The SH4 twin carburetted engine is few and far in between. Mechanic who are well versed in SH4 twin carburetted engine is few and far in between and it is not surprising that you are not able to find any who can help you.
There are not too many vacuum lines so it should not be a problem but I don't have any vacuum lines diagram so if you could show me some pictures, I might be able to help.
The vacuum component that affects the idming speed would be the Fast Idle Up Control for A/C. This is straightforward. Just ensure the vacuum hose to the solenoid is not reversedly attached. Reversing would result in the vacuum pump not releasing when the solenoid is turned off. Ensure the idle-up adjust screw is not pushing against the throttle when A/C is not turned on.
The component most likely to cause high idling would be the automatic thermal choke mechanism. Ensure the hoses to the thermal unit are not clogged and the choke lever is fully released when engine is at operating temperature. Ensure the thermostat is working and you have one that has not been removed.
Sunday, December 16th, 2012 AT 9:08 AM