1600 dual port won't idle below 1500rpm

[Chris deguire]

Hello everyone,

Just wanted to ask if anyone has run into this issue before. 68 bug with a 73 1600 ae engine, last year car ran good, alittle hard cold starting but would eventually start up. Did a valve adjustment last August about 100 miles ago. After a while we noticed whenever you let off the accelerator coming to a stop or at idle sitting at a light the engine would just quit. I assumed at that point it was a carburetor issue as me since I was have a hard start issue I sent the carburetor (34 Pict 3 VW original) to carb guys in Oakville Ontario for restoration and rebuild, got the carburetor back they did a beautiful job, carburetor looks like new inside and out. Installed back on the car, also installed new plugs wires cap and rotor on 009 distributor, set the points-did notice a slight pit on the points. Reinstalled distributor, started the car-now starts very easily with 2-3 pumps, but still cuts out once the choke is completely open and off the stepped cog. Also installed new intake manifold gaskets along with slight bit of silicone for good seal, also installed new rubber intake manifold elbows, also has new gasket under the carburetor. Volume and bypass screws both out 2.5 turns. Tomorrow I'm going to double check my timing to make sure it's correct and that my valve adjustment was correct. Is there anything else I should be looking at or anything someone else has run into? Engine is stock other then a new stock style intake manifold. I have read a few people opted for a larger idle jet

[minirailz]

Have you tried a compression test?

My engine didn't idle either last weekend and it's because it has 0 compression on one side...

Dennis

[busman78]

Look for a vacuum leak somewhere in the intake/carb. Try screwing the air volume screw in to a 1/2 tun out, if the idle stays the same then air is getting sucked into the system from somewhere.

[wcfvw69]

As someone mentioned, rule out any vacuum leaks if you're confident that you have good compression on all 4. Do the valve adjustment before checking your compression.
Your symptoms sound like a clogged idle jet circuit. Make sure you have a good idle solenoid and the connections are good. You may need to tear the carb down and blow out the passages and jets.
The other thing is you have a bad distributor/carb combo. The mechanical advance only 009 matched to the 34-3 is not good. They are famous for off idle hesitations, flat spots and poor mileage.
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[beetlenut]

The title of your post is "won't idle below 1500rpm", but then you say "cuts out once the choke is completely open and off the stepped cog". So does it idle or cut out?

Then you say Volume and bypass screws both out 2.5 turns. Those are the initial settings to start the tuning process from, not the final settings that the carb should run at.

If the throttle plate adjustment is not right, no amount of carb tuning will get your carb running right. It's critical! That's done by the long screw on the throttle arm. If it's in too far, the lower progression hole will be exposed. If it's not in far enough, there will be a lag in the response when you step on the gas.

As Bill also mentioned, 009's and 34 PICT 3's do not play nice together.
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[Starbucket]

Check the manifold pre-heat pipes by starting a cold motor and feel the manifold under the carburetor, if it's ice cold after a few minuet's, the pre-heat pipes are clogged and the gas in the manifold is liquid not vapor and the motor will die at idle.

[heimlich]

Did you adjust the idle RPM screw? The large one on the side.
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[ashman40]

A common mistake is to think you should set the idle timing to 5ATDC listed for the stock '73 Beetle. That would be correct if you had the original '73 Beetle DVDA distributor, but you don't. You have an aftermarket OO9 distributor. Setting a OO9 idle timing to 5ATDC would be much too retarded and the engine would struggle just to idle. At higher rpms it would lack power.

With a OO9 distributor start with static timing it to 7BTDC. This is good enough to get it running and run fine at lower rpms.


If your timing is good, then I too suspect you have a vacuum leak. The tell-tale sign is that the choke masks the problem. While the choke is ON it runs the engine rich. This compensates for the extra air leaking into the intake flow from the vacuum leak. Once the choke is OFF the idle mixture thru the carb returns to normal but the air leaking into the intake results in a lean mixture and the engine struggles/dies.
A simple test for this...

Warm up the engine until the choke is OFF.
Manually rotate the fast idle cam to one of the steps until you can just barely keep the engine running (1500rpm?).
With the engine idling, cover 50% of the opening of the carb with your flat hand to block off the air flow.
Slowly move your hand to cover more and more of the carb opening. At some point you will start to restrict the air flow and you will choke the amount of air allowed into the carb. Normally, this would be the same as closing the throttle plate to reduce the air flow and the idle rpms should go down. Listen to the engine as you choke off the air flow. Does the engine instead run better and the rpms go up? This suggest the engine was running lean and by choking off the air flow down the carb you are balancing the mixture and the mixture moves closer to ideal air-fuel mixture (stoichiometric) so the engine runs better/smoother.

Now you know there is a leak, finding it is the challenge. Use some carb cleaner spray while the engine is idling (using the fast idle cam). Attach the red straw and spray common leak spots. All the rubber connections (intake, hoses), seals (gaskets below the carb and at the heads), carb opening (throttle shaft bore). If there is any change in the rpms when you spray you have found a leak into the air flow. Fix this leak.

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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}