Gunson Colortune…..set up

[TR Rob]

Have acquired a Gunson Colortune and intend to check the air/fuel mixture on the SU carbs. on my TR3A.

I suspect the engine is running a bit rich.

I’m hoping this will be a relatively straight forward job, but judging by other straight forward jobs on this car, I am realising on a 63 year old car nothing is straightforward.

If anyone on the forum has any tricks or techniques for this operation I would be grateful to receive them.

In anticipation…….thanks

[Lebro]

You are aiming for a blue flame , just on the edge of turning yellow.  Solid blue is too lean, solid yellow is too rich.

Don't forget to clean the glass bit after every use.

Bob

Edited November 26, 2023 by Lebro

[TRier]

Hi Rob, I’ve recently overhauled the H6 SUs on my 3a and tuned it with a colour tune, very impressed with it. I tuned it initially according to the “instructions” on the overhaul kit from SU and admittedly in a hurry. It ran quite well, I had done a lot of work to it so went on a 500 mile shakedown, nice and responsive to drive, 23 mpg, not very impressed with that. Got a colortune kit and re tuned it, couple of videos attached here, one showing number 1 running too rich and the second one showing it pretty much right. After re tuning with colortune I went to Spain for 10 days, 1800 miles, full luggage, 2 up and roof down, I did two tests over th 1800, 35.5 and 35.7. The speedo is right.

So videos showing the colours aside, I found that the front carburettor was very fiddly to get right. It did not adjust as easily as the rear one, tended to max out the mixture screw and then with it maxed out be close to right but not perfect. I was loath to take the carb out and do a realignment but in the finish I had to, it took a couple of goes to get a nice linear smooth dropping of the piston on that carb, I almost gave up on the basis that something was wrong with it but luckily in the finish it came right. Then with the piston dropping nice and smooth the mixture adjustment worked properly, it required a bit of fiddling. The other thing that’s important is to use the two little spanner’s that SU give you or make one, you have to lock the adjustment base with a spanner when adjusting the back nut and it’s a bit awkward, if you don’t hold that outer hex whilst adjusting the backnut then it’s difficult to get repeatable results. I haven’t put an AFR analyser on this thing yet but I will at some point but the mpg and it’s performance in mountainy country would indicate it’s pretty much on the money. 
Worth all the effort though. Hope that helps.

Edited November 26, 2023 by TRier
Typo

[Lebro]

    Click on to enlarge

This shows how mixture can vary between cylinders fed from the same carb

Bob

[TRier]

7 hours ago, Lebro said:

    Click on to enlarge

This shows how mixture can vary between cylinders fed from the same carb

Bob

Hi Rob,  that's an interesting one.  What did you find that down to?

 

[Lebro]

Nothing definite, maybe because the engine is at an angle (& even more so in my garage which is on a slope !)

& the fuel runs down hill in the manifold ? who knows.

Bob

[Ian Vincent]

I’ve noticed the same thing. My inner two cylinders run slightly richer than the outer ones. 

Rgds Ian

[Smithfire67]

On 11/25/2023 at 6:24 PM, TR Rob said:

Have acquired a Gunson Colortune and intend to check the air/fuel mixture on the SU carbs. on my TR3A.

I suspect the engine is running a bit rich.

I’m hoping this will be a relatively straight forward job, but judging by other straight forward jobs on this car, I am realising on a 63 year old car nothing is straightforward.

If anyone on the forum has any tricks or techniques for this operation I would be grateful to receive them.

In anticipation…….thanks

Hi Rob

How did using the Gunsom Colour tune go?

I also have sooty plugs and am wondering which the best plan of attack is?

Many thanks 

Clive 

[TR Rob]

7 hours ago, Smithfire67 said:

Hi Rob

How did using the Gunsom Colour tune go?

I also have sooty plugs and am wondering which the best plan of attack is?

Many thanks 

Clive…. bought a unit off EBay and it has only just arrived. Seems to be in good condition, but I have not used it yet, the main reason being my garage is so cold , I can’t muster any enthusiasm for being out there. I did buy the special SU jet nut adjusting spanner as a “normal”spanner would be difficult to use. 
If we get a bit of warmer weather I will have a go at adjusting the mixture and report back to the forum !!

Edited December 1, 2023 by TR Rob
Grammar

[Smithfire67]

13 hours ago, TR Rob said:

 

I totally know what you mean with enthusiasm Rob. It is particularly grim and cold out there in shed land at the moment!  

Clive

[TimG]

My Colour tune has a tube which clips on the plug hex & has a mirror so you can angle it to view plug over the engine while adjusting the carb.

[Smithfire67]

51 minutes ago, TimG said:

My Colour tune has a tube which clips on the plug hex & has a mirror so you can angle it to view plug over the engine while adjusting the carb.

That's a good idea Tim. Did you find tuning this way to be effective? 

[Keith Wigglesworth]

I recommend pointing the front of the car into the garage and turning the lights out as you tune. Use two colourtunes if you can. Go for the blue colour recommended by the instructions..I found this to result in a lean mix. I then richened a couple of flats and all was well. 
Keith

[Smithfire67]

50 minutes ago, Keith Wigglesworth said:

I recommend pointing the front of the car into the garage and turning the lights out as you tune. Use two colourtunes if you can. Go for the blue colour recommended by the instructions..I found this to result in a lean mix. I then richened a couple of flats and all was well. 
Keith

Out of interest Keith, which cylinders did you pick to tune by?

Clive

[Keith Wigglesworth]

I used no 1 and 4

[TimG]

On 12/2/2023 at 5:07 PM, Smithfire67 said:

That's a good idea Tim. Did you find tuning this way to be effective? 

The tube with mirror came with the colortune. It has worked well tuning my 1930 Sunbeam. With the TR you can see the view window but I have not yet managed to get it to run smoothly. Have new plugs to fit, I hope that improves running to get tune.