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914World.com _ 914World Garage _ PMO Carburetor help needed.

Posted by: defianty Dec 28 2019, 06:32 AM

Some of you may have seen my build thread where I mentioned I stripped down my PMO's for a good clean. Sitting around for a couple of years with remnants of old fuel in didn't do them any favours.

Now all clean and back together I'm having an issue I can't find a solution to and I need help.

So with everything installed back on the car and connected correctly - when the car starts it instantly idles at 4,000rpm+ rather scary! So it's switched off immediately.
This has absolutely nothing to do with the idle adjustment screws, the throttle linkage or the accelerator cable - they're all disconnected.

Yesterday whilst trying to troubleshoot further I confirmed the fuel pressure is correct at 3.5psi from the PMO fuel regulator so I thought I could rule that out. However when I then tried to recheck the timing with the fuel pump disconnected the car fired up and straight away and idled at 900rpm fairly smoothly with the fuel in the bowls and continued to run well until the fuel ran out. Fuel pump back on - bowls filled - restarted and back to a 4,000rpm idle.

Any suggestions welcome!

Posted by: Mark Henry Dec 28 2019, 06:48 AM

I don't know the PMO's, but did the float level shims change or are the float gross valves sticking open?
Look for fuel overflowing and spilling into the throats with the pump on.

If it is you've likely messed up the float level (shims), the valve(s) is sticking or maybe the top gasket is catching on the float mechanism.

Posted by: wndsrfr Dec 28 2019, 07:25 AM

It's an air leak to be going 4000...disconnect throttle linkage first... if is still fast use a propane torch (not burning) to probe around carb base and pivot shafts to find possible leak location...

Posted by: dr914@autoatlanta.com Dec 28 2019, 11:23 AM

I would call Richard Parr at PMO and speak with him. Good guy and the best to troubleshoot

Posted by: defianty Dec 28 2019, 12:04 PM

Thanks guys.

I'll investigate further tomorrow and see if I can find anything.

However as strange as it sounds I think it could have been a starter motor/ wiring issue. Something odd happened today and the car idle jumped up after idling smoothly for about five minutes. As the idle raised quickly I heard a not very pleasant sound followed by black smoke from the starter?

I really don't know what happened yet but I'll report back my findings.