40 IDF vent/jet choice

[udidwht]

Seems your not the only one with MPG issues:

http://www.itinerant-air-cooled.com/viewtopic.php?t=2890

[Mark]

Well this guy found a nice solution to the problem with springs flying out of the IDFs.

http://www.thesamba.com/vw/forum/viewtopic.php?t=303670&highlight=idf+spring
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[mharney]

That's exactly what I do with the enrichment plungers.

Mark, T4 engines appreciate air speed and like smallish carbs. They're not RPM engines, unless built that way. 28 vents oughta be ok, all things being right, like mixture, etc. They may wane on the top end, but you shouldn't be up there unless your engine is built for that. 28 vents would give you solid response and torque. 32s can work too, but at a cost.

If it were me, I'd probably pick 30mm vents.

[Jake Raby]

[Mark]

Well I've pulled the plates for the year until I get this nailed down. With this uber-lousy mileage, I'm concerned about washing down the cylinder walls. I'll update this as time allows. Of course, with a baby on the way soon it's not like I'll have much time on my hands after that happens.
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[Oil Phil-M]

My westy has a 2.0L, Raby cam, 1.7L heads with 28 vent 40 IDFs jetted 50-130-200. On the highway RPM is the limiting factor. There is still lots of power when I'm at top speed and it has a soild pull through the rpm range.

What type of distributer are you using? I thought I read somewhere that accelerator pump and timing advance are somewhat related. If your advance is slow it would need more fuel to stop it feeling like it was stumbling.

When I was setting up my carbs the thing that suprised me the most was how little accelerator pump boost I needed. I also found a rich acc pump can hide an undersized jet if you always testing your jets on how you bus accelerates. It wasn't until I found a long hill and drove up it slowly going up in rpm increments before I found the right jet settings then backed off the acc pump to the point where only couple of mm or about 6 threads were left at the end. Even when I thought I had it right and it passed through our air quality testing facility I was still able to unscrew the nuts out a few more turns.

[Mark]

This is all good info, thanks for the input. The distributor is a new Bosch SVDA, with the vac signal fed from both IDF's T'd together.
At this point, I'm going to start from ground zero and go over everything.
The bus isn't going anywhere right now, so I may as well take the time and get this sorted.
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[Oil Phil-M]

Ignition should be fine with that dizzy.

Jetting takes time and patients. The only tools I had were a fuel pressure gauge, airflow gauge and a jet ream set with micrometer when I was playing around with things. Make small changes to one thing at a time and note the differences both in a log and how the engine runs. Once you think you have it right, play around with it again. Drop down a jet size or 1/2 size and see if it makes a difference. When climbing a hill under load holding the rpm steady (negates the acc pump action)pay attention to whats happening around the upper rpm of a jet range (idles 2800-3000) (mains 3800-4000). If I noticed hessitation at or before these levels I went up a size or half size.

You may even want to try doing a double swap: Go up one size with the idle and drop a size with the main (if bigger than 115) or the other way around. I noticed that idle jet size can have a slight impact in the main jet range. After all the hill testing the accelerator pump was adjusted based on acceleration. I didn't bother with the air correction jet. It doesn't start comming into play till 4k which only briefly exceeded during some acceleration actions.

I had a set of idle jets and mains that I would ream, resolder and drill out again to play with started small and going big till too big. Once I got things feeling good then I went out and bought a set of new jets. Even then after replacing them and things feeling good I bought a set smaller jets for both when it wouldn't pass the air testing. Ended up dropping the idles at 50 which helps keep things cleaner putting around town but the 125 mains would hesitate too much so I kept it up at 130. My feeling is that you souldn't be loading an engine under 3k rpm anyways so going a bit leaner on the idle and keeping things perhaps a bit richer on the mains would be the better way to go.

[Guack007]

Sounds like youve checked everything out correctly and according to your plug readings it does seem to be running rich. Only thing I can think of that hasnt been mentioned is an "outside the box" idea:

Perhaps your losing fuel elsewhere. Got any shaddy neighbors that might be stealing your fuel?

Seriously though, ever smell any fuel? Perhpas a very small leak near the tank?

Just a thought since it hasnt been mentioned and it sounds like all the obvious has been checked out.

Either way good luck and I hope you post your fix.

[74 Thing]

Have you checked your fuel pressure?

[Mark]

I haven't had much garage-time recently, but did manage to drop the engine & pull the heads. Here's two thousand words worth of photos.

1 & 2 side

3 & 4 side



#3 Exhaust looks like it got mighty toasty! These are new AMC heads with about 2500 km on them. On the bright side, there's no sign of blowby leaking on them. Yarrrr....

Tops of pistons look the same as the chambers, nice carbon buildup but not oily.


It's a good thing I pulled the engine, as I also found signs of exhaust leaks from where the copper sealing rings 'should' be sealed. I had to pull the lower sled tins and it was very evident.

At this point, I'm thinking the carbs and/or the fuel pressure are the culprit(s).

Oddly, I have checked fuel pressure previously, although it's entirely possible my gauge is off. I'll get my hands on another gauge to confirm this.

I doubt my neighbors are siphoning, unless they know a way to get in the locked garage with the alarm enabled. No fuel leaks or drips anywhere under the bus. The whole fuel system was re-done before the engine was installed almost 2 years ago.
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