Acceleration stops at 50mph - max speed=50mph

[Matrix]

i have installed a new air filter johnnydog, maybe i will have someone to check the exhaust just to be sure.

As it turned out the best scenario happened: the serious issue is solved, thanks to all of you that pushed me to do the job on my own. I hesitated at first because i had zero experience but all your comments helped me to do what was needed.

[johnnydog]

Sorry, maybe I didn't explain my thoughts properly! Whilst adjusting carbs, the air filter box is usually removed, and often (I do it myself!) a test run is carried out before actually replacing it in case further adjustment is needed. Strombergs generally perform without issue without the air filter box in place, whereas SU's aren't quite as forgiving in my experience. It was just a thought in case you hadn't yet replaced the actual air filter box after fitting the air filters to it!

[Matrix]

I had done a small test without the filter box inside the neighbourhood, so i could only do 10-25mph.
I was about to do a 'heavier' test on the national road with faster speeds but a friend suggest me installing the filter ASAP to avoid having dirt again inside my carb. So i avoided doing the fast run after the adjustments without the filter.
Finally when new filters arrived i just installed the filter box.

I am thinking of visiting the mechanic who uses a gas metering unit via the exhaust system that helps adjusting the carbs very precisely.
I read somewhere that lean mixture can damage the engine (pistons and valves) and that engine temperature rises considerably.
Apart from that i also need to have the clutch slave cylinder replaced. My current one is leaking.

[johnnydog]

Checking the mixture on a gas analyser will indicate whether the mixture is correct or otherwise - however it gives an 'overall' mixture reading and won't tell you whether one carb is richer or leaner than the other. If you get the mixture as near as possible the same on both carburettors (either rich or lean, but the same on both), then adjusting both carbs by the same amount using the gas analyser, including the idle speed, should get them somewhere near, although I think any final small adjustments are best done on the road during a test drive.
From personal experience, I find the mixture is best set at the upper end if the co range. My S for example has the recommended mixture settings between 2.5% and 4.5% - it always seems to run better towards the upper end of the two without compromising performance or economy.
And yes, a weak mixture can ultimately cause damage to the valves and pistons over time, and can cause an increase in the engine temperature.
I still prefer to set the mixture by ear though!!

[Matrix]

I understand regarding the gas analyzer, it collects the sum of carb behavior.
But the good thing is that after doing a 1/4 turn on the rear carb, now all spark plugs have the same color - the 'whiteish' weak mixture color .
Even better, the orientation of the slot on the head of the screw is the same for both carbs and this will help much with the
parallel adjustment.
So if i have to do a 1/8 to enrich the mixture, i will do the same with both carbs and have homogenous results.
I will take note what you said regarding the zone of CO values and act accordingly.
Too bad i do not have the experience to adjust mixture using my ear.

[johnfrancis898]

I have tried various methods for tuning but I always go with the colour of the spark plugs to begin with. Initially, before you start any tuning, you need to check valve clearances and ignition timing is correctly set. I have to agree with Johnnydog on using my ear . I have also had good results with Colourtune but you need 2 sets for our cars fitted to no’s 2 &5 cylinders. With regard to carburettor settings, my TC has twin HS6 carbs and I start at 2 turns down and go from there. Both carbs end up with different settings normally the back one is about 2 flats different to the front. I managed to get hold of a gas analyser to check settings and found it difficult to get any where near the recommended settings. I ended up at around 2.5% CO2. Fuel also plays a big part. I was using Shell Vpower but have changed to Tesco Momentum and it seems just as good and it’s a bit easier on the wallet. The only other thing is temperature, it can make a difference. I have had it said to me ‘why do I bother?’ or ‘I counldnt be bothered with all that’ But each to there own, I actually enjoy a couple of hours every month having a tune up!ũ

[Forkie]

As a tag on to this thread - when you mention temperature - i assume you are talking about ambient temperature?
My own questions - what is the average RPM of SU carbs on a cold start ( the book only gives idle, presumed at running temp) .
And regarding the 'new ' E5 fuel - how long can it last in the tank before problems may occur - weeks, months etc.
I await replies.

[johnfrancis898]

As well as having the engine at working temperature the ambient temperature can make a difference also. That’s what I mean.
With regard to RPM on start up, this is increased when the choke is out and I have mine set at approx 1200 rpm. As the engine warms I try to get the choke in as soon as possible. I normally wait a couple of minutes before moving off.
I’ve had no trouble with the Tesco Momentum fuel or any other of the E5 premium fuels. I’ve always used Millers VSPe additive. I’ve also upgraded all rubber hoses. If I were going to store my car for any length of time I would probably drain the carbs, fuel line and tank.

[Forkie]

When you say ' store my car for any length of time ' what would your opinion be of that length of time-? I am genuinely asking. I ask as i am having certain issues that i never used to have - i need to know what tree im barking up.

[johnnydog]

I also use either Tesco Momentum 99 fuel or similar , such as Shell V Power (which is expensive though relatively) or Esso Synergy 99, with Millers VSPe additive which provides a further 2 RON rating and protection against the ravages of ethanol, and I also understand helps stabilise the fuel during periods of being laid up. I usually don't use my Triumphs between October / November and March the following year, and (touch wood!) have not any fuel related problems.
As I am fortunate to have more than one, some are laid up for longer periods which doesn't seem to cause any adverse issues.