What Happened to my Webers??

[bobswei]

After removing the engine from my 72T, for painting and cleaning the whole car, I put the thing back in and now pops and backfires. Everyone is pointing at the carbs. I had then off to clean and thought dirt might be plugging some circuts. If I pour a little gas down the tops of the carbs, it starts up and runs smooth for about 4 seconds, then starts poping and dies. I've had the things apart 4 times shooting air and carb cleaner through all the jets and passages. The pump nozzels are now clear, jets, idle screws all flow cleanly. Is there a main passageway the could be blocked that will let air escape out another hole? (air goes in a jet and comes out in venturi - still maybe not sucking gas?)
Any ideas? Thanks
Bob

[fred hannah]

if you pour in gas and it runs, then maybe your fuel pump is bad, or not hooked back up correctly? just a thought

[bobswei]

My thought to about the fuel pump. I disconected the fuel lines from the carbs and stuck them in a can, then turned on the pump and seems to pump more then enough. Thanks.

[J P Stein]

A WAG would be vacuume leak/s. ....particularly at the carb/manifold juncture.....not that *I've* ever had this problem :-).

[911_Dude]

I would suspect an air leak in the intake. It sounds like its lean. Did you use the old gaskets? May need new ones. Also, it may help to use a torque wrench when installing the carbs because the gaskets are thick and crush a bit. Tighten each one down a little bit at a time. You may have tightened one side down too much.

[RoninLB]

Carbs are easy to fix w/ some specific experience with each model. That is why I'm keeping quiet. Before the Texan solves the problem, I wonder if cows in Texas serve milk and cookies for Christmas??

[T Bird]

You say that you had your carbs apart 4 times, but don't say whether, or how, you set them up after you put them back together. If you removed the idle mixture screws and idle air correction screws to spray cleaner in the passages, you are going to have to set up the carbs from scratch. You should do the following, in this order:

--check/adjust float levels.
--check/adjust accelerator pump volume.
--equalize vacuum on each barrel. You do this by disconnecting the linkage between the L & R carbs. Now screw the idle air correction screws in all the way on one carb at a time. Determine which barrel draws the most air with a synchrometer. Then turn the other 2 idle air correction screws out until each barrel draws equal vacuum. Lock down the idle air correction screws and repeat the process for the other carb.
--balance vacuum between each carb. You do this by reconnecting the linkage and then adjusting the idle stop screws until each bank draws equal vacuum at idle. Check at 3000 rpm too. If vacuum doesn't balance at 3000 rpm, then the linkage needs to be adjusted. Make sure that you get vacuum to balance at the higher RPM. This is critical.
--adjust mixture screws at 1200 rpm.
--set idle speed to the recommended setting.
--recheck balance and mixture adjustments.

A book could be written on performing each of the above steps. You will need to get the car running so as to perform the balancing, mixture and idle adjustments.

Popping/stalling can be caused by a lot of things. You may have the idle mixture screws turned in too far and are starving the engine of gas. Try turning them all out about 2.5 turns from the fully seated position, as a starting point. Also, make sure that the o rings around the idle mixture screws are not broken. When you installed these o rings, you should have oiled them so that they seated properly and were not pulled into the threads and thus ruined.

If you can provide more specific details about what you did or didn't do to the carbs, some one here may be able to provide you with more detailed advice.

Good luck.
John

[bobswei]

Thanks for the replies. Some of the advice I did do, and some I didn't. All the idle screws were put back in the same turns as removed, as well as air screws. I put on new o-rings but forgot to oil them. I left the float levels the same. The advice on the vacuum leaks makes sense since I used new gaskets were I thought it needed them and the old gaskets that looked ok.
I will start doing all the checks this weekend but I'm not sure if it will run well enough to do vacuum checks. Maybe backing out the idle screws will help this. It was so dramatic to how it ran before taking the carbs off to putting them back on. I think the gaskets are a good starting point.
Thanks for all the help.
Bob

[T Bird]

Bob
I could be wrong (and often am), but I think it would take a good size vacuum leak to get you to the point where the car won't run for more than a few seconds. My instinct tells me that these carbs have lost their tune-- that is, that the idle mixture and idle air correction screws aren't adjusted properly.

If you succeed in getting it started, try to give it enough throttle to get it off the idle circuits-- say 3000 to 3500 rpm. If it runs there, but won't idle, then I would say that my instinct is probably correct. If so, you need to start with initial settings on the idle mixture screws (out 2.5 turns) and the idle air correction screws (out 1/4 turn) and go from there. Careful when turning those screws in- many an idle mixture screw seat has been ruined by overzealous tightening.

Another thought- if I try to start my car without pumping the gas pedal 3 times, I get the same symptoms that you report --popping, coughing, stumbling and eventually, stopping. The fuel that the accelerator pump provides for initial starting/running is critical. Don't dismiss the importance of testing the accelerator pump delivery. I have found that .75cc per stroke works well. Others suggest .5cc. Indeed, I would check that first before tampering with the idle mixture and air correction settings or removing the carbs from the manifold. I suggest this because you report that the car runs well initailly when you pour gas down each throat.

The best of luck to you.
John