Setting my SU carbs

[UKPhilTR7]

Setting the timing with a strobe light should be done from #1 spark plug lead.
Could be yours are fitted in the wrong sequence.
At idle the dynamic advance should be the same as static; 10°BTDC

So going on this, if mine is 12.5 BTDC and not 10 BTDC on spark plug 1, this means that mine is out to start with?

[Stag76]

Hi Phil,
10 degrees or 12.5 degrees will not matter, as long as it's not pinking under load.

By adjusting screws, do you mean the small screws with a spring under the head, or the brass gland nuts
on the under-side of the carbies.

[Beans]

... The points are 5 degrees apart ...

Make that 4 degrees apart
So the lower yellow marker is the 10° BTDC point

[REPLIC8]

I tuned LOG 7 X at home last year. Started with basics, plug gaps, points gap, new air filter etc. Then I set the static timing at 10 degrees btc. I then followed the factory manual to set up the carbs using as carb balancer and a Gunsons exhaust analiser.
Took a couple of hours of fiddling about but not too difficult a job. Once I'd finished I took it down to my local rolling road tuner to see how I'd done. Pretty amazed to find I'd got it to 106.8 bhp, and the tuner could only get it to 108.2 bhp. It's not the best photo but you can see from the printout the before and after power and torque curves are almost identical.
So if you take your time and work methodically even an amateur can achieve decent results.

[UKPhilTR7]

I must admit that the two yellow paint marks look like they were put on at the same time (hopefully by someone who know what they were doing). This is leading me to think that the yellow mark below the tdc is where the mark on the pulley should align up with. If the second mark is 10°BTDC, that would be great. I just need to confirm that now as that is where the manual states that idle should be.

I need to check lead 1 now as the alignment was done on lead 4. When I did it on lead 1 first of all it did not look right, but I was not sure of what I was doing so I didn’t follow it up. I will do this over the next few days and let you guys know. I would think that it would be OK on lead 1 though as if 4 is OK, then it should be. If not I may have found an issue lol.

@Stag76, the screws that I have been turning up until now has been the ones on the top to the side of the carb. Not too sure where the small screws with a spring under the head, or the brass gland nutson the under-side of the carbies are. Have you any pictures I can see?

Oh I would love a Gunsons exhaust analyser, but a bit costly for me at this stage, when just getting my head around it all, but sure something to look at for the future.

[Hasbeen]

Phil it sounds like you are working on the throttle stop screws. Use these to adjust the closed position of each carb. They allow you to adjust & equalise the suction through each carb. This is the balance we talk about.

If you look at the bottom of the float bowl you will find a tube going from it, to the bottom of the main body of the carb. This is the jet tube. Fuel flows through it to get to the main jet.

The mixture of an SU is adjusted by raising or lowering the main jet in the main body of the carb. Follow that tube, [probably red], to the carb & you will find it attaches to a brass tube. This is the main jet, & it will pass through the other brass nut you have to adjust to correct the mixture.

Turning that nut clockwise looking from under the carb will raise the jet & lean the mixture. Vice Versa & you richen the mixture.

To tune, Adjust the jet height as described by Stag 76. Disconnect the 2 carbs throttle spindles by just loosening the clamp nut. Set the revs at about 1000. Adjust the suction through each carb to be equal. Use a plastic tube from carb to ear, or one of the tools designed for this.

Now gently lift each piston in turn about 2 or 3mm , either with the lifter if fitted, or by inserting a small screwdriver under the front of the piston & turning it.

The engine revs will respond to this lifting. If they increase somewhat, wind the large nut under the carb up, [clockwise from under the carb] one flat to slightly lean that carb. If they fall wind down one flat to richen. Continue this process until the engine revs increase very very slightly when you lift either piston.

You should give the engine a little rev to about 2000, sustained for 30 seconds or so, every minute or so to keep everything clean. You probably will have to rebalance the suction through each carb a adjust the revs at the throttle stop a number of times as you tune, as your mixture adjustments will alter this as you approach the correct mixture.

One final thing. I would rather have an oil leak from my tappet cover, than either riding or low clearance valves, or noisy tappets from excessive clearance. That said, if you can get it to run really nicely, the valve clearances can't be too bad.

This took longer to type than tunning your SUs should take. It's easy if someone is available to show you. Good luck.

Hasbeen

[Stag76]

Hi Phil,
I sent you a PM.

[Stag76]

Hi Phil,
My PM has crossed with Hasbeen's post, so a lot of it will be repetition.

[Hasbeen]

Hi Stag 76.
About time you took a little drive to the east.

You could practice SU tuning on mine, as I don't think you have any these days, & must miss them.

Hasbeen

[UKPhilTR7]

Gents, all I can say is thank you so much for your help. The old English saying comes to mind here; the penny has dropped, (I bet some may be saying finally lol). I take my hat off to you and your excellent detailed explanations and pm’s

The issue here is that I have not even thought about doing anything like this before. The last time the carbs went into be reconditioned, I paid a guy to do it at great cost. However, now in Australia, I am finding I have to do these kind of jobs myself. I did not even know about the brass jet adjuster nut below the spring under the carby, let alone that it was responsible for the mixture being lean or rich. I was always lead to believe that all carb tuning was always only done with the two screws on the top of the cards.

My car is running rich at the moment. While she was running down in the communal garage area last night, after about ten minutes I was feeling really high lol. The good news is that after checking again with the timing gun, leads 1 and 4 are showing the mark on the pulley with the lower yellow mark btdc perfectly. I am going to take it that this is correct, with the lower yellow mark being 10 or 12.5 degrees btdc. I totally agree Hasbeen and will take the cam cover off to check the clearance. I have a spare gasket and sealant, so all will be good.

I think I will have a look at this possibly the weekend and see if I can get the air filters off and sync the carbs. I will for sure have to turn the nuts anti-clockwise to raise the jets and get the mixture lean. I will start off by using a vernier caliper depth gauge, to set the top of the jet to .125'' below the jet holder though.

Just a question for you:
Is the colour tune used with the jet adjustment brass nuts or the mixture screws on top of the carbs? I am assuming that the colour tune is used with the mixture screw (on top of the carb) and the carb balancing gauge is used with the jet adjustment brass nut at the bottom of the carbs.

[UKPhilTR7]

Hi Stag 76.
About time you took a little drive to the east.

You could practice SU tuning on mine, as I don't think you have any these days, & must miss them.

Hasbeen

I think a trip to Sydney would be a great idea

[UKPhilTR7]

I took this picture yesterday to clarify the correct nut, before I read both your replies. It looks rather dirty to me and I wonder if the top nut is not tight enough as my dash pots always seem to be a bit dry. It looks like the oil I am putting in is leaking through and making it all dirty.

[Stag76]

Hi Phil,
The oil should not be leaking from the slide damper tube and ending up under the carby.
It's probably part of the BL Corrosion Prevention System.
The ColorTune plug is used when adjusting the mixture with the brass gland-nut.

Those are the WaxStat Type of jet.
They have a wax pellet that expands and contracts with temperature changes to slightly
alter the height of the jet and therefore richen or lean the mixture. They do not
always work correctly.
They can be modified by replacing the Wax Pellet with a $2 coin, or something
roughly the same size, but, if they are giving trouble, it's easier to purchase some jets that
do not incorporate the waxstat, similar to the one in this picture. (This is an HS4, and I
think the jets for TR7 HS6 Carbies are Red).

[Hasbeen]

Two other little things to watch out for phil.

There is, or should be a little cam plate attached to the choke spindle system, This opens the throttle a little when the choke is used. This is adjustable. It needs to be checked that it is not in operation when the choke is closed. Om my 7 due to a little wear in everything it really only operates the rear carb, & could give tuning problem if not adjusted properly.

Secondly, the operation of the choke is to pull the main jet down, thus richening the mixture. Due to dirt wear or damage the jet may not go back up by the spring pressure, when the choke is pushed off. The action is not a positive movement by the choke cable, but depends on that spring you can see in Stags picture to push it back to normal running position.

You can easily push the jet back up by fingers when it sticks, Before mucking with the tuning check that the jet is free & moves back when the choke is off. Clean the area, then operate the choke a few times to see the jet is responding properly.

Sorry Phil, Sydney is a bit far for me for a Sunday drive. What part of Sydney are you in? My son has been called up to do some reserve time, training people in the navy. He's down there somewhere, the Navy probably have him too busy to help, but perhaps not. Is the car fully mobile at the moment? You might be able to get a quick lesson if it is, & he is not too far away.

Hasbeen

[UKPhilTR7]

Thanks guys, will keep an eye out and look over things and make sure there is no oil leak.

So I have the Waxstat Type - for Carbs FZX1242. Is it OK to change them for the Main Jet - for Carbs AUD634. Is it OK to swap them over if needed or is it best to replace like for like or add the two dollar coin at the bottoon of the jet?

@Hasbeen, live just outside of the cbd near to Chatswood.