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  View original topic: '59 rebuilt 36hp idle very high
Sham Tue Nov 30, 2021 8:21 am

Hello guys,

So, I have fully rebuilt my 36hp (details here : http://shamwerks.com/Beetle-page-2), and it runs great - well, I had a bit of a misadventure due to a fuel pump spring breaking the lever, but that's been fixed be putting back the original spring.

Anyway.
My issue is that I have a pretty high RPM idle, like 1500 rpm. I'm trying to bring it down, sprayed some brake cleaner squirts at the base of the manifold chasing air leaks (there was none), checked that the cable wasn't pulling on the throttle, same for the choke, checked that the butterfly properly closes... And I still fail to bring down the idle RPM.

The 28PCI has been fully rebuilt ; before the engine rebuild it idled fine at around 500-600RPM .

Would you have ideas to help me lower the idle RPMs? Thank you!

Lingwendil Tue Nov 30, 2021 1:08 pm

If you screw the adjuster in does the butterfly close before the engine begins to stall? Or start running funky?

my59 Tue Nov 30, 2021 3:11 pm

Have you made sure the accelerator and choke cable are routed correctly and have been lubricated in their housings?

mukluk Tue Nov 30, 2021 3:17 pm

Since the carburetor was fully disassembled for cleaning, I would try slightly loosening the nuts at either end of the throttle butterfly shaft where the linkages mount. If these are overtightened, they will cause the throttle shaft to stick and prevent full travel.

Sham Wed Dec 01, 2021 3:56 am

Lingwendil wrote: If you screw the adjuster in does the butterfly close before the engine begins to stall? Or start running funky?
You're talking about the adjuster screw on the butterfly lever itself?
I'll give it a try this week end and let you know how it behaves.
my59 wrote: Have you made sure the accelerator and choke cable are routed correctly and have been lubricated in their housings?
Yep, cables changed, greased, and properly routed (I had to redo it twice, got it wrong first try).
mukluk wrote: Since the carburetor was fully disassembled for cleaning, I would try slightly loosening the nuts at either end of the throttle butterfly shaft where the linkages mount. If these are overtightened, they will cause the throttle shaft to stick and prevent full travel.
That's a pretty good idea, I'm going to check that, thanks!

Actually, I've just rewatched the video of the very first start of this engine a few months ago, and it looks like back then I could get to a reasonnable idle RPM :

Hmmm. Food for thoughts, I'll look into your inputs and let you know what I find out.

Airstream65 Wed Dec 01, 2021 5:27 am

First off, starting fluid should not be needed to start the car. Have you double checked the valve lash, points gap, and timing? Start from the beginning!

Sham Wed Dec 01, 2021 6:02 am

Airstream65 : Starting fluid was used only this one time, as it was the very first start of the engine. Oil pressure had been primed before by running the starter motor but disconnecting the ignition. I wanted to ensure the very first sparks would start th engine.

As for points gap, valves, timing, yes, of course those had been adjusted before (and timing checked with a stroboscopic lamp after) this first start.

Obviously starting fluid isn't needed any longer, and the engine happily starts right when the key is turned.

KTPhil Wed Dec 01, 2021 11:38 am

Many are not familiar with the somewhat picky throttle return spring/cone/washer arrangement of the early cars, and it often binds when not cleaned, deburred, straightened, and assembled correctly.

Erik G Wed Dec 01, 2021 1:34 pm

KTPhil wrote: Many are not familiar with the somewhat picky throttle return spring/cone/washer arrangement of the early cars, and it often binds when not cleaned, deburred, straightened, and assembled correctly.

right. I would start by disconnecting the cable altogether and work backwards from there

KTPhil Wed Dec 01, 2021 1:50 pm

A more far out possibility is that the heat riser has burned through to the intake manifold pipe and you are getting extra air through that path. Rare, but it's been reported here.

Yes, take the cable off completely to eliminate/confirm it's a contributor! Easy things first!

motofly196 Thu Dec 02, 2021 12:10 am

Check that your manifold to head nuts are tight too. Could of loosened up over a few heat/ cool down cycles.

Sham Thu Dec 02, 2021 1:40 am

KTPhil wrote: Many are not familiar with the somewhat picky throttle return spring/cone/washer arrangement of the early cars, and it often binds when not cleaned, deburred, straightened, and assembled correctly. Erik G wrote: I would start by disconnecting the cable altogether and work backwards from there
I've had that car for over 26 years now, I'm very familiar with the spring setup. But you're right, I'll take it off completely, give it another check, and see how disconnecting the cable affects the idle.

KTPhil wrote: A more far out possibility is that the heat riser has burned through to the intake manifold pipe and you are getting extra air through that path. Rare, but it's been reported here.
No, I think I can strike out that option. I've modified the manifold to shorten it (in the process of increasing compression ratio - details here), and doing so I've pressure tested it for leaks.

motofly196 wrote: Check that your manifold to head nuts are tight too. Could of loosened up over a few heat/ cool down cycles.
Good point. I have squirted brake fluid at the manifold bottom looking for leaks, but I'll check the nuts are tight too.

KTPhil Thu Dec 02, 2021 10:11 am

Another common source is NOT removing the old manifold sealing rings (easy to do since it gets squashed and looks like part of the head), and putting an "extra" one on when installing the manifold. You really have to look carefully at the inlet port to tell the difference!

motofly196 Thu Dec 02, 2021 10:18 am

I was actually going to mention the same thing! But I didn't want to "mechanic shame" anybody :lol: Sometimes the crush washer on the intake can blend right in with the color of the head. You've gotta get a pick in there and lift up.

KTPhil Thu Dec 02, 2021 10:23 am

Sounds like the OP has a thick skin and at least a few brain cells between the ears, so I wouldn't worry!

He's covered all the easy sources, so we need to think outside the box and consider rarer options, so keep 'em comin'!

Sham Mon Dec 06, 2021 7:43 am

No worries about mechanic shaming, I'm not taking anything personally, and even though I've been into VWs for about 3 decades, I can will make dumb mistakes just like the next guy. :D :D :D

Crush washer, you know what, since I bead blasted the heads I inspected them veeeeeeery closely. Yet, digging into my pictures library, I found one where... Well, I have the tiniest doubt now. Damn. One more thing to check, though I wouln't put that on top of the list as 1/ no RPM change when squirting brake fluid at the base of the manifold 2/ I did have a correct idle when I first started the engine.

Back to the workshop it is! :wink:



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