New carburettors - one step back

It's already over two weeks ago that I got round to fitting the refurbished SU HS6 carburettors to my TR7 DHC. And I also managed to take the car for a ride to see how the new set up behaved. Overall pretty pleased with how the engine runs now! Pick up has been clearly improved, and the engine also revs much freer compared to the old set up. Sadly though there were also a few issues that have prompted me for some drastic action, removing the carburettors!

And the two reasons for this is that the choke mechanism doesn't function properly. Also the jet adjusting nuts on both carburettors are very stiff. Let's start with the first problem, the choke mechanism. Compared with the (original spec) carburettors that came of the car, the refurbished  ones have much more free travel before the jets are lowered and the throttle discs start opening. With the carburettors of the car the mechanisms could be compared:

It is clearly visible that the cam which activates the throttle disc is rotated slightly compared with the old carburettors. This results in the throttle disc not opening as far as with the original set up. And another choke related problem is that the bracket for lowering the jets is activated even later. So the jets are hardly lowered when the choke cable is pulled. The reason for this was more difficult to spot. But it turned out that the bracket that came with the overhaul kit has a slightly different shape that causes this:

The second problem was caused by the very stiff action of the mixture adjustment nuts. With the back plate of the air box in place it was almost impossible to adjust the mixture. The fact that newly supplied (non wax stat) choke's lever link is preventing good access to the adjusting nut doesn't help there. As a result of this fine tuning of the mixture was impossible. So after spending an hour or so in the shed, with the parts for the '76 FHC, I decided to use the newly plated carburettor parts that I prepared last year, together with the choke lever links from the old carburettors. To be continued!

Another MOT part 2

Almost a month ago the DHC got a clean bill of health during its biennial safety and environmental inspection (or APK as it officially called here). And today was 't Kreng's turn. I hadn't had time to give her a final check before I set of this morning. As she was checked earlier in the year, I presumed everything should be OK.

But while travelling to Garage Moorthaemer there was a decisive petrol smell entering the interior. And while carrying out the first check, the emissions, we found the cause for the smell. As the CO level was almost 5,5% the carburettors needed some slight adjustment. With the bonnet open the cause for the smell became immediately clear. One of the joints of the fuel line to the carburettor was leaking. Tightening up the joint's bolt removed the leak, and it also lowered the CO emissions to round 4%! So we had the first pass, though it is slightly worrying that I haven't got a clue why the joint came loose!

Next in line were the brakes. These passed with flying colours! The front brakes were as impressive as ever with a measurement of almost 4900N per wheel, with only a small difference between left and right. The rears also showed almost equal numbers on the test bench's display. Around 1700N this time. Which is more than my last standard TR7 front brake set up could manage! And the handbrake managed a perfectly equal left - right number of just over 1000N!

With the dynamic tests done, it was time for the visual part of the inspection. Again nothing wrong and no advisories. Time to enjoy the car for another two years! Which I did on the drive home!

After which she was promptly returned to the shed to be reunited under cover with my other FHC! Being idle together for the time being ...

I also used the opportunity to have a look around in the shed, to get a feel of all the parts I have collected over the years:

But I am afraid it will take some time before all of these are sorted. But certainly a job that has to be done because there's just to much in there!

A change of carburettors

I had a few days of from work so decided to fit this set of refurbished SU HS6 carburettors to the DHC's engine. At last I should say, as they have been collecting dust for almost a year now!

The job itself proved rather straightforward with a few random challenges thrown in! To start with the old carburettors had to be removed. Pretty straightforward, despite the lower nuts being rather awkward to reach. And in no time the old carburettors were removed from the engine:

But while disconnecting all hoses and cables I again found a very porous piece of fuel hose, between the fuel pump and the carburettors this time. So had to clamp another hose to prevent the fuel tank from emptying itself on the drive! And time to visit my local automotive supplier for some 6mm and 8 mm fuel hose. At least the various gaskets remained in place and were undamaged.

After returning home with a fresh supply of fuel hoses, fitting the new carburettors proved rather uneventful.

Except for the moment when I had connected the choke cable to the carburettors linkage. When I was checking the choke's action, the cable snapped ...

Time for another unscheduled trip, to the shed this time. Initial plan was to pick up one of the used choke cables but in the end I decided against it and took the new choke cable which was meant for the '76 FHC. As this car won't see any action within the next one or two years, there's enough time to order a new one. The joys of parts exchangeability.

With everything connected it was time for a basic set up of the carburettors, and some final checks. Or the final preparation for the first start attempt. And for this I used mostly simple tools:

After this check came the always dreaded moment of truth! Will it start and will there be a fuel leak? I shouldn't have worried after a dose of quick start the engine fired up immediately, accompanied by a nice fuel fountain! Luckily easy to rectify by using a different hose clip. After that it was time to set up and balance the carburettors a bit.

I had set the jets slightly leaner (=higher) compared to the old carburettors. And this has everything to do with the fact that I fitted different needles, which are overall richer. Which brings me to the last stage of this job.

When the carburettors were refurbished last year I thought I could use the old needle set up. But Club Triumph's 10 Countries Run 2017 proved that the breathing modifications I've carried out over the past few years were more effective than expected. As a result of this the fuelling of the engine was on the lean side.

When this engine was rebuilt in 1994 it was set up on a rolling road, where we found out that BDL needles gave the best performance (approximately 135 BHP @ 5500 rpm). But not anymore! Time to get behind the computer for some needle comparison. Here I found out the joys of the internet (digital SU needle charts) and the computer, to compare the various needles quickly and clearly. And for comparison I used The TR7's standard needle (BDM) and a popular choice for slightly upgraded engines (BAL).

As the BCE needle is slightly richer overall, I opted for a set of those. Hopefully I will be able to do a test run this Saturday morning and see how she behaves now!