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New Webers - Adj Help Needed
I've recently installed my Webers and have some questions that I am sure some of you can answer after having done a few yourself.
First - Can they be correctly tuned w/o the Velocity stacks installed? 2) Does it matter if you adjust the Air Vacuum first or the Idle Mix screws first? Does one have to be done before the other? 3) When adjusting the Mix Screws starting w/ a baseline of 2 turns Out. Do you have to start w/ Cylinder #1 and work through the Cylinders per #1-6 (I dont mean firing order) Once they are set to the 2 turns out and you begin Adjusting while having an Assistant hold the throttle at 1200 - Do you turn them IN until the RPM changes and then instantly back them out 1/2 turn from that point? Then move on to the Next? 4) Air Corrector Screws - I had set the linkages the best I could w/ No play and they are opening the plates as they should - 1/2 way. My STE read a little above 5 on Each Barrel, however in order to get the #6 cyl there the Air Corrector screw was Bottomed out while the rest were turned out, some much more than others. Is this NORMAL? If anyone is very familiar with the adj procedure would it be possible to call and talk in more detail..? You can pm w/ your phone, I would Greatly Appreciate it.. Thanks! Mitch |
There is an excellent, step-by-step Weber tuning post on Rennlist - but you may need to become a registered user to search for it there. I'm sure there is something similar here.
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1. Yes, it's easier too.
2. Air first, mix 2nd 3. Doesn't matter. One method is to get one of them tuned and then turn the others blindly by the exact same amount. Yes, that's about right with the procedure. Instantly shouldn't be a word used when tuning carbs though. Take it slow. Grab yourself a case of beers. Turn the screws by small amounts and wait a few seconds each time. 4. I'm not sure about this one but you shouldn't have big differences like this. - Are your carbs clean? There could be dirty passages that block air on the bad barrels. - Are your screws in similar condition? Maybe some of them are damaged? - Make sure none of the air inlets on the carb cover are blocked by the carb cover to stacks assembly gasket. Some of these are not perfect fits. Before you adjust your carbs you need to be sure that the rest of the components are in proper working order: fuel delivery, ignition. Post 13, 14: http://forums.pelicanparts.com/showthread.php?t=67957 |
Weber Adj Reference Questions
I have been using a previous post to go off of to adjust the carbs. Here are some questions regarding the process
1) "Now, you have all three barrels on the one carb pulling equal vacuum. Repeat the process for the other carb. " - Does the other carb need to be pulling the Same vacuum as the First carb or just Equal vacuum to itself? 2) Side To Side Balance "If one carb is pulling more vacuum than the other @ 3000 rpm, lengthen or shorten the right/left press rods to compensate. When you get vacuum to balance at 3000 rpm, check that the linkage adjustment hasn’t screwed up idle balance." I cant understand that At 3000 if I adjust one of the press rods to balance the carb when I let it back to Idle with the press rod changed surely it wont be balanced - bc I've disturbed the press rod.. I mean, whats the difference of Adjusting the press rod at Idle or at 3k, making an adjustment makes a change.... Here is where I had began to go off.... 3) Mixture Adj - "Now start with barrel 1. Slowly turn the mixture screw in until you hear slight popping in the muffler- a little more and the idle speed drops. " "As soon as the idle speed drops, slowly turn out the screw until idle speed comes back up- this should take about 1/8 of a turn. You may hear that faint popping in the muffler at this point. If you do, turn the screw out a bit more until the popping disappears and the engine runs smoothly." If my assistant has any deviance in holding the pedal down at 1200 it will give an incorrect change on my screw adjustment. BUT, lets say they hold it at Exactly the 1200 with NO change- How much will the Idle Drop from 1200 before I have to Turn it back out? 4) "Now, note the position of the screw and slowly give it 1/2 a turn more. This is the initial setting. If it continues to pop or spit up before moving on to the next barrel, turn out the mixture screw an additional 1/8 turn. All should be well with that barrel for the moment. Proceed to barrel 2- same process- then 3, 4, 5 and 6. If it took ½ plus 1/8 of a turn to get barrel 1 to behave, then turn out the mixture adjustment screws for all of the other barrels the exact same amount" Give the Mix Screw an Additional 1/2 Turn OUT from where the idle began to smooth? Why? Turn out all the other Mix adj screws the Same? From the Baseline of -2 turns out? Turn them an Additional 1/2 + 1/8 OR Equivalent to what I turned out the First barrel.. I dont fully understand because when I began w/ Barrel one It was set to 2 turns OUT.. I then begin Turning it IN Slowly until Idle Drops then OUT again til it smooths PLUS an additional 1/2 OUT HOW CAN I REFERNCE how much I turned it out? From the stop point? IF so, Do I turn the other 5 out the Same amount or just the Other 2 on that Carb? THEN WHAT? |
1) no, this step is to make sure all barrels of the same bank are pulling the same. You only do this once in the whole procedure. Side to side balance is the next step when you will adjust the idle screws so that both banks are pulling the same... and hence all barrels since you previously adjusted the 3 barrels of each bank to be pulling the same... phew :)
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...pressed submit by accident. So,
2) At idle speed, your rods should not be putting any pressure on your throttle shafts. This means that whatever you do with them for the 3k rpm adjustment, it will not alter your idle balance. 3) I am no expert since my first tuning has been over these past few days. Idle mixture is the 'magic' in tuning the carbs. I have by no means managed to do it successfully yet. As Sherwood told me in another post, it's all about getting the best fuel/air ratio. This may mean (I'm not sure yet :p) that you may have to increase the air (by opening up the idle air screws from their initial setting) and after that adjusting the idle mixture... :confused: This is the part of the procedure where the expert's ear comes into play (among other things). Try variations, take it out for a spin, try more. I guess we'll get the hang of it, as with everything else :) 4) I think I covered this in (3). The easiest thing you can do is adjust one barrel. I'll try and explain it a bit better. Initial PMO settings are such that they will make sure your car will start and hold an idle long enough so that it can warm up and allow you to start the tuning process. This means that they give a rich mixture because lean would kill the engine. You have set your air mixture so that all barrels are pulling the same amount of air. If we were to say that this amount is say 50 and the best possible amount of fuel is 50, then supposedly, the idle mixture screws (which control the amount of fuel going in) are above 50 (at the initial setting of 2 turns out) thus ensuring a rich mixture. Hope you got that. Now, you need to bring this down to 50. To do this you turn IN the idle mixture screw. Now, when you go well below 50, you're leaning the mixture (too much air not enough fuel) so the exhaust starts popping and the rpms start dropping. A rule of thumb is that you need to turn the mixture screw out by 1/2 a turn from the point where the rpms started dropping. But this is rule of thumb. You'll see in the post I linked above that I turn in one of my mixture screws and the rpms go up!!! wtf?!?! I need to figure this out. Just as you need to see what is best for your setup. So, try the above method for one barrel, but count how much you've turned the screw in and then out from its initial two turns out. Then adjust the other 5 by the same amount. It will most probably be something less than 2 turns out. |
I wrote this recently for a project that I'm working on, and posted it on Rennlist. You might find it helpful. Unfortunately I do not have the exploded view with numbered parts to key off of as I did on Rennlist.
Carb balance – please follow the instruction steps in order, there is a certain logic to it all, even though that logic might not be readily obvious! 1. The engine should have new spark plugs, either Bosch (WR5DC) copper core of a comparable NGK (BP7ES), gapped equally to .030”, and the point dwell must be within factory spec, as well as the ignition timing set properly. If your gas is as lousy as ours you might consider using spark plugs that are one heat range hotter (higher number for Bosch, lower number for NGK). Of course, depending on the application differences with tuning requirements may exist - this article is geared toward stock early 911s that were originally built with Webers. 2. Remove air filters, but leave velocity stacks and filter bases installed. Each carb must be fitted with a throttle return spring hooked to its operating lever. 3. Warm engine to about 140 F oil temp. 4. Use a small end wrench, 10mm, possibly 9mm, to disconnect carb drop links by popping the rods loose from the balls. Turn each spring-loaded idle mixture screw (your #xx) gently clockwise until it seats, then back each of them out five ½ turns (there is one for each cylinder). 5. Use your Unisyn to check the cyl #1-3 (left) carb (use lowest air draw position on tool). Now check the cyl #4-6 (right) carb with the tool at the same setting. Are they close side to side? If no, use the idle speed screw on the operating lever (your #xx) to increase air draw on the low carb. Now are they close? If yes, go to the next instruction. 6. Do you have one cylinder that draws more air than the other 5 cyls? If yes, loosen the jamb nut on that cylinder’s air screw (your #xx), aka cheater screw, and gently turn it clockwise until it seats. Is it still higher? If yes, that’s OK, but it should be a little lower than before the cheater screw was turned. Now, using the Unisyn, adjust those same “cheater” screws to equalize all six throats as close as possible. 7. OK, now hook up the drop rods and rev the engine a couple of times to clear its throat. Disconnect the rods and try to achieve a 1,000 rpm idle speed by using the idle speed screws (your #xx) in conjunction with your Unisyn, keeping the air draw as close as possible side to side by measuring air draw on throats #1 and #4. 8. Starting with cyl #1 idle adjustment screw (your #xx) turn that screw slowly clockwise (maybe an eighth of a turn at a time and then stopping for a moment) until you can hear the engine start to labor (listen at the tailpipe for a slowing of the idle speed). 9. When the engine labors, stop turning the screw, and turn it counter clockwise ½ turn, and immediately move to cyl #2, do the same thing, then on to #3, 4, 5 and 6. 10. Time to get that Unisyn out again and check air draw for all six cyls. Use the cheater screws to make any fine adjustments necessary to equalize air draw. Make sure that you snug down all cheater screw nuts in order to lock the screws. 11. Repeat instruction #8. 12. Clean both drop rods, be sure that the lock ring inside each ball cup moves freely, and apply a small dab of good quality grease (amber disc brake wheel bearing grease works very well) to each ball, on both the cross shaft and carb levers. 13. Connect one of two drop rods between the cross shaft and carb lever. There should be no preload, and the rod should rotate slightly once it’s clipped into position. If there is preload, or the rod won’t turn freely a small amount on its ball cups, adjust as necessary (this instruction can be done with the engine off). 14. Connect the opposite drop rod to the carb lever, and move its other end into position near the cross shaft. Adjust length of rod as necessary so that the rod connects to the ball with no preload. Like the first drop rod, this one must also be able to turn slightly on its upper and lower balls, almost as though it’s floating in place. 15. With the engine off have a helper push the gas pedal to its stop and hold it there. You should be able to push the carb drop rods a very small amount toward achieving full throttle – you do not want the linkage to fully open the carbs, rather, you want the gas pedal stop to act as your full throttle position, but still provide a safety margin to prevent damage to the butterfly valves. You never want the carbs to achieve full throttle before the gas pedal reaches its stop. The above process must be done in order; any variation can easily skew your results. There is a possibility that you won’t be able to achieve “engine labor” on one or more cyls, post if you have a problem with this. If the engine seems rough, and moving an individual cyl’s idle screw (your #xx) doesn’t seem to help, let me know. If you have light backfiring at steady speeds, especially in the 3600-4200 rpm range, let me know. If you don’t have full throttle, or if your gas pedal doesn’t snap back when released, let me know. The system can have any number of minor glitches; if that’s the case with your car we’ll work through them one at a time. |
That one's going in the notebook in the garage...thanks Peter.
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Is it Ok for some of the Air corrector screws to be all the way in, while others are not?
I started with the Mix screws 1.5 turns out and begin turning 1/8 turn in on All 6 carbs and ran the car. I turned them in overall about 1/4 turn from the 1.5 mark. I still seem to believe that it is not Exactly right because of popping in the exhaust here and there. And If I Flog the accel I get a little bit of spitting on a couple of the barrels What to do? |
GotaT,
The idle air correction screws reflect the air flow around and past the butterfly's of each individual throat. The more air flowing past a closed butterfly, the less air required to flow through the idle air passage. Remove the carbs and look through the bottoms against a light. Note how one or two butterfly's pass more light. Those same butterfly's pass more air at idle and require less air to pass through the idle air screws. To properly fix this requires re-seating the butterfly in the bore of the carburetor or adjusting the butterfly shaft connecting collar between the bores. Once all three of the butterfly's are properly seated and closed the air flow past each butterfly will be similar to the adjacent bores. If the air flow is the same or nearly so, the idle air correction jets will end up being set close to each other. Differences then will reflect the individual cylinder air draw. Regarding the idle fuel screws in from 1-1/2 turns indicates idle jets that are too large. Go down .05 mm from what is in now. That is if you are running 55mm idles, go to 50mm idles. This will also help the rich condition at 2500/3000 rpm. Popping in the exhaust indicates rich, popping in the carbs is lean. |
Here's the pic to go with Pete's instructions. I've filled in the corresponding reference numbers. The pic was originally from this thread http://forums.pelicanparts.com/showthread.php?t=314726&highlight=weber+diagram
QUOTE=2.7RACER;2929826]http://forums.pelicanparts.com/uploa...1163573710.jpg http://forums.pelicanparts.com/uploa...1163573767.jpg[/QUOTE] Quote:
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Using Petes way of doing it, what should the Starting points be on the Air Corrector screws - as he mentions "turning them in"
Mix screws? and the 2 Idle screws? |
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Idle mixture screws: 5 half turns out from gently seated. Air (cheater) screws: 1 half turn out from gently seated. If you finish with one cheater screw in all the way that is OK. Idle speed screws: Only used as necessary to obtain equal draw left & right, as well as a good idle speed. |
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C4 Pazzo: Thanks for posting that!
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One question that's been bugging me: when I pulled off the carbs I noticed that the idle jets had o-rings on them which were nowhere to be seen in the original weber diagrams I found, both on the web (Ronin's post above) and in Tomlison's book.
Today I was amazed to see them in the diagram posted above by C4. So, what's the deal? |
Early version Webers used idle jet carriers without o-rings, later Webers were fitted with o-rings, which are supplied in all Weber kits. The jets fit both types of carrier.
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when my bro owned my car in LA Pete kept it running. I met him on my 1st x-country 911 ride about 10 yrs ago. yep... pay attention to every word he says. |
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Yep, this is what I was referring to on Rennlist in post #2 above - sorry I wasn't more helpful with the reference...great write-up, Pete! Wish I had had this when my car still had Webers...
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Finally got the carbs to run Really good, but I still think that after the fresh rebuild they should run Perfectly.
I am experiencing some hesitation off Idle and a little popping in the exhaust here and there. My current settings are 1 5/8 turn OUT on mix screws. Seems that when I turn the Mix screws in slightly I start to hear more Spitting and doesnt seem to have As much power.. Do I need to turn them OUT MORE? |
Normally the mixture screws all end up in different positions, and the five 1/2 turns mentioned is only a starting point. The key is to start with all of them at that position, because it ensures that the screws are far enough out that popping from one of them won't skew your adjustment. I made no mention of the final adjustment position of the mixture screws, because that doesn't matter. One screw might end up two 1/2 turns out, another four 1/2 turns out - it doesn't matter. What's important is that all the screws end up past the engine labor point, usually by about one 1/2 turn.
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If that is true - How can you tell which Mix screw needs adjustment if it is Popping in the exhaust? Or a little hesitant off idle? |
I always thought the 'idle stop screws' or 'idle speed screws' (whatever they're called) are supposed to be screwed all the way out, and are just meant to act as a stop for the throttle shaft.
Because once you start screwing them in, they open the butterflies, thus exposing the first progression hole. In so doing, the carb is no longer running off of the idle circuit. Please advise. Jeff |
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8. Starting with cyl #1 idle adjustment screw (your #xx) turn that screw slowly clockwise (maybe an eighth of a turn at a time and then stopping for a moment) until you can hear the engine start to labor (listen at the tailpipe for a slowing of the idle speed). 9. When the engine labors, stop turning the screw, and turn it counter clockwise ½ turn, and immediately move to cyl #2, do the same thing, then on to #3, 4, 5 and 6. 10. Time to get that Unisyn out again and check air draw for all six cyls. Use the cheater screws to make any fine adjustments necessary to equalize air draw. Make sure that you snug down all cheater screw nuts in order to lock the screws. 11. Repeat instruction #8. |
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Lets go over some basics.. The condition (rich or lean) , and the Fix (screw Adjustment)
If there is popping in the Exhaust at idle = ? TOO RICH? Turn in Idle Mix Screw? If there is Spitting on the Intake at idle = ? Spitting on Deceleration = Popping on Deceleration = Spitting on Acceleration = Popping on Acceleration = I seem to be currently getting some spitting/minor popping on deceleration and a little spitting if I accelerate slowly and go through the revs. At idle the car runs smooth. Coming right off of idle I have a small amount of surge. Idle Mix screws all turned out about 1 3/4 or 1 3/4 + 1/8 Vacuum Balance looks Great and all 6 are within a 1/2 on my STE My #4 idle mix screw doesnt seem to be making much difference, why? and If I turn out the Idle air jet I dont seem to be getting a drop in idle but it is not clogged w/ trash. |
Guys, Yesterday after making all sorts of minor adj I figured out my Biggest problem... There was the smallest piece of metal in one of the Idle Jets! Cleaned it thoroughly and Voila! RUNS GREAT! NO spitting/ poppin, SMOOTH EVERYWHERE..... I just love being able to put it in 5th at 1100 RPM and still be glass smooth...
THANKS for All the posts! I now wonder whats the best way to getting the most power out of them? |
Hey, that's great. Dirt in the idle jets is the #1 reason Webers run poorly. I have seen people chase all kinds of issue$ only to find it was that simple. Check your fuel filter condition. That junk in the idle jets came from someplace.
One last thing. If you are new to setting mixtures use a low speed tach to see the results of your adjustments. As you slowly turn each screw you can see the RPM at idle change slightly. Go over each screw and maximize the RPM. Once done you can lower the idle back down using the stops and get in the road. |
GotaT - Quit while you are ahead, enjoy your car for awhile, THEN go for the 'power' !
Tom |
Thanks again guys... Mossguy.. Absolutely!.. its my daily driver. Hoping to take it on a road trip to Houston next weekend.. Should be fun
Pics to be posted soon of the 3yr Completed drivetrain project! |
I might as well put it in this thread as it's related. I started my quest to tune my carbs in this thread. I'll continue here.
I have gone through the 'Zimmermann procedure', as I have christened it, 3 times up to now. I must say that the car is running overall much much better than when I bought it a year ago. My first tuning attempt resulted in a pretty smoothly running engine but with rough idle. The second attempt was worse and the third is the best yet. Something important: maybe it isn't clear (I missed it in the first two rounds) but it is important that you go back to step #8 after step #10. That is, after you balance the vacuum, adjust the mixture and then go back and balance the vacuum again because it might be off. During the mixture adjustment procedure this is what happens: I set all mix screws to 5 half turns out. I set idle to 1000 by turning in/out the idle stop screws whilst keeping left right vacuum equal. I start turning in the first mix screw and after a turn or so, the engine starts to pick up rpm's. Of course, when they start dropping again, I stop and turn it back out half a turn (as per the procedure). With each screw, my idle picks up even more, reaching more than 1200 rpm's at the end of the 6th cylinder. I don't know if this is good or bad (it sounds good) but I just thought it was important that I said it. So, here are the problems I'm having: Idle I have a relatively rough idle. When it's cold it needs some gas pedal. When it's warm, it doesn't jump around much but there are traffic lights when it's running at over 1000 and others where it drops to the low 900's (my tach is acting up and jumping around a bit). Bumper to bumper traffic I think is the worst. After a while I start to get occasional backfiring (at the carbs). With a bit of gas it clears. Blipping (when I momentarily press the gas pedal a few times) gives the occasional backfire, especially after the heavy traffic. Transition Transition from idle or less than 1500 rpm is a bit rough, again especially after the traffic. Acceleration In first gear, the car labors noticeably until 5000 (maybe even more) after which it takes off (but there's only 2000rpm left :(). 2nd pulls normally although I'm not sure that it's full power - it feels OK. Same with the rest of the gears. I've been told by a friend that was following that there is black smoke from the exhaust and a gas smell when I accelerate hard. I cannot replicate this in the garage except for a bit of black smoke after long idling. Deceleration I think all is well here. Since I'm guessing that someone is going to ask me this: Air correction: 180 Emulsion tubes: F26 Idle jets: 55 Main jet: 110 My float bowl levels should be OK after my first gauging attempt but I plan to gauge them again for good measure. Same with the accelerator pump. Another issue that I have is that my dwell angle is low at about 32*. I'll be fixing that tomorrow but I doubt (from what I've read) that this is the cause of my problems. |
OK, Pope, now we can get serious. But first, (1) what size venturis are you using (look into one of the six carb throats - you'll see a small number cast onto the venturi), and (2) is your engine, including cams and int/ex port size, stock 2.2 liter "E"? Let me know!
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Sorry forgot to add the venturi size, 30.
I do not know what cams I have, nor the size of the ports. I have no reason to assume that they have been tampered with but this car has had at least 4 PO's that I know of and its history before 1990 is dark. |
There may be other factors, but 110 main jets are fairly lean. 2 liter T engines used 27mm venturis and 110 main jets. You might consider going to larger 125s and see if the symptoms change for the better.
Sherwood |
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Also, since my lead time for jets is significant, I think it would be best if I put in one order for all the sizes that I should be trying out. |
Pope: Given your car's history, do you have a set of jet gauges, or good quality drill bits, that you can use to measure/verify the jets that you have?
If the car were mine I would use the 30mm venturis that you have, 125 mains, 170 airs, and have a set of 50 idle fuel jets on standby. With your symptoms you might find debris somewhere (in an Air Correction jet, or possibly an idle fuel jet), and you might also discover that your "110" mains aren't... Emulsion tubes are a tough call without knowing what cams your engine has - how hard would it be for you to remove the upper rocker covers, put dial indicators on #1 & #4 intakes and measure timing at overlap? |
Damn.
I have no gauges or drill bits and I don't know what or how to measure either... I'm assuming it will be just as time-consuming to get these gauges as getting the other jets themselves. Why would a jet be stamped as being a different size than it actually is :confused: There may be debris in there but it's not likely since I've basically just put the carbs back on after a rebuild. Here's what my main jet looks like just in case it says something to you: http://forums.pelicanparts.com/uploa...1212083333.jpg Quote:
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