Webers Popin' ???

bobswei · bobswei's Garage

Hi All, I've been working on this Weber problem for a while. (my engine rebuild didn't take this long). And have one question:
Can plugged passages cause popping and flashes out the tops of the carbs? I'm thinking of having them dipped but don't want to spend money that I don't have to. Gaskets are all new and new o-rings on idle screws, if that helps the answer.
Thanks for the help.
Bob

Joeaksa · 01-09-2002, 09:00 AM

Bob,

Popping out of the webers usually means a lean mixture. Check the acc pump jets and confirm that they are squirting fuel out each time you move the throttle. I have seen a diaphram bad and one or more throat not getting any fuel from the acc pump, and that could cause a lean mixture initially when you try to accelerate.

If you are not 100% positive that all the jets and passages are clear, then you are wasting your time in trying to get the motor running correctly.

After cleaning the carbs out, make sure that the fuel level is at the correct height and the same in all four of the bowls, then proceed with setting up the carbs.

While you are cleaning the carbs, confirm that all the jets and venturi's are the same and orginal size. You might want to go up a bit on the idle or main jets but I have found mixed up parts in various carbs and until you have everything at the same "level" you will never get them to run right.

Also check the fuel bowls for dark specks, which usually indicate rust in the fuel tank or line leading aft. Older cars have this problem and it clogs up the idle jets, causing problems.

Hope this helps, when they work right, Webers are excellent, but can be difficult when not set up correctly.

Joe

Steve in SLO · 01-09-2002, 09:00 AM

Bob,
Sometimes the carbs pop if you're running too lean at idle. This may be the case if a majority of the popping occurs just as some throttle is applied. Fatten up the idle a bit and see if that helps.
Steve

Alan.UK · 01-09-2002, 10:04 AM

Have you had the engine running at all?
Is it popping in one cylinder or all/variety of them?

I only ask as mine acquired the same symptoms in 3 or 4 cylinders at the same time. I simply increased the richness of the mixture a little . Strange as the carbs were set-up exactly on a dyno (rolling road here in the UK) but as winter approached they started popping. It seems that the extra moisture in the air was affecting the mixture. I may even beef the idle jets up slightly yet.

HTH

Alan

bobswei · bobswei's Garage

Last time I had the carbs off, (yesterday), all but one pump nozzle was spraying. I cleaned that one so at least air and carb cleaner goes through it. (haven't checked the diaphragms). I put smaller venturies in, 27mm, and seems to rev better but pops like crazy. Not even close to driveable. Turning out the idle screws seems to make no difference and I've started with settings of 2 turns out and air screws 1/8 turn out. It ran ok before I took the carbs off "just" to clean, but sat around for 6 months.
Does this help find the problem?
Thanks.

T Bird · 01-09-2002, 10:10 AM

Clogged passages usually create more pronounced problems, like no idle or no transition. Before you start changing jets or adjusting mixture screws, you need to get the carbs balanced. You do this after checking accelerator pump volume and float level.

To balance the carbs, turn in the idle air correction screws (the ones with the lock nuts) fully on one carb. Find the barrel that pulls the most vacuum and open the idle air correction screws up on the other two barrels to match. Do the same to the other side. Next, set side to side balance at idle speed with the idle stop screws. Get both sides pulling equal vacuum. Then, check that you balance at 3000 RPMs too. This is critical. When you do this, have an assistant in the car hold it at 3000 RPM with the gas pedal- don't use the crossbar for this procedure.

Once you have these adjustments made, you can play with the mixture screws. Turn in the idle stop screws until you get a nice 1200 RPM idle with equal vacuum side to side. Start at barrel No. 1 and turn the mixture screw in slowly until you hear slight popping in the exhaust. Turn it in a bit further until the RPMs drop. (When I do this adjustment, I use my Fluke 88 in RPM mode so I can visually see the RPM drop, as well as hear it.) When you turn in the screw, do it slowly. Changes in the position of the screw do not produce instantaneous results. As soon as the idle drops, slowly begin turning the mixture screws out until the idle comes up and you hear the popping. At that point, go 1/2 -3/4 a turn out more. Repeat for each barrel. Now using the idle stop screws, lower the idle to 900 RPM (with vacuum balanced side to side) and take it for a test drive. If it still pops, repeat the mixture adjustment and turn the screw out just a bit more, like 1/8 of a turn.

Remember that they can all be a bit lean, or all a bit rich, but they must all be equal.

If you find that your mixture screws are turned out more than 3-3.5 turns from full in and you still can't tame the popping, you may need bigger idle jets.

If the car doesn't respond to changes in the position of the mixture screw, you may have a blockage. If you didn't oil the O rings, they may have been drawn into the threads and broken the seal.

Good luck.

T Bird · 01-09-2002, 10:27 AM

Bobswei
I posted the response above without the benefit of the additional information that you provided. If the car ran fine before with different venturis, then put those back in. Also, you must sort out the problem with one of the accelerator pump nozzles. If one isn't squirting out gas, the car isn't going to run right. Get the volume at each nozzle equal (.6 to .8 cc). The problem with the nozzle won't cause the popping, but it will play havoc with smooth acceleration and perhaps cold starting.

bobswei · bobswei's Garage

Thanks T Bird,
Even with origional venturies it's been popping (no fifference). I've had these apart 6 times now, squirting air and carb cleaner through everthing and appears to flow ok. No rust flakes and with the initial setup, it starts fine but will not come close to idleing or running smooth at any rpm. One P-mech. has diagnosed at least one dead barrel and was told to back out the idle "jets", one at a time, to find the bad one. But I can't keep the thing idleing long enough to do this. I'm at the point where I'll pay a mech. but don't want to throw money away on something that's not broken.
Thanks for all the suggestions.

Zendalar · 01-10-2002, 03:48 AM

If you removed the carbs and intake manifolds, did you make sure that the gaskets are new and they don't leak. I had to put gasket lacquer in addition to new gaskets before my popping went away.

They leaked after I cleaned the carbs and it popped all the time, well, it ran like crap.

Joe911 · 01-10-2002, 04:26 PM

Going through a similar process. Thoroughly cleaned the Webers by soaking them overnight and have reassembled. Initially they ran very poorly with lots of popping and an idle mixture screw that did not seem to make any difference. Just changed the plugs -NEW and slightly hotter (BP7ES - BP6ES) and the difference was dramatic. Still not perfect - but much better with 80% of the popping gone. Will get back at them this weekend and see if the idle screw has an effect on idle speed now. So have a new set of plugs around to eliminate their contribution to the problem.