No idle after back fire - 34DMS(A) Weber

[pressonregardless]

Looking for any information on cleaning / rebuilding a Weber 34 DSMA on my 1974 Spider 1756.
It has run very smoothly on several trips over the summer and I was running around town on some errands and all was fine. The engine sat in the drive for about 1 hour in 95' temps and I went to start things to put it away for the day. As I cranked, the engine (what I call backfired, or burped in the carb/air cleaner assy). I cranked again and now I have no idle. I drove around the block and all is fine above 1500 rpm, but can't idle. I pulled all plugs and wires, all clean.

Any thoughts, I believe it is something in the Carburetor circuit since the problem instantly appeared when the engine choked up on starting. Charlie

[So Cal Mark]

the backfire may have blown a vacuum hose off, causing a large vacuum leak

[pressonregardless]

Wow, I am rusty, exactly how it acts. I know this model does not have many but will check that. Thanks Mark!

[pressonregardless]

Mark, I owe you! I had checked vacuum lines around the carb, but not on the fenders. Found a 3/8" line going to a solenoid on the drivers fender, (I assume for fast idle that does not work) blown off and the pretty little brass fitting staring me in the face. Well, of course I put a piece of clean hose on and sucked/tongue trick and the diaphragm was still good, so tap, tap, with a brass hammer to insert the fitting and hose back on.

Now, on the passenger fender is a device with a diaphragm and 1" air line from the air pump (drive belt removed) and going to the air injection rail. Right next to the fender is a 1/4" vacuum line that come directly from the intake manifold. Well this fitting was all cracked and just sitting on their. AaaHaaa! Vacuum leak # 2 ( also visual inspection showed a 2 wire connector which had rubbed though the pvc protector and rubbed the insulation off the wires so exposed to the frame for the R.FT. side marker light). So I used the golf tee trick on this line, put a proper rubber cap on the fitting for the diaphragm on the air valve and she fired right up! BTW, what should vacuum be at 900 rpm idle, I have a slightly shaky 15 in mg.

My next question is there is hot air being pushed up the air injection rail into the 1" rubber hose, so much so it has blown though the connection and melted some of the 38 yr old hose. I have disabled the Air Pump (belt off to protect the engine when/if the pump does lock up) so what do you recommend? Pull and plug the Air Rail? I think I read the fittings are 12 x 1.25 but not sure. Kinda hopping to leave stock look, as this is a wine cruiser, not a racer.

Again, thanks Mark, I also see your close to my Daughter & Son-in-laws restaurant, The Salted Pig across from the Riverside Court house down town, they feature craft beers on tap and premium Root beer too! Stop in and tell 'em Charlie sent you!