CB750 & Triumph Trident

[flatfour]

Part 2, Learning

On arrival, my daughter named the Trident The Purple Popsicle. This I changed to The Purple Peril, following my initial experiences.

Whilst recuperating from back strain, I contacted a near neighbour, who has substantial experience with Tridents, both on the road and track. He came to visit and we looked at the bike together, agreeing that the 12,004 miles displayed looked original, backed up by photos of it amongst a number of other bikes at its home in Michigan. Clearly part of a private collection, as described. It was also factory - fresh in every way, the wiring in the traditional cotton - covered fleck and grey vinyl, connectors all branded Lucas, even the bulbs showing the maker's name.

This all backed up the history of it living in the dry for all of its life. It was originally sold in 1972 and re - imported to the UK in 2009, when it was registered and sold locally in Norfolk. Between 2009 and 2023, it covered only 184 miles and the sole MOT, which was carried out for registration purposes in 2009 backed this up.

After I had recovered, I decided to ride the bike again. This time it became apparent that the surging was quite serious at moderate throttle openings and required immediate attention, together with the non - existent idle. I returned to the workshop and tested compressions (all good, and very even) checked plugs (outers white, centre black) and decided that I would need to go much further into it all if I was to make it usable and, more importantly pleasant to ride. I also noticed that the number plate had fallen off on the ride and the right front indicator was pointing up at 45 degrees. I went over my route in the car and found the number plate lay on the ground undamaged, at the point where I turned around using a side road. This was refitted very securely!

A further conversation with my (now close) neighbour friend elicited the response that chokes do apply themselves as a matter of course, however as they are not really needed it was best to lock up the screw in the centre of the lever and just flood carburettors - something that has held true even in the now much colder weather. He also told me that things do tend to fall off at random and if I wanted to avoid immediate disaster I should fit an oil pressure gauge before even running it again, and ensure that it displayed the required 75 psi hot at 3,000 rpm. He also said that to use the main stand without injury to my back I should fit an aftermarket lifting handle.

I decided to service the bike thoroughly and fit the oil pressure gauge. Oil filters were changed/cleaned (all three of them) the oil changed in the engine and gearbox, new plugs fitted and points timing checked and the air filter replaced. All oils drained were clean and the air filter seemed as new. On startup the oil pressure was 85 psi, eventually dropping to just below 80 psi hot and 50 at 1,000 rpm. Unfortunately, the bike ran no better, so obviously further work would be needed. I also fitted the recommended lifting handle.

[flatfour]

Part 3, investigation and remedial work

I decided to remove the carburettors as the plugs varied so widely in colour. On first inspection they seemed to be synchronised (bench check with a drill bit, no vacuum takeoffs fitted) however removing the slides showed that the centre carburettor needle was in its richest position, whilst the two outers were in their weakest position. This corresponded with the plug colours so I removed the needles, intending to refit all into the mid - position. It was then that I realised, following some serious effort, that a special tool was needed to refit them into the slides. This tool is no longer available.

I reassembled the carburettors loosely to take to a friend of the seller, who had this tool and, whilst packing them found that the slide in the centre carburettor would rattle in its sleeve, whereas the others didn't. A call to Burlen (who now own Amal carburettors) solicited the response that this was a common occurrence, resulting in air leaks and an erratic mixture causing all sorts of running problems. The technical person there then told me that owners often tried to richen the affected carburettor by changing the needle position, weakening the others in compensation, to improve running. I asked if this problem was likely to be found at 12,000 miles, to be told that it was not unusual at 2,000 miles! This all fitted in with the issues that I had found.

The answer was, it seemd a new set of carburettors with hardened slides. These were, I thought very reasonable at £600 all in.

They were delivered to the seller's friend for the cables to be fitted and, with them assembled onto the gantry and bench set, I put them back onto the bike. This resulted in an immediate improvement in running, all surging had now disappeared. However, the idle was still very erratic.

I next adjusted the valve clearances, work not carried out earlier as I not thought to order gaskets for the valve covers. Despite excellent compression readings both cold and hot all were tight, with the number one cylinder inlet valve showing no real clearance at all. Apparently, many owners set them tight to reduce clatter! A further improvement in running was evident, with a now easily set idle which was reliable and, although I settled on 800 rpm, as low as 500 rpm was easily achievable.

Finally, with the bike now riding well, I decided to replace the exhaust downpipes and silencers, which were stainless steel (another aftermarket mod, apparently to avoid "blueing") with O.E. items. This improved matters yet again and, just as importantly the bike now sounded much more mellow. Exhaust parts were just over £300 all - in, again I thought very reasonable.

[flatfour]

Part 4 - conclusions and comparisons

These are my own, totally unscientific opinions of the main differences between the Trident, CB750 and my other Honda's, where this is necessary for comparison purposes.

General appearance and finish - the Trident has really deep, lustrous paint work and chrome and heavy, quality fittings such as the castings for switchgear. Whilst I cannot use my CB 750 as a comparison because it had been restored, my other Honda's, all bought new in period, used far more plastic parts with chrome less durable and not so deep in appearance. Even at 51 years of age, the spokes on the Triumph (original I believe) show no signs of rust or tarnish. Frame welds/brazing on  the Triumph are well made, almost invisible, less so on the Honda.

The Honda was much easier to ride, with switchgear falling to hand and light controls. The Trident switchgear is a complete hash of flip paddles and buttons, not all of which have any purpose at all due to their use on different models in the range. The clutch on the Trident is quite light, however the throttle is extremely heavy. The gear change on the Trident is far better than on any of the many Honda's that I have ridden.

The Trident is very involving to ride (read more difficult, at least for me) but is far more powerful in the 3,000 - 5,000 rpm bracket, accelerating fiercely and comparable in this area I think with my BMW K1300GT.

The Honda vibrates far less, although mirrors blur. In the 3,500 - 4,000 rpm bracket the Trident really shakes, although outside of this it is quite smooth. Mirrors do not blur at any speed.

Neither bike leaks or uses any appreciable amount of oil. (Note: 790 Trident miles only to date, compared to 14,000 on the CB750).

Overall, I'm pleased to have bought the Trident whilst I can still start it. This, my initial concern has proven unfounded. It was bought on the understanding that I took it "as is", although the seller has insisted on helping out with cost of repairs. A real gentleman, I think! I expect to keep this bike until I can no longer manage it, and might even send it over to Japan to use there.

END

[Oddjob]

Your definition of reasonable and mine don't tally. 

[flatfour]

I don't mind spending for my pleasure, most of my other classics have consumed far more money to put them in the condition that I want them to be in. In any case, the odd bike that I've sold has always returned at least its original investment to me.

Mindful of the fact that 30 years of owning aircraft has consumed far more money than all of the motorcycles that I've owned over a lifetime, I see motorcycling as quite a bargain these days.

[Nurse Julie]

Can you post a phot of your bike Colin?

[flatfour]

Julie, that's probably above my skill level

If you want to pm me your email address though, I could send you over a couple that you're welcome to put up for me?

[Nurse Julie]

Julie, that's probably above my skill level

If you want to pm me your email address though, I could send you over a couple that you're welcome to put up for me?

OK Colin, I'll PM you.

[davidcumbria]

Very interesting thread thanks. I like how you compare the manufacture quality of the bikes - not all one way as per received wisdom but that carb issue is a shocker. Great problem solving. Regarding the centre stand have you tried this which I have heard about in the past
Quote
If I am at home and only need to pull the bike up while it’s in the garage or on the driveway. I use a piece of wooden planking about 6 or 8 inches square, 1 inch thick and chamfered at a shallow angle on one side. Place this just behind the bike, chamfered edge towards the rear wheel, roll the bike backwards up onto the piece of plank, drop the centre stand and just a gentle pull backwards will have it up and stable. It’s using mechanics rather than muscle. I suppose you could carry the piece of plank in a tail bag or pannier if necessary.
Unquote

Enjoy your bike 👍

[Nurse Julie]

Colin has sent me a couple of photos of his Trident for me to share. Wow, what a stunner 😍😍😍😍

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[K2-K6]

A good read flatfour, thank you for taking the time to write about the bike.

I've always liked the triples, never owned one of these but have a Hinckley speed triple. 

Recently got talking to someone at a bike meet on one, turned out he raced them and has ridden quite a few of the famous race bikes too. I was at Mallory in 1971 to see the Cooper Agostini race of the year, we also spoke of Cooper at Daytona and the stories around at that time of the winning bike being sold etc, which I had read in MCN etc at that time. You meet some fascinating people that ride bikes.

Recently, near Northampton I passed a little car bike meet on the way somewhere and stopped to look at the vehicles on my return journey. Approaching there a X75 triple passed me in traffic, only to see it, an original, displayed at the meet.

All the triples just sound so nice, a lovely looking bike too.

[taysidedragon]

Back in the mid-seventies I had just bought a 650 Bonneville when a friend of mine bought a brand new T160 Trident in the red and white colour scheme. It was a beautiful looking bike and sounded awesome. I've always fancied one ever since. Either that or a Hurricane! X75s are crazy money now, so that's not going to happen.

It's not too late for me to get a T160, just need a bigger garage!

[McCabe-Thiele (Ted)]

A nice looking Trident indeed - there is something about a three cylinder engine thrum that is quite attractive.

I've only ever ridden one three cylinder bike back in the late 1970's it was a shaft drive Yamaha XS750 iirc.

[Bryanj]

That should be a 4 speed, remember at speeds over 50 to turn on BOTH petrol taps and dont run out of fuel, changed many a holed piston where owners didnt read that part of the handbook

[Johnny4428]

That’s a lovely looking bike. Never owned a Triumph so not qualified to comment.


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