I've spent the past couple of weeks rebuilding a pair of Weber 44 IDF carbs (28mm chokes) with a set of recommended jets to make these large carbs work on a smaller engine.

I spent a lot of time with these carbs getting all new parts for the bodies - new bearings, screws, everything. I put them on the car and it started right up!

.... right up to 2300 rpm at 7 degrees BTDC set static with my fancy timing light. I can't actually get the idle down no matter what I do except for rotating the distributor, which I've also rebuilt stem to stern.

The idle speed screws are all the way out. The air corrector jets are all the way in. The throttle plates are super smooth and snap back nicely. The vacuum line is plugged.

Fuel pressure doesn't seem to be the issue either, given that it's a new CB Performance rotary 3.5 PSI pump. But I will order and install an inline gauge to verify.

I have also purchased synchrometer (STE). The carbs all seem to pull exactly the same vacuum (18-20).

The only way to get the idle down is to retard the timing, which arrives with a bonus exhaust backfire that my neighbors dislike. Something about ruining an outdoor dinner party or some such.

Help?

My guess is you have a major vacuum leak somewhere. Squirt some carb cleaner around the base of the carbs and see if the idle changes.

Ruining an outdoor dinner party with a few backfires? Do they wear flowers in their hair and peasant dresses? Geez!! What whiners. Does their patchouli ruin your breathing? LOL

are you sure the throttle plates are fully closing when the spring snaps them closed? retarding the timing to bring the idle down is not the solution. re-establish the correct timing. if the webers have the helper springs on the shafts disconnect the drop links at the throttle stop arms and see what happens. if the idle drops try lengthening the links a bit.

Are the throttle plates in upside down? There is a right way.

Wait, what?

When I assembled the carbs I took several hours to pick and choose from a stash of throttle plates to get the best match I could get. I know that there's a slight deformation on the plate for the bearing side of the body vs the center. Is that what you mean?

Having said that, it's entirely possible that air is getting past the plates despite my best efforts. However, no matter if the engine is at lower or high idle based on the dizzy position, the engine runs very smooth. I wonder if it would run that smooth if only one of the two carbs had a air gap problem with the throttle plates.

Note: when the carbs came to me there were two assembled (incorrectly) and two unassembled bodies with a bunch of extra parts. I didn't bother to note the positions of the plates because I knew that the starting positions were incorrect. I took the best parts of the batch and replaced all of the wear items with new replacements.

I shot some starting fluid around the bases of the carbs just now without change in idle speed. I have a smoke machine and am willing to try that out for kicks. There are no other vacuum intersections that I can think of except for the breather ports in the heads but I don't think those count.

It's raining again so I'll wait for the car too cool down and pull the carbs and examine the throttle plates. Just to verify, I know that the plates should close. BUT is there any tolerance there? As in feeler gauge tolerance for gap? Completely shut can be a relative term.

I'll also make sure (as mrholland2 suggests) that the throttle stop linkage isn't getting the way.

Thanks, everyone.

No, they're respectable folk. Perhaps a little too respectable. But apparently they're the kind of people who don't enjoy a series of loud explosions while trying to make for polite conversation, or Yahtzee, or wife-swapping, or whatever it is that they're in to.

incase you're unaware. the throttle plates have a bevel at the circumference. prob a * and a number. they should be visible while looking down the carb throat.

In fact, I was ignorant of that fact. Even following the manual I was dumb enough to overlook this interesting fact. Now I have something to do. Will report back.

I agree with Kev. Check to make sure the bevel is facing the correct way so the plates close all the way. Ensure they close by shining a light in the throat from the other side. Also make sure you're using the correct throttle plates. Early vs late Webers use different bevel degrees. either way, the progression holes must be completely covered.

Okay. I just removed the carbs and re-fit the throttle plates - this time with the bevel in the right place with no light showing through. Two were incorrect of the four. I have to wait until morning to start it up, lest I offend my neighbors.

Besides, my stupid muffler is stupid loud. I hate it.

Will report back.

You trying to impress or show your neighbors respect? That moment passed once you drove or towed the 914 home! I say backfire away!

Well if two were incorrect, then that is definitely your issue. this is a perfect reason why asking here on the forum is the best thing to do when you are stumped with a problem. Lots of different ideas to the problem and one is usually homed in on and turns out to be correct.

And ... SOLVED.

It was indeed the throttle plates out of order and alignment. I just spent some time with the initial tuning. At 7.5 degrees of timing I have the car running at 900rpm on the dot. The synchrometer shows 5 kg/h exactly on each barrel thanks to the air corrector adjustments.

How pleasing! And nary a backfire!

Thanks, everyone!

-marcus

Kev (rhodyguy) knows his stuff. He's the one who taught/put up with me. Glad you got it fixed!

marcus, did you try the throttle stop trick?

k

Congrats! You should drive down to show it off

I totally will drive it down. Once Mark sends me the linkage. Geez already.