This weekend’s Saturday afternoon was spent tuning up the carbs on the GT6. This was achieved with some degree of success however the car isn’t running as sweetly as I would like.
Last weekend the car wouldn’t even idle on its own so tuning from its current state wasn’t really an option. As such I did what the Haynes manual suggested on both carbs; screw up the jet (part 56) right up to the top of the air piston (part 41) and then proceed to unscrew it three full turns. With this setting the car started on the second attempt which was better than last week and isn’t too surprising as it normally needs a bit of fuel pumping through from the tank. Once the engine had warmed up it was obvious that it was running much better than last week, however it was idling at 900 RPM which is far too high as it should idle at about 600 ~ 650 RPM.
The way to test if a carb is running too rich or too weak is to raise the air piston 0.8mm (about the width of the pointy end of a flat blade screwdriver). If the carb is set up right there should be no change in the RPM or engine note. If the RPM increases it is running to rich, if it goes towards a stall it is running too weak. Needless to say I had one running too weak and one too rich. So I started adjusting the jet by 1/8 turns on the adjusting screw on both the carbs. Doing this I have managed to get the engine idling at about 700 ~ 800 RPM. I can artificially get the engine to tick over at 600 ~ 650 RPM by partially covering up some of the air intake on the carbs. You can tell it is supposed to tick over at this speed as the engine note totally changes and the engine sits perfectly still on its mountains. Even so it is now running better than it ever has while it has been in my ownership and my dad commented when I drove it up and down the road that it sounded much smoother so it is at least drivable again now. However, no matter what I tried I couldn't get it down to its proper idle speed and it was at this point I noticed two things as to why the RPM wasn’t going down as much as I expected.
1. The vacuum hose between the distributor and the front carb had split.
2. The air piston wasn’t returning right to the bottom on the front carb after the engine was reved. Below is how it should look, however it was sitting about 1.5mm higher than this one.
Point one shouldn’t have made much difference, however it will have to be fixed before I do any more setting up. I may as well have everything correct before I go any further.
Point 2 is much more likely to be the cause of why the RPM wasn’t going down. At first I though this was happening because we replaced the diaphragm and it wasn’t allowing the correct travel of the air piston. However after speaking with some people it would appear much more likely that it is the jet and needle that are not quite in alignment. This can be fixed by undoing to jet holding chamber (Part 59) and then re doing it up again. A simple fix (if it works) but at this point it had started to rain/hail and I didn’t fancy leaving the car out in those weather conditions. Plus the fact that the vacuum hose needed fixing so I couldn’t really do much more carb tuning I thought it would be best get the car back inside.
So the next thing to fix is the vacuum hose before I can move forward. Currently it is just a rubber hose that runs along the fuel pipe. While this is functional enough it doesn’t look too nice. As most of the pipe work on the car (brake and fuel pipes) is copper I’m going to make the vacuum pipe out of copper also. Problem is the vacuum pipe is just over 3 feet long and goes right round the front of the engine. This will evolve quite a large piece of copper pipe (not cheap for its size) and some very precise pipe bending. To do this I have ordered a mini pipe bender which should hopefully arrive sometime this week. This will mean I will be able to make the new vacuum pipe one evening in preparation to look at the carbs again next weekend.
So even though I haven’t got the car up and running perfectly, it is running and it is drivable again which is essentially what I wanted out of the weekend. Hopefully next weekend I’ll be able to get the carbs sorted and move onto the next thing.
Oh and for everyone who commented on how how small it is, here are a couple of comparison photos between it and my dads TT and my C30. As you can see the modern cars are so much bigger than it which can be a little daunting when you are out driving and a huge truck decided to overtake you
Last weekend the car wouldn’t even idle on its own so tuning from its current state wasn’t really an option. As such I did what the Haynes manual suggested on both carbs; screw up the jet (part 56) right up to the top of the air piston (part 41) and then proceed to unscrew it three full turns. With this setting the car started on the second attempt which was better than last week and isn’t too surprising as it normally needs a bit of fuel pumping through from the tank. Once the engine had warmed up it was obvious that it was running much better than last week, however it was idling at 900 RPM which is far too high as it should idle at about 600 ~ 650 RPM.
The way to test if a carb is running too rich or too weak is to raise the air piston 0.8mm (about the width of the pointy end of a flat blade screwdriver). If the carb is set up right there should be no change in the RPM or engine note. If the RPM increases it is running to rich, if it goes towards a stall it is running too weak. Needless to say I had one running too weak and one too rich. So I started adjusting the jet by 1/8 turns on the adjusting screw on both the carbs. Doing this I have managed to get the engine idling at about 700 ~ 800 RPM. I can artificially get the engine to tick over at 600 ~ 650 RPM by partially covering up some of the air intake on the carbs. You can tell it is supposed to tick over at this speed as the engine note totally changes and the engine sits perfectly still on its mountains. Even so it is now running better than it ever has while it has been in my ownership and my dad commented when I drove it up and down the road that it sounded much smoother so it is at least drivable again now. However, no matter what I tried I couldn't get it down to its proper idle speed and it was at this point I noticed two things as to why the RPM wasn’t going down as much as I expected.
1. The vacuum hose between the distributor and the front carb had split.
2. The air piston wasn’t returning right to the bottom on the front carb after the engine was reved. Below is how it should look, however it was sitting about 1.5mm higher than this one.
Point one shouldn’t have made much difference, however it will have to be fixed before I do any more setting up. I may as well have everything correct before I go any further.
Point 2 is much more likely to be the cause of why the RPM wasn’t going down. At first I though this was happening because we replaced the diaphragm and it wasn’t allowing the correct travel of the air piston. However after speaking with some people it would appear much more likely that it is the jet and needle that are not quite in alignment. This can be fixed by undoing to jet holding chamber (Part 59) and then re doing it up again. A simple fix (if it works) but at this point it had started to rain/hail and I didn’t fancy leaving the car out in those weather conditions. Plus the fact that the vacuum hose needed fixing so I couldn’t really do much more carb tuning I thought it would be best get the car back inside.
So the next thing to fix is the vacuum hose before I can move forward. Currently it is just a rubber hose that runs along the fuel pipe. While this is functional enough it doesn’t look too nice. As most of the pipe work on the car (brake and fuel pipes) is copper I’m going to make the vacuum pipe out of copper also. Problem is the vacuum pipe is just over 3 feet long and goes right round the front of the engine. This will evolve quite a large piece of copper pipe (not cheap for its size) and some very precise pipe bending. To do this I have ordered a mini pipe bender which should hopefully arrive sometime this week. This will mean I will be able to make the new vacuum pipe one evening in preparation to look at the carbs again next weekend.
So even though I haven’t got the car up and running perfectly, it is running and it is drivable again which is essentially what I wanted out of the weekend. Hopefully next weekend I’ll be able to get the carbs sorted and move onto the next thing.
Oh and for everyone who commented on how how small it is, here are a couple of comparison photos between it and my dads TT and my C30. As you can see the modern cars are so much bigger than it which can be a little daunting when you are out driving and a huge truck decided to overtake you
