A

adrian pagdin

New Member
My 1986 V8 3.5 is in great running order, excepting the fact that she sat in a barn for ten years. I've started to notice over the past few days that upon coasting to a standstill the idle is high when she has been running for a while. This tends to knock the temp guage up past halfway and make me very nervous.
Any thoughts? IS there a correlation between temp and idle?
Thank you.
Adey
 
Are you still on carbs and if so are they Strombergs or SUs?

If SUs it could be the overrun valves in the butterflies are sticky from the years in the barn. When you coast to a standstill the vacuum increases in the inlet manifold which opens the overrun valves to let air in. If they stick open then it's similar to having the throttle slightly open. Not sure whether Strombergs had something similar.

The engine would warm up if idling fast but if it only rises slightly then stops then that's OK as it just shows the viscous fan and thermostat are doing their job.
 
Pete-B said:
Are you still on carbs and if so are they Strombergs or SUs?

If SUs it could be the overrun valves in the butterflies are sticky from the years in the barn. When you coast to a standstill the vacuum increases in the inlet manifold which opens the overrun valves to let air in. If they stick open then it's similar to having the throttle slightly open. Not sure whether Strombergs had something similar.

The engine would warm up if idling fast but if it only rises slightly then stops then that's OK as it just shows the viscous fan and thermostat are doing their job.
Click to expand...
Thanks Pete
 
Possibly but you might want to let it evaporate before starting the engine. If you remove the elbows leading into the carbs and open the throttle fully you should be able to see the overrun valves and see if they move easily with a long screwdriver.
 
I wouldn't lubricate them with anything. I would remove the butterfly and chuck it in the bin. Replace it with a plain butterfly which does not have the over run valve fitted. Not only will you never suffer from this problem again, but you will also remove a significant impediment to airflow
 
I had the same idling speed problem on mine. When I rebuilt the engine I replaced the butterflies with ones without the overrun valves as Neil suggests. Not sure whether it was that that fixed the problem but it is OK now. It's worth doing as there's no downsides.
 
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