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GT6 Engine tune help...

Rui Guimaraes

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Hello everyone!

Today I had a change to take a good ride on my 1967 Mk1 GT6.
This was the first long ride since I've bought her.
Everything went perfectly, the engine is running very smooth the suspension and steering working very nice, etc... the only annoying thing was that every time I switched off the ignition (with the car warm) it keeps firing for few seconds before stopping.
The temperature of the engine is perfect, the temperature sensor is brand new, the gauge was calibrated and tested and it was reading (after warming up) exactly in the middle of the gauge. I have confirmed the gauge and sensor and they are measuring fine.
This only happens with the engine warm.
Can anyone tell me what should I look for?


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  • 2 weeks later...


Sorry for the late reply but I'm working away from home and I only have the chance to be near the car on some of my weekends.

Last weekend I have changed the fuel to 98 octane and it looked to improve a bit but still not perfect.
Today I have checked the contact breaker points setup and static timing and they were a mess...
The contacts were almost not openning and I've set them to the recommended 0.4 mm of the workshop manual.
In regards to the static timing, it was around 5º moved from the 13º recommended.
I've putted everything by the book and started the engine...
Incredible! Without touching the choke or the throtle the engine started and kept working very stable but with a higher idle speed (around 1300 rpm) when compared to the previous setup (around 1100 rpm).
In the past it was impossible to start the engine without pulling the choke and touching the throtle for a few seconds.
I had not the chance of trying the engine to run for more than a few seconds because I had a problem with the water pump which is still out of the engine.
What should be the next step? Should I touch the idle speed setting?? or should I wait for the pump and try the car first?


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Just putted the new water pump in and tried it out...
It started easily and almost without pulling the choke.
The engine sounds much more tunned (now it sounds more as a Six Cylinder...! :)). After a 30 minutes ride, tried to turn the ignition switch off and no run-on at all.  ;)
My concern is about the idle speed that is far too high (cold - 1300 rpm, warm - 1600 rpm). :-/
Tried to lower it on the throtle stop screw but I can not since it is already at the minimum...???
As far as I understand, this should mean that the mixture is probably too lean???....Right??
Should I try to follow the workshop manual and re-setup the cabs? After a first reading the procedure looks to be a little confusing?..
Anyone has some advices... or a more clear procedure?? With diagrams, pictures or videos??
Any suggestions?


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Fast idles are often due to the butterflies still being slightly open, or an air leak in the manifold. I'd start by loosening the connecting rod between the carburettors, and looking into each one to make sure the butterflies are snapping shut. If they are, and the engine still idles too fast, then the air is leaking in somewhere.

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You were absolutely right, there was a leak of air...
I have tried to re-setup the carbs and nothing! looked for a leak on the manifold and nothing again!
Then I have decided to remove the carbs for cleaning and there is was...
... a missing bolt that holds the butterfly of the rear carburetor and the air was going through the hole.
I have changed the carbs for a reconditioned pair that I had in stock and now it perfect!
Idle speed is now around 800 rpm.


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