High revs problem solved

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Roccola
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High revs problem solved

Post by Roccola » Wed Mar 24, 2021 12:16 pm

A bit of info for anybody with a fast tick over problem.
I've done a lot of work recommissioning my mk2, which had been off the road for 4yrs,
and although I'd got it running ok (if a bit rough) it suddenly developed a tick over which wouldn't drop below 2100 revs.
I would have suspected the waxstat but I'd fitted a new one already.
I got all ready to refurbish the carb and even bought a 2nd hand pierburg with a manual choke conversion to refurbish off the car and a Haynes carburettor manual...
I'd previously drained down the coolant fitting the timing belt/coolant pump, and thought it was worth checking whether there was a connection here. Was the waxstat getting the heat it needed?
Purged the system of air and revs dropped to a steady 900! I'd had an air lock that isolated the waxstat from the coolant.
I know the waxstat causes so many issues, so thought it might be worth sharing.



GT_II
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Re: High revs problem solved

Post by GT_II » Wed Mar 24, 2021 1:18 pm

Roccola wrote:
Wed Mar 24, 2021 12:16 pm
I'd had an air lock that isolated the waxstat from the coolant.
I know the waxstat causes so many issues, so thought it might be worth sharing.
I would second that. The coolant flows through both the wax stat and the choke cover - a blockage in either can cause excessive idle speed and over-rich mixture. I wonder how many Pierburgs have been condemned for this simple fault.

On my GT II, there was some internal corrosion in the choke cover inlet tube. This considerably slowed down the coolant flow through the wax stat and choke, causing it to idle fast until well after the engine had warmed up. Having cleaned up the choke cover, renewed the choke cover seals, and thoroughly flushed and replenished the coolant, the problem has not returned in 4 years.

It is easy to check whether this is likely to be an issue by feeling the temperature of the coolant hoses feeding the wax stat and choke as the engine warms up on idle. If they don't warm up at the same rate as the main coolant hose they are connected to, a blockage or air lock is very likely.


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Roccola
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Re: High revs problem solved

Post by Roccola » Wed Mar 24, 2021 5:42 pm

Ta for reassuring me that it's not just me. I was Googling carb repairs and checking the price of Webers, when it just needed the coolant to burp a bit.