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I helped a mate tune his car recently and when we took his car for a test drive, I realised how much my own car was down on performance. 

My daily driver TR2 has a high port head with 1 3/4" SUs and new SM needles. The carbies are in good condition having done about 30,000 miles.

I usually set the mixture a bit rich but I moved to an inner-city location 5 years ago and consequently spend a fair bit of time at idle. Over time I have gradually been adjusting the mixture to get a smoother idle in the traffic I now face. Over time it had become so lean it was affecting performance.

I richened it 4 flats and on Wednesday went for a high speed drive for a club coffee meet. Performance was better but on arrival I checked the plugs and they were white. I dropped the mixture another couple of flats for the drive home.

Performance improved again but when I got home the plugs were still white. I dropped them another two flats. I'll check the plugs on the next long drive to see how they look, light tan is the aim. The car's performance is now comparable to my mates' car.

The book says to start at 2 1/2 full turns or 15 flats down as a starting point.  Mine are now 8-10 flats down. The car's performance has improved markedly, at the cost of a rougher idle and the need for an increased idle speed to 8-900.

I have had them another 2 flats down but the exhaust note indicated it was too rich so I put them back to where they are now. It feels a good balance. The revs increase with a lift of the piston (using the button) but the idle is OK at 900 or so. 

It had me thinking what the average mixture setting would be. If the book says start at 15, 8-10 seems quite lean still. I know that it will depend on carbie and needle condition and other factors but there are lots of owners here so it would be good to know the range of settings.

What do others have their carby mixture set at?

Edited by John McCormack
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Brother and I both run 4 cyl TRs and have done since the 70's

Typically we would drop the jet by up to 2 flats on each carb for winter running (and curse the lumpy tickover if stuck in traffic) 

Would raise the jet by one flat each as spring arrived and then summer.

Turning down the jet by 8-10 flats says there is something odd going.

This is a bit 'suck it and see' I know but works for us.

What do other all year TR users do?

 

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24 minutes ago, BlueTR3A-5EKT said:

 

Brother and I both run 4 cyl TRs and have done since the 70's

Typically we would drop the jet by up to 2 flats on each carb for winter running (and curse the lumpy tickover if stuck in traffic) 

Would raise the jet by one flat each as spring arrived and then summer.

Turning down the jet by 8-10 flats says there is something odd going.

This is a bit 'suck it and see' I know but works for us.

What do other all year TR users do?

 

The jets are down 8-10 flats from being fully up. As the manual says to start at 15 flats down 8-10 might indicate it is still too lean, but it might also be that the manual sets it up too rich to start so that you tend to run it a bit too rich than a bit too lean. It is far preferable to have it richer than leaner to avoid burning out valves and pistons with a too lean mixture.

We don't really have a winter summer change here down under. Our summer can be very hot (this one is surprisingly mild with very few days so far over 30 deg C) but then winter is usually very mild compared to the UK. The bigger variable here is heavy traffic versus open road, especially in summer. 

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Unfortunately all the manuals for tuning SU were written back in the days of real petrol, the guff we`re running on these days bears no relation in terms of how it burns etc so its really down to individual tuning of your engine and the type of fuel available in your location. A good session on a rolling road with someone who knows what theyre doing will make a lot of difference. Or conversely buy yourself a Wide band AFR kit and then you have your own rolling road.

Stuart.

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I had my TR set up on a rolling road and afterwards I measured the height of the jets relative to the bridge with a depth mic. From memory the front carb was at .89mm and the rear one 0.6mm. I don’t know how that translates into flats. 

Rgds Ian

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6 hours ago, stuart said:

Unfortunately all the manuals for tuning SU were written back in the days of real petrol, the guff we`re running on these days bears no relation in terms of how it burns etc so its really down to individual tuning of your engine and the type of fuel available in your location. A good session on a rolling road with someone who knows what theyre doing will make a lot of difference. Or conversely buy yourself a Wide band AFR kit and then you have your own rolling road.

Stuart.

Stuart, I have been meaning to do this for some while, a great suggestion.

Iain

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11 hours ago, John McCormack said:

The jets are down 8-10 flats from being fully up. As the manual says to start at 15 flats down 8-10 might indicate it is still too lean, but it might also be that the manual sets it up too rich to start so that you tend to run it a bit too rich than a bit too lean. It is far preferable to have it richer than leaner to avoid burning out valves and pistons with a too lean mixture.

We don't really have a winter summer change here down under. Our summer can be very hot (this one is surprisingly mild with very few days so far over 30 deg C) but then winter is usually very mild compared to the UK. The bigger variable here is heavy traffic versus open road, especially in summer. 

The 8-10 flats down.  Is that as an adjustment from the engine running ok ish?   Or from turning the jets up to be level with the bridge and then setting them downwards to give a basic setting.?   Our 2 flats down is from the engines running nicely during the summer.

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1 hour ago, BlueTR3A-5EKT said:

The 8-10 flats down.  Is that as an adjustment from the engine running ok ish?   Or from turning the jets up to be level with the bridge and then setting them downwards to give a basic setting.?   Our 2 flats down is from the engines running nicely during the summer.

8-10 flats down from the jet being level with the bridge. I put the adjusting nuts all the way up and then adjusted them to be 12 flats down. It was too rich there so I adjusted them to get a better mixture and they ended up being 8 flats down on the front carby and 10 on the back carby. It is still a bit rich there going on lifting the piston and on the exhaust note but I want it richer than leaner. The next highway run I'll check the colour of the plugs and adjust further as needed.

I figured that some owners could check where their adjusting nuts are set and compare them.

Interesting about the modern fuels changing settings. I watched the video on this site about modern fuels and ethanol and learnt a great deal. That could be why the carbies are set leaner than what the manual says to start tuning them with.

We are fortunate here with 98 being ethanol free as are many 91 and 95 fuels. Ethanol use is essentially optional in Oz. I only use 98 in all my cars.

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John,

One flat is equal to 0.006” linear jet movement according to SU.

http://sucarb.co.uk/technical-su-carburetters

Good reading in the above article.

Questions for you.

Is this engine of yours 83 or 86 mm?  Is it a standard cam?  Is it a standard high port head and valves?

What weight spring is in the carbs?   Push it down on the kitchen scales to check?  You want 4 ozs which is a spring with a red identifier mark.   Heavier springs will richen the entire rpm range   Weaker spring does the opposite.

If yes to above engine specs then  SM needles red springs and 0.100” diameter jets is a great place to start.   The needle valve in the float chamber wants to be the bigger one too.  (0.096”)  I know it as GSU 102 or WZX1101.  

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5 hours ago, BlueTR3A-5EKT said:

John,

One flat is equal to 0.006” linear jet movement according to SU.

http://sucarb.co.uk/technical-su-carburetters

Good reading in the above article.

Questions for you.

Is this engine of yours 83 or 86 mm?  Is it a standard cam?  Is it a standard high port head and valves?

What weight spring is in the carbs?   Push it down on the kitchen scales to check?  You want 4 ozs which is a spring with a red identifier mark.   Heavier springs will richen the entire rpm range   Weaker spring does the opposite.

If yes to above engine specs then  SM needles red springs and 0.100” diameter jets is a great place to start.   The needle valve in the float chamber wants to be the bigger one too.  (0.096”)  I know it as GSU 102 or WZX1101.  

The engine is largely standard TR2 but with 86mm liners, high port head and 1 3/4" SUs. I'm assuming they are stock carby springs, they have no colour marks now but they might have had once upon a time. Float chamber needles are the upgraded viton?? ones which I believe are bigger. The cam is standard or very close to it. Stock exhaust.

The SM needles are new and the jets show no signs of wear. The carbies aren't that old, I found a set of brand new old stock carbies about 8 years ago.

I checked the needle positions again and the aft carby was a spoofteenth proud of the piston face. Adjusted it back to level and adjusted the mixture up one flat to compensate. Went for a test drive (only 10 minutes at 80 km/h in top so not a good test) and checked the plugs. Still a bit light in colour so both carbies jets are now down one more flat to 10 flats. Timing is advanced to the point where it just doesn't ping.

The engine is pulling really well, a marked improvement from a few days ago. The idle is a bit lumpy but maintains itself at 800-900 after a 30km drive. It idles about 1000 until it gets nice and hot.

What I'd like to know is where other cars have their jets set. If others are a long way different to mine I will look for other causes.

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I have also found that the 1950s quoted number of flats is no longer ideal for modern fuels - but it is a good sanity check. They must both be the same and less than 10 flats down (else something is probably wrong) but if no gas analyser is to hand then the trusty Colortune devices as #1 AND #4 spark plugs is still valid as the flame colour remains a valid indication of A/F ratio irrespective of fuel composition.  I don't think you referenced ethanol but as the % increases you may/should/perhaps (!) notice that the engine runs weaker due to the oxygen in the ethanol part, I'm tracking this adjustment on my '3 as well as other impacts of E10. 

MikeJ

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Have you used an airflow meter to check that you have the same vacuum flowing through each carb? Also is the oil level the same in each dashpot. If the pistons do not lift together this will effect mixture and performance. After a decent run the exhaust pipe end should look greyish rather than black if set corrrectly.

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11 hours ago, Phil Read said:

Have you used an airflow meter to check that you have the same vacuum flowing through each carb? Also is the oil level the same in each dashpot. If the pistons do not lift together this will effect mixture and performance. After a decent run the exhaust pipe end should look greyish rather than black if set corrrectly.

Yes the carbies have been balanced with a flow meter and the oil levels are the same. The exhaust colour as a measure of the mixture was lost when we took the lead out of the fuel. I use to be constantly checking the exhaust colour but all exhausts are black now.

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13 hours ago, mikej said:

I have also found that the 1950s quoted number of flats is no longer ideal for modern fuels - but it is a good sanity check. They must both be the same and less than 10 flats down (else something is probably wrong) but if no gas analyser is to hand then the trusty Colortune devices as #1 AND #4 spark plugs is still valid as the flame colour remains a valid indication of A/F ratio irrespective of fuel composition.  I don't think you referenced ethanol but as the % increases you may/should/perhaps (!) notice that the engine runs weaker due to the oxygen in the ethanol part, I'm tracking this adjustment on my '3 as well as other impacts of E10. 

MikeJ

I'm chasing a colour tune. Global supply chain issues mean they aren't easily available here at the moment, I'm trying to borrow one.

No ethanol in the fuel I use.

Mine are now 10 flats down on each carbie and it is a bit rich so after a high speed run I may adjust them to 8 or so flats.

Why do you say they should be less than 10 flats down?

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11 hours ago, John McCormack said:

Yes the carbies have been balanced with a flow meter and the oil levels are the same. The exhaust colour as a measure of the mixture was lost when we took the lead out of the fuel. I use to be constantly checking the exhaust colour but all exhausts are black now.

Must be something wrong with mine then.

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15 hours ago, Phil Read said:

Must be something wrong with mine then.

Different fuels I suspect.

 

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My 1968 SU book says start with two complete turns from the level-with-the-bridge jet position. This is 12 flats so perhaps my 10 suggestion is too little. Mine are on 8 at the moment.

Being the same is important.

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21 hours ago, mikej said:

My 1968 SU book says start with two complete turns from the level-with-the-bridge jet position. This is 12 flats so perhaps my 10 suggestion is too little. Mine are on 8 at the moment.

Being the same is important.

My TR2 manual says 15 flats, 2.5 full turns, to start. Both mine are also on 8 now and that seems good if a little rich.

Thank you. It gives me some level of confidence it is about right.

Edited by John McCormack
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Hi all my carbs set up at approx 2 1/2 full turns anti clockwise which brought the colour tune into spec but when the piston raising pin is operated the revs drop and do not  return until the pin is relesed, car is still being rebuilt so can not road test. I have noted that the force required to lift the SU piston with SU oil in the dashpots was different for each cab. As supplied carb 1 required 2.8 lbs pressure to lift and carb 2 3.9 lbs, I then swapped the dampers in each carb and got values of carb 1 3lbs and carb 2 3.5 lbs. Does anyone know if the lift would have been checked and calibrated during manufacture and subsequent testing?. I have checked lift force with no damper installed and both carbs are broadly similar at 0.8 lbs. I completed the checks with lifting arm of measuring device through the air filter removed and under the piston. Any thoughts anyone?

 

Thanks

Adrian

 

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Seems like the damper rods are not a matched pair, If the rods are swapped over do the lift weights change too. I would think they need to lift at the same rate otherwise one carb would run lean ( or the other rich) during acceleration.

Ralph

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2 hours ago, Ralph Whitaker said:

Seems like the damper rods are not a matched pair, If the rods are swapped over do the lift weights change too. I would think they need to lift at the same rate otherwise one carb would run lean ( or the other rich) during acceleration.

Ralph

Damper check.  See pdf

 

 

Change of carburetor damper.pdf

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An update.

The Colourtune arrived today. It shows both carbies running rich at idle with the mixture adjustment all the way up, fully lean. The Colourtune does show the mixture still rich but getting to blue as the engine revs increase to 3000. As the engine isn't under load this seems a meaningless test

I have had to repair my distributor since the last mixture adjustments so have tried advancing the timing to see if it changes the reading at idle. No change, still rich.

After the Colourtune test I set the mixture on both carbies to 2 flats down just because I don't want them all the way up. The car idles well and has some real punch, it is performing well.

The needles are SM and new so I'm assuming my jets are worn. The carbies were new about 10-15 years ago so have done about 60,000miles. There is no sign of wear when inspected closely. I have checked the plugs after a good run and they don't show a  lean mixture.

At this time I'm going to ignore it and enjoy driving the car. I have a 2nd set of 1 3/4" SUs and may fit them one day but I don't want to stuff around with a car that drives very well.

Edited by John McCormack
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As far as I am concerned I would prefer an engine running richer at Tickover so it doesn’t lean out too much when running faster or under load.

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12 hours ago, Hamish said:

As far as I am concerned I would prefer an engine running richer at Tickover so it doesn’t lean out too much when running faster or under load.

That is my thinking. But I would like to be able to do it by adjustment and not because I don't have a choice.

 

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