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There is not a lot of valve train clatter and I readjusted the valves already after a few miles of driving.

I also checked that there is oil at the top end too.

The sound it more is weird and hard to describe …. 

The cam has the TR5 profile and the tappets are NOS.

As there is good oil pressure and the engine revs well I will continue with the carb setting up and stop imaging problems which are not there :whistling:

JC

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Forged pistons?  Does it get quieter when it warms up?

Or are you just suffering from the same random fears/paranoia I always have when running an engine I've built...... that something is wrong and it's sure to blow up soon.....  Usually I've got over it after the first 1000 miles!

Keep at it!

Nick

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As Nick said sound quality makes it hard to identify. HAd what I thought was noisy valve train/tappets after this winters head off, but did turn out to be blowing manifold gasket. Also last year blown collector box on exhaust manifold has me on a similar wrong track for a while. Sound does weird things under the bonnet, and also has a habit of sounding serious!  Try a cheap £5 stethoscope off ebay they are remarkably good at helping finding where noise emanates from.  Also try quick test with fan belt off, as will remove water pump and alternator noise. 

Alan

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Quick alternative to a stethoscope is a broomstick!    Or any length of solid material, best longer that the longest screwdriver for safety.

Hold one end to the engine, the other firmly against your earhole, or the bone behind it for a variation in the sensitivity to high and low tones.

Can quickly locate where a noise comes from.

John

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Thank you for the suggestions, it actually has forged pistons and its probably paranoia :unsure:

The engine runs pretty well and pulls quite hard, so I did further testing with a mobile CO-tester.

Started with BAE needles and with the CO already at 6 % at idle it goes down to under 1 % from 1/2 to full throttle.

Switched to BBW needles which start to get richer from measurement point 6 (Su needles have 16 points).

At point 10 the BBW needle is 10% richer, at point 12 already 15 % richer and at point 14 about 22% richer.

Ended up with an idle CO level of 7 % and the car still leaned out from 1/2 to full throttle to around 1,5 % …..

On both tests I used the yellow 8 oz needles and the car doesn't hesitate and pulls really well.

CO_1.thumb.png.c872f1e9b3b543126a00947adea41578.png

What should be my next step, even richer needles or a stronger spring ?

I read somewhere that performance wise I should go for richer needles and if I prefer good economy go for a stronger spring.

Its a pain the the mintylamb site is down at the moment, but it seems that it will live on :thumbsup:

JC

 

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17 hours ago, triumphlux said:

Started with BAE needles and with the CO already at 6 % at idle it goes down to under 1 % from 1/2 to full throttle.

Switched to BBW needles which start to get richer from measurement point 6 (Su needles have 16 points).

At point 10 the BBW needle is 10% richer, at point 12 already 15 % richer and at point 14 about 22% richer.

Ended up with an idle CO level of 7 % and the car still leaned out from 1/2 to full throttle to around 1,5 % …..

On both tests I used the yellow 8 oz needles and the car doesn't hesitate and pulls really well.

What should be my next step, even richer needles or a stronger spring ?

I read somewhere that performance wise I should go for richer needles and if I prefer good economy go for a stronger spring.

 

Hi 

OK hope I'm not teaching my grandmother to suck eggs, if I am I apologise! Having spent several years now data logging AFR's on 1.5 and 1.75 carbs on a 2Ltr Vitesse I have learn't a fair bit, but also know the more I learn the more I need to learn. Also my work has been on Stromberg not SU's which have some different characteristics particularly in abrupt acceleration pick up, where it appears the almost perfect vacuum seal provided by a diaphragm has some advantages over the clearance principle in the SU chambers.   However for all intense and purposes in standard running the Strombergs and the SU's are very similar.

It has been intimated many times over the years that twin 1.5" carbs are a tad too small for the 2ltr 6, and twin 1.75's are a tad too large. I think in all my experimentation I tend to agree, with the following addendum.  Twin 1.5 actually work better than 1.75's up to around 4K rpm, then up to around 5.5K they are much of a muchness, after which point the 1.75's are better particularly at protracted WOT when 1.5's have a tendency to enter an ever decreasing over rich spiral.  With a little work and experimentation you can get the 1.75's to perform sufficiently well in the lower rpm range, I am led to believe (although haven't tried it) that with a lot of work 1.5's can be made to work in the 6-7.5K range, although I also believe that their characteristics then in the low-mid range just sucks.

So if you have a 2ltr 6 road car that spends 99% of its time below 5.5K then actually the engineers at Triumph and Zenith knew what they were doing in fitting 1.5" carbs, if like me high rpm full WOT is required then 1.75's are a better choice all be it work is required to get the cruise characteristics under control.  NB this doesn't appear to be generic to all 2ltr engines, 4 pot 2ltrs seem to prefer 1.75 everywhere, this I believe to be because of carb pulsation at the needle/jet orifice, a 4 pot making four big gulps to the 6 pots six smaller sips.

It's the depression and airflow speed over the orifice (plus the pulsation effect) that determines how much fuel is sucked up to mix with the air flow, the volume of air for all purposes if the manifold airflow isn't restricted is  identical on the same displacement engine at the same rpm regardless if 1.5 or 1.75 carbs are used, but what they do affect is the air speed.  In theory with the lifting piston on CD carbs,  the piston lifts enough to permit the required airflow, so a 1.5 carb has to lift further to provide the same cross sectional area (choke) than 1.75 carb has to,  but a 1.75 piston is also heavier and resists rising more than 1.5 piston, so for the same air flow demand change the 1.75 carb has less needle movement in the jet to  play with and also a shallower wider passage over the jet bridge which alters the air speed and thus the suction on the jet.

Why did I bother just writing all that, its really a long winded way to say that the size of the needle in the jet (or what looks to be a measurable orifice size) doesn't really indicate how rich a particular needle will be.

So back to JC's question.

Again all I can report is what I have found, but as I tune by measuring and adjusting to get desired AFR's I don't know how this correlates to CO percentages.

I have played with all the spring weights available for my 1.75's and on the Vitesse I have never found that a heavier spring improves anything, whilst it can slow piston lift on acceleration, its a permanent not transient load (its like adding weight to the piston) I found that the lightest spring possible but using a heavier weight dash pot oil (I use 75w-90 synthetic gear oil) works best. (synthetic as its thinner when cold, but doesn't thin out as much when the carbs get warm).

So on to jets needles.  The Stromberg and SU 1.75's both use the same size jet, and as in theory they are the same size bore carb flowing the same amount of air, the needle requirements should be similar.

SU and Stromberg needles are all measured at 1/8"  0.125 increments,  The Stromberg needles are measured over 13 points and the SU's over 16, a quick bit of maths, plus the knowledge that on neither carb do the pistons actually lift 1.75" between idle and full lift its more like 1.25" you will see that on both needles there is actually a maximum of 10 contiguous needle steps that have any effect, allowing for a max 1 step needle adjustment, it means anything beyond step 11/12 doesn't have any effect on either (except on an SU if you have the choke pulled open and the jet pulled down, but who drives at WOT with the choke open?).

Also remember that you should only be aiming for full piston lift on a 1.75 at WOT approaching 6K rpm, so most of the time we are looking at probably a max 8 contiguous needle steps.

I'm currently using a Stromberg B1DH needle so thought I'd compare with JC's BBW

B1DH   980   951   927   901   875   842   807   777   754   732   712   703   703
BBW     990   950   923   900   870   832   792   750   717   682   647   610   577   540   505   470

The BOLD steps I think we can regard as being out of range.

Which is interesting as both needles in the idle to mid cruise range (1-6) are fairly similar, after which the BBW starts going what on gauging by size only would be for me a lot richer. I do know from recent RR runs that my 754 and 732 steps could do with being  a tad richer, from the logs at around 5250-5750 my AFR's were drifting back up towards 14, but did pull down nicely again at 6k+ to high 12's, which say that 712 is about right on the limit.

So will be interesting to see what profile JC ends up finding suitable if he thinks he is running lean currently.

NB. Testing the mixtures at 3/4 - Full piston lift (WOT) even if you can data log them, is tricky you either need a RR, or a very steep hill so you can get to max rpm and hold it in a lower gear for long enough, or a very long straight road where you can attain and hold 5.5-6k rpm (which in a Vitesse with a 4.11 diff is still a bit of a white knuckle ride).  Otherwise you find the rev counter is in the red way too quick! :biggrin:

Alan    

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Hi Alan,

thank you for taking your time to explain your conclusions from lots of testing  :thanks:

I think I will try the red springs (4,5 oz) first and then with thicker 75W-90 oil as you did, to check what a lighter spring does. 

And with some luck my engine builder will show up this week so we can continue  tinkering :banana:

JC

 

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Well that was an interesting week :yes:

Gareth turned up on Wednesday evening and we did our best to find out what is going on.

We continued testing with the BBW needles and different springs and found out that the softer springs make things even worse.

Next step was to modify the BBW needles and make them even richer.

GT_20180530_2.thumb.png.86f39f18b7bd9d2cbe62dfdeef7398dd.png

After that the car misfires up to a certain point when it cleares and revs up like crazy to 6.000 + revs :ohmy:

I got pretty late and we had to stop.

Come Friday evening and we put the BAE needles with the yellow springs back in. It is actually possible to make it run fine overall except at full acceleration.

Then the gearbox stick ball falls to bits for the first time and the fuel pump starts to leak badly …. we need to file the seal seating surface as the casting is really bad.

So on Saturday morning we fix all this and start to modify the BAE needles at the lower 1/3. In the end we had to take off around 0.20 mm at the lower 1/3 to make the car run fine everywhere.

There is still a small problem that it seems to go rich after idling for some time. Will check the float bowls as we also noticed that they have sometimes different levels …..

GT_20180602_5.thumb.png.372a0e1eceacff6fe6882a6ebeaead90.png

BTW the engine goes quiet after it warms up fully :banana:     AND it pulls like a train, torque from low down and it wants to rev above 6.000 rpm :yes:

Engine is run in by now with only 120 km.

But the overdrive conversion gearbox I bought years ago is VERY noisy …… and the new radiator leaks too …..

JC

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1 hour ago, triumphlux said:

There is still a small problem that it seems to go rich after idling for some time. Will check the float bowls as we also noticed that they have sometimes different levels …..

Fuel pressure too high?  Common problem with pattern pumps.  Or maybe leaky needle valves.  The new ones (from Burlen) in Chris's Spitfire are not as well behaved as they should be and that's with a Huco pump which are suitably low pressure.

 

1 hour ago, triumphlux said:

BTW the engine goes quiet after it warms up fully :banana:

Forged pistons......

Good news that it goes well - not so good about the gearbox......

Nick

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Thanks for the suggestions with the fuel issue.

How did you sort the issue with the leaky needle valves ? 

I have the new viton needle valves but still the original floats.

JC

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9 hours ago, triumphlux said:

How did you sort the issue with the leaky needle valves ?

We just ignored it and hoped it would go away.  Surprisingly this has actually seemed to work as they appear to have settled, though it took a while.

Nick

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