....

My point to that story is an idea so simple and yet made everyone who thought they had the solution just look like dunce hat wearers lol....

Make sure the intake is sealed..... I can't stress that enough...

JW
 
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