Anybody ever remove these? Anybody NEED to remove these to clean blockages? Actually find debris, etc obstructing passage? The 308's are definitely classic now that this is a concern Thanks!
I had to remove a couple of plugs because of leakage. I did not see any debris or corrosion in the passage. Good design practice would be to make the passages much larger than needed for flow purposes so that some blockage in the passages could be accommodated and would have minimal impact on fluid flow. Metering is accomplished with precision brass fittings. Bill
Thank you. Did your car sit for an extended period? My car was stored for a while and now I have this carb problem.
2dinos, I replaced a couple of lead plugs on my OEM 40DCNF72-75 carb set. My GTS had an unknown history and did a lot of sitting for my first 3-years of ownership. I later replaced all the carbs with new 40DCNF 45-48 carbs because the overall condition of the OEM carbs was suspect and at least one mixture screw/thread was loose/leaking/damaged. VIZSLA, IIRC, extraction of a couple of lead plugs was performed after a failed attempt to restake and seal the leaking lead plugs. I just used a punch and small ball peen hammer and while it worked on one, it did not work on a couple of other lead plugs. I was afraid to hammer the lead slug too far into the passage as I didn't want a piece to break off or obstruct a side drilling if one happened to be just out of sight. It was not clear what the geometry of the punch tip should be, but I used a flat punch tip. Perhaps a pointed center punch would be better as it would tend to spread the plug and seal against the ID of the drilling. The OEM shape seems to be convex, so the punch tip was likely concave. The other issue was the availability of lead plugs. I first attempted to buy some lead shotgun shot, but was not knowledgeable enough to specify the size. Eventually, I settled for a short length of solid solder. I think this is probably not a real difficult job if new plugs are used and the drilling is clean. I really didn't want to experiment too much at the time, so made an attempt that was partly successful, but eventually replaced the carbs with some of the last new ones available. The new carbs also had what I thought were a couple of leaker plugs, I did a little hammering on these an they seemed to seal. A little sealant on a new plug, stake with a punch and hammer, would likely be the way to go. In the old days it was possible to purchase Weber service tools. In fact, about 10-years ago I had a chance to purchase a complete set from a Weber R&D branch in Detroit. I balked at the $1500 asking price and they disappeared. In any event, it was once possible to purchase the correct peening punch, passage scrappers, jet seat renewal tools, shaft pullers, brushes, and a host of other tools for which there is now no known source. If anyone has some vintage Weber tools available, please let me know. Bill
Some use shotgun shell led balls and I believe there is a post of a modified punch to stake the new plugs. I have also seen the use of an epoxy over the leaking plugs which will seal them up.
Hi Bill, Yes!! Many thanks for the great input. I hessitate to remove these unless absolutely necessary. I have a carb issue with the idle circuit not flowing properly unless huge (like ~72) idle jets are used on one of the carbs, and I can't explain it with air leaks etc. I even repacked the throttle shaft bearings with grease going after the ity bitsy air leaks, and it still wants those large idle jets. Someone mentioned the fuel formulations now need larger jets, but the other cylinders are doing ok. My logic is: IF the passage were obstructed,,,,, why would it allow enough fuel to satisfy the 72 jets? So therefore, the passage is not obstructed. The plug removal is kind of a last ditch effort. BTW - I'm considering new carbs as the frustration continues. Again - thanks. How we love them so
2dinos, It may be you have an obstruction somewhere in the idle circuits on the one carb but before I tore it apart I'd try a few more things. Do both barrels of the single carb act the same, in that they both want a 72 idle jet? It seems unlikely that two idle circuits on one carb would be obstructed but it is possible. Check the all the progression holes on the affected carb. If there has been misfiring on the carb it's possible that one or more of the progression holes have plugged up with carbon/coke. The progression holes pretty fine so it doesn't take too much of a deposite. I found two progression holes clogged on one barrel and one hole clogged on the adjacent barrel of one of my carbs. The carb must be on the bench to really check this as it requires opening the throttle plate fully and probing the individual holes with a straight pin held in a pair of straight forceps. One gently feels for the hole and carefully works the point of the pin into the center of it. The carbon feels relatively hard and brittle but will fracture and can be pushed out of the hole with out damaging the base metal. On the bench check the holes and work them clean of necessary without taking anything apart. Failure to set the mixture can be caused by insufficient air flow. If in doubt, increase the air flow using the appropriate linkage adjustment(s) and try again. Where are your interbarrel balance screws set? At least one should be closed. If both are open too much, air will bypass the throttle plate, vacuum will drop, and the idle circuit will not function. What do the spark plugs look like on the affected cylinders. Are the plugs firing? Plugs can foul do to too much or too little fuel or an ignition fault. Stock idle jet size on my /72-/75 carbs was a 55, probably a little lean even in the day. When I changed over to a new set of /45-/48 carbs I tried the same 55 idle jet. I eventually came to the conclusion that it was too lean for today's gas and went to 57's. Better, but still got an occasional lean misfire at light throttle cruise. Changed to 60 idles, good throughout the range, but some minor back firing during shifting. I think I need something like a 58-59 idle jet to be just right. I'll have to ream up a couple of smaller idle jets to get to where I want to be, but I have to do a test to see how uniform the 55-60 idle jets actually flow. I have a burette and will time how long it takes to flow say 10 cc's of distilled water through each of a population of 55, 57, and 60 jets. Then I'll ream a set of 55's (they are too lean) to a flow value between the 57 and 60 idle jets. Reamers are still available but I've never actually done this before. The only way to evaluate how well they flow is to test them under controlled conditions. Steve, A dab of sealant on the lead plugs probably does no harm and my actually work. There is really no pressure in the drilled passages as flow is driven by vacuum. Liquid fuel pressure ceases at the float inlet valve. After that, the only positive pressure is due to liquid height (head) in the bowl and of course the pump jet action. Leakage at a plug may cause additional air to be mixed with the fluid in that passage during running and weep liquid fuel when not running. Bill
2dinos, You wrote, "My logic is: IF the passage were obstructed,,,,, why would it allow enough fuel to satisfy the 72 jets? So therefore, the passage is not obstructed." Fluid in the idle/progression circuit is an emulsion of liquid gas and entrained air. A larger idle jet allows relatively more liquid gas than air, a richer mixture if you will. If the passage is not be fully blocked, the mixture coming out of the progression holes will be richer and will mix with the air flowing past the throttle plate to support combustion. Blockage to some extent can be compensated with a richer emulsion. One other thing to check is the position of the throttle plate relative to the first progression hole in the pattern (not the single hole farther down the bore and corresponding to the needle valve). The throttle plate should be just about ready to uncover the first progression hole when the throttle is fully closed. I had a 40 DCOE carb with a progression hole that was drilled slightly off by the factory. The fix in this case was to file a relief in the edge of the throttle plate, about half way through its thickness. This notch established the necessary hole to edge of throttle plate geometry and the manufacturing issue was never again an operational issue. Bill
Thanks again! So I have not tried opening up the butterfly to see if exposing more of the progression holes will help fatten it up. I'm getting pretty confounded by this. I pulled two lead plugs exposing the two channels between the main jet well and idle jet. They are clean as can be (so that was as I feared - a big waste of effort and factory Weber plugs). But I know now that isn't the problem. I'm using a nice gas analyzer looking at cylinder sampling tubes. I see thru the roof HC, with 0 CO. The engine confirms this by running terrible. If I install the ~72 jets, I can adjust the mixrure screws in the ~3 turn out range w great resolution, and the motor runs correspondingly better. OR, I can crack the 55 jets off of there seats, and use the idle jet holder as a "coarse" adjustment on idle mixture. Something is still screwed up here. Again, when I have the mixture dialed, it idles like a watch, and gas readings are right in-spec. But I'm not happy knowing I need to be 4 to 5 sizes up on idle jets for this carb. BTW - I raised the float ~1mm just to see, and it made very little improvement - if any.
I didn't see what position the offending carb is. Any chance it is by the brake vacuum fitting and has a big vacuum leak from that? Or any of the smaller vacuum ports in the manfolds? Still if you have x air flow measured from all throats and such a disparity in mixtures it shouldn't be caused by that. Any chance someone modified a carb? Redrilled progression ports?
