OK, I replaced the suspect plug extender. And every other extender on that bank, just in case one was cracked... Also put new plugs in. And just to make sure, I put a new set of plug wires on. IT'S STILL POPPING THROUGH THE REAR BANK! I am changing out the mains to 135's, just out of curiosity. I have to emphasize that it was not popping like this before the belt service and it was running 125's then. (and yes, for those joining us late that may not have read the beginning of the thread, I am ABSOLUTELY sure that the cam didn't slip a tooth.) I am at a loss at this point....
Gas formulations change not only over years, but season to season. As summer came and ambient temps went up, and summer gas was at the pumps, it unmasked a borderline lean condition from the emissions friendly 125 mains. I feel that you have been very thorough looking into other causes, and the 135 mains will improve the cars running across the board compared to the 125 mains, as suggested in Post #2 in this thread. Good luck!
SNJ- I'll give it a shot. I've got the jets soaking right now, (they are a little stiff and difficult to get out of the tubes...) One thing though, doesn't it seem odd that it is only one bank and all banks are running the same jets? By the way, I thought it was 125's with 220 air correctors, but in fact it was 125's and 200 air correctors...
Now running 135 mains and 200 air correctors; still popping :-( Looks like I'll be starting at square 1 again tomorrow... I hate to do it, but I think I'll swap distributors, front to back, and see what that does. Otherwise, I am once again, out of ideas....
You seem to have beaten the old it's not the carb it's the ignition question to death. So, have you checked for a restriction in the fuel supply/lines distribution block(s) for the back of engine? I don't have a carbed 308 but how is the fuel pump and filter, any weakness there starving the rear carbs and letting foat levels drop? Wierd weber stuff I have encountered: slightly loose needle and seat assembly, floats that stick in the float bowl when the carb empties, float levels that aren't exactly right so the carb circuits don't enguage at the same time, missing or damaged orings for various adjustment needles. A few more igintion thoughts: bad powersupply to the rear bank ignition system only at full throttle...is some sort of ignition timeing emission control device acting up? Faulty or weak grounds to engine block ignition system? Ok, done guessing. PB
Carb's still sync'ed Float height checked and good... Fuel filter replaced... I don't think it is a restriction in the fuel line just because if the rear bank wasn't getting fuel, then half of the front bank wouldn't either, just by the way the fuel line is routed. It does seem like an awful lot like fuel starvation though, just by the way it comes on: Perfectly smooth on easy accel. Then with mid range rpm and increased rate of acceleration it pops on both rear carbs, like suddenly it's running out of gas and going lean... The float height would have made sense, but it checked good. Also cleaned out the needle and seat while I was in there, and it seemed fine... Still out of ideas.... New development though... Idle mixture screws on rear bank have zero effect. all the way in and no rough running or decrease in rpm, runs the same ????
i wondered about this, reading a way back when you mentioned that the idle mix screws were turned way out (or in), i cant remember. Pull the idle mix screws AND the idle jets, and blow compressed air thru the whole circuit at the carb body (air in thru the idle jet hole and thru the idle mixture screw hole - they are connected) . then blow air thru the idle jets. put back to gether, start at 3.5 turns out on the mix screws.
I would also set your overall idle rpm at 850, then the idle mixture will have more of a presence in the circuit.
This definitely was a problem, but only was affecting the starting circuit... (by the way, I think I now have a fairly firm grasp on normal, starting, idle and progression circuits; the workshop manual does a great explanation of the pathways of the carb...) OK so that was paraphrased, but thanks for your post. It got me to do exactly that. I feel like an idiot and I'm still not sure how I did it even while I am looking at it. In fact, the set up still looks right, but there is no doubt that the rear bank IS TIMED 90deg OUT!! I set up the rear distributor by taking the flywheel marks to 3deg ATDC and verifying that the cam marks were aligned on the journals (so as not to go 180 out). Then I rotated the distributor shaft to align the rotor with the number one wire position from the cap. This was my rough setting until I could start and then set by timing light.... Well, of course I marked PM1-4, 3deg above, 7 below the EXACT SAME WAY I marked PM5-8, 3deg above, 7 below. So when I timed it, the back cylinders where timed for the marks for the front cylinders. The only reason I noticed was that while I was re-setting this up (thanks again Artvonne) , I decided to mark one set of markings "F" for front and the other "B" for back. Low and behold, when I timed it out, both were perfectly timed for the front bank settings.... So my question is this. Rather than follow the procedure ( at least I think I was reading it right) should I just pull the distributor and back the shaft up a couple of notches in the gears until I can time it to the correct settings? Are you supposed to lead the rotor a few degrees before the #1 wire terminal? Or is there something else wrong inside the distributor? Or am I just an idiot? Probably all of the above would be correct...
Yeah, I aren't tat brite... We'll after I finally figured out where to start with the distributor set up (see pic below) everything went fine. To me, it still looks like it is off on the initial setting (a little more than half way between the bottom two bolt holes for the distributor cap). It seems like it would be well past where the lead for the #1 wire is located.... OH WELL, IF THAT'S WHAT WORKS DON'T ARGUE. Anyhow, It runs great now. No popping (except a little burble from the exhaust on decel, probably from jetting up on the carbs (135). I took it back down to 130 to see how that does. I guess I'll HAVE to go for another test run an pull the plugs to see how the 130's are running. Darn. The sound of this engine is absolutely amazing! Now all the frustration of the last 4 weeks is paying off! So let's recap what I did wrong: Didn't do the initial timing on the rear distributor correctly... Didn't match the rebuild kit gasket with the old gasket... Tried to run the engine with a bad plug extender... And was running the throttle plate too open at idle (to make up for the bad timing)--this is what caused my idle screws to not work. (it was already open to the idle progression holes.... A friend once told me "Life is hard. It's harder when you're stupid..." Image Unavailable, Please Login
They ARE amazing once they are correctly set up....congratulations, my 308 brudda! Signed, Not a carb guru, but I knew one once.......
