Beetle idle issues

[robp1999]

I'm a little lost trying to get the beetle idling properly when engine temp somewhere between cold and warm. 1776, Engle 100, refurbished German 34pict3 from Volkzbitz, refurbished German 034 SVDA from Bill. 135 main, 65 idle and 75 air correction Jets. Valve clearance set, base timing 7.5 btdc. Car cold starts easy, runs rough for a couple minutes then smoothes out. As it warms up as soon as the choke releases and it comes of the high idle cam it doesn't want to idle until fully warm. When warm it idles at 900rpm but will drop below that momentarily as the throttle is released then recover when pulling to a stop. Do I start with adjusting the choke a little tighter? I'm at a loss here.

[VW_Jimbo]

I am betting the throttle plate stop screw is incorrectly set. I would start with setting the basics. Check for any vacuum leaks. Then go through fine tuning.
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Jimbo

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[robp1999]

Okay I'll start from the beginning. I've never checked the throttle plate stop screw.

[beetlenut]

I have that same carb and distributor combo from those same two people. I started the tuning process by backing the throttle plate stop screw out until it was not touching the fast idle cam at all. You need to make sure the throttle plate is closing completely so that it covers the bottom most progression hole in the throat of the carb. The best timing set-up I got was with vacuum hose off and plugged, with a timing light at 30-32 degrees at max advance. This produced a strong high idle that I was able to then tune the carb with (small screw), and then set my idle with the bypass screw. Then once warmed up, I screwed the throttle plate stop screw in until it barely touched the bottom cam of the fast idle cam.
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[74 Thing]

What kind of exhaust are you running and are your preheaters cleaned and not clogged?

As mentioned above, start by warming up the engine and adjusting the carb properly.

[robp1999]

Vintage speed exhaust and preheaters work great

[ashman40]

[robp1999]

I have my son warm it up in the driveway since his commute is really short plus it misfires for about a minute when first started. I'll adjust the choke tomorrow morning and see what that does for us. I'll mark it so I can go back if it doesn't help. Trying to do one thing at a time so I don't get lost. We will get the cable for our air fuel gauge next week and gain real data to go by if we can't get it figured out before then. Thanks so much for all the responses.

[rayjay]

On these carbs the idle screw that contacts the fast idle cam is NOT used for setting the idle speed when the engine is fully warmed up. You may be aware of this, if not check youtube for setting the idle speed.

[robp1999]

Oh yeah I'm cool. Tim gave me a tuning sheet with the carb. I bet it's the choke. I checked for vacuum leaks last night and it runs pretty great when warm.

[beetlenut]

[heimlich]

You should get your rebuilders on an email together to help with the diagnosis. They built the units. They know all about them.

Sometimes the timing will kick back when the diaphragm in the vacuum canister gives way after being under pressure.

Do you have a gold or a silver vacuum canister?
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[heimlich]

Here are pictures of what the vacuum canister looks like. Note the Bosch stamp on them.

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[robp1999]

Mine is silver but not Bosch. Good idea to get the rebuilders on a group email. Thanks for the advice.

[Xevin]

Did you ever go through the choke adjustment procedure? Out of curiosity and perhaps unrelated. What style of air cleaner are you using? Do you have working thermostat and flaps? What coil and have you tested it lately? Did you set your timing with a timing light with hoses off? What are the setting details? What’s the timing numbers with vacuum hose on?
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[robp1999]

Tightened choke which made it a little better. We use a factory air cleaner with warm air hose connected. Functioning flaps and thermostat. New Bosch blue coil. Timing with strobe light at idle is 7.5btdc with or without vacuum hose connected. at full advance it's around 42btdc with hose connected.

[ashman40]

[wcfvw69]

Hello Rob,

Let Tim and I know how your doing via email. I hope some of the suggestions we both sent you via email helped you dial it in. You have a nice looking engine.
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[robp1999]

Okay guys got to check things and found adjustments were all about right. I fine tuned the idle mixture, double checked timing, looked for any vacuum leaks, pulled idle jet and flushed it, and tightened the choke a little. To be honest everything got better when the temperature rose above 20°f. I'm having him drive around the neighborhood to warm it up and he has had no issues since. Seems it's the little things sometimes. Thank you guys very much for your help. I can't recommend Bill and Tim enough for their services.

[VW_Jimbo]

Glad you got it!
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!