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High idle - tried everything. Help
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E.Murray
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PostPosted: Mon Feb 27, 2012 8:01 pm    Post subject: High idle - tried everything. Help Reply with quote

I have a 1600 dual port with a Weber 45 DCOE ahead of a Rayjay turbo (draw-through setup). I just got the car (an Aztec 7 kit car). When the delivery driver unloaded it off the carrier, it fired right up with a jump. He left it idling while we did the paperwork. After a mile or so of driving, it coughed, sputtered, and died. It turns out that it didn't have a fan belt. Thinking I had probably done a very bad thing, I towed the car home.
The next day, I ran through the standard checks. Valves checked good (.005"-.006" each); compression was 120-130 on all four cylinders; head nuts were properly torqued. I fired it up and it wouldn't stay running under about 2100 RPM. Since that time, I have checked absolutely everything I can think of. I have:
pulled the idle jets, cleaned them out and blown out the idle circuit
checked timing (009 distributor, so I checked advance at over 3000 RPM)
replaced all vacuum hoses
replaced all intake-side gaskets
checked for vacuum leaks using both propane and starting fluid (none)
installed wideband O2 sensor and air-fuel ratio meter
changed cap, rotor, plugs, fuel filter, fresh gas, etc. etc. etc.
According to my AFR meter, the car is lean. I can twiddle the idle mixture screws all day and it still won't idle. If I keep it choked and aboved 2000 RPM or so, it runs great (I even took it for a short drive). Below that, though, it stumbles and dies.
Here's my question, then (finally!): Is there anything about the overheating that could cause this? The car idled fine when it was delivered, so I have to think the problem is related to its getting hot. the only odd thing I've noticed is that there was oil pooled in the intake side of the head when I pulled the intake runners off. That may be normal, though. I've rebuilt American and foreign engines, but this is my first VW. The car is beautiful and in incredible shape in every other way. I want to drive it! Any suggestions are appreciated.
Thanks,
Eric
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Buellistic
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PostPosted: Mon Feb 27, 2012 10:35 pm    Post subject: Reply with quote

Probably ruined a number of areas related to combustion chamber seal.

The rings could be burnt up.
The valve guides could be leaking oil.
The cylinders could be warped.

I'm sure there are other things I'm not thinking of. Do a compression and Leak-Down test to see if you've lost any the above seals.

Oh, also, there should be no oil in the intake or exhaust what-so-ever.
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E.Murray
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PostPosted: Tue Feb 28, 2012 7:23 am    Post subject: Reply with quote

If I've lost the rings or warped the cylinders, though, shouldn't I see lost compression? A leak down test tries to bring the compression back up using oil and then see if it bleeds off, right? If so (I haven't ever done a leak down test), then wouldn't normal compression mean the leak down test wouldn't work?
Even then, would these things cause the symptoms I'm seeing (refusing to run below 2000, but running fine above)? Sorry if these are dumb questions. School me, please.
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[email protected]
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PostPosted: Tue Feb 28, 2012 8:34 am    Post subject: Reply with quote

I've seen this a lot with DCOEs. First, verify there are no vacuum leaks.

Next, what is your ignition timing at idle and 3500 RPM? Too much timing can cause a racing idle.

Next, look into the barrel of the carb and see if the throttle plates have a hole in them. A lot of "experts" drill holes in them (some large) in doing their "Special tunes".
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Dale M.
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PostPosted: Tue Feb 28, 2012 9:39 am    Post subject: Reply with quote

E.Murray wrote:
A leak down test tries to bring the compression back up using oil and then see if it bleeds off, right? If so (I haven't ever done a leak down test), then wouldn't normal compression mean the leak down test wouldn't work?


A leak down test indicates the amount of leakage in percentage...

LD test require a air compressor ... Typically you set up a leak down test gauge at 100 psi gauge reading with outlet closed. When you put LD test unit into sparkplug hole and open port (outlet) the pressure will drop... IF it drops to say 80 psi, it means you have 20% leakage in cylinders or valves...

By listening at intakes or exhaust or at oil filler and you can hear the air escaping you can pinpoint damage or condition of each cylinder...

Here is just a few articles on I-net about LD tests...

http://www.carcraft.com/techarticles/116_0406_cylinder_leakdown_tester/viewall.html

http://www.mobiloil.com/USA-English/MotorOil/Car_Care/DIY/Engine_Leakdown_Test.aspx

You can also make your own unit with a couple gauges, a ait pressure regulator and some plumbing...

http://vmaxoutlaw.com/tech/leakdown_tester.htm

Does not matter if its a motorcycle or a AC VW or big V8 leak down is leak down, principle is all the same...

A leak down test is just a more definitive process than straight compression test...

Dale
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E.Murray
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PostPosted: Tue Feb 28, 2012 6:26 pm    Post subject: Reply with quote

Wow, great stuff on the leak-down test. I'll do that next. As far as the carb stuff, something along those lines was my thought, too. I sure can't find anything ignition or timing related wrong, though. Thanks for the help.
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rs58rag
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PostPosted: Fri Apr 05, 2013 11:00 pm    Post subject: Reply with quote

45 DCOE is too big for 1600 cc.
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