TR6 76 TR6 fast idel problem

[pware]

My Father in law says that after about a hour drive the TR6 starts ideling fast. Before the first hour it idels as it should. What could be causing this issue. I do not have RPM figures yet, but will try to get if it is needed to answer this question.

 

[TR3driver]

Any chance the TVS is activating? 72-onward "emissions" TR6 had a Thermal Vacuum Switch that disables the vacuum retard when the radiator gets hot. That jacks the idle rpm way up (to hopefully avoid boiling over).

The thermal compensators on the carbs shouldn't make such a dramatic difference, but might be the problem.

 

[pware]

Good point. How do you test the TVS? Sounds like a good culpret.

 

[poolboy]

If it's the Thermostatic Vacuum Switch, the next time it happens pull the rubber connector off the distributor retard unit.
See if you can feel a slight vacuum at the hole on the RUBBER FITTING, not the nipple on the retard unit. If there is no vacuum, the TVS may have blocked the vacuum from the carbs. Also if the engine picks up even more speed when you unplug it, then the TVS has not gotten hot enough to block the vacuum. From the test I've made with the TVS the engine has to get plenty hot to activate the switch and shut down the retard, very close to boil over.
Another possibility is that the Throttle Bypass Valve is malfunctioning. The diaphram that surrounds the brass valve can get old, and brittle or split, allowing extra fuel to bypass the nearly closed throttle disc(at idle) or it might need adjustment. But suddenly getting out of adjustment is unlikely.
There is an adjustment screw that, if it doesn't have the "tamper-proof" cap, that he can push with his finger tip, which will force the valve closed and the idle will return to normal. If that happens, he's found the culprit and needs to replace the "throttle bypass diaphram" which is Moss # 365-745.
Let us know there may be some other ideas.

 

[pware]

Thanks guys, I will pass this info on to him.

 

[kodanja]

check your timing'