So I've just swapped out my 1.8L engine for a 1.7L, of unknown build but looking like it was rebuilt and never run before. I'm reusing the dual Webers as-is from the 1.8. I have a brand new 123Distributer.

I can start it up, but it only runs (poorly) if I continuously pump the throttle. It seems like it needs that extra fuel from the accelerator pump to keep it running.

Here's what I've done:
-I've checked I've got the right TDC based on the fan mark and getting a compression stroke on cylinder 1 (using the thumb over the sparkplug trick).
-I've set and double checked valve clearances using cap'n crusty's method.
-I've cleaned the idle jets and main jets.
-I set the idle mixture screw to 3 turns out.
-I drained the fuel and put fresh fuel in the tank.
-I've checked spark on cylinder 1.
-Timing curve on distributer set to 10 degrees at 1000 rpm, 27 degrees at 3500 rpm
-Haven't checked sync on the carbs, because it won't run well enough to do so, but physically they look synced.

Under the assumption that the engine was built correctly, what could be going on here? I'm struggling, so any suggestions would be greatly appreciated!

Thank you in advance.

Fuel pressure?
3 turns on the idle screws sounds a bit much, drop to two.

Thank you, I will try that.

Will that adjustment affect the upper rpm ranges too? Because the behaviour is the same across the rpm range -- as soon as I stop pumping, the engine dies.

Sounds like timing might be a little retarded. I would try rotating the distributor ccw a bit while running and see if that helps. Setting the curve on the 123 is only half the process, the static timing needs to be at TDC. Set the timing with a light to 10 degrees at 1000 rpm once you get it running, then you can tighten the distributor for good and use the app to mess with the timing if needed. I agree 2 turns on the mixture is a better starting point. I assume the carbs worked good on the old engine.

Thank you! Yes, the carbs worked well on the old engine, although they've been sitting on a shelf in the garage for a year, or maybe it has been two years already.

I've tried rotating the distributor a bit both ways already, and it doesn't seem to help. I can't use the timing light yet, because the engine won't run on its own.

You might need to rebuild your carbs. Wouldn't hurt.

See my post here about Bob Tomlinson's Weber Tech Manual for dialing in your carbs, pp 49 - 53.

http://www.914world.com/bbs2/index.php?s=&...t&p=2931348

Seems 2 1/2 turns out is good place to start on your idle mixture screws.

GN

Sounds like fuel pressure to me. If you don’t already have one get a fuel pressure tester. Cheap at harbor freight or on line and see what you have at each carb. Could be a blocked filter, line or a bad pump.

Make sure all 4 accel jets squirt when you move the throttle. The diaphragms can dry rot while sitting and/or the nozzles clog with dried fuel residue. Pull the carb tops and see if the bowls are nearly full of fuel. Does it pop thru the carbs? Engines typically pop thru the carbs if it’s running way lean.

Where are the air bypass screws set? Go ahead and close them. Or base line all of the settings again. You can use the ABPS later to equalize the flow on all 4 Venturi later if needed. Try using ONE idle speed adj screws to raise the idle. If the linkage is set correctly, the other carb will follow suit.

Thank you! I did just drain the old gas using the pump, so I don't think that's the problem.

Although now I'm wondering how long it will take to use up all the old gas that was still in the fuel lines. I will trying running it for longer tomorrow, and see if that improves anything.

Thank you! I just double-checked that all 4 accel jets squirt fuel. Is there a way to check that fuel is being delivered other than through the accel jets??

Thank you! I double-checked that all air bypass screw are fully closed. I also double checked that both carbs are (statically) synced with the idle stop screws matching at 1-1/2 turns out with the linkage off, then re-attached the linkage.

Pull the fuel line off the drivers side carb and stick it in a jar and turn the ignition on. Not start just on. You should get a steady stream of fuel. If not work back towards your tank. If you get a steady stream of fuel start with the screens in the carbs just past where the lines connect above the accelerator pumps.

Are you sure you don't have a pair of plug wires swapped around?
Check to make sure you don't have a vacuum leak.
Check your fuel pressure.

I agree you have to eliminate any carb issues but don't forget that it could be an ignition or even mechanical issues.

Have you done a simple compression test? I could lend you my leakdown tester, but you need a fair size compressor.

Are you positive you're on TDC? When in doubt I always remove the #1 valve cover, roll the engine through the strokes watching for the intake valve to close, half turn more to TDC and you're good to go. At this point I'd yank the dizzy and make sure the drive is correctly orientated.

I had a similar issue while starting the engine in the 68 911 recently for the first time. I could get it to start and idle but it wouldn’t pick up when I opened the throttle. After doing everything you did, I pulled the distributor up and turned the shaft one tooth so I could get more advance. it fired right up then and responded as it should.

Charlie

The winner goes to... vacuum leak!

I will post a picture later, but the gasket under the carburetor was missing a huge chunk.

Feels great to have it running again! Thank you to everyone for their input and advice!

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